http://www.iger.bbsrc.ac.uk/igerweb/NWNew/IPTW/iptw2001.htm

28 August to 1 September 2001,

Robbins Centre,

Plymouth University

Plymouth, Devon, England

However, despite such a high international profile, the scientific basis for connecting on-farm practices to impacts of P loss on surface water quality presents many challenges. These arise from:

• The multidisciplinary nature of the issue, drawing researchers from different fields and thus different spheres of understanding. Agronomists, aquatic ecologists, chemists, hydrologists and soil scientists all have a perspective on the problem that is different. The main aim of this workshop is to bring these disciplines together, to help educate one another and work towards an improved common research understanding of the processes and impacts of P transfer and its control.
• The semi-empirical / anecdotal aspect of the problem. We know that soil P levels are rising in some countries and that P is transferred from fields into first order streams. The challenge is to establish the connectivity of P on impacts surface waters i.e. scaling-up the problem.

We have designed an exciting workshop format that we hope will provide for an interactive and innovative think-tank to make progress on this challenging issue.

Ms. Jo Chisholm, IGER North Wyke, Okehampton, Devon, EX20 2SB, UK

A. L. Heathwaite (University of Sheffield, Sheffield, UK)

L. M. Condron (Lincoln University, Canterbury, New Zealand)

M. McHugh (Soil Survey and Land Research Centre, North Wyke, UK)

P. Butler, A. Joynes, S. C. Jarvis, P. Whitehead, F. Wood (Institute of Grassland and Environmental Research, North Wyke, UK)

A. I. Fraser and T. Harrod (Soil Survey and Land Research Centre, North Wyke, UK)

N. Griffen (University of Plymouth, Plymouth, UK)

K . Chell and R. Barrett (Slapton NNR and Field Centre, UK).

For each Theme, an Invited Speaker will give a critical overview of the topic aimed at provoking discussion. A Chair and a Reporter have been allocated to each Theme. The Reporter is required to work closely with the Chair to help reach a consensus and present the conclusions to each Theme on the final day of the Workshop.

Invited Speaker: The Invited Speaker will give an incisive and critical overview of the Theme, with the aim of generating discussion and debate. Some Themes have more than one Invited Speaker.

Chair: The Chair is the team leader and will co-ordinate discussion towards the workshop questions during the indoor presentation and presentation session and during the ‘Consensus Sessions’. The Chair leads and co-ordinates the team.

Reporter: The Reporter will summarise the conclusions and points raised during all the Theme discussion sessions, and present these during the summary session on the final Workshop day, aimed at answering the Workshop Questions.

Groups aim to report their view back to the workshop. Each group has an allocated leader and also a local guide to assist. It is the role of the leader to inspire and co-ordinate the group. It is the responsibility of the group leader to make time on the field workshop (and at other times, evenings, lunches, etc.) to co-ordinate and rationalise your group views.

Owen Carton, TEAGASC, Ireland

Leo Condron, Lincoln University, New Zealand

Emmanuel Frossard, ETH, Switzerland

*In the Concensus Session Dr Stamm will chair in place of Professor Beven

• solubilisation transfers
• physical transfers

• incidental transfers

• the key omission(s) in our technical knowledge of P transfer and future research area(s)
• a theme for the next P workshop in three years time.

On August 30^th, Workshop Day 2, delegates will leave Plymouth to spend the day at Slapton Ley, a mixed agricultural catchment in Southeast Devon.

Slapton Ley is a National Nature Reserve situated in the South Devon Area of Outstanding Natural Beauty. Its main feature, the freshwater Ley, is separated from the sea by a narrow shingle bar and is the largest natural freshwater lake in Southwest England. The reserve is renowned for the richness of its plant, fungi and bird life and is managed to enhance and conserve this wildlife while promoting education and research through the Field Centre, which was established in 1959.

Slapton, which means Slippery Place, has been populated since the Bronze Age and had a population of 200 at the time of the mid-12^th century Domesday Survey. During the second World War, some 750 residents of Slapton and the surrounding parishes were evacuated to make way for US troops preparing for the D-Day landings on the Normandy Beaches. Many troops lost their lives over the next year and a half, either from ‘friendly’ fire or from a surprise attack by German e-boats during Operation Tiger. Today, a memorial on Slapton Beach and a Sherman tank, raised from the seabed and on display at Torcross, remind visitors of Slapton’s difficult past.

The following table outlines the structure of the IPTW Field Day. On each coach, theme leaders and the local guides will discuss the Field Day and offer insights into the South Devon countryside.

At no point will delegates enter farmland or will they come into contact with livestock.

Throughout the Field Day, delegates will continue to discuss the three IPTW 2001 themes of sources, movements and impacts of P, with particular focus on the Workshop Questions. It is the role of Group Leaders to co-ordinate and target discussion and present (or nominate someone to present) the main conclusions arising from these discussions, under topic headings, to the workshop on Friday (August 31^st).

Authors were responsible for having the abstracts internally refereed prior to submission. The editors did not review the abstracts. However, it was necessary to undertake some minor changes, in respect to clarity and consistency. Thus, presentation of the work does not reflect scientific merit per se, and therefore cannot be considered a refereed publication. Rather, the purpose is to communicate to peers in the workshop, for the purpose of facilitating discussion.

Agriculture Victoria Ellinbank, RMB 2460 Hazeldean Road Ellinbank, Vic. 3821, Australia

Phosphorus (P) exports from agricultural land are a worldwide problem. Exports are generally initiated when P is entrained in moving water as a result of dissolution or physical processes. The amount of P exported depends on the source quantity, mobilisation rate and transport properties. Critical incidents, such as spreading fertiliser and animal wastes or grazing, increase P availability, P concentrations and P exports. Partitioning P concentrations in exported water into base (systematic) and incremental (incidental) components provides a useful research and management framework for addressing nutrient management at a farm scale.

When water is exported from land P is exported with it. Given the episodic nature of weather events and nutrient loads being the product of export volume and concentration, it is not surprising that export volumes rather than export concentrations primarily determine P loads per event. Unfortunately, at a farm scale the land manager often has little if any control over export volumes, to reduce P exports they must rely on reducing P concentrations when runoff occurs.

For a given hydrology the concentrations of P exported can be partitioned into a base or systematic component that varies with land-use, and an incidental component resulting from decisions, premeditated or not, made by the land manager.

Using this framework and non-linear modelling techniques, P concentrations can be attributed to incidental factors and to a lesser extent systematic factors (Equation 1). While these techniques do not demonstrate causality and noise in field data may reduce levels of statistical significance, the physical interpretation of the equations provides useful management information.

Equation 1 refines an earlier model applied to an Australian grazing system (Nash et al., 2000) in which P export concentrations were related to the time (days) between fertiliser application and runoff (DF), grazing and runoff (DG) and total runoff volume (TF). The ‘base plus increments’ model given by Equation 1 (adj. R² = 0.75) characterises the effects of DF and DG as additive exponential decay terms. Hydrological (dilution) differences are allowed for by the multiplicative flow term (TF).

[1]

The half-life of fertilisers in this example was in the order of two days (95% confidence interval 1 and 6 days). By incorporating a year factor into the analyses (k _i) the longer-term systematic effects of changing background soil fertility can be compared with the short-term, incidental impacts of fertiliser and grazing. The dilution effect of TF on TP was weak (a = 0.10 ± 0.067) but when removed the model yielded some non-sensical results presumably due to the effects of a few large storms.

At a farm level these data have been used as justification for rescheduling fertiliser application to times when runoff is unlikely and the development of a withholding period for irrigation water following fertiliser application. At a research level these data are justification for developing fertiliser compounds that reduce P exports by optimising P release for the hydrology of the irrigated or rain-fed system in which they are to be used.

An additional benefit of partitioning nutrient exports in this way is that it provides the benchmark against which we can compare land-uses within particular landscapes. Numerous authors have demonstrated the considerable between- and within- year variation in P export concentrations. The constant (k _i) is an estimate of the minimum P concentration in runoff that might reasonably be expected with our current technology.

Small decisions often have significant impacts. Using a simple ‘base plus’ framework and appropriate data and statistical techniques helps us identify how to most effectively and efficiently reduce P exports. We can manage incidental P exports. Future gains will be made where strategic research brings more of the systematic component under our management control (ie. converting it to an incidental component).

Nash, D., Hannah, M., Halliwell, D and Murdoch, C. 2000. Factors affecting phosphorus exports from a pasture based-grazing system. Journal of Environmental Quality 29: 1160-1166.

Institute of Water and Environment, Cranfield University at Silsoe, Bedfordshire, MK45 4DT

This paper will review the processes controlling the detachment of particulate phosphorus (P) from soils into overland flow and its subsequent transport and deposition, and will highlight some of the interactions between these processes.

Overland flow is an important source of the P reaching surface waters and contributes both dissolved and particulate P. Solubilisation processes are the main controls on solution losses, however, the short contact time between the water, soil surface and sediment particles entrained in the flow suggests that losses of dissolved P will be low. This is normally the case with most of the P moving in this pathway doing so while attached to sediment or organic matter (Figure 1).

Before particulate P can be transported it must first be detached. We can describe at least three mechanisms: physical detachment caused by the impact of raindrops and the flow of water over a soil surface, and the physio-chemical process of dispersion. The physical processes of detachment are well described by erosion scientists and mathematical descriptions are included in a number of process based soil erosion models. However, physio-chemical detachment has largely been ignored by erosion scientists, and the interactions between physical and physio-chemical detachment and its implications for P loss have been ignored my almost everyone. If we want to understand, and predict, P transfer then it becomes important to know not only how much soil is detached by these processes, but what its characteristics are: is it still an aggregate or is it a primary particle? Is the P from the outer edge of an aggregate, where P concentrations may be higher, or from an aggregate centre, where P concentrations may be lower? What is the particle’s size and density? All these factors will influence how much and how far the detached P will be transported, and not only require us to have a better understanding of the detachment process, but also to know what the initial distribution of P within the surface of the soil is. Without this information we cannot predict how much P will be detached since we do not know how much P is associated with particular aggregates or soil particles.

Once detached, sediment may be transported by overland flow. The generation and description of overland flow mechanisms has also been explored in depth by hydrologists and erosion scientists. Overland flow is variable, in space and time, and is often driven by the variability in rainfall patterns. Overland flow may be generated on a hillslope only to infiltrate further down the slope when the rainfall stops. Flow conditions can also change within a storm: at the storm’s peak the flow may be able to transport particles of all sizes, but during periods of lower discharge only the smallest particles may be transported. This variability in flow conditions leads to selective deposition of P, since lower flow velocities and depths will encourage the deposition of coarser particles, with some colloidal material only being deposited when all the flow has infiltrated. Flow conditions will also influence the connection of P bearing overland flow to surface waters, since travel distances from some contributing areas may be high requiring long flow durations.

The interaction between the overland flow and soil detachment processes can produces unexpected results. For example Quinton et al (2001) have shown that smaller events transfer proportionally larger amounts of phosphorus (Figure 2) and that frequent small erosion events accounted for more phosphorus transfer than infrequent large events. This suggests that small events should not be ignored when targeting control measures and that the phosphorus transport associated with sediments may be more widespread than previously thought.

Jordforsk - Centre for Soil and Environmental Research, Frederik A. Dahls vei 20, 1432 Aas, Norway

Many countries has experienced periodical extreme weather conditions during the last years. In Northern Europe, the autumn 2000 had extremely high precipitation and high temparatures. In southern Norway precipitation up to five times the 30-year-average was recorded from October to December. Since precipitation has a major influence on erosion and phosphorus (P) losses – the question arises of how these extreme weather conditions influence the losses of suspended solids (SS) and P from agricultural land. This abstract presents preliminary results from measurements in southern Norway in the autumn 2000.

Results were based on The Agricultural Environmental Monitoring Program in Norway (Bechmann and Våje, 2001). Four catchments (65-680 ha) and two field scale studies (4-6 ha) in the south eastern Norway were included. Water discharge and losses of P and SS were measured in the stream outlet of the catchments and for the fields both surface and subsurface runoff were measured.

The results presented here are preliminary and cover only the first part of this extreme event. Results for the whole autumn period will be available for presentation at the workshop.

The runoff in autumn 2000 was from 2 to 14 times higher than the earlier measured runoff in October-November (Table 1). The effect of high precipitation on loss of SS and P in the catchment studies were higher, 7 to 27 times for SS and 4 to 20 times normal losses of P.

