Critical Source Areas Research Articles

Control division of agricultural non-point source pollution at medium-sized watershed scale in Southeast China

This paper presents the study carried out for controlling agricultural non-point source pollution (NSP) in a medium-sized watershed covering 1.47 × 104 km2 in Southeast China using quantitative analysis coupled with geographic information system (GIS), universal soil loss equation (USLE), soil conservation service-curve number (SCS-CN), nutrient loss equations, and annualized agricultural nonpoint source model (AnnAGNPS). Based on the quantitative results derived from GIS and environmental models, five control division units were generated for NSP control in Jiulong River watershed, namely, controlling unit for soil losses, controlling unit for livestock breeding and soil losses, controlling unit for excessive fertilizer use and livestock breeding, controlling unit for soil losses and fertilizer use, and controlling unit for excessive fertilizer use and soil losses. This study proved that integrating GIS with environmental models can be adopted to efficiently evaluate major sources and contributors of NSP, and identify the critical source areas of NSP, which enables adjusting measures to local conditions by further control division units developed through such study for control and management of water quality degradation induced by NSP in the Jiulong River watershed.

Hydrogeological characterization of an altered wetland

Summary Spatiotemporal changes in the hydrogeology of the Hula altered wetland may influence the water quality of Lake Kinneret, which provides up to 30% of the potable water for the state of Israel. The main objectives of this work were to study the groundwater-flow characteristics in this wetland and assess the potential impact on downstream water quality. We constructed variograms of hydraulic heads, computed decision-tree models of major ions, and determined the hydraulic conductivity ( K ) and δ 2 H/δ 18 O ratios, to ascertain the spatial and vertical distribution of hydrogeological parameters. We also performed large-scale field experiments (⩾1 km 2 ) to assess the connectivity between the waterways and the wetland’s aquifer. The aquifer is fragmented by three parent materials: deep peat, shallow peat/marl complex and marl. The decision-tree-based model, the isotopic ratios and K determinations suggest that the deep peat subaquifer is composed of one homogeneous layer characterized by low K (0.001 m d −1 ). The two other subaquifers consist of three hydrostratigraphic layers: (i) the vadose zone, (ii) a layer with well-developed macropores at a depth of 1.5–4 m and (iii) an aquitard layer at a depth of 4–15 m. The temporal head fluctuations, the high K values of the second layer (>170 m d −1 ), and the large volume of water flowing into and out of the two subaquifers during large-scale field experiments all attest to excellent connectivity with the waterways. These results support the concept of critical source area which claims that most of the P loss in a catchment derives from small areas in which specific P release and transport mechanisms coincide with high connectivity. We conclude that the high connectivity of this Mediterranean altered wetland to waterways, coupled with the high P release that has occurred in recent years following soil flooding, provides the loading mechanism that partially explains the observed P increase in the Jordan River.

PSYCHIC – A process-based model of phosphorus and sediment mobilisation and delivery within agricultural catchments. Part 1: Model description and parameterisation

PSYCHIC is a process-based model of phosphorus (P) and suspended sediment (SS) mobilisation in land runoff and subsequent delivery to watercourses. Modelled transfer pathways include release of desorbable soil P, detachment of SS and associated particulate P, incidental losses from manure and fertiliser applications, losses from hard standings, the transport of all the above to watercourses in underdrainage (where present) and via surface pathways, and losses of dissolved P from point sources. The model can operate at two spatial scales, although the scientific core is the same in both cases. At catchment scale, the model uses easily available national scale datasets to infer all necessary input data whilst at field scale, the user is required to supply all necessary data. The model is sensitive to a number of crop and animal husbandry decisions, as well as to environmental factors such as soil type and field slope angle. It is envisaged that the catchment-scale model would provide the first tier of a catchment characterisation study, and would be used as a screening tool to identify areas within the catchment which may be at elevated risk of P loss. This would enable targeted data collection, involving farm visits and stakeholder discussion, which would then be followed up with detailed field-scale modelling. Both tiers allow the effects of possible mitigation options at catchment scale (Tier 1) and field scale (Tier 2) to be explored. The PSYCHIC model framework therefore provides a methodology for identifying critical source areas of sediment and P transfer in catchments and assessing what management changes are required to achieve environmental goals.

