Critical evaluation of the implementation of mitigation options for phosphorus from field to catchment scales

Best Management Practices for Diffuse Nutrient Pollution: Wicked Problems Across Urban and Agricultural Watersheds

Extensive time and financial resources have been dedicated to address nonpoint sources of nitrogen and phosphorus in watersheds. Despite these efforts, many watersheds have not seen substantial improvement in water quality. The objective of this study is to review the literature and investigate key factors affecting the lack of improvement in nutrient levels in waterways in urban and agricultural regions. From 94 studies identified in the academic literature, we found that, although 60% of studies found improvements in water quality after implementation of Best Management Practices (BMPs) within the watershed, these studies were mostly modeling studies rather than field monitoring studies. For studies that were unable to find improvements in water quality after the implementation of BMPs, the lack of improvement was attributed to lack of knowledge about BMP functioning, lag times, nonoptimal placement and distribution of BMPs in the watershed, postimplementation BMP failure, and socio-political and economic challenges. We refer to these limiting factors as known unknowns. We also acknowledge the existence of unknown unknowns that hinder further improvement in BMP effectiveness and suggest that machine learning, approaches from the field of business and operations management, and long-term convergent studies could be used to resolve these unknown unknowns.

The state of phosphorus balance on 58 Virginia dairy farms

Managing a sustainable dairy farm requires balancing phosphorus (P) imports and exports that enter and leave through the farm gate. Over the long term, P surpluses will elevate soil-test P concentrations above crop requirements through routine land applications of manure. The objectives of this study were aimed at Virginia dairy farms (a) to determine P mass balances, (b) to define potential guidelines for a sustainable and feasible zone of operation based on P balance and P use efficiency, and (c) to assess risk factors driving P surplus and P use inefficiencies. Data on farm-gate P imports and exports via feed, manure, crops, fertilizers, bedding, animals, and milk were collected for 58 dairy farms in Virginia. There was no relationship between farm P balance and milk production, indicating that a P surplus was not necessary for good milk productivity. A feasible P balance limit was calculated below which 75% of farms could operate, and this was 18.7 kg P ha^-1 . Two risk factors were identified for farms having a P balance above this limit: (a) land application of poultry litter and (b) excessive import of P through feed. Combined dairy and beef operations generally had more land and a lower P balance, whereas having combined dairy and poultry did not raise the P balance as long as poultry litter was exported. Dairy farms in Virginia can operate with a sustainable P balance as long as they avoid using excessive poultry litter and pay attention to P imported through purchased feed.

Mobility, distribution, and potential risk assessment of selected trace elements in soils of the Nile Delta, Egypt

Environmental pollution has received considerable attention over the last 50 years. Recently, there has been an increasing interest in pollution of the Nile Delta, Egypt, which is one of the longest settled deltaic systems in the world. Pollution in the delta is increasingly recognized as a serious health concern that requires proper management of ecosystems. Therefore, this project aimed to study the distribution and assess the risk associated with selected trace elements (TEs) in different soils (i.e., marine, fluvial, and lacustrine parent materials) in the northern Nile Delta. Mehlich-3 extraction was used to determine the availability of antimony, vanadium, strontium, and molybdenum in agro-ecosystems in this area and their spatial distributions were investigated. Five indices were used to assess ecological risk. Results showed that TEs were higher in the southern part of the study area because it is affected by multiple pollution sources. The available concentrations of TEs were Sr < V < Sb < Mo. The bioavailability of Sr was highest among the studied TEs. The studied indices suggested the study area was moderately polluted by Sr and Sb. Furthermore, the results showed that marine soils had higher TE levels then lacustrine and fluvial soils. The ecological risk assessment indicated that V and Mo were of natural origin, while Sr and Sb were anthropogenically linked. Therefore, the situation calls for planning to reduce pollution sources, especially in the protected north Nile Delta, so these productive soils do not threaten human and ecological health.