The two field scale studies (Vandsemb and Bye) showed insignificant surface runoff during the whole runoff event. The transport of SS and P resulted mainly from subsurface water for both fields. The subsurface runoff increased 5 and 6 times, for Vandsemb and Bye, respectively, while subsurface losses of SS and P only increased to three times compared to the mean losses in October-November the previous 7 years.

Erosion in the streams may explain a part of the increased transport of SS and P measured in the catchment studies.

During this continuous runoff period of one and a half month, the concentration of total P in subsurface water declined significantly at Vandsemb field and stabilized at around 0.13 mg L^-1. The concentration of total P in subsurface water at Bye field decreased to 0.007 mg L^-1. The soil P content measured as P-AL was 17 and 7 for Vandsemb and Bye, respectively. Soils may have reached their minimum P concentration in leaching water.

Results show that extreme precipitation in autumn leads to increased losses of SS and P in subsurface runoff, while no increase were observed for losses in surface runoff in the field scale studies. Losses of SS and P increased less at field scale than at catchment scale, accordingly the contribution from other sources, i.e. stream erosion, needs further evaluation. Stream erosion may explain some of the differences in 2000/mean ratio between catchments. The concentration of P in subsurface runoff from the fields declined during this event and stabilized at a higher level for the field with highest soil P content.

Bechmann, M., and Våje, P. 2001. Monitoring erosion and nutrient runoff losses from small basins representative for Norwegian agriculture. IAHS Red Book (in press).

Centre for Soil & Environmental Quality, PO Box 84, Lincoln University, Canterbury, New Zealand

High concentrations of phosphorus (P) in soil resulting from long-term application of inorganic P fertilizers can lead to P loss which in turn may cause accelerated eutrophication of natural waters. Similarly, continuous applications of animal excreta in intensive dairy farming systems can result in enhanced P leaching, especially in free draining soils. This study reports incidental P leaching losses from a stony grassland soil immediately following application of dairy shed effluent (DSE).

Lysimeters (50-cm diameter, 70-cm depth) were collected from a free draining stony Lismore silt loam soil (Udic Haplustept) (Cameron et al., 1992). The experiment included 4 replicates of the following annual treatments: P45, P45+DSE200, P45+DSE400, P45+DSE400+U (P45 = 45kg P ha^-1 as single superphosphate; DSE = dairy shed effluent at 200 or 400 kg N ha^-1, U= urine at 1000 kg N ha^-1). Flood irrigation (100 mm per application) was applied every three weeks between November and April. Leachate was collected following DSE application in 1999 (Aug, Nov) and 2000 (Feb, May, Aug, Nov). Dissolved reactive P (DRP) and total dissolved P (TDP) were determined in filtered (<0.45 m m) samples, and total P (TP) was determined in unfiltered samples.

The amount of TP present in DSE varied from 28-62 mg L^-1 (Table 1). Of the TP in DSE, dissolved (DRP and DUP) and particulate (TPP) fractions accounted for 49 and 51 %, respectively. For the dissolved fractions in DSE, 44 % was DRP while DUP constituted only 5 %. The average TP loss in leachate ranged from 144 (P45) to 950 - 1385 m g L^-1 across DSE treatments; PUP was the main constituent in the leachate (70-79 %) followed by DUP (11-16 %), PRP (7-11 %) and DRP (2-5 %). This suggests that reactive forms of P (DRP) are adsorbed in the soil profile while P in unreactive fractions (DUP and PUP) is more mobile. The higher adsorption of P in reactive forms is particularly related to the higher amounts of Fe and Al oxides and hydroxides present at various depths in the Lismore soil (Sinaj et al., 2001).

*data in parenthesis are concentration ranges;

DUP = dissolved unreactive P (TDP – DRP); TPP = total particulate P (TP-TDP);

PRP = particulate reactive P (TRP – DRP); PUP = particulate unreactive P (TPP – PRP)

Dairy shed effluent contained equal proportions of dissolved and particulate P, although 70-79 % of the P loss from soil following DSE application occurred as particulate P (PUP).

Cameron, K.C., Smith, N.P., McLay, C.D.A., Fraser, P.M., McPherson, P.J., Harrison, D.F. and Harbottle, P. 1992. Lysimeters without edge-flow: an improved design and sampling procedure. Soil Science Society of America Journal 56: 1625-1628.

Sinaj, S., Stamm, C., Toor, G.S., Condron, L.M., Hendry, T., Di, H.J., Cameron, K.C., and Frossard, E. 2001. Phosphorus availability and loss from irrigated grassland soils. Journal of Environmental Quality (in press)

• Phosphorus sorption maxima were related to Fe_ox plus Al_ox but not to clay content.
• CaCl₂-P_r and CaCl₂-P_t increased markedly with fertilizer level. The percentage CaCl₂-P_ur of CaCl₂-P_t decreased as P fertilizer level increased.
• Less P was desorbed from soils with high sorption capacities, whereas more P was desorbed from soils with low sorption capacities
• Both P sorption and desorption capacity should be considered when predicting P leaching risks in Swedish soils.

Hesketh, N. and Brookes, P. C. 2000 Development of an indicator for risk of phosphorus leaching. J. Environ. Qual. 29:105-110.

Martin, M., Celi, L. and Barberis, E. 1999. Determination of low concentrations of organic phosphorus in soil solution. Commun. Soil Sci. Plant Anal. 30: 1909-1917.

Rothamsted Experimental Station, Harpenden, Herts., AL5 2JQ, UK

The movement of phosphorus (P) from terrestrial to aquatic environments poses a threat to the quality of surface waters. Since eutrophication may start at P concentrations as small as 20 m g P l^-1 water, P losses from soil to water, while insignificant in direct economic terms, may have very serious implications for the environment.

It is widely considered that P leaching from the surface soil in drainage water is usually insignificant as the P is so firmly fixed on the soil surface. Recently published results from the Broadbalk Continuous Wheat Experiment at Rothamsted have challenged this assumption (Heckrath et al., 1995). This experiment, now in its 155^th year, has soil P concentrations which range from about 10 to more than 100 mg 0.5 M NaHCO₃-extractable (Olsen) P kg^-1 soil. At Broadbalk’s inception, field drains were set at 65 cm below the soil surface of each plot so that drainage waters could be collected. These drains were only replaced a few years ago.

Drainage water samples were collected at the drain outlets of plots selected to cover a wide range of P concentrations on five occasions between October 1992 to February 1994 and analysed for P. Full analytical details and results are given by Heckrath et al. (1995). Briefly, below about 60 mg Olsen P kg^-1 soil total P concentrations in the drainage waters were small (about 0.15 mg P l^-1). However, above about 60 mg Olsen P kg^-1 soil there was a rapid linear increase in both Total P (TP) and Molybdate Reactive P (MRP) concentrations in the drainage waters up to the maximum Olsen P concentration of about 100 mg P kg^-1 soil. Generally, MRP ranged from about 70 to 90% of TP, and TP could be more than 3 mg P l^-1.

The Broadbalk results, we believe, uniquely imply that there is a certain soil P concentration below which there is little P leached in drainage water but that above this soil P concentration (which we term the ‘Change Point’) P leaches to drainage water in proportion to the soil P concentration. We need to know if the ‘Change Point’ is similar in different soils or does it differ depending upon soil type of management? Because of the almost complete lack of other suitable experiments we had to find an indirect method to predict if ‘Change Points’ differed between soils. Other work has indicated that the ratio between Laboratory 0.01 M CaCl₂-extractable P and Olsen P might be a useful indicator of ‘Change Points’ under field conditions. We present data to support this hypothesis showing that ‘Change Points’ measured by CaCl₂ were readily detectable in other soils and differed widely, ranging from 21 to 104 mg Olsen P kg^-1 soil.

There was also, unexpectedly, a very close (r² = 0.87) negative linear relationship between the ‘Change-Point’ measured in CaCl₂ and total soil iron (Fe) concentration. This is exactly the opposite of that which we expected, implying that as soil Fe concentration increases, P is held less strongly, so the ‘Change Point’ decreases. The use of this empirical relationship as an indicator of P leaching losses from soil to water is illustrated and discussed.

Heckrath, G., Brookes, P.C., Poulton, P.R. and Goulding, K.W.T. 1995. Phosphorus leaching from soils containing different phosphorus concentrations in the Broadbalk experiment. J. Environ. Qual. 24: 904-910.

These results suggest that the increase in extractable P concentration per kg of P fertiliser applied is greater both in the short and medium term, on low P buffered soils. This raises the issue of how long a single P fertiliser application will maintain elevated extractable P concentrations in low P buffered soils, which is important information for developing accurate P fertiliser budgets in these soils.

The University of Tennessee, P.O. Box 1071, Knoxville. Tennessee. USA 37901-1071

Institute of Grassland and Environmental Research, North Wyke, Okehampton, EX20 2SB, Devon, UK

Sixteen days after reseeding, 94 mm rain fell, with 57 mm over 22 hours. This resulted in 7.5 tonnes of soil lost from one 1 ha plot, with an estimated load of 3.75 kg P ha^-1 in 16 days on a reseeded treatment, compared to normal annual losses of around 0.8 kg ha^-1 on non-reseeded treatments.

Table 1. Ranges of total phosphorus (TP) concentration in water discharges following pasture reseed

Composite = Surface and subsurface flow to 30 cm; Drained = Flow from Mole drain to 60 cm

Table 1 shows that on undrained plots mean and maximum TP concentrations for the reseeded plots are higher than for permanent pasture. The drained plots show a reversal of this trend.

Short term soil detachment

Rapid P transfer can occur when reseeding is followed by intensive rainfall, particularly on undrained grassland. This may be especially common on grassland soils which often occur on sloping land.

Following sward establishment on undrained soils, concentrations of P transfer are higher on reseeded grassland. Drained soils appear to respond differently to undrained soils; tilling and reseeding soil allows percolation of P into the soil, which has the effect of reducing P transfer dramatically.

Eisenreich, S. J., Bannerman, R.T., and Armstrong, D.E. 1975. A simplified phosphorus analysis technique. Environmental Letters. 9:43-53.

Haygarth, P. M. and Jarvis, S. C., 1999. Transfer of phosphorus from agricultural soils, Advances in Agronomy, 66, 195-249.

University of Turin, DIVAPRA, Chimica Agraria, v. L. da Vinci 44 , 10095 Grugliasco (TO), Italy

Phosphorus losses from agricultural soil to water bodies are mainly related to build-up of soil available P, as a result of continued inputs of fertiliser P and manure in excess to crop requirements. In the evaluation of P loss, besides dissolved P, particulate forms must be considered. These are represented by the amount of P retained by erodible soil particles and are regulated by the dispersion/flocculation behaviour of soil colloids. This, in turn, depends on size and surface properties of particles and can be P-dependent (Barberis and Whithers, 1998).

Applications of manure and slurries can increase considerably soil organic P levels (Sims, 1992). Fresh animal manure contains from 3 to 15 g Kg^-1 of organic P and 50-70% of it is represented by inositol phosphates (Sun and Zhang, 1992). In soils organic P can constitute from 20 to 80%, depending on several parameters, such as the area, the type of soil and the profile depth. Unlike inorganic P, which can be readily fixed in the soil, some organic P forms are more mobile and can move along the profile and relatively easily reach waters. In an area of intensive cattle breeding in the Po Valley (Italy) we observed that dissolved organic P accumulated in the subsurface horizons up to 92% of total P while the amount in the particulate form was less than 1%, probably due to the flocculation of colloids by CaCl₂, used as extractant. Thus, dissolved organic P can constitute the largest P fraction in subsurface soil solution as observed also by Ron Vaz et al. (1993) and Chardon et al. (1997). However, the build-up of organic P in soils has been reported to be due to sorption of P mono esters, such as inositol phosphates, by soil minerals that hamper their biodegradation. Moreover, P has been shown to be also transported with dispersed soil particles in the percolation water (Hartikainen, 1978).

This work is aimed to evaluate the molecular aspects of organic P interaction with minerals while assessing the sorption extent and its effects on the particle charge and size. Inositol phosphate was used in this study, as it represents the main organic P form in soils. These results could help to better interpret the trend and distribution of P in the different forms in agricultural soils subjected to intensive fertiliser and manure application.