Review of indexing tools for identifying high risk areas of phosphorus loss in Nordic catchments

Summary Compliance with the Water Framework Directive (WFD) will require substantial reductions in agricultural phosphorus (P) losses in the Nordic countries Denmark, Norway, Sweden and Finland. Falling P surpluses in agriculture for more than a decade and voluntary programmes of good agricultural practice have not reduced P losses to surface waters, while general regulatory measures have primarily focused on nitrogen. Without addressing the role of critical source areas for P loss, policy measures to abate diffuse P losses are likely to be ineffective. This has created a demand by environmental authorities for instruments that assess the risk of P losses from agricultural land and facilitate the planning of mitigation measures. In Nordic countries index-type risk assessment tools for diffuse P losses are under development inspired by experiences with P indexing in the USA. A common feature is that they are empirical, risk-based, user-friendly decision tools with low data requirements. Phosphorus indices vary between the four Nordic countries in response to different agriculture, soil and climate. These differences also result in different recent average annual agricultural P load estimates to the sea of 0.3, 0.5, 0.5 and 1.1 kg total P ha−1 in Denmark, Norway, Sweden and Finland, respectively. In initial evaluations, Nordic P indices explained a large degree of variance in P losses at the field or catchment scale, but comparative data are still limited. To gain acceptance amongst stakeholders and inform river basin management planning in Nordic catchments as part of the WFD, it is crucial to more thoroughly evaluate the performance of these indices’ at the field and catchment scale.

Agriculture, phosphorus and eutrophication: a European perspective

The enrichment of European waters with anthropogenic sources of nutrients (nitrogen (N) and phosphorus (P)) contributing to eutrophication, and the resulting impairment of water use for recreation, industry and drinking, has become a major environmental issue in recent decades. Concern over eutrophication first emerged in Europe’s coastal waters with subsequent commitments by bordering countries to reduce nutrient emissions to the sea (De Walle & Sevenster, 1998). National surveys of standing and flowing freshwaters in different EU countries also identified a widespread incidence of eutrophication and led to the development of various indicators to monitor trends in water quality (EEA, 2003). Whilst both N and P contribute to eutrophication, there is ample evidence that the main focus for reducing eutrophication should remain with phosphorus (Sundareshwar et al., 2003; Foy, 2005). With the introduction of the EU Water Framework Directive (WFD) in December 2000, there is now a legislative framework to implement catchment controls over P inputs to EU waters from all sources, including those from agriculture. According to EEA (2005), the agricultural contribution to total annual P loads in EU waters is often about 50% (range 25–75%) with higher proportional contributions in countries where point-source P inputs have been markedly reduced by wastewater treatment. Controls over transfers of P from agricultural land have therefore been judged a necessary part of the integrated catchment management needed to achieve the good ecological status demanded by Europe by 2015. Until the early 1990s, there had been very little EU research conducted on phosphorus transfer in runoff from agricultural land. As the potential linkages between agricultural intensification, increased P concentrations in land runoff and eutrophication became more widely appreciated (e.g. Tunney et al., 1997; Edwards & Withers, 1998), research to quantify the accumulation, loss and impact of P from land to water increased amongst different disciplines. In July 1997, EU COST Action 832 (Quantifying the Agricultural Contribution to Eutrophication) was set up to help co-ordinate this research activity in order that the agricultural contribution to eutrophication could be more uniformly assessed across Europe. The specific aims of the Action were to develop a common conceptual understanding of the processes of P transfer to water and to identify appropriate methodologies for quantifying the use, cycling, transfer and impacts of phosphorus in runoff from agricultural land. The Action involved 18 countries (Austria, Belgium, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Norway, Poland, Romania, Spain, Sweden, Switzerland, the Netherlands and the UK) and over 140 scientists participated. This special issue of Soil Use and Management draws together the knowledge base and selected research studies conducted across Europe as part of COST 832 and supporting national research programmes. It succeeds an earlier special issue of Soil Use and Management that summarized research into phosphorus loss from agriculture in the UK (Edwards & Withers, 1998). The COST Action adopted the P transfer continuum theme outlined by Haygarth et al. (2005), in which four working groups discussed P inputs to agricultural land (sources), release of P from the soil or P amendments (mobilization), P transfer from the point of mobilization to the stream (delivery) and the fate of P on entering different types of water body (impacts). This is illustrated conceptually in Figure 1. This theme is continued in this special issue and complements other publications from the COST Action (Chardon & Schoumans, 2002; Kronvang, 2002; Chardon & Withers, 2003). The first four papers describe the range in P surpluses, the relative importance of the different processes of P transfer and the main controlling factors prevalent in the diverse landscapes of Europe. What is clear is the very large spatial and temporal variability in P transfer that occurs between different countries and also within countries as a result of differences in climate, topography, soil type, land use patterns and P surpluses, and the way in which these surpluses are managed. The role of intensive livestock farming, soil P accumulation and consequent leaching of P Correspondence: P. J. A. Withers. E-mail: Paul.Withers@adas.co.uk Soil Use and Management