The future depends on what we do today - Projecting Europe's surface water quality into three different future scenarios

There are infinite possible future scenarios reflecting the impacts of anthropogenic multiple stress on our planet. These impacts include changes in climate and land cover, to which aquatic ecosystems are especially vulnerable. To assess plausible developments of the future state of European surface waters, we considered two climate scenarios and three storylines describing land use, management and anthropogenic development ('Consensus', 'Techno' and 'Fragmented', which in terms of environmental protection represent best-, intermediate- and worst-case, respectively). Three lake and four river basins were selected, representing a spectrum of European conditions through a range of different human impacts and climatic, geographical and biological characteristics. Using process-based and empirical models, freshwater total nitrogen, total phosphorus and chlorophyll-a concentrations were projected for 2030 and 2060. Under current conditions, the water bodies mostly fail good ecological status. In future predictions for the Techno and Fragmented World, concentrations further increased, while concentrations generally declined for the Consensus World. Furthermore, impacts were more severe for rivers than for lakes. Main pressures identified were nutrient inputs from agriculture, land use change, inadequately managed water abstractions and climate change effects. While the basins in the Continental and Atlantic regions were primarily affected by land use changes, in the Mediterranean/Anatolian the main driver was climate change. The Boreal basins showed combined impacts of land use and climate change and clearly reflected the climate-induced future trend of agricultural activities shifting northward. The storylines showed positive effects on ecological status by classical mitigation measures in the Consensus World (e.g. riparian shading), technical improvements in the Techno World (e.g. increasing wastewater treatment efficiency) and agricultural extensification in the Fragmented World. Results emphasize the need for implementing targeted measures to reduce anthropogenic impacts and the importance of having differing levels of ambition for improving the future status of water bodies depending on the societal future to be expected.

Approach for predicting P sorption/desorption behaviour of potentially eroded topsoil in watercourses

This study focuses on the quantification of the impact of potentially eroded topsoil particles on the available watercourse P concentration. We used 56 topsoil samples for determining the relation existing between the molar ratio of sorption-active Fe- and Al-(hydr)oxides to plant available P, as determined by the commonly used oxalate and Mehlich 3 extractions (P_M3). Our sample set covers the most common combinations of non-calcareous soil types, land and agricultural uses. By using Freundlich isotherms, we found that the concentration of adsorbed/desorbed P (Q) by soil particles in water with specific soluble reactive phosphorus (SRP) concentrations are significantly correlated to P_M3 (Q=a∗P_M3+b) and also to the degree of P saturation as measured by oxalate extraction (DPS_ox; Q=c∗DPS_ox+d). The observed relations varied in slope and intercept parameters for discrete equilibrium P concentrations in water. However, in the environmentally important range of PO₄-P concentrations, i.e., from 20 to 220μgL^-1, a strong non-linear correlation was found between the individual parameters and equilibrium P concentration. Accordingly, we derived equations useful for quantitatively predict P exchange between topsoil particles when potentially eroded into watercourse and the recipient water of either known or targeted P concentrations. This approach might refine erosion models, and thus facilitates the quantification of the impact of soil erosion on the in-stream bioavailable P concentrations.

Phosphorus Accumulation and Sorption in Calcareous Soil under Long-Term Fertilization

Application of phosphorus (P) fertilizers to P-deficient soils can also result in P accumulation. In this study, soil P status and P uptake by apple trees were investigated in 5-, 10-, and 15-year-old orchards in the semi-arid Loess Plateau, China, and subset soils with different soil P statuses (14–90 Olsen-P mg kg⁻¹) were selected to evaluate the characteristic P adsorption. Due to the low P-use efficiency (4–6%), total soil P increased from 540 mg kg⁻¹ to 904 mg kg⁻¹, Olsen-P ranged from 3.4 mg kg⁻¹ to 30.7 mg kg⁻¹, and CaCl₂-P increased from less than 0.1 mg kg⁻¹ to 0.66 mg kg⁻¹ under continuous P fertilization. The P sorption isotherms for each apple orchard were found to fit the Langmuir isotherm model (R² = 0.91–0.98). K (binding energy) and Q_m (P sorption maximum) decreased, whereas DPS (degree of phosphorus sorption) increased with increasing P concentration. CaCl₂-P increased significantly with the increase of Olsen-P, especially above the change point of 46.1 mg kg⁻¹. Application of surplus P could result in P enrichment in P-deficient soil which has high P fixation capacity, thus posing a significant environmental risk.