The adsorption extent depended on the nature and properties of the mineral surfaces. Iron oxides retained more inositol phosphates than phyllosilicates, such as kaolinite and illite. All these minerals showed a higher affinity for inositol phosphate than for inorganic phosphate as deduced by the Langmuir K values. In terms of P, a higher amount was retained in the organic form with respect to the inorganic one. The adsorption occurred through the phosphate groups of inositol hexaphosphate similarly to the free orthophosphate ion, forming a binuclear complex while the organic moiety affected the mechanism only in terms of conformational hindrance (Ognalaga et al., 1994). In calcareous soils inositol phosphate retention was governed by CaCO₃ with complexation and precipitation of Ca salts at any inositol phosphate concentration. The sorption reaction with ferrihydrite and goethite was found to be nearly irreversible. The adsorption of inositol phosphate caused a net increase of the negative charge and particle dispersion of all minerals under investigation. This was noticeable also at the lowest inositol phosphate addition.

These results lead to two conclusions: a great inositol phosphate-fixing capacity of minerals that may affect its accumulation in soils and P bioavailability, and a considerable change of mineral electrochemical properties and particle size distribution that modify soil particle charge and colloidal stability. This therefore suggests that organic P can greatly react with soil minerals, such as iron oxides, clays, calcite. This results in a rapid removal from solution, but organic P sorption increases the mobility of erodible particles and hence P transfer as particulate through the profile and to water bodies.

Barberis E. and P. Withers. 1999. Influence of soil processes on detachment of P forms: A review of experimental data. COST action on Phosphorus meeting, Cordoba (Spain) May, 13-15 1999.

Chardon W. J., Oenema O., Del Castilho P., Vriesema R., Japenga J. and Blaauw D., 1997. Organic phosphorus in solutions and leachates from soils treated with animals slurries. J. Environ. Qual. 26: 372-378.

Hartikainen, H. 1978 Leaching of plant nutrients from cultivated soils. II Leaching of anions. J. Scient. Agric. Sco. Finl. 50: 263-269.

Ognalaga M, Frossard E and Thomas F (1994) Glucose-1-phosphate and myo-inositol hexaphosphate adsorption mechanisms on goethite. Soil Sci Soc Am J 58: 332-337.

Ron Vaz M. D., A.C. Edwards, C.A. Shand, and M.S. Cresser. 1993. Phosphorus fractions in soil solution: Influence of soil acidity and fertilizer additions. Plant Soil. 148: 179-183.

Sims, J.T. 1992. Environmental management of phosphorus in agriculture and municipal wastes. In: Sikora F.J. (ed). Future directions for agricultural phosphorus research. Natl. Environ. Res. Center, Muscle Shoals.

Sun, X. and Y.S. Zhang. 1992. Study on inositol phosphate in organic manure and paddy soils and its effects on rice growth. Acta Pedol. Sinica 29: 365-369.

1University of Maryland, College Park, Maryland, USA.

During the final phase of testing, between 25 and 30 farm fields were identified in each of Maryland’s 23 counties that, when taken in aggregate for a given county, reflected the diversity and proportion of soil types, topographies, farming systems, and nutrient management practices prevalent in that county. Data were collected from 646 field sites beginning in the spring of 1999 and continuing through the spring of 2000.

The State of Maryland has defined an 'environmental threshold' for conventional soil-test P equal to 150 FIV (fertility index value), or three-times the agronomic critical level of 50 FIV. According to new Maryland nutrient management regulations, agricultural fields with conventional soil-test P greater than or equal to 150 FIV must be evaluated by the PSI to determine the nutrient management planning requirements for that site. The frequency distribution of PSI outcomes or 'performance' was evaluated for several sub-categories of the statewide data set. The various categories of PSI performance distributions were divided into groups: all data, fields with soil-test P (STP) less than 150 FIV, and fields with STP greater than or equal to 150 FIV (Table 1).

Table 1. Number and percent of evaluated fields in each P loss rating category for the Maryland P Site Index (PSI) evaluation. Soil-test P sub-categories include fields with soil-test P (STP) less than 150 fertility index value (FIV) or greater than or equal to 150 FIV.

Currently available data can not determine if the Maryland PSI is 'right' or 'wrong'. The frequency distribution data presented represent how the Maryland PSI has performed on the sites evaluated. The proportion of evaluated sites that fell within each of the four final P loss rating for the statewide data set or any subdivision of the statewide data set was strictly determined by the numerical definitions of the P loss rating categories. Although the P loss rating categories were numerically defined based on best available data and professional scientific judgements, it may be necessary in the future to redefine the P loss categories as warranted by new research findings and more experience in using the PSI.

Runoff ranged from 0.4 – 10% of annual rainfall. Over 90% of this was overland flow. Losses of P and other elements each year were highly variable and strongly related to rainfall patterns. Over the study period an average of 98% of P was lost in overland flow. The proportion of P present in the particulate form was highest in the wettest year.

The results of pattern analysis appear to reflect the interplay of two major transport processes - Dissolved and Particulate. In wetter years, the particulate process dominates the magnitude of element losses, but becomes an increasingly minor component of element loss as annual rainfall decreases. This appears to be a relatively simple mechanism for losses of a wide range of elements from dairy pasture.

Fleming, N.K., and J.W. Cox. 1998. Chemical losses off dairy catchments located on a texture-contrast soil: Carbon, phosphorus and sulphur and other chemicals. Aust. J. Soil Res. 36:979-95.

Fleming, N.K., J.W. Cox, D.J. Chittleborough, and C.B Dyson. 2001. Prediction of chemical loads and forms in overland flow from dairy pastures on duplex soils in South Australia. Hydrological Processes (in press).

Young, W.J., F.M. Marston, and J.R. Davis. 1996. Nutrient Exports and Land Use in Australian Catchments. J. Env. Manage. 47:165-183

Department of Applied Chemistry and Microbiology, P.O. Box 27, 00014 University of Helsinki, Finland

Restriction of phosphorus (P) losses in agriculture requires identification of the fields of the highest risk. However, despite a lot of effort, no consensus on proper methodology has been obtained. There are indications that a risk assessment based on conventional chemical tests may lead to ambiguous conclusions (Sharpley, 1995; Hooda et al., 2000). One disadvantage of the chemical tests is that they give an estimate only for the P intensity or quantity.

Water extraction, that predominantly measures P intensity has been proposed also as an indicator for P loading risk (Yli-Halla et al., 1995; Gächter et al., 1998). Dilute CaCl₂ solution has been extensively used for determination of P intensity as well. It is also a common background solution in sorption tests used to describe the P buffering properties of soils. Even if both sorption and desorption control the P buffering, they do not follow the same pathway but more or less hysteris can be found. Therefore, in risk assessment a desorption curve would be a more relevant tool to integrate information about factors contributing to the potential P release from soil than a sorption curve. Desorption obtained at progressively increasing solution to soil ratio (SSR) would simulate the P buffering reactions during surface runoff. A narrow ratio approaches the field conditions and wider ratios correspond to conditions prevailing during erosion process. Because the P desorption is dependent on the bathing solution, this study was undertaken to compare the sensitivity of water and dilute CaCl₂ solution in reflecting fertilisation-induced changes in P intensity and quantity at various extraction ratios.

Soil samples from four P fertilisation field trials were taken from blocks cultivated for seven years without P addition or amended annually with 30 or 60 kg of P per ha. Inorganic P reserves were analysed according to a modified Chang and Jackson's procedure. Degree of P saturation (DPS) was calculated as a molar ratio of Al and Fe bound P to oxalate soluble Al and Fe. For desorption curves, soil samples were extracted with water (P_w) or 0.01 M CaCl₂ at solution to soil ratios of 2:1, 5:1, 10:1, 50:1, 150:1 and 400:1. For comparison, P status of the soils was investigated using Bray P1 test and an acid NH₄-acetate method (AAAc) used in routine soil testing in Finland.

Phosphorus fertilisation increased Al and Fe bound P and DPS, excluding one soil of very high DPS where added P had obviously leached to lower horizons. The P concentrations in CaCl₂ extracts were much lower and less affected by SSR than in water extracts. Consistently with P fractions, P_w in a given soil rose with increasing accumulation of P, whereas CaCl₂-P showed differences between the P treatments only in soils of high DPS. As expected, increasing SSR decreased the P concentration in solution. However, this hold truer for P_w than for CaCl₂–P which was quite weakly dependent on the extraction ratio. CaCl₂ extraction was also rather insensitive in reflecting fertilisation-induced changes in P reserves, whereas water extraction responded even to the presence of competing ligands (organic matter) contributing to P desorption tendency. The salt effect and the divalent cation reduced the sensitivity of CaCl₂ solution in the determination of potential P release, especially at narrow SSRs. Also a single water extraction at conventional solution to soil ratio of about 50:1 may give an inaccurate estimate for P release potential. However, at the ratio of 400:1 water extracted P more than AAAc, and in some soils even to the same extent as Bray P1. The results indicate that a desorption curve with water at SSRs varying from very narrow to large might be a promising method to describe the P supplying power of soils and to simulate the P release from soil particles during surface runoff.

Gächter, R., J.M. Ngatiah, and C. Stamm. 1998. Transport of phosphate from soil to surface waters by preferential flow. Environ. Sci. Technol. 32:1865-1869.

Hooda, P.S., A.R. Rendell, A.C. Edwards, P.J.A. Withers, M.N. Aitken, and V.W. Truesdale. 2000. Relating soil phosphorus indices to potential phosphorus release to water. J. Environm. Qual. 29:1166-1171.

Sharpley, A.N. 1995. Dependence of runoff phosphorus on extractable soil phosphorus. J. Environm. Qual. 24:920-926.

Yli-Halla, M., H. Hartikainen, P. Ekholm, E. Turtola, M. Puustinen, and K. Kallio. 1995. Assessment of soluble phosphorus load in surface runoff by soil analyses. Agric. Ecosystems & Environm. 56:53-62.

1ADAS Gleadthorpe, Meden Vale, Mansfield, Nottinghamshire, NG20 9PF, UK

Tile drain discharges were continuously monitored and water samples collected during runoff events using automated water samplers. Samples were analysed for total P, total dissolved P and molybdate reactive P.

Data will be presented on the impact of the time of application, and method of incorporation, on P concentrations and loads observed in tile drain discharge. Cognisance will be given to the importance of soil moisture status at the time of application. The results will be discussed in light of any implications for current best management practices (MAFF, 1991) and provisional recommendations will be made as to how to minimise P loss following slurry applications to drained clay soils.

Hodgkinson R. A., Williams J.R. and Chambers B.J. 1998. Phosphorus loss from manure application to a drained clay soil In: Foy R and Dils R [eds] Practical and innovative measures for the control of agricultural phosphorus losses to water Proceedings of an OECD Sponsored Workshop.

MAFF. 1998. Code of Good Agricultural Practice for the Protection of Water. MAFF Publications, London (PB0585).

1University of Vermont, Burlington, VT, USA

Alterra, Wageningen University and Research Center, Wageningen, the Netherlands

A loamy sand soil, enriched with P in the past, was depleted in a pot experiment by cropping grass during 32 months in a greenhouse on either a 5 or 10 cm soil layer. At 8 times, 2 pots of both treatments (5 and 10 cm) were sacrificed to sample the soil. Grass was harvested every 3 to 6 weeks, and total N and P contents were determined. After each harvest, soil was fertilized (N and K). The following soil extractions were used: water (P-1:2, 1:2 w:v; Pw, 1:60 v:v) and 0.01 M CaCl₂ (P-CaCl₂, 1:10 w:v), FeO-impregnated filter paper (Pi) and ammonium oxalate (P-ox). The phosphorus saturation degree (PSD) was calculated by: P-ox/a *[Fe+Al]-ox with P-ox and [Fe+Al]-ox in mmol kg^-1 of soil and a =0.5.

Chardon, W.J., Oenema, O., Schoumans, O.F., Boers, P.C.M., Fraters, B., and Geelen, Y.C.W.M. 1996 Exploration of options for management and restoration of phosphorus leaking agricultural soils (in Dutch). The Netherlands Integrated Soil Research Programme, Wageningen, vol. 8.