Using critical source areas for targeting cost‐effective best management practices to mitigate phosphorus and sediment transfer at the watershed scale

AbstractThe impact of implementing different best management practices (BMPs) at the small watershed scale were examined for the Petzenkirchen catchment in Austria and Lake Vico in Italy, in terms of data needs, hydrological processes, tools and models involved. Identification of critical source areas for targeting soil and phosphorus losses turned out to be crucial for correct allocation of BMPs. Comparison of environmental effectiveness and costs, both calculated using various modelling approaches, enabled us to compare different levels of introducing BMPs ecologically and economically. Within each catchment, small areas of land tended to be the source of disproportionately large amounts of pollution. Therefore, confining mitigation to these areas costs less than targeting wider areas. This suggests that a policy for environmental programmes should be focussed on hydrological units and critical source areas within these units instead of introducing universal controls – the ‘watering can’ principle – as practised today.

An environmental soil test to estimate the intrinsic risk of sediment and phosphorus mobilization from European soils

AbstractMethodologies are required to help identify soils that are vulnerable to both suspended sediment (SS) and phosphorus (P) transfer in land run‐off to combat the adverse impacts of agriculture on water quality. A laboratory test that quantifies dispersed particles and associated P in the same suspension was developed to estimate the potential mobilization of SS and P due to rainfall impact from 26 European soils with varied soil physical and chemical properties and P inputs. The test recovers an aliquot of the clay and fine silt (<20 μm) fraction of soils after gently shaking in distilled water for 1 min at a 1:50 soil‐to‐solution ratio and measures the dry residue, total P and dissolved (<0.45 μm) P content. The results of the test correlated well (r2 = 0.7–0.8) with the amounts of SS, total P and dissolved P in overland flow generated by indoor simulated rainfall (intensity 60 mm h−1 for 30 min and a 5° slope). Variation in SS and particulate P mobilization was linked to soil pH, organic matter (or clay) and sesquioxide content, although a multiple regression analysis showed these factors accounted for no more than 55% of this variation. Ranking showed that the soils generating the most sediment did not necessarily generate the most P loss due to variable degrees of P enrichment of the particulate fraction and variable contributions of dissolved P. Particulate P enrichment was related weakly (r2 = 0.5) to soil total P, while dissolved P fractions were predicted well (r2 = 0.8–0.9) by conventional soil P tests (water and Olsen). The environmental soil test has a potential role in identifying the comparative risk of sediment and P mobilization from critical source areas connected via both surface and subsurface pathways, and in providing data for incorporation into models predicting sediment and P transfer at the field and catchment scale.