Past, present, and future use of phosphorus in Chinese agriculture and its influence on phosphorus losses

Large inputs of phosphorus (P) in chemical fertilizers and feed supplements since 1978 have improved soil P status in arable land in China, but have also created challenges by increasing P concentrations in manure and exacerbating water quality degradation. Arable land in China can be divided into five management zones based on soil P chemistry, with 15-92 % of arable land having lower P status than the agronomic optimum and 0.3-7.2 % having severe risks of P leaching losses. A scenario analysis of soil P budget and agronomic P demand during 2011-2030 highlighted the great pressure China faces in sustainable P management and the need for drastic changes in current practices. This includes new policies to reduce P supplementation of feed and improved P use efficiency by livestock and programs to expand the adoption of appropriate fertilization, soil conservation, and drainage management practices to minimize P losses.

Stewardship to tackle global phosphorus inefficiency: The case of Europe

The inefficient use of phosphorus (P) in the food chain is a threat to the global aquatic environment and the health and well-being of citizens, and it is depleting an essential finite natural resource critical for future food security and ecosystem function. We outline a strategic framework of 5R stewardship (Re-align P inputs, Reduce P losses, Recycle P in bioresources, Recover P in wastes, and Redefine P in food systems) to help identify and deliver a range of integrated, cost-effective, and feasible technological innovations to improve P use efficiency in society and reduce Europe's dependence on P imports. Their combined adoption facilitated by interactive policies, co-operation between upstream and downstream stakeholders (researchers, investors, producers, distributors, and consumers), and more harmonized approaches to P accounting would maximize the resource and environmental benefits and help deliver a more competitive, circular, and sustainable European economy. The case of Europe provides a blueprint for global P stewardship.

Environmental potentials of policy instruments to mitigate nutrient emissions in Chinese livestock production

To minimize negative environmental impact of livestock production, policy-makers face a challenge to design and implement more effective policy instruments for livestock farmers at different scales. This research builds an assessment framework on the basis of an agent-based model, named ANEM, to explore nutrient mitigation potentials of five policy instruments, using pig production in Zhongjiang county, southwest China, as the empirical filling. The effects of different policy scenarios are simulated and compared using four indicators and differentiating between small, medium and large scale pig farms. Technology standards, biogas subsidies and information provisioning prove to be the most effective policies, while pollution fees and manure markets fail to environmentally improve manure management in pig livestock farming. Medium-scale farms are the more relevant scale category for a more environmentally sound development of Chinese livestock production. A number of policy recommendations are formulated as conclusion, as well as some limitations and prospects of the simulations are discussed.

Managing manure from China's pigs and poultry: the influence of ecological rationality

We have investigated manure management practices at three farm scales in Chinese pig and poultry production. The concept of ecological rationality was employed to explore empirically how environmental concerns drive adoption of environmental-friendly manure management technologies at different farm scales. The more developed Rudong County in Jiangsu Province and the less developed Zhongjiang County in Sichuan Province were chosen as cases for study of 258 animal breeders. On the contrary to our hypothesis, medium-scale farmers were not always found to be laggards in adoption of manure management technologies. Government ecological rationality played a key role to induce environmental-friendly technology adoption on its own, but also in cooperation with ecologically rational individual or network drivers. Authorities no longer applied their efforts in a conventional command-and-control way, but more in the form of incentives, stimulation, and information to farmers. Individual farmers in general showed low environmental responsibility in relation to manure handling.

Measurement and modeling of phosphorous transport in shallow groundwater environments