1Department of Agronomy, 210 Waters Hall, University of Missouri, Columbia, 65211

Institute of Water and Environment, Cranfield University at Silsoe, Bedfordshire, MK45 4DT

Overland flow is the movement of water over the soil surface and down slope. It can lead to problems with soil erosion and sediment transport. The loss of phosphorus (P) associated with overland flow is often considered to be greater than that likely to occur via leaching because of the ability of soil to sorb P from infiltrating water. Overland flow transports both dissolved and particulate P (PP) but it is the PP associated with eroded soil particles which accounts for the majority of the P transported.

The efficiency of this pathway for P transport is dependent upon many soil and rainfall characteristics. Numerous studies have focused on the role individual soil physical and chemical properties play in influencing P release to overland flow. However, few studies have looked at how these soil physical and chemical factors interact together and the role they play in influencing P release. This study will investigate these interactions and the importance of both soil physical and chemical characteristics with the aim of developing a new procedure for P risk assessment. With this is mind the 9 metre indoor gravity fed rainfall simulator at Cranfield University, Silsoe was used to compare the potential for P transfer in overland flow from 24 soils under different land management practices and agricultural P inputs. The simulated rainfall rate was 60 mm hr^-1 and water and sediment samples were collected at intervals for 30 minutes. Samples were analysed for total P (unfiltered), total P (<0.45 m m) and reactive P (<0.45 m m). The amount of P in samples was then related to soil physical and chemical characteristics.

G. L. Mullins¹, W. L. Daniels¹, L. W. Zelazny¹, M. R. Brosius¹, M. A. Beck¹, W. L. Wolfe², A. Vincent² and J. W. Pease³

Public concern over the effects of animal manure and other organic nutrient sources on water quality in Virginia and other Mid-Atlantic States in the eastern U.S. has increased markedly in recent years. Protecting water quality from nutrient pollution will require the development and implementation of farm-level management tools that can be used by Virginia producers to minimize environmental impacts resulting from the land application of nitrogen (N) and phosphorus (P) nutrients in organic and inorganic fertilizers. One promising P management tool is the P Index. The U.S. Natural Resources and Conservation Service has developed a P indexing tool that can be used to assess the potential for P losses from agricultural fields to the environment. This tool was developed to include the solubility of soil P, the type, rate, and method of P source management, and transport factors which can affect P losses from agricultural fields to surface and ground water supplies. Adaptation of the P Index as a nutrient management tool for Virginia will require tailoring of the index to soil, management and transport conditions specific to varying Virginia soil landscapes.

Development of a working P Index that can be used for nutrient management planning in Virginia is being approached through an interdisciplinary effort at Virginia Tech. The first phase of this project included a statewide sampling of Virginia soils, focusing on three counties characterized by intensive animal and row crop agriculture. Samples were collected from Accomack (Eastern Shore), Amelia (South Central) and Rockingham (Shenandoah Valley) counties. Sites represented a wide range in soil test P levels and varied management of organic amendments. Samples were subjected to soil testing procedures to characterize soil P forms including the relative degree of soil P saturation. Samples were collected in the fall of 1998 from 19 fields in Accomack County, 15 fields in Amelia County and 28 fields in Rockingham County.

Total soil P and the distribution of soil P among different chemical forms differed considerably for the three counties and among fields within a given county. In general, soils impacted by long term applications of animal manure (Rockingham County) or high applications of commercial fertilizer for vegetable production (Accomack county) contained the highest levels of water-soluble and soil test P. Mehlich 1 extractable P ranged from 42 to 779 mg kg^-1 in Rockingham, 31 to 1083 mg kg^-1 in Amelia, and 2 to 330 mg kg^-1 in Accomack counties. Several fields (74% of the fields sampled) in all three counties (highest proportion for Rockingham County) had soil test P levels that were high enough to maintain crop production for several years with little or no additional P fertilizer application.

The soil P data suggest several practical implications for Virginia producers. Fields with a history of receiving long-term annual applications of P from organic and/or commercial P fertilizers had elevated levels of total soil P and soil test P. Therefore, applying P in either fertilizer or organic forms at levels above crop P needs will result in further buildup of soil P levels. For these Virginia soils, the relative degree of soil P saturation increased as the level of soil test P increased (r² of 0.97, 0.68 and 0.92 for Amelia, Accomack and Rockingham counties, respectively). In addition, water-soluble soil P increased with increasing soil test P. Since higher levels of water-soluble soil P have been reported to be associated with greater potential for P losses in surface runoff, this data set suggests that long-term over-application of P in organic-P sources at rates in excess of crop needs increases the potential for P losses in surface runoff from these soils.

Investigating the relationships between soil P levels and potential P losses in surface runoff using portable rainfall simulators has expanded the laboratory phase of the project. Soil data collected as part of the statewide survey and data from the rainfall simulators are being used to calibrate a model for predicting P losses from agricultural fields on a watershed basis. Work is on going to improve a process-based model of P fate and transport. The ANSWERS-200 model is a continuous, distributed parameter, watershed-scale model that simulates rainfall runoff, erosion, sediment delivery, and N and P transformation processes and transport. Updated algorithms are being incorporated into the model and the detailed data from the statewide survey and rainfall simulations are being used in testing the model. Further work will estimate the economic consequences of practices altered by manager use of the P-index for nutrient management planning.

Department of Soil Science, The University of Reading, Whiteknights, PO Box 233, Reading, RG6 6DW, UK

The restoration of wetland habitats by the flooding of agricultural fields is becoming increasingly common. Through prescribed water level management, the land encourages a variety of wetland wildlife during the winter and spring, and allows low density grazing during the summer and early autumn. From a water quality point of view, one of the main problems associated with flooding former agricultural land is the release of phosphorus (P) to the overlying water column and to adjacent water bodies.

In many wetland soils, organic P (Po) makes up a significant proportion of the total P. Because of the existence of Po in different forms and with varying degrees of availability, it is hypothesised that the mineralisation of Po can make an important contribution to the release of inorganic P to the overlying water column. In wetlands that are subjected to alternating waterlogged and drying conditions (seasonal wetlands) the soil switches back and forth between aerobic and anaerobic conditions. In such an environment, the potential for P release from soil Po to water may be modified through seasonal changes in i) the forms and stability of the soil Po and ii) the turnover of the microbial biomass. The general aim of the current research is to evaluate the short-term dynamics of soil Po and microbial biomass P in peat soils of seasonal wetland.

Peat samples were taken during the summer (August 2000) and winter (January 2001) from the surface (0 – 20 cm layer) of a recently created wetland in the Somerset Levels and Moors. Formerly, the site comprised agricultural fields that had received high inputs of P fertiliser for the production of vegetable crops. Owing to its current water management regime, the land is drained in the summer, but the soil surface is still moist, depending on rainfall and temperature conditions. In the winter, the whole site is flooded. A preliminary evaluation of the amounts of readily mineralisable soil Po for the two sampling periods was conducted by performing a short, sequential fractionation scheme, involving 0.5 M NaHCO₃ followed by 0.1 M NaOH. In upland soils, Po turnover studies have shown that NaHCO₃-extractable Po is rapidly mineralised (Bowman and Cole, 1978) whilst NaOH extracts more biologically resistant forms of Po that are involved in the long-term transformations of P (Batsula and Krivonosova, 1973). Solution-state ³¹P-NMR spectroscopy is currently being used to identify and quantify the distribution of the major forms of P (inorganic ortho P, ortho-P monoesters and ortho-P diesters) and relate these to the chemical fractions.

At both sample times, NaHCO₃-Po constituted a very small proportion (< 5 %) of soil total P, indicating the highly humified nature of the peat. However, NaHCO₃-Po in the soil sampled in August (40 mg kg^-1) was 25% higher than that in the following January (32 mg kg^-1). The amounts of Po subsequently extracted in NaOH were not significantly different between the two sample dates. It is likely that the warm, moist soil conditions during the summer stimulated the microbial decomposition of soil organic matter, thus increasing the release of P into the labile pool. Also, the increased rates of microbial activity in the summer may have accounted directly for the higher NaHCO₃ – P through an increase in biomass decomposition.

Future work will evaluate the contribution of microbial biomass to the labile Po pool as a function of seasonal wetting and drying cycles. More detailed and frequent soil sampling, combined with laboratory microcosm studies, will provide a fuller evaluation of the short-term changes in the fractions and molecular forms of Po in the soils of seasonal wetlands. It is also expected that the relationship between Po forms and phosphatase enzyme activities will be elucidated, for the purpose of improving our understanding of the role of enzyme activity in the cycling of Po in the peat soils of seasonal wetlands.

Batsula, A.A., and G.M. Krisonova. 1973. Phosphorus in the humic and fulvic acids of some Ukrainian soils. Soviet Soil Science 5:347-350

Bowman, R.A., and C.V. Cole. 1978. Transformations of organic phosphorus substrates in soils as evaluated by NaHCO₃-extraction. Soil Science 5:49-54.

Rubæk, G.H., Djurhuus, J., Heckrath, G., Olesen, S.E. and Østergaard, H.S. 2000. Are Danish soils saturated with phosphorus. In: Jakobsen, O.H. and Kronvang, B. (eds.) Phosphorus loss from agricultural areas to the aquatic environment. DIAS report nr 34, Plant production. p. 17-30. (In Danish with English abstract).

van der Zee, S.E.A.T.M., van Riemsdijk, W.H. and de Haan, F.A.M. 1990. Het protocol fosfaatverzadigde gronden, Wageningen, Landbouwuniversiteit, Vakgroep Bodemkunde en Plantevoeding.

Department of Soil Science, The University of Reading, Whiteknights, PO Box 233, Reading, RG6 6DW, UK

Five topsoils (0 – 20 cm) were incubated for 20 d with sewage sludge, poultry litter, cattle slurry or KH₂PO₄ at rates equivalent to 100 mg P kg^-1 soil. The soils were selected to represent typical, continuously cultivated loam soils that display a range of Olsen-extractable P values. After the incubation period, P sorption and availability parameters were determined, including values for EPCo obtained from P sorption isotherms, P sorption index (PSI), and amounts of P extracted in 0.01 M CaCl₂ and anion exchange resin.

Application of all the P sources decreased the PSI and increased the EPCo, CaCl₂-P and resin P in all five soils. In all soils, cattle slurry and KH₂PO₄ consistently had a much larger influence on PSI, EPCo, CaCl₂-P and resin P than did sewage sludge and poultry litter. For example, following slurry and KH₂PO₄ additions, the decreases in PSI ranged from 37 to 111 L kg^-1, and from 29 to 85 L kg^-1, respectively. Following sludge and litter additions, the decreases in PSI ranged from 16 to 36 L kg^-1, and from 12 to 45 L kg^-1, respectively. With regard to EPCo, following slurry and KH₂PO₄ additions, increases ranged from 0.07 to 2.8 mg L^-1, and from 0.05 to 1.6 mg L^-1, respectively. Following sludge and litter additions, the increases in EPCo ranged from 0.03 to 0.8 mg L^-1, and from 0.01 to 0.5 mg L^-1, respectively.

Clearly, there is a need for more detailed inorganic and organic analysis of animal manures and sewage sludges in order to identify and explain fully those properties of organic wastes that influence the availability and potential mobility of both native and applied P in the soil matrix. For a range of animal manures and biological sewage sludges, current research is attempting to evaluate the following:

1. Simple relationships between the contents of polysaccharides, proteinaceous compounds and humic acids, and metal solubility.
2. The fate of major classes of organic P (monoesters and diesters), that are found in animal manures and biological sludges, after they are released in to the soil matrix.

Gerritse, R. G. 1981. Mobility of phosphorus from pig slurry in soils. p. 347-366. In T.W.G. Hucker and C. Catroux (ed.) Phosphorus in sewage sludge and animal wastes. D. Reidel Publ. Co., Dordrecht, the Netherlands.

Reddy, K.R., M.R. Overcash, R. Khaleel, and P.W. Westerman. 1980. Phosphorus adsorption-desorption characteristics of two soils utilized for disposal of animal wastes. J. Environ. Qual. 9:86-92.