Phosphorus indices as risk‐assessment tools in the U.S.A. and Europe—a review

AbstractThe “phosphorus index” (PI) is a semiquantitative tool to assess the risk of P loss from fields to surface waters, which is based on simple arithmetic computations of source (soil test phosphorus (STP), P applications as manure and fertilizer, plant residues) and transport factors (erosion, surface runoff, subsurface drainage, connectivity). Work done since the 1990s in the U.S.A. and several European countries has shown that this approach is capable of delineating critical source areas for P export within a watershed. It is intended to adopt such a PI tool in Germany as well. However, there is no “standard” PI, and the variety of P indices is confusing, since each state and country has developed its own version to account for special regional conditions which are important for P loss. This paper reviews the factors of P loss which are taken into account in P indices and different modifications of P indices according to their components and structural approach. The literature concerning single source and transport factors of P loss is overwhelming, and a structured selection is given in this review.Most P indices can be classed into one of three groups: 1. additive approach, 2. multiplicative approach, and 3. multiplicative‐additive approach.For Germany, it is suggested that specific factors of P loss are incorporated into the basic backbone of a Pennsylvania‐style PI. Realization of the factors could be adopted from existing Scandinavian P indices or from other research results.

Hydrological approaches to the delineation of critical‐source areas of runoff

Five hydrological approaches, ranging from empirical to physically based, were applied in two headwater catchments (Silverstream and Glenomaru) in Otago, New Zealand, to delineate the critical‐source areas (CSAs) of runoff, the areas that are directly linked to contaminant transport to surface waterways. Comparison of observed and simulated flows for selected rainfall events indicated that in one catchment (Glenomaru) the empirical approaches performed better than physically‐based approaches, while the converse was true in the other catchment (Silverstream). However, spatial mapping of simulated CSAs indicated that the approaches failed to recognise areas where subsurface flows can potentially emerge to the surface as seeps and springs on steep hillsides bordering the valleys. The approaches were also evaluated based on the availability and processing times of input data, representation of hydrological processes, reliability of simulations, likely economic impact, and the ease of implementing alternative management on the CSAs identified. Due to minimal input data needs, minimal likely economic impact, and ease of CSA management, empirical approaches may prove to be the most useable approaches. Process‐based approaches simulated unconnected and poorly manageable CSAs that if managed would have a negative economic impact. Economic analysis based on CSAs simulated using the empirical approaches indicated that by managing CSAs to mitigate phosphorus losses, significant decreases in phosphorus losses on a catchment scale can be achieved without any loss in profitability, or even a gain. However, we concluded that these approaches should be examined further and the simulated CSAs validated to allow a better linkage of sources of contaminants and runoff at a catchment scale.

Evaluation of the AnnAGNPS Model for prediction of runoff and sediment yields in St Lucia watersheds

The Annualised Agricultural Non-Point Source Pollution Model (AnnAGNPS) was used to predict runoff and sediment losses from a forested and an agricultural watershed of St. Lucia Island in the Caribbean. Digital elevation models (DEM) of the agricultural and forested watersheds were generated from digitised topographic data. Based on the critical source area (CSA) and minimum source channel length (MSCL) specifications, the agricultural watershed was discretised into eight cells and three channel reaches, and the forest watershed into 12 cells and five channel reaches. The weighted curve numbers (CNs) were used for the cells with multiple land uses. The CN was observed to be the most sensitive parameter in the prediction of runoff and was adjusted during calibrations. The calibration runs of the AnnAGNPS resulted in errors between observed and simulated values of 0–33% for the agricultural watershed and 3.3–46.2% for the forested watershed for runoff prediction. The sediment yield prediction error percentage during the calibration run varied from 18.2% to 40.5% for the agricultural watershed and 9.1% to 50% for the forest watershed. However, validation of the calibrated model for different rainfall events resulted in errors of 6.7–36% and a value for the coefficient of prediction (CP′A) of 0.028 (agricultural watershed) and 3.4% to 36% with a value for the CP′A of 0.23 (forested watersheds) for runoff prediction. Validation of sediment loss for both the watersheds resulted in higher errors (23% to 55%) and CP′A value of 0.341 for both the watersheds. Also, the model prediction of average annual runoff and sediment loss revealed that the agricultural watershed sediment loss (73.3 t ha−1 year−1) was significantly higher than for the forest watershed (7.2 t ha−1 year−1). Further, the validated model was used to simulate the runoff and sediment losses under a recommended land management regime for the agricultural watershed, which resulted in an 18.5% reduction in runoff and a 63% reduction in sediment loss as compared to the current management practice. This study revealed that the AnnAGNPS can be successfully applied for assessment of runoff and sediment losses and subsequent land use planning to conserve the natural resources in the watersheds of St. Lucia.