Leaching of phosphorus (P) from agricultural soils, especially those that are sandy, is adversely impacting P-limited ecosystems like Florida's Everglades. A more developed understanding of P and water management strategies and their effects on P leaching is needed to achieve reductions in subsurface P losses, especially from intensively managed dual cropping systems under plastic mulch in shallow water regions. We compared the effects of conservation P and water management strategies with traditional practices on P transport to groundwater. A 3-year experiment was conducted on hydrologically isolated plots with plastic-mulched successive cropping systems to compare high (HEI) and soil test based recommended (REI) external input (water and fertilizer P) systems with traditional sub-irrigation (seepage), and REI with a potential water conservation subsurface drip irrigation system (REI-SD) with regard to groundwater P concentrations above and below the low conductivity spodic horizon (Bh). The REI treatments had higher available storage for rainfall and P than HEI. Use of both REI systems (REI=2098μg/L and REI-SD=2048μg/L) reduced groundwater P concentrations above the Bh horizon by 33% compared to HEI (3090μg/L), and results were significant at the 0.05 level. Although the subsurface drip system saved water, it did not offer any groundwater quality (P) benefit. Mixing and dilution of influent P below the low conductivity Bh horizon between treatments and with the regional groundwater system resulted in no significant differences in groundwater P concentration below the Bh horizon. Groundwater P concentrations from this study were higher than reported elsewhere due to low soil P storage capacity (SPSC), high hydraulic conductivity of sandy soils, and a high water table beneath crop beds. The HEI system leached more P due to ferilizer P in excess of SPSC and used higher irrigation volumes compared with REI systems. Despite a 40% difference in the average amount of added fertilizer P between HEI (187kg P2O5/ha) and REI (124kg P2O5/ha), soil Mehlich 1 P (M1P) values were similar for both systems while they received Pinput. Soil M1P for REI and REI-SD increased to a maximum of 55mg/kg while they received Pinput, and then gradually decreased after Pinput ceased. However, M1P for HEI increased steadily to a maximum of 145mg/kg by the end of the study with continued Pinput. Mehlich-1 P measured six years after the study still showed relatively high levels of P, a legacy effect of Pinput. The main factors influencing groundwater P concentration varied by seasons. During fall with frequent rainfall, the concentrations were influenced mainly by M1P and Pinput, and highlight a need for greater focus on Pinput management (vs. water management) during this season. However, during the dry period of spring, a greater focus on irrigation management is required since depth to water table and rainfall also become contributing factors. Three multivariate models (r(2)=0.67 to 0.93), for spring, fall, and annual periods, were developed for predicting groundwater P concentrations for a wide range of water and P inputs (0 to 191kg P2O5/ha of Pinput). The uniqueness of these models is that they use readily available hydrologic (rainfall and water table depth), management (Pinput), and soil (M1P) data commonly monitored by growers when managing water and nutrient inputs on agricultural landscapes. The development of similar models may not be necessary for other agro-ecosystems in similar regions since long-term data collected in these regions may be applied, with verification, to the models presented here.

Centrifugal spreader mass and nutrients distribution patterns for application of fresh and aged poultry litter

A spin-type centrifugal spreader was evaluated using fresh and aged poultry litter upon dry mass, product nitrogen (N), phosphorus (P) and potassium (K), incubation study soil available N and particle size distribution patterns. Relative to the aged litter (37% moisture content), the fresh litter (17% moisture content) had greater <1.00 mm particle size fraction weights and atmospheric particulate was launched, which posed as a potential fallout to adjacent fields, waterways and residences. Relative to the aged litter, the broadcast fresh litter resulted in higher coefficients of variation (CV) over its transverse distance, a narrower calculated space distance between passes for uniform spread and lower soil available N concentrations. For nitrogen application over the broadcast transverse distance the fresh litter displayed a high R(2) best fit 4th order polynomial distribution pattern, while the aged litter showed high R(2) best fit 6th order polynomial distribution pattern. A soil incubation study of the fresh and aged broadcast litter resulted in a more variable or lower R(2) best fit 2nd order polynomial distribution pattern. For both the fresh and aged litter, the calculated distance between passes to achieve a uniform mass distribution was greater than that required for the broadcast of soil available N. For the fresh litter, the soil available N and litter P concentration levels strongly correlated (relatively high p and R(2) values) with the <1.00 mm fraction weight, while for the aged litter this relationship was not as significant. In addition to reducing the health risk (i.e. pathogens, antibiotic residues and resistant bacteria) and/or environment issues (particulate fallout onto waterways, adjacent fields and/or residences) our study mass, particulate and N distribution patterns results suggest that poultry litter should be allowed to age before broadcast application is attempted.

Phosphorus retention and remobilization along hydrological pathways in karst terrain

Karst landscapes are often perceived as highly vulnerable to agricultural phosphorus (P) loss, via solution-enlarged conduits that bypass P retention processes. Although attenuation of P concentrations has been widely reported within karst drainage, the extent to which this results from hydrological dilution, rather than P retention, is poorly understood. This is of strategic importance for understanding the resilience of karst landscapes to P inputs, given increasing pressures for intensified agricultural production. Here hydrochemical tracers were used to account for dilution of P, and to quantify net P retention, along transport pathways between agricultural fields and emergent springs, for the karst of the Ozark Plateau, midcontinent USA. Up to ∼ 70% of the annual total P flux and ∼ 90% of the annual soluble reactive P flux was retained, with preferential retention of the most bioavailable (soluble reactive) P fractions. Our results suggest that, in some cases, karst drainage may provide a greater P sink than previously considered. However, the subsequent remobilization and release of the retained P may become a long-term source of slowly released "legacy" P to surface waters.