Alterra Green World Research, PO BOX 47, 6700 AA Wageningen, The Netherlands

The present high levels of agricultural production require relatively high soil phosphorus (P) levels. Large uncertainty exists on the magnitude of the P surplus necessary to maintain these relatively high soil P levels. To formulate manure reduction plans that are acceptable from both an agronomic and environmental point of view more knowledge on the faith of P on fields used for dairy farming is essential. To obtain this information a monitoring program has been started in 1996 on four grassland soils in the Netherlands. Two of these sites are situated on relatively well drained sandy soils, one on a well drained clay soil and one site on a poorly drained peat soils. At each sites three plots were established that received different combination of N and P surpluses: a surplus of 180 kg ha^-1 N and 0 kg ha^-1 P, 180 kg ha^-1 N and 10 kg ha^-1 P and 300 kg ha^-1 N and 20 kg ha^-1 P

During the first three years of the measurements no significant changes in the phosphate pools were found. This is mainly caused by the large size of the pools compared to the applied phosphate surplus. On basis of the size of the pools, significant changes over the period 1997-2000 may only be expected for the amount of easily available ('labile') P or in Pw values (water soluble P). However, these changes were obscured by a strong year to year variation in the measured values. Average P losses, due to leaching and runoff, ranged from 3.7 kg ha^-1 P at one of the sandy sites to 0.4 kg ha^-1 P at the clay site. Average leaching fluxes at the two other sites (peat and sand) were respectively 2.1 and 2.6 kg ha^-1 P. Differences in P surplus were hardly reflected in the P leaching losses from the different plots due to the high amounts of adsorbed P. However, measured P losses were strongly related (R²_adj. = 0.80) to the present P content (Pw level) at the bottom of the rootzone (20-30 cm) of the plots.

The validated model was used to simulate the long-term effect of P surpluses of 0, 10 and 20 kg ha^-1 jr^-1 on both the P leaching and the changes in P levels. These calculations were carried out for both the monitoring sites and a number of characteristic Dutch sites to get an impression on the national variation in losses as a response to different manure scenarios.

The agricultural activity could be a cause of the phosphorus (P) dispersion in to the environment (Haygarth and Sharpley, 1997). The P surplus, not used in agricultural production, is the main source of this dispersion. A farmstead and its vicinity is an integral part of the farm, where a constant flux of matter, including P, between the farmstead and rest of farm takes place. The goal of these investigations was to recognise the 'hot spots', which are mainly responsible for the P input from farm into the soil and groundwater.

The investigations were made on the basis of soil samples taken from 20 cm soil layers down to the 200 cm, as well as from 0-10 cm and 10-20 cm soil layer taken in the same places. The P content in the fresh soil samples was measured volumetrically and determined in the extract of 1% K₂SO₄ (more mobile form) and in 0.5 M HCl (potential pool of P) colorimetrically with Mo-blue reaction by the means of flow autoanalyser. The 1% K₂SO₄ soil extract is used to determine N-NO₃ and N-NH₄ content in the same soil samples (Sapek & Sapek, 1997). The P content in the soil was calculated in mg dm^-3 of fresh soil or recalculated to kg ha^-1. The groundwater samples were taken from the control wells installed at the similar monitoring points as the soil samples. The water samples from unused farm wells were also collected. The P concentration in water samples (RP_unf, according to Haygarth and Sharpley, 2000) was determined without filtration, in the same manner as the soil extract. The monitoring points were installed at 12 demonstration farms in different part of Poland within the project 'Baltic Agriculture Runoff Program' (BAAP) and at one farm of experimental station at Falenty.

The highest P contents determined in the soil extract of 1% K₂SO₄ (about 300 kg ha^-1 in 0-20 cm soil layer and about 700 kg ha^-1 in 0-200 cm soil layer) were confirmed in the vicinity of manure storage, by the barn or slurry tank. The P content determined in 0.5 M HCl extract of soil from these places corresponded to about 1800 kg ha^-1 in 0-20 cm soil layer and to 9300 kg ha^-1 in 0-200 cm soil layer. The mean P concentration in groundwater in such places was about 2.6 mg l^-1 and maximum concentration was 27.5 mg l^-1. The increased P concentration could happen also in the water samples from unused farm wells (0.33-0.74 mg l^-1).

The soil in poultry paddock in demonstration farms was normally enriched in P. The mean content of more mobile P form in 0-20 cm soil layer was about 40 kg ha^-1 and maximum 200 kg ha^-1. In comparison to that, P content in the soil at farm¢ s garden was about 6-17 kg ha^-1.

The risk of farmstead effect on soil and water pollution with P depends closely on the manner of animal wastes management. The soil enrichment with P in farmstead and its vicinity in experimental station was also high but lower in comparison to demonstration farms (Table 1).

Summarising, animal waste storage places, animal and poultry paddocks and housing as well as silage storage places and sewage tanks are the 'hot spots'. These could be the main sources of P dispersion and transfer of this element from the farm in to the environment.

Haygarth A.N., Sharpley A.N.2000. Terminology for phosphorus transfer. J. Environ. Qual. 1:10-14.

Sapek A. Sapek B. 1997. Methods of organic soils chemical analyse. Materialy Instruktazowe 115:80p. Falenty IMUZ Publication (in Polish).

Sharpley A.N., Rekolainen S., 1997. Phosphorus in agriculture and its environmental implications. p.1-53. In H. Tunney at al. (ed.) Phosphorus loss from soil to water. CAB International.

¶: isotopically exchangeable P within 1 minute (Frossard and Sinaj, 1997)

Four different amendments were used in this study: hematite Fe₂O₃ (98.5%), aluminium-oxide Compalox AN/V-801 (Alusuisse Martinswerk, D) and lime CaCO₃ (76%). Subsamples of 800 g field moisture soil (60% of waterholding capacity) were mixed with different amounts of amendments (control, 1:0.1; 1:0.01 and 1:0.002 soil/amendment weight/weight ratios). Samples taken immediately after mixing, 1 and 4 weeks of incubation were analysed for desorbable P according to Freese et al. (1999) and exchangeable P according to Frossard and Sinaj (1997). For every treatment we conducted a pot experiment with ³³P labelled soil to estimate the effect of the amendments on P availability for Lolium multiflorum.

For some amendments a strong effect on isotopic exchange parameters (n, C_p) was observed immediately after mixing soil and amendment. Aluminium-oxide application to soil at 1:0.01 ratio increased the P sorption capacity (n) from 0.29 to 0.46, at site I and from 0.36 to 0.41 at site II. With the 1:0.1 soil/amendment ratio n values increased to 0.57 and 0.58 respectively. For the 1:0.01 soil/amendment ratio the P concentration in the soil solution (C_p) decreased from 0.42 to 0.27 mg P L^-1 and from 0.26 to 0.15 mg P L^-1 for the site I and II respectively, and to 0.05 and 0.1 for the ration soil/amendment 1:0.1. The lime amendment had a strong influence on C_p of the soil from site II: 1:0.01 soil/ CaCO₃ ratio lead to a 70 % decrease of P in the soil solution. With hematite the effect was smaller and only large addition (1:0.1 ratio) increased n from 0.36 to 0.49 and decrease the C_p from 0.26 to 0.13 mg P L^-1. For the soil from site I no strong effect was observed for the hematite and the lime amendment. The application of aluminium and iron oxides lead to a higher P-fixing capacity by increasing the number of sorption sites. For the lime amendment the decrease in C_P could be explained by the precipitation of P as calciumphosphate-species and the increase in P-sorption capacity (n) due to a stabilisation of metal-P-bonds by Ca²⁺ ions.

For P-rich grassland areas with a high risk for P-losses to surface waters, application of lime and aluminium-oxide may be considered as remediation measures but further investigations should be conducted researching the environmental effects of amendments in field conditions prior to application.

Freese, D., Weidler, P.G., Grolimund, D. and Sticher, H. 1999. A Flow-Trough Reactor with an Infinite Sink for Monitoring Desorption Processes. Journal of Environmental Quality 28: 537-543.

Frossard, E., Sinaj, S. 1997. The Isotope Exchange Kinetic Technique: A Method to describe the Availability of Inorganic Nutrients. Applications to K, P, S, and Zn, Isotopes Environ. Health Stud. 33: 61-77.

All U.S. states and Canadian provinces that directly incorporate subsurface P transport into a Phosphorus Site Index are being surveyed to determine the best management practices (BMPs) specifically recommended to reduce P loss by subsurface pathways. Results of this survey will be summarized and presented to: (i) provide information on the rationale for the recommended BMPs, and (ii) summarize key research findings that justify the BMPs that are recommended, or required, to minimize the potential for subsurface P loss.

Centre for Soil & Environmental Quality, PO Box 84, Lincoln University, Canterbury, New Zealand

Intensive grazing and associated application of fertilizers and manures increase phosphorus (P) accumulation in soils and losses to water bodies which can result in eutrophication. Studies have indicated that some soils high in P are vulnerable to leaching losses and P concentrations up to 10 mg P L^-1 have been reported (e.g. Sims et al., 1998). This paper provides information on amounts and forms of P leaching losses from an irrigated grassland soil.

Lysimeters (50-cm diameter, 70-cm depth) were collected from a free draining stony Lismore silt loam soil (Udic Haplustept) (Cameron et al., 1992). The experiment included 4 replicates of the following annual treatments: P45, P45+DSE200, P45+DSE400, P45+DSE400+U (P45 = 45kg P ha^-1 as single superphosphate; DSE = dairy shed effluent at 200 or 400 kg N ha^-1, U= urine at 1000 kg N ha^-1). Flood irrigation (100 mm per application) was applied every three weeks between November and April. Leachate was collected after irrigation or a significant rainfall event. Dissolved reactive P (DRP) and total dissolved P (TDP) were determined in a filtered (<0.45 m m) sample, and total reactive P (TRP) and total P (TP) were determined in an unfiltered sample.

Phosphorus loss in reactive fractions (DRP and PRP) constituted only 10 % of total P in leachate while 90 % of P loss was accounted for in unreactive fractions (DUP and PUP). It was observed that PRP loss was higher than DRP in all treatments, except P45 (Table 1). For unreactive fractions, 58-61 % of total P loss occurred as PUP compared with 28-33 % for DUP (except P45). The P loss was significantly higher for DSE treatments. The annual TP loss for the 1999-2000 year were 930, 1303, 1728 and 2139 g ha^-1 for the P45, P45+DSE200, P45+DSE400, P45+DSE400+U treatments, respectively.

*data in parenthesis are concentration ranges;

PRP = particulate reactive P (TRP – DRP); DUP = dissolved unreactive P (TDP – DRP);

PUP = particulate unreactive P (TPP – PRP); TPP = total particulate P (TP-TDP)

Results of this study showed that 90 % of the P in leachate was present in unreactive particulate and dissolved forms which are believed to be organic P.

Cameron, K.C., Smith, N.P., McLay, C.D.A., Fraser, P.M., McPherson, P.J., Harrison, D.F. and Harbottle, P. 1992. Lysimeters without edge-flow: an improved design and sampling procedure. Soil Science Society of America Journal 56: 1625-1628.

Sims, J.T., Simard, R.R., and Joern, B.C. 1998. Phosphorus loss in agricultural drainage: Historical perspective and current research. Journal of Environmental Quality 27:277-293.

The relation is non-linear, but DRP consistent with for good water should be feasible at the lower end of the range of STP of 3 to 6 mg P L^-1 for optimum grassland production. Indeed it would appear that good water quality might only be possible if soil P were reduced to these levels. However, STP is only one factor in determining P losses to water. Data from a continuously monitored drain site in Northern Ireland, with a Morgan STP equivalent of 8 mg P L^-1, shows a wide variation in mean annual DRP concentrations and is consistent with many other studies (Lennox et al., 1997). These high values reflect the impact of manure P additions, followed by drain-flow and winter grazing of animals. Other studies in England have also argued the need to account for these ‘incidental’ losses of manure P as well as detached soil particles and colloids as part of a holistic approach to the problem (Haygarth and Jarvis, 1999).

The National Program for Sustainable Development in Ireland includes a target to reduce fertiliser P use by 10% per year, over five years. This will help reduce the current P surplus in Irish agriculture, which imports large amounts of P in animal foodstuffs, and perhaps reverse the national increase in soil P. In recognition of the importance of incidental losses of P, attention is increasingly being focused on measures that will reduce their impact by avoiding applications when the hydrological transport potential is highest in winter.

Haygarth, P. M. and Jarvis, S. C. (1999) Transfer of phosphorus from agricultural soils, Advances in Agronomy, 66, 195-249.

Lennox, S.D., Foy R.H., Smith R.V. and Jordan C. (1997) Estimating the contribution from agriculture to the phosphorus load in surface water. In: Tunney et al., (1997), Pages 55-75.

OECD (2000) Papers presented at OECD Workshop Antrim,Northern Ireland, June 1998. Journal of Environmental Quality, 29:1-176.