Upflow Filtration for the Treatment of Stormwater at Critical Source Areas

One approach to the treatment of urban runoff is to treat the runoff from critical source areas before it mixes with runoff from less pollutant areas. Some of …

Influence of Slope Position and Hog Manure Injection on Fall Soil P and N Distribution in an Undulating Landscape

Investigation of how soil nutrients are distributed over the landscape in the fall is a prerequisite to identify critical source areas (CSA), which contribute soil nutrients to surface waters through snowmelt runoff. The objectives of this study are to investigate: (1) the distribution of soil nutrients in the landscape before soil freeze-up, and (2) how manure application in the fall affects this distribution. The study site, located in an undulating landscape in the Canadian prairies, is a closed drainage basin with moderate to fine textured soil. The basin received hog manure in fall 2001 and fall 2003. The landscape was classified into the shoulder, backslope, and footslope using a digital elevation model (DEM). Soil samples, collected from each landform segment in fall 2003 and fall 2004, were analyzed for available soil phosphorus (ASP), nitrate (NO3-) and ammonium (NH4+). In the undulating landscape, ASP levels had a distribution pattern of backslope < shoulder < footslope in fall 2003. The NO3- levels increased from the shoulder to the footslope. The NH4+ levels did not vary between the shoulder and the backslope, while the footslope had significantly higher NH4+ than the other two landform segments. Manure application appeared to change these distribution patterns of ASP, NO3-, and NH4+ temporally. However, one year after manure application, the manure effect was only seen for ASP. The soil moisture level at the footslope was significantly different from that of the other landform segments in fall 2004. The shoulder and backslope were homogeneous in terms of soil moisture for both fall seasons.

Assessing field vulnerability to phosphorus loss in Beijing agricultural area using Revised Field Phosphorus Ranking Scheme

Abstract Guanting Reservoir, one of the drinking water supply sources of Beijing, suffers from water eutrophication. It is mainly supplied by Guishui River. Thus, to investigate the reasons of phosphorus (P) loss and improve the P management strategies in Guishui River watershed are important for the safety of drinking water in this region. In this study, a Revised Field P Ranking Scheme (PRS) was developed to reflect the field vulnerability of P loss at the field scale based on the Field PRS. In this new scheme, six factors are included, and each one was assigned a relative weight and a determination method. The affecting factors were classified into transport factors and source factors, and, the standards of environmental quality on surface water and soil erosion classification and degradation of the China were used in this scheme. By the new scheme, thirty-four fields in the Guishui River were categorized as “low”, “medium” or “high” potential for P loss into the runoff. The results showed that the P loss risks of orchard and vegetable fields were higher than that of corn and soybean fields. The source factors were the main factors to affect P loss from the study area. In the study area, controlling P input and improving P usage efficiency are critical to decrease P loss. Based on the results, it was suggested that more attention should be paid on the fields of vegetable and orchard since they have extremely high usage rate of P and high soil test of P. Compared with P surplus by field measurements, the Revised Field PRS was more suitable for reflecting the characteristics of fields, and had higher potential capacity to identify critical source areas of P loss than PRS.

Assessment of Sediment Yields for a Mixed-landuse Great Lakes Watershed: Lessons from Field Measurements and Modeling

The Soil Water Assessment Tool (SWAT) was implemented to determine annual sediment yields and critical source areas of erosion for the Buffalo River Watershed. Model calibrations were performed by comparing simulated streamflow discharge and sediment concentrations against measured values. Monte-Carlo simulations were performed to identify the most sensitive parameters and the “best-fit” parameter ranges. This study especially highlighted the importance of snow parameters, which, previously had not been identified as sensitive for model simulations. The cover (C) and practice (P) values for croplands had to be reduced considerably from default model values to constrain simulated sediment yields within the observed data range. The model did not simulate an ice-scour event which generated a substantial amount of sediment. The average annual sediment yield simulated by SWAT for the Buffalo River watershed (108,593 ha) amounted to 0.8 tons/ha/yr. The Cazenovia Creek subwatershed contributed the largest portion (45%) of the total sediment yield from the Buffalo River watershed. We attribute the higher sediment yields from Cazenovia Creek to the greater proportion of steep slopes in this subwatershed. The accuracy and reliability of SWAT sediment predictions at the small watershed (second order or less) and storm-event scales will depend on the accuracy of input information, especially the resolution of the landuse-landcover (LULC) layer, the number of rainfall stations used in simulations, and the number of internal sites against which the model has been calibrated.