Phosphorus mitigation to control river eutrophication: murky waters, inconvenient truths, and "postnormal" science

This commentary examines an "inconvenient truth" that phosphorus (P)-based nutrient mitigation, long regarded as the key tool in eutrophication management, in many cases has not yet yielded the desired reductions in water quality and nuisance algal growth in rivers and their associated downstream ecosystems. We examine why the water quality and aquatic ecology have not recovered, in some case after two decades or more of reduced P inputs, including (i) legacies of past land-use management, (ii) decoupling of algal growth responses to river P loading in eutrophically impaired rivers; and (iii) recovery trajectories, which may be nonlinear and characterized by thresholds and alternative stable states. It is possible that baselines have shifted and that some disturbed river environments may never return to predisturbance conditions or may require P reductions below those that originally triggered ecological degradation. We discuss the practical implications of setting P-based nutrient criteria to protect and improve river water quality and ecology, drawing on a case study from the Red River Basin in the United States. We conclude that the challenges facing nutrient management and eutrophication control bear the hallmarks of "postnormal" science, where uncertainties are large, management intervention is urgently required, and decision stakes are high. We argue a case for a more holistic approach to eutrophication management that includes more sophisticated regime-based nutrient criteria and considers other nutrient and pollutant controls and river restoration (e.g., physical habitat and functional food web interactions) to promote more resilient water quality and ecosystem functioning along the land-freshwater continuum.

Phosphorus losses from low-emission slurry spreading techniques

Low emission slurry spreading techniques are known to improve nitrogen use efficiency, but their impact on phosphorus (P) losses in surface runoff has received little attention. The current study was designed to examine the effect of slurry spreading technique on P losses in runoff. Twelve treatments were examined on 0.5- m by 1.0-m plots in a nominal 2 × 6 factorial design experiment. Treatments comprised grass swards at two different stages of growth, a stubble and a 4-wk regrowth, and six different slurry application treatments: control (no slurry), and slurry applied to simulate splash-plate, injection (across and down slope), and trailing shoe (across and down slope) spreading. Slurry was applied by hand (40 m ha). Rainfall simulations (40 mm h) were conducted at 2, 9, and 28 d post-slurry application. When slurry was applied to the stubble, dissolved reactive P (DRP) concentrations in runoff at Day 2 were 47 and 37% lower ( < 0.05) from the injection and trailing shoe treatments compared with the splash-plate treatment. Similarly, at Day 2, TP concentrations in runoff from the injection treatments were 27% lower ( < 0.05) than the splash-plate treatment. In contrast, application technique had no effect ( 0.05) on P concentrations in runoff following slurry application to the regrowth treatment. Phosphorus concentrations in runoff were unaffected by direction of slurry spreading (across or down) at both applications. Our results indicate that trailing shoe and injection techniques offer the potential to reduce DRP concentrations in runoff during the period immediately after slurry application.

Phosphorus indices: why we need to take stock of how we are doing

Many states have invested significant resources to identify components of their Phosphorus (P) Index that reliably estimate the relative risk of P loss and incentivize conservation management. However, differences in management recommendations and manure application guidelines for similar field conditions among state P Indices, coupled with minimal reductions in the extent of P-impaired surface waters and soil test P (STP) levels, led the U.S. Natural Resources Conservation Service (NRCS) to revise the 590 Nutrient Management Standard. In preparation for this revision, NRCS requested that a review of the scientific underpinnings and accuracy of current P Indices be undertaken. They also sought to standardize the interpretation and management implications of P Indices, including establishment of ratings above which P applications should be curtailed. Although some states have initiated STP thresholds above which no application of P is allowed, STP alone cannot define a site's risk of P loss. Phosphorus Indices are intended to account for all of the major factors leading to P loss. A rigorous evaluation of P Indices is needed to determine if they are directionally and magnitudinally correct. Although use of observed P loss data under various management scenarios is ideal, such data are spatially and temporally limited. Alternatively, the use of a locally validated water quality model that has been shown to provide accurate estimates of P loss may be the most expedient option to conduct Index assessments in the short time required by the newly revised 590 Standard.