Tunney, H. (2001) Phosphorus needs of grassland soils and loss to water. Publ: International Association of Hydrological Sciences Journal, Wallingford, UK. (In press and due to be published in early 2001).

Tunney, H., Carton, O.T., Brookes, P.C. & Johnston, A.E. (1997) Phosphorus Loss from Soil to Water. Publ: CAB International, Wallingford, Oxon. UK. 467.

Pasture Systems and Watershed Management Unit, USDA-ARS, University Park, PA, USA

Development of strategies for assessment and management of nutrient loss from agricultural land should consider and incorporate the critical source-area (CSA) concept. In the case of phosphorus (P) loss specifically, CSAs result from the co-location of areas of high available P source (i.e., high soil test P and/or high rates of fertilizer and animal manure application) and high potential for P transport to a water body (catchment areas generating runoff and erosion). Much research has been conducted at the laboratory, plot, and field scales to characterize the source aspects of P availability to runoff as a function of soil test P levels and amounts and methods of fertilizer and manure application. However, only limited research results are available to quantify the transport aspects of P loss incorporating the spatial and temporal variability of surface runoff generation and its relationship to streamflow.

Here, we address the transport aspect of the formation of phosphorus CSAs – water movement at the landscape/catchment scale – with the primary hydrologic control on P transport considered to be surface runoff and its associated water-borne sediment. Although subsurface P transport can exist under limited conditions, we will not address it here. We view the P transport potential as being composed of two factors: 1) initiation of runoff at specific and identifiable locations over the landscape, and 2) the 'connectivity' of these runoff-producing areas with a downgradient water body where the impact of P loss from the landscape may be manifested.

The catchment-oriented research community has come to generally accept the concept of variable-source-area (VSA) hydrology. Its basic premise is that there is a dynamic runoff-contributing subcatchment within the topographically defined catchment. The contributing subcatchment expands and contracts seasonally, as well as during a storm, as a function of precipitation, topography, soil, geology, ground water levels, and catchment moisture status. Much of the research related to VSA hydrology has focused on saturation-excess runoff as the dominant flow component. When concerned with P transport across the landscape however, we cannot neglect the possible impact of catchment areas that generate runoff by the infiltration-excess mechanism. While perhaps not as widespread areally and temporally as is saturation-excess runoff under the humid-climate conditions addressed here, these areas still have the potential to develop and contribute to streamflow under the proper combination of soil, precipitation characteristics, and connectivity to the stream.

We are attempting to link the concept of VSA hydrology with expressions of causative precipitation, landscape topography, soil properties, and ground water status, to express both the generation of surface runoff over the landscape, and the 'connectivity' between these areas of surface runoff generation (e.g., fields or actual points) and the downgradient water body potentially affected by P loss. Here, we report our efforts to characterize VSA hydrology by field-, landscape-, and catchment-scale studies of surface runoff generation processes and the connectivity of runoff source-areas with the stream. These studies encompass both mechanistic hydrology suitable for incorporation in process-based catchment models (e.g., AnnAGNPS, SWAT), and design hydrology more applicable to user-oriented tools for P management (e.g. P Index). To the extent possible, the latter research thrust considers extrapolation of landscape-specific results to the catchment scale based on design storms, interpretive soil survey maps, available DEMs, and catchment-scale runoff and geomorphic characteristics.

Locations, along with time and space scales, of runoff source-areas are illustrated with specific research results from the Mahantango Creek Watershed in east-central Pennsylvania, USA. Results of studies examining runoff mechanisms as controlled by precipitation, initial moisture status, topography, detailed soil properties, and catchment-scale ground water status are presented. The results of these studies are also extended to interpretation of spatial and temporal patterns of P concentration in the stream during storm hydrographs to illustrate the connectivity aspect of P transport within the catchment. Additionally, using design storm characteristics and catchment-scale runoff and geomorphic characteristics, we illustrate how these catchment-specific results can be extended to the ungaged catchment setting in such a manner that they might be applicable to a user-oriented tool such as the P Index. Finally, we consider the implications of these results, both mechanistic and design oriented, for development of land-management strategies to mitigate P loss.

1Teagasc, Oak Park Research Centre, Carlow

This is good agreement in this kind of measurement. The WT model has dealt successfully with downward and upward flow regimes. It should be tested further on other sites and in other hydrological conditions.

In the preliminary assessment, the max level indicators in the laboratory differed from tape measurements by 9 +/- 1.7 mm (p< 0.05). In the field, the difference between two indicators was 2.3 +/- 13.5 mm (p<0.05). An error closer to 3.5 mm was expected. This did not seriously affect the operation of the model. The use of max level indicators may allow fieldwork to be reduced. Tests with other labour saving devices are ongoing.

McGarrigle, M. 1999. Mimeograph report. EPA, Johnstown Castle Estate, Co. Wexford, Ireland

¹Swedish University of Agricultural Sciences, Division of Water Quality Management, Box 7072, S – 750 07 Uppsala, Sweden

Beven K. and Kirkby M.J. 1979. A physically-based, variable contributing area model of basin hydrology. Hydrological Sciences Bulletin 24: 43-69

Haygarth P.M., Hepworth L. and Jarvis S.C. 1998. Forms of phosphorus transfer in hydrological pathways from soil under grazed grassland. European Journal of Soil Science 49: 65-72.

Kirkby M.J. and Cox N.J. 1995. A climatic index for soil erosion potential (CSEP) including seasonal and vegetation factors. Catena 25: 333-352

Centre for the Environment, Trinity College Dublin, Ireland

Identification of phosphorus (P) movement via all hydrological pathways has been identified as a key research need in addressing the eutrophication of surface waters (Sharpley et al., 2000). Groundwater P movement has received less attention than other transfer mechanisms; however, P can occur in groundwater at environmentally significant levels, and P leaching has been reported in sandy soils, high organic matter soils, and soils with high P concentrations (Sims et al., 1998). This paper examines groundwater P fractions in three catchment areas in the west of Ireland: the Fergus catchment in County Clare, a highly karstic Carboniferous limestone aquifer; the Robe catchment in County Mayo, a moderately karstic Carboniferous limestone aquifer; and County Limerick, containing catchments with non-karstic aquifers, predominantly fissured Carboniferous limestones and Devonian sandstones. This work forms part of a larger project to determine the circumstances in which groundwater discharges contribute to surface water eutrophication.

Over 500 samples were taken periodically from 56 springs and 67 wells in the three areas between July 1998 and March 2000. All samples were analysed for total P (TP) and 30% of the samples were also analysed for total dissolved P (TDP) and dissolved reactive P (DRP). Dissolved organic P (DOP) and particulate P (PP) were derived by calculation, i.e., DOP=TDP-DRP and PP=TP-TDP.

Mean TP levels for the Fergus, Robe and Limerick catchments were 65, 68 and 76 µg l^-1 respectively. Median TP levels for the same catchments were 26, 29 and 20 µg l^-1 respectively. The disparity between the means and medians highlights the skewed nature of groundwater P data. Extreme values of over 1000 µg l^-1 were reported in all catchments at a small number of sites experiencing pollution events. Thus medians are a more appropriate summary statistic and indicative of background P levels. Table 1 provides a summary of median levels of each P fraction for springs and wells in each catchment.

Dissolved reactive P was the dominant fraction for springs and wells in all catchments. Thus, in situations where groundwater P is contributing to surface water loading, it is doing so in the most biologically available form. The karst aquifers had higher DRP, DOP and PP levels than the non-karstic Limerick aquifers. This could reflect the influence of point recharge from surface waters via swallow holes, combined with less attenuation of P in karst systems due to rapid conduit flow. Springs had more PP than wells probably due to more turbulent flow. Karst aquifers pose a particular threat by providing rapid transfer of both dissolved and particulate P from land to surface waters.

Sharpley, A., Foy, B., and Withers, P. 2000. Practical and innovative measures for the control of agricultural phosphorus losses to water: an overview. Journal of Environmental Quality 29: 1-9.

Sims, J.T., Simard, R.R., and Joern, B.C. 1998. Phosphorus loss in agricultural drainage: historical perspective and current research. Journal of Environmental Quality 27:277-293.

J. Langlois and G. R. Mehuys

McGill University, Department of Natural Resource Sciences, 21,111 Lakeshore Road. Sainte-Anne-de-Bellevue, Canada

Relationships between surface runoff discharge and dissolved phosphorus (P) loads are complicated by a hysteresis effect. Until now, researchers have investigated hysteresis loops using qualitative tools describing their direction (e.g., clockwise or counterclockwise). The quantitative study of these loops would ease comparison of results of dissolved P losses in surface runoff between events and therefore help to evaluate the impacts of hydrologic characteristics, such as soil moisture conditions, on P transfer from fields to water bodies. The objectives of the present study were to 1) develop a technique to quantify the hysteresis of P transport in runoff water and 2) use this technique to compare hysteresis behaviour on an event basis.

Since fall 1998, measurements have been performed on two undrained raised beds (290 m x 33 m each) separated by a ditch along their length. Trenches were dug on each side of the ditch and waterproof polyethylene membranes were laid in them to intercept runoff from the adjacent beds. At the end of each trench, continuous monitoring of runoff volume was carried out using tipping buckets. Manual sampling of runoff water in both trenches was performed every 5 minutes for the first hour after initiation of a runoff event and at 15- minute intervals thereafter. Aliquots of runoff water were filtered (0.45 m m) and analyzed for dissolved P. Finally, rainfall volumes were measured using a recording raingage.

For each rain event, P concentrations were coupled with discharges during the rising limb and the falling limb of the runoff hydrograph. The resulting hysteresis curves were characterised by 1) computing a regression equation for each part of the hydrograph and 2) calculating an index (H) as the ratio of the intregral of the equation of the rising limb to that of the falling limb. Soil antecedent moisture conditions were estimated by using the ratio of runoff to rainfall volumes. The results show that soil antedecent moisture conditions affect hysteresis loops. Indeed, as the soil prior to a rainfall event is wetter, the P hysteresis behaviour of the loops shifts from a counterclockwise (H<1) to a clockwise direction (H>1). Quantitative assessment of hysterist behaviour contributes to a better understanding of the effects of hydrology, with its complexities of temporal variability, on P transfers from soils to water bodies.

Swiss Federal Research Station for Agroecology and Agriculture (FAL), CH-8046 Zurich

The loss of agricultural phosphorus (P) into soil due to surface runoff, soil erosion and leaching leads to unintended accumulation of nutrients in waters. In grassland-dominated regions with a high density of cattle and agricultural use coupled with manuring, surface runoff of dissolved phosphorus (DP) is seen as the major source of diffuse water pollution with P in surface waters. In 1993, a package of ecological measures among other things to reduce water pollution by agriculture has been introduced in Switzerland. They call for a biological and sustainable agricultural management and also for introducing of ecological compensation areas. One aim is to reduce agricultural P-loads into surface waters by 50% until 2005 (reference period 1990-92) (Forni et al., 1999). The effectivity of these ecological measures is investigated in the Lippenrütibach catchment (central Switzerland) which discharges into Lake Sempach, the lake which is most suffering from eutrophication in Switzerland.

The catchment (334 ha) is situated between 500 and 800 m.a.s. and mean annual precipitation is about 1000 mm. The agricultural area of 255 ha consists of 80% grassland and 20% arable land. Hourly P- and runoff-data of the creek Lippenrütibach are available. The creek discharged between 1986 and 1998 in average 0.86 t P (0.32 t DP and 0.54 t sediment bound P) into Lake Sempach.

Phosphorus-loss into waters due to surface runoff are estimated by an empirical-statistical modelling approach similar to the P-index of Gburek et al. (1996). Factors for the assessment of the risk for P-runoff due to natural conditions of individual plots (soil type, topography, distance to gully drains), due to agricultural practices (land use, livestock density, agricultural use, measures against P-loss into fields) and due to indvidual events (manuring, precipitation) are collected for each of 270 fields in the catchment. Connections between these factors and the measured P- and runoff-data in the creek can thus be related to each other. The assessment of total risk for P-runoff for each plot results from the links between these described factors. The risk for P-runoff is classified into four classes (low, medium, high, very high). According to classified total risk for P-runoff, an area-specific P-loss-value is introduced for each plot.