Modifying And Evaluating a P Index For Denmark

The European Union recently adopted the Water Framework Directive aiming at protecting and enhancing the status of aquatic ecosystems. The Water Framework Directive mandates EU member states to develop river basin management plans for each river basin. Consequently, water district managers need tools for identifying critical source areas within a catchment in order to target cost-effective remedial measures. The P Index could be well suited for screening large areas because of its low demand for input data and manpower compared to mechanistic, process based models. The P Index needs to be modified to local or regional conditions in order to incorporate all potential P loss pathways. In Denmark tile drains and leaching are considered major P loss pathways. We modified the Pennsylvania P Index to reflect Danish conditions. The Pennsylvania P Index and the modified Danish P Index were applied on a 1000 km2 catchment. In order to test the P Indices we examined their capability to correctly rank measured annual diffuse total P losses from twelve sub-catchments within the 1000 km2 catchment. Both P Indices, calculated on a sub-catchment basis, correlated with total P losses. The Danish P Index, however, performed distinctly better than the Pennsylvania P Index and explained 85% of the variation in measured diffuse total P losses.

Role of Rainfall Intensity and Hydrology in Nutrient Transport via Surface Runoff

Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study evaluated P and N in surface runoff in relation to rainfall intensity and hydrology for two soils along a single hillslope. Experiments were initiated on 1- by 2-m plots at foot-slope (6%) and mid-slope (30%) positions within an alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) field. Rain simulations (2.9 and 7.0 cm h(-1)) were conducted under wet (spring) and dry (late-summer) conditions. Elevated, antecedent soil moisture at the foot-slope during the spring resulted in less rain required to generate runoff and greater runoff volumes, compared with runoff from the well-drained mid-slope in spring and at both landscape positions in late summer. Phosphorus in runoff was primarily in dissolved reactive form (DRP averaged 71% of total P), with DRP concentrations from the two soils corresponding with soil test P levels. Nitrogen in runoff was mainly nitrate (NO3-N averaged 77% of total N). Site hydrology, not chemistry, was primarily responsible for variations in mass N and P losses with landscape position. Larger runoff volumes from the foot-slope produced higher losses of total P (0.08 kg ha(-1)) and N (1.35 kg ha(-1)) than did runoff from the mid-slope (0.05 total P kg ha(-1); 0.48 kg N ha(-1)), particularly under wet, spring-time conditions. Nutrient losses were significantly greater under the high intensity rainfall due to larger runoff volumes. Results affirm the critical source area concept for both N and P: both nutrient availability and hydrology in combination control nutrient loss.

THE IMPACT OF RUNOFF GENERATION MECHANISMS ON THE LOCATION OF CRITICAL SOURCE AREAS1

ABSTRACT: Identifying phosphorus (P) source areas and transport pathways is a key step in decreasing P loading to natural water systems. This study compared the effects of two modeled runoff generation processes ‐ saturation excess and infiltration excess ‐ on total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations in 10 catchment streams of a Catskill mountain watershed in southeastern New York. The spatial distribution of runoff from forested land and agricultural land was generated for both runoff processes; results of both distributions were consistent with Soil Conservation Service‐Curve Number (SCS‐CN) theory. These spatial runoff distributions were then used to simulate stream concentrations of TP and SRP through a simple equation derived from an observed relation between P concentration and land use; empirical results indicate that TP and SRP concentrations increased with increasing percentage of agricultural land. Simulated TP and SRP stream concentrations predicted for the 10 catchments were strongly affected by the assumed runoff mechanism. The modeled TP and SRP concentrations produced by saturation excess distribution averaged 31 percent higher and 42 percent higher, respectively, than those produced by the infiltration excess distribution. Misrepresenting the primary runoff mechanism could not only produce erroneous concentrations, it could fail to correctly locate critical source areas for implementation of best management practices. Thus, identification of the primary runoff mechanism is critical in selection of appropriate models in the mitigation of nonpoint source pollution. Correct representation of runoff processes is also critical in the future development of biogeochemical transport models, especially those that address nutrient fluxes.