Application of the WFD cost proportionality principle to diffuse pollution mitigation: a case study for Scottish Lochs

The Water Framework Directive (WFD) aims to deliver good ecological status (GES) for Europe's waters. It prescribes the use of economic principles, such as derogation from GES on grounds of disproportionate costs of mitigation. This paper proposes an application of the proportionality principle to mitigation of phosphorus (P) pollution of 544 Scottish lochs at national and local water body scales. P loading estimates were derived from a national diffuse pollution screening tool. For 293 of these lochs (31% of the loch area), GES already occurred. Mitigation cost-effectiveness was assessed using combined mitigation cost curves for managed grassland, rough grazing, arable land, sewage and septic tank sources. These provided sufficient mitigation (92% of national P load) for GES to be achieved on another 31% of loch area at annualised cost of £2.09 m/y. Mitigation of the residual P loading preventing other lochs achieving GES was considered by using a "mop-up" cost of £200/kg P (assumed cost effectiveness of removal of P directly from lochs), leading to a total cost of £189 m/y. Lochs were ranked by mitigation costs per loch area to give a national scale marginal mitigation cost curve. A published choice experiment valuation of WFD targets for Scottish lochs was used to estimate marginal benefits at national scale and combined with the marginal cost curve. This gave proportionate costs of £5.7 m/y leading to GES in 72% of loch area. Using national mean marginal benefits with a scheme to estimate changes in individual loch value with P loading gave proportionate costs of £25.6 m/y leading to GES in 77% of loch area (491 lochs).

Phosphorus load to surface water from bank erosion in a Danish lowland river basin

Phosphorus loss from bank erosion was studied in the catchment of River Odense, a lowland Danish river basin, with the aim of testing the hypothesis of whether stream banks act as major diffuse phosphorus (P) sources at catchment scale. Furthermore, the study aimed at analyzing the impact of different factors influencing bank erosion and P loss such as stream order, anthropogenic disturbances, width of uncultivated buffer strips, and the vegetation of buffer strips. A random stratified procedure in geographical information system (GIS) was used to select two replicate stream reaches covering different stream orders, channelized vs. naturally meandering channels, width of uncultivated buffer strips (≤ 2 m and ≥ 10 m), and buffer strips with different vegetation types. Thirty-six 100-m stream reaches with 180 bank plots and a total of 3000 erosion pins were established in autumn 2006, and readings were conducted during a 3-yr period (2006-2009). The results show that neither stream size nor stream disturbance measured as channelization of channel or the width of uncultivated buffer strip had any significant ( < 0.05) influence on bank erosion and P losses during each of the 3 yr studied. In buffer strips with natural trees bank erosion was significantly ( < 0.05) lower than in buffer strips dominated by grass and herbs. Gross and net P input from bank erosion amounted to 13.8 to 16.5 and 2.4 to 6.3 t P, respectively, in the River Odense catchment during the three study years. The net P input from bank erosion equaled 17 to 29% of the annual total P export and 21 to 62% of the annual export of P from diffuse sources from the River Odense catchment. Most of the exported total P was found to be bioavailable (71.7%) based on a P speciation of monthly suspended sediment samples collected at the outlet of the river basin. The results found in this study have a great importance for managers working with P mitigation and modeling at catchment scale.

Integrating economic and biophysical data in assessing cost-effectiveness of buffer strip placement

The European Union Water Framework Directive (WFD) requires Member States to set water quality objectives and identify cost-effective mitigation measures to achieve "good status" in all waters. However, costs and effectiveness of measures vary both within and between catchments, depending on factors such as land use and topography. The aim of this study was to develop a cost-effectiveness analysis framework for integrating estimates of phosphorus (P) losses from land-based sources, potential abatement using riparian buffers, and the economic implications of buffers. Estimates of field-by-field P exports and routing were based on crop risk and field slope classes. Buffer P trapping efficiencies were based on literature metadata analysis. Costs of placing buffers were based on foregone farm gross margins. An integrated optimization model of cost minimization was developed and solved for different P reduction targets to the Rescobie Loch catchment in eastern Scotland. A target mean annual P load reduction of 376 kg to the loch to achieve good status was identified. Assuming all the riparian fields initially have the 2-m buffer strip required by the General Binding Rules (part of the WFD in Scotland), the model gave good predictions of P loads (345-481 kg P). The modeling results show that riparian buffers alone cannot achieve the required P load reduction (up to 54% P can be removed). In the medium P input scenario, average costs vary from £38 to £176 kg P at 10% and 54% P reduction, respectively. The framework demonstrates a useful tool for exploring cost-effective targeting of environmental measures.

Change point analysis of phosphorus trends in the Illinois River (Oklahoma) demonstrates the effects of watershed management

Detecting water quality improvements following watershed management changes is complicated by flow-dependent concentrations and nonlinear or threshold responses that are difficult to detect with traditional statistical techniques. In this study, we evaluated the long-term trends (1997-2009) in total P (TP) concentrations in the Illinois River of Oklahoma, and some of its major tributaries, using flow-adjusted TP concentrations and regression tree analysis to identify specific calendar dates in which change points in P trends may have occurred. Phosphorus concentrations at all locations were strongly correlated with stream flow. Flow-adjusted TP concentrations increased at all study locations in the late 1990s, but this trend was related to a change in monitoring practices where storm flow samples were specifically targeted after 1998. Flow-adjusted TP concentrations decreased in the two Illinois River sites after 2003. This change coincided with a significant decrease in effluent TP concentrations originating with one of the largest municipal wastewater treatment facilities in the basin. Conversely, flow-adjusted TP concentrations in one tributary increased, but this stream received treated effluent from a wastewater facility where effluent TP did not decrease significantly over the study period. Results of this study demonstrate how long-term trends in stream TP concentrations are difficult to quantify without consistent long-term monitoring strategies and how flow adjustment is likely mandatory for examining these trends. Furthermore, the study demonstrates how detecting changes in long-term water quality data sets requires statistical methods capable of identifying change point and nonlinear responses.

Diffuse phosphorus models in the United States and europe: their usages, scales, and uncertainties

Today there are many well-established computer models that are being used at different spatial and temporal scales to describe water, sediment, and P transport from diffuse sources. In this review, we describe how diffuse P models are commonly being used in the United States and Europe, the challenge presented by different temporal and spatial scales, and the uncertainty in model predictions. In the United States, for water bodies that do not meet water quality standards, a total maximum daily load (TMDL) of the pollutant of concern must be set that will restore water quality and a plan implemented to reduce the pollutant load to meet the TMDL. Models are used to estimate the current maximum daily and annual average load, to estimate the contribution from different nonpoint sources, and to develop scenarios for achieving the TMDL target. In Europe, the EC-Water Framework Directive is the driving force to improve water quality and models are playing a similar role to that in the United States, but the models being used are not the same. European models are more likely to take into account leaching of P and the identification of critical source areas. Scaling up to the watershed scale has led to overparameterized models that cannot be used to test hypotheses regarding nonpoint sources of P or transport processes using the monitoring data that is typically available. There is a need for more parsimonious models and monitoring data that takes advantage of the technological improvements that allow nearly continuous sampling for P and sediment. Tools for measuring model uncertainty must become an integral part of models and be readily available for model users.

International phosphorus workshop: diffuse phosphorus loss to surface water bodies--risk assessment, mitigation options, and ecological effects in river basins

Agriculture is a major source of P to the aquatic environment in many countries. Although efforts have been made to improve the P utilization in agricultural production, which is reflected in modestly declining P surpluses in many countries, increasing agricultural P surpluses are still observed in some countries. The IPW5 Special Submission included in this issue addresses and discusses four key topics that emerged from the workshop: (i) managing agricultural P losses-effectiveness, uncertainties, and costs; (ii) P modeling at different scales; (iii) functioning of riparian buffers; (iv) ecological responses to P loadings and impacts of climate change. Each of these four topics interacts with each other as well as with the four tiers of the P Transfer Continuum (Source, Mobilization, Transport, and Ecological Effects). In this review paper we highlight the main outcomes of the workshop and the special collection of eight papers. Moreover, we identify the main gaps in our knowledge and future research directions on P, which are linked to important issues such as addressing scale effects, improved P models with the ability to quantify uncertainty, the linking of P losses with ecological effects, and climate change.