Results for 1998 show on 21% of all plots no or low, on 26% medium, on 48% high and on 4% very high total risk for P-runoff into surface waters (Braun et al., 2001). Since in 1998 mean annual precipitation was comparatively low (950 mm), classes of total risk may partially move towards higher classes by modelling additional years with average or above-average mean annual precipitation.

Calculated potential of P-reduction for 1998 amounts to 94 kg P, respectively 19% of agricultural P-loads (Braun et al., 2001). This reduction can be attributed to the introduction of ecological measures. However, it is still far smaller than the planned P-reduction of 50%. A scientifically reliable evidence for the efficency of ecological measures will only be possible after analyzing additional years. These investigations will be continued until 2005. In addition to the statistical modelling approach presented here, more physically based modelling approaches will be developed.

Braun, M., Aschwanden, N. und Wüthrich-Steiner, C., 2001: Evaluation Oekomassnahmen: Abschwemmung von Phosphor. Agrarforschung 8 (1), 36 – 41

Forni, D., Gujer, H. U., Nyffenegger, L., Vogel, S. und Gantner, U., 1999: Evaluation der Oekomassnahmen und Tierhaltungsprogramme. Agrarforschung 6 (3), 107 – 110

Gburek, W. J., Sharpley, A. N. and Pionke, H. B. 1996: Identification of critical source areas for phosphorus export from agricultural catchments. – Advances in Hillslope Processes Vol. 1, 263 - 281

Institute for Land Reclamation and Grassland Farming at Falenty, PL-05-090 Raszyn, Poland

It is commonly supposed, that phosphorus (P) compounds in peat soil are better soluble then in mineral soils. Therefore, a higher P leaching can be expected. There are some opinions, that the dewatering of peaty bog would reduce the solubility of P compounds and in opposite, the renaturisation of peatland through raising the groundwater level would result in increasing this solubility. The better solubility of P compounds could cause a risk of eutrofication of surface water below the peatlands. The aim of this work was to identify the changes in solubility of compounds in peats, which are exposed to some changes in hydrological regime.

The investigations were localised in great area of peatlands in Poland - the valley of Biebrza river. Particularly, the Biebrza National Park of Peatlands (about 170 000 ha), and Kuwasy bog used as a productive meadows (about 1000 ha). On all objects, the groundwater level was lowered due to dewatering the valley for the agricultural use of some parts of peatland. Now, there are making some attempts to heighten the groundwater level in National Park area as well as in agricultural used site. The peats occurring in Biebrza River Valley are rich in P due to phosphate flow from the mineral soils in surrounding watershed. The agricultural use peat soils in Kuwasy bog were heavy dressed with P during last 40 years.

In National Park, two trans-sections were established, where a set of plastic tube were installed in direction downward to the subsurface runoff. 9 tubes were installed on the Grobla Honczarowska trans-section and 8 on he Gugny trans-section. 10 tubes were installed on in Kuwasy bog. Water samples of groundwater and surface water from nearby streams were taken once a month, and P concentration were determined calorimetrically in unfiltered samples by use of molybdate blue method.

The P concentrations in stream water were much higher then usually observed in Polish river water. While, these concentrations were rather high in some samples of groundwater (Table 2). The highest concentrations were found in samples from Gugny trans-section, where the increasing groundwater level was greatest during last few years, in spite of that the P content in peat was the lowest (Table 1). The P fertilisation on Kuwasy object has no visible effect on its concentration in water. There are observed some regular changes in P concentration along the trans-section, but the number of measurements made at the preliminary stage of investigation does not allow to do any conclusion.

This work has been done in scope of Environment Project EVK1-1999-00121 'PROWATER'

1Environmental Water Resource Engineering, Department of Civil and Environmental Engineering, Imperial College of Science Technology and Medicine, London, SW7 2BU

The quality of surface waters throughout Europe, in terms of risk of eutrophication, is a major current concern because of increasing concentrations of phosphorus (P). Current legislation has focused on point sources and in many cases this has not resulted in alleviating the eutrophic conditions (Foy et al., 1995). With the introduction of the Water Framework Directive a shift in emphasis towards diffuse sources is required and a more integrated approach in the management and control of eutrophication. This necessitates the use of catchment-scale models in quantify the contribution from point and non-point and therefore where expenditure is best targeted.

Many catchment-scale hydro-chemical models require a large number of spatially distributed parameters making application and calibration difficult and resulting in large uncertainties in the model output. However, simple export coefficients have been advocated as empirical tools to assess the annual export of total phosphorus (TP) in relation to land use (Johnes, 1996). Previous regression analysis has also indicated that dynamic phosphorus export can be approximated as a direct function of discharge (Lennox et al. 1997). Here a simple hypothesis to integrate these 2 approaches and produce a simple dynamic model (Daldorph et al. 2000) is tested against data flow and total phosphorus concentrations from the Rutland Water, UK. Annual loads derived using export coefficients are disaggregated using the relationship between the flow and TP load in headwater streams. The diffuse TP load can then be estimated as a direct function of the daily runoff volumes and the annual TP export.

Calibration and sensitivity analysis is conducted in a Monte Carlo framework with uncertain parameters sampled at random from a uniform distribution. The performance of each model (here ‘model’ refers to the parameter set model combination) is assessed against different aspects of the observed data. The results are analysed using the Monte Carlo Analysis Toolkit, a series graphical techniques developed at Imperial College, (MCAT, Wagener et al., 2001).

Results of the sensitivity analysis show there is a trade off between fitting the different objective functions with estimated parameter values derived from different areas of the parameter space. Points which lie along this ‘trade-off’ form the Pareto set, where: ‘a solution is said to be Pareto optimal (i.e. part of the Pareto set) if the value of any objective function cannot be improved without degrading at least one of the other objective functions’ (Chankong and Haimes, 1993). Model simulations using the Pareto set also failed to encompass important aspects of the observed data, suggesting error in the model framework. However the analysis highlights areas the model performance could be improved. The assumption that the TP available in the soil remains constant is clearly an oversimplification and the inclusion of an exhaustion effect would improve model performance.

Chankong, V. and Haimes, Y.Y. 1993. Multiple optimization: Pareto optimality. In Young, P.C. (ed.) Concise encyclopedia of environmental systems. Pergamon Press, Oxford, UK, 387-396.

Daldorph, P.W.G., Lees, M.J., Wheater, H.S. and Chapra, S.C. 2000. Integrated Lake and Catchment Phosphorus Model: A Eutrophication Management Tool. I Model Theory (In press).

Foy, R.H., Smith, R.V., Jordan, C. and Lennox, S.D., 1995. Upward trend in soluble phosphorus loadings to Lough Neagh despite phosphorus reduction at sewage treatment works. Water Research 29: 1051-1063.

Johnes, P.J. 1996. Evaluation and management of the impact of land use change on the nitrogen and phosphorus load delivered to surface waters: the export coefficient approach. Journal of Hydrology 183: 323-349.

Lennox, S.D., Foy, R.H., Smith, R.V.& Jordan, C. Estimating the contribution from agriculture to the phosphorus load in surface water. In P loss from Soil and Water (ed H.Tunney). Cabs International. 1997.

Wagener, T., Lees, M.J. and Wheater, H.S 2001. A framework for the development and application of parsimonious hydrological models. To appear in Singh, Frevert and Meyer (Eds.) Mathematical models of small watershed hydrology – Volume 2. Wat. Resour. Publ. LLC, USA, in press.

Department of Soil Sciences, Division of Water Quality Management, Swedish University of Agricultural Sciences Box 7072, SE-750 07 Uppsala, Sweden

As a part of nation-wide monitoring of the impact of agriculture on the aquatic system, phosphorus (P) transport was measured from subsurface drained fields in Sweden. The measured transports was a mixture of P from surface, subsurface and groundwater contribution. Fourteen of these fields together with a similar experimental field have been studied for at least ten years and most of them for much longer. Transport of total phosphorus (TP) from four of the fields together accounted for 74% of the total transport. Five other fields together accounted for another 19%, while transport from the other five fields was more or less negligible. Based on factor combinations, a simple regression model for calculating TP concentration was used for prediction of the losses. The parameters included were livestock density (LD), HCl extractable P (P-HCl) in the topsoil, duration of high water flow (DHF) and soil specific areas (SSA). The model was found to satisfactorily predict the TP transport in the streams of 32 small agriculture-dominated catchments in different parts of the country, with a P loss from arable land that was calculated as varying from 0.03 to 0.50 kg ha^-1 y^-1. However, for a very few catchments, the model worked only for transport by drainage water and not for P transport measured in the stream water.

Eleven of the observation fields had been investigated since 1977 or earlier. During this period, a surplus of P added to the soil during the initial years was transformed to a slight negative balance of P. Transport from most of the fields was found to be relatively constant, but the two fields with the highest P transport showed an increased trend during the 1970s and 1980s.

Agricultural Research Centre of Finland, FIN-31600 Jokioinen, Finland

In the clayey soils of south Finland, particulate phosphorus (PP) is typically the major phosphorus (P) fraction in runoff waters (Turtola, 1999). Most of the PP in these waters is considered non-desorbable, i.e., mostly non-bioavailable in aerobic environments (Ekholm, 1998; Uusitalo et al., 2000). However, there are no published data about the potential for P release from the suspended soil material in anoxic conditions. In this paper we report the transport of different P forms from a clayey field at Jokioinen, southwestern Finland, and assess the potential for release of PP both in aerobic and in strongly reduced environment.

The soil of the Jokioinen field was a very fine Typic Cryaquept, having 48 % clay, 2.5 % organic C, and 31-45 mg kg^-1 Olsen-P (for a detailed description of the field, see Turtola, 1999). Flow-proportional sampling of surface and subsurface runoff was arranged by tipping buckets, allowing all runoff waters to be analysed for dissolved molybdate-reactive P (DRP; filtration through a 0.2 m m polycarbonate filter), and total P (TP; digestion with peroxodisulfate and sulfuric acid in an autoclave). Particulate P was taken as the difference between TP and DRP.

To find out how much of the PP is released when the environment is aerobic, we extracted 205 runoff samples by anion exchange resin (AER). The extraction followed the procedure of Sibbesen (1978), with minor modifications given in Uusitalo et al. (2000). Preliminary assessment of the potential for P release in a strongly reduced environment (less than –400 mV) was done for 37 samples by using a modification of bicarbonate-dithionite (BD) extraction step of the P fractionation of Psenner et al. (1984). Extraction of a 30-ml water sample was conducted on an orbital shaker (120 rpm, 15 min) at room temperature after additions of 1 ml 0.223 M NaHCO₃ and 1 ml 0.431 M Na₂S₂O₄ (freshly prepared solutions). After shaking, the sample was immediately filtered through a 0.2 m m filter, and the filtrate digested with peroxodisulfate and sulfuric acid in an autoclave in order to destroy excess dithionite which otherwise caused major interferences in P determination by a spectrophotometer.

Annual P loss from the Jokioinen field during 1992-1998 averaged 920 g ha^-1 (Turtola, 1999), and the proportion of PP was 87 % of TP, i.e. 800 g ha^-1. According to the results of the AER and BD extractions, 6.6 % of PP was desorbable in aerobic environment, whereas 10-80 % (mean 31 %) of the PP in the samples studied was released when the redox potential was lowered by dithionite addition. When compared to the mean annual DRP loss of 120 g ha^-1, we estimate that two third of the potentially bioavailable P load from the Jokioinen field was in dissolved form, as long as the eroded sediment remained in aerobic environment. The situation would, however, be very different if the eroded soil material would end up in a strongly reduced environment. Then, the suspended sediment would be a source of twice as much potentially bioavailable P as was transported as DRP, and little less than half of the TP would be potentially available for primary production in the receiving waters.

Ekholm, P. 1998. Algal-available phosphorus originating from agriculture and municipalities. Monographs of the Boreal Environ. Res. 11, 60 p.

Psenner, R. von, Pucsko, R., and Sager, M. 1984. Die fraktionierung organisher und anorganisher Phoshorverbindungen von Sedimenten. Arch. Hydrobiol./Suppl. 70:111-155.

Sibbesen, E. 1978. An investigation of the anion-exchange resin method for soil phosphate extraction. Plant Soil 50: 305-321.

Turtola, E. 1999. Phosphorus in surface runoff and drainage water affected by cultivation practices. Agricultural Research Centre of Finland and Univ. of Helsinki. 108 p. Diss. ISBN 951-729-555-3.

Uusitalo, R., Yli-Halla, M., and Turtola, E. 2000. Suspended soil as a source of potentially bioavailable phosphorus in runoff waters from clay soils. Wat. Res. 34: 2477-2482.

1 The University of Adelaide, Australia

The effect of Ca on P and DOM adsorption to a clay mineral (kaolinite) was investigated by a batch methodology. Solutions (150 ml) containing 1 mg L^-1 P, at ionic strengths of 0.001, 0.01 and 0.05 M NaCl and with or with out DOM (at 18 mg L^-1) and Ca (at 100 mg L^-1) were adjusted to 3 pH values (5, 7 and 9) and were added to 500 mg of kaolinite. Three replicates of the 36 possible combinations of the variables were shaken for a period of 24 hours.

Results of the batch study indicated that, in the absence of DOM, Ca reduced the amount of P left in solution. This reaches a maximum at pH 9. The effect of ionic strength was dependent on the presence or absence of Ca. In the presence of Ca, P removal from solution decreased with increasing ionic strength. In the absence of Ca, the reverse trend was true. DOM appeared to have considerable effect on P removal. Ca has little effect on P removal in the presence of DOM.

If the P removed from solution in the batch trials was assumed to be by adsorption to kaolinite, then it appears that Ca acted as a cooperative cation in P adsorption. If this is the mechanism, then the different effect of variation in ionic strength in the presence or absence of Ca suggests different adsorption mechanisms (He et al., 1997). Increasing adsorption with increasing ionic strength in the absence of Ca suggests adsorption is dominated by inner sphere or specific adsorption mechanisms. The reverse pattern in the presence of Ca suggests outer sphere or non specific ion pair bonding mechanisms. Literature suggests however that a more likely removal mechanism in the presence of Ca maybe precipitation of Ca-phosphates (Hawke et al., 1989). While there was no evidence of Ca-phosphate precipitation in blank trials (no kaolinite) it is further suggested that this precipitation maybe enhanced by the presence of the mineral surface (Hawke et al., 1989). However with no indication by XRD of Ca-phosphates present in the kaolinite containing batches, and the significant competitive effect of DOM on phosphate removal in the presence of excess Ca, the mechanism of phosphate removal requires investigation.

Hawke D., Carpenter P.D., and Hunter K.A. 1989. Competitive adsorption of phosphate on goethite in marine electrolytes. Environmental Science and Technology 23:187-191.

The study revealed a strong correlation between small and large-scale P transfers. There was also a clear progression in the timing of the peak P concentration as scale increased, consistent with the hypothesis that river fluxes are composed of local inputs plus those travelling in from upstream. We believe that P entrainment from channel banks is likely to be low, because soil P distribution and river erosion studies (Haygarth et al., 1998; e.g. Walling and Woodward, 1995) have shown that extractable P concentrations in the local soil decrease dramatically with depth, and that channel erosion in local rivers generally accounts for no more than 12% of the suspended sediment flux. This implies that edge of field transfers from agricultural land are likely to be a significant source of associated river P fluxes. These may not be the only source, as the total storm flux of P per unit area of catchment does vary considerably from site to site, and tends to be greater than the flux measured from our field scale sites. However, there is some evidence that higher transfers generated from other land types within the catchment might account for this variation between sites.

We therefore conclude that although the relationship between scales is not simple, there is a significant underlying connectivity of transport of P from diffuse agricultural sources to downstream water bodies.

Haygarth, P.M., Hepworth, L., and Jarvis, S.C. 1998. Forms of phosphorus transfer in hydrological pathways from soil under grazed grassland. European Journal of Soil Science 49(1): 65-72.

Jordan, C. and Smith, R.V. 1985. Factors affecting leaching of nutrients from an intensively managed grassland in County Antrim, Northern Ireland. Journal of Environmental Management, 20: 1-15.

Rowland,A.P. and Haygarth,P.M. 1997. Determination of total dissolved phosphorus in soil solutions. Journal of Environmental Quality 26(2): 410-415.

Walling, D.E. and Woodward, J.C. 1995. Tracing sources of suspended sediment in river basins: a case study of the River Culm, Devon, UK. Marine and Freshwater Research 46: 327-326.

We thank Marta Alfaro, Mark Butler, Jane Hawkins, Elaine Jewkes, Carly Kenny, Kevin McTiernan, and Neil Preedy for their help with sampling. This study was funded by the Ministry of Agriculture Fisheries and Food, UK, grant awards NT 1043 and AE 9199.

Swedish Meteorological and Hydrological Institute (SMHI), Norrköping, Sweden

Eutrophication is a well-known problem in many Swedish lakes that causes poor drinking water quality, overgrowth, large algae blooms, etc. By stream inflow the lakes receive nutrients leached from soil and emitted from point sources. However, several measures can be taken to restore or preserve the water quality; measures can either be ecotechnological in the lake itself, or changed emissions and drainage-basin management. The choice between nutrient reducing strategies is a question of combining biological effects in the lake with other considerations. A decision support system simulating the effects and costs for water management is currently under development in Sweden within the VASTRA program (Wittgren, 1998). This paper presents how a lake model within this system can simulate the biogeochemical response to different management scenarios.

The newly developed biogeochemical model is linked to an existing physical lake model developed at SMHI (Svensson, 1998). The model is horizontally homogeneous, but vertically divided in a discrete number of layers (typical 20). The only exception is the variable macrophyte, which has a horizontal variation.

The most important variables for nutrient dynamics in lakes are the dissolved nutrient concentrations (nitrogen and phosphorus) and the phytoplankton. Ordinary, phytoplankton use dissolved nutrients to grow, but in phosphorus-rich lakes nitrogen fixation by algae may be important. Shallow lakes are dominated by macrophytes or phytoplankton and can switch between these states. Sediments can be a source or a sink for nutrients. Zooplankton feeds on phytoplankton, but has other food sources (e.g. detritus), which stabilises the population. Top-down control can also be processed from further up in the food web (i.e. from fish). All these variables are potentially important factors for the nutrient dynamics and are therefore included in the model. Totally 14 state variables are used.

Other important processes included in the model are inflow/outflow of water and nutrients through tributaries/discharge, denitrification, nitrification, degradation of detritus and organic matter in sediment, sedimentation of phytoplankton, detritus and macrophyte.

In an application where the model results are used for management of a specific lake, data from that lake should be included in the model before doing simulations. So far, the model is run with hypothetical data to investigate the model’s response, however, during the first half of 2001 the model will be evaluated against observed data in a highly eutrophied lake. The present base scenario was complemented with runs with increased nutrient input through inflow, inducing phosphorus (P) and nitrogen (N) limited primary production, and with increased fish. A long run has also been performed to look at long term levels and seasonal variations of different variables.

The base scenario was run for seven years. After the first year the seasonal pattern were similar from year to year. Nitrogen fixating algae dominated all year with a peak in August-September, other phytoplankton were much less abundant and peaked earlier in summer before being grazed down. Zooplankton was most abundant in autumn, while macrophyte peaked in spring.

A doubling of the N inflow increased the macrophyte, which started to take up N from the water when sediment N ran out. It also suppressed the development of N fixating algae compared to the base run, although they still were dominating during autumn due to their lower edibility for zooplankton. A doubling of the P inflow did not influence the macrophyte or phytoplankton except for N fixating algae, which became even more dominating using atmospheric N. An increase in planktivorous fish stock decreased the zooplankton, but increased the phytoplankton in a top-down control.

The model has shown to be able to simulate effects of changing nutrients and plankton dynamic, and even top-down control by fish. The macrophyte part of the model is still immature. It needs to be studied further and the model adjusted. Still, the model shows promising results to be used as an evaluation instrument for various measures to improve water quality in lakes.

Svensson, U. 1998. PROBE Program for Boundary Layers in the Environment System Description and Manual. Swedish Meteorological and Hydrological institute, Report RO No. 24, Norrköping.

Wittgren, H. B. 1998. Water management research towards catchment-based strategies for sustainable resource use. Vatten 54: 295-300.

Environment Agency, National Centre for Ecotoxicology and Hazardous Substances, Evenlode House, Howbery Park, Wallingford, Oxon, OX10 8BD, UK

Aquatic eutrophication was historically regarded by some as an exacerbation of a natural phenomenon giving rise to local problems in a small number of areas in England and Wales. Recent evidence, particularly as regards the freshwater environment, indicates that it is more than a limited localised problem in England and Wales. From 1989 to 1997, for example, some 3,000 different freshwater bodies (mainly standing, but also running waters) have been affected by algal blooms. To date, 80 Sensitive Areas (Eutrophic) have been designated under the Urban Waste Water Treatment Directive, of which 62 are rivers or canals, 13 are lakes/reservoirs and 5 are estuaries. Under this initiative, waters receiving discharges from large sewage treatment works were assessed for the effects of eutrophication using chemical, biological and use-related criteria. Excessive weed growth and changes to macrophyte communities were the main ecological impacts detected, although benthic and floating mats of blue-green algae have caused problems in some slow flowing rivers. Eutrophication is also implicated in depreciating the conservation value of many stillwater Sites of Special Scientific Interest (SSSIs). In a survey commissioned by English Nature, 84% out of a sample of 102 SSSIs showed symptoms of eutrophication, and in 68% of cases this ‘had overtly affected the nature conservation interest’ (Carvalho and Moss, 1995).

In response to the impacts and risks associated with aquatic eutrophication, and the range of statutory and international commitments requiring action to be taken to address such problems, the Environment Agency (of England and Wales) launched a eutrophication management strategy in August 2000 (Environment Agency, 2000). The strategy aims to strike a balance between the recognised need for further and improved management action and the uncertain benefits of control measures, stemming from a relatively poor, albeit improving, understanding of cause and effect. Supporting further research into improved methods for assessing and monitoring the impacts of eutrophication is a key component of the strategy. The need for increased use of biological indicators and ecological assessment is recognised, although the relationship between nutrient levels and the desired ecological objectives can be unpredictable and differs according to waterbody type. This shift in emphasis from predominantly physico-chemical parameters towards biological parameters is in line with the newly adopted EU Water Framework Directive, which specifies the need to assess ecological quality (including physico-chemical, biological and hydromorphological elements) and to achieve good ecological status.

Historically, there has been limited linkage between monitoring for nutrient levels and biological parameters. For standing waters, the OECD trophic classification is based on the observed relationship between total phosphorus and phytoplanktonic chlorophyll concentrations, but has limited application for some water bodies (e.g. shallow lakes). In recent years, biological indicator schemes for rivers, such as the trophic diatom index (TDI), and trophic ranking scheme for macrophytes (MTR) have been developed. These have been employed in assessing the extent of eutrophication for some locations (e.g. for the designation and review of Sensitive Areas (eutrophic) under the Urban Waste Water Treatment Directive). However, these methods may still need refinement, and biological classification systems for other water bodies are less well developed. Further research is required before nutrient conditions and biological quality indicators can be linked with an acceptable degree of reliability. The ability to link nutrient conditions with biological quality elements will significantly affect decisions taken regarding the Water Framework Directive, implementation of the Agency’s eutrophication strategy, UK Biodiversity Action Plans, Habitats Directive, Nitrates Directive and Urban Waste Water Treatment Directive.

In this paper, we will discuss current methods and best practice in England and Wales for assessing and monitoring eutrophication. We will also discuss the implications of the Water Framework Directive, in particular, the need to improve current understanding of the relationship between nutrient concentrations and biological quality for different water body types and different levels of ecological status.

Carvalho, L. and Moss, B. 1995. The current state of a sample of English Sites of Special Scientific Interest subject to eutrophication. Aquatic Conservation: Marine and Freshwater Ecosystems 5: 191-204.

Environment Agency. 2000. Aquatic eutrophication in England and Wales; a Management Strategy. Environment Agency, Bristol, 32pp.

The aims of the present study were to identify whether the concentrations of SRP and other P fractions in drainflow had further increased in the period 1989-1997 and assess the response to a new management regime introduced in 1998 and 1999. From 1998, slurry was no longer applied to the site and only sufficient fertiliser P was applied to maintain each field at Index 2 (16-25 mg P kg^-1) according to ADAS recommendations (MAFF, 1994). In effect, the changes imposed an average P deficit for the site during 1998 and 1999 of 15.0 kg P ha^-1 yr^-1 compared to a mean surplus of 23 kg P ha^-1 yr^-1 for the period 1989-1997.