Mapping hydrological pathways of phosphorus transfer in apparently homogeneous landscapes using a high-resolution DEM

Agriculture is a significant contributor to the diffuse loading of phophorus (P) in fresh water systems. At the landscape level, source areas and targeted surface waters are connected through different hydrological pathways. One of these pathways, P removal through surface runoff, may increase in relative importance when storm events occur and in wet seasons. With Digital Elevation Models (DEMs) it is possible to identify dominant surface pathways in the landscape although resolution of available DEMs is often not detailed enough for areas with low relief or for more detailed landscape-field studies. New high-resolution DEMs that do combine a high resolution with substantial spatial coverage provide the opportunity to develop site-specific management alternatives for sensitive or critical source areas at the landscape level. The objective of this paper is to map hydrological pathways of P for a relatively flat glacial till landscape in the Northern part of the Netherlands and to compare two strategies (A and B) in this landscape for minimizing P loading of surface waters following different scenarios. Strategy A assumes equal lowering of phosphate input rates for all fields and strategy B takes into account the relative sensitivity of fields for removal through overland flow. Available soil data, which did not allow to geo-reference individual fields, showed high soil P levels in about 5% of all fields. Data on field inputs of total phosphate (P 2O 5) were available for 29 farms and showed that fertilized fields received on average 124 kg ha − 1 in the year 2000. Transfer potential of each individual field was evaluated on the basis of two characteristics in a 5 × 5 m resolution DEM: 1) the degree of internal drainage through re-distribution and 2) the degree of external drainage, which indicates the overland flow potential. Almost every field was characterised by sinks (98%) and external drainage into along-field ditches (99%). In addition, almost half of the fields showed drainage directly into surface waters (47%). Applying a classification scheme to rank the sensitivity for losses through overland flow provided a framework to distribute catchment inputs of phosphate at field level (strategy B). Comparing the strategy of distributed phosphate inputs (B) with generic phosphate inputs (A) showed that catchment input-to-output ratios are higher for strategy B for three out of four of the applied scenarios.

Full Scale Evaluation of Upflow™ Filter – A Catch Basin Insert for the Treatment of Stormwater at Critical Source Areas

Stormwater runoff from critical source areas, such as pa rking lots, vehicle fueling and maintenance stations, and public works storage areas, may contain pollutant loadings of hydrocarbons, toxic trace metals, nutrients, pathogens, and/ or other toxicants and pollutants that are greater than the loadings of “normal” storm water runoff (Bannerman, et al . 1993; Pitt, et al . 1995; Claytor and Schueler 1996). One alternative to end-of - pipe treatment for stormwater runoff is to treat the more contaminated run off from problem sources before this runoff mixes with the runoff from other areas (Bannerma n, et al . 1993; Pitt, et al . 1995; Claytor and Schueler 1996). Critical source area treatment devices need to incorporate a variety of treatment processes that can be targeted fo r different classes of pollutants of concern and to respond to the variability of stormwater quality conditions that can originate from different types of critical source areas (Pitt, et al. 1999). This paper will describe one such device, the UpFlo TM Filter that has undergone development and testing under the EPA’s SBIR and ETV programs.

Manure Phosphorus (P) and Surface Water Protection II: Field and Management Factors Contributing to P Loss Risk

The importance of managing agricultural phosphorus (P) to protect water quality was addressed in module I. Factors contributing to P loss from the land to surface waters include site and management factors (source factors) and transport factors. An interaction of source and transport factors is needed to have runoff P loss. If one set contributes minimally to risk, then risk is not likely to be great even if the other set of factors offers much potential for risk. This raises the concept of “critical source area”; the risk is greatest when both the source and transport factors are high. This lesson describes how the source factors, including soil characteristics and management practices, affect P delivery to surface waters. Crop producers have some control over these factors, and management practices are discussed. This is a lesson in a series found in the Plant and Soil Sciences eLibrary (http://plantandsoil.unl.edu). Upon completion, a student should be able to: