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Highlights • The coupled SWAT-MODFLOW model is able to effectively predict stream flow, sediment, and nutrients on long term and high resolution configuration. • The groundwater and surface water shows strong interactions in terms of the exchanges of both water quantity and quality between streams and aquifer. • The agricultural best management practices (BMPs), particularly combined BMPs, are effective in reducing NPS pollution loads in a predominately agricultural coastal watershed. Abstract The predominantly agricultural coastal watershed located in tropical–subtropical Island has served as a pathway for nonpoint source (NPS) pollution loading into the downstream coastal ecosystems. The present study aims to assess watershed hydrology and water quality by applying a watershed model to long–term high–resolution monitoring data, and to evaluate the reduction of nonpoint–source pollution by implementing best management practices (BMPs) in a small agricultural watershed located in southwestern Japan. The Soil Water and Assessment Tool (SWAT) was coupled to a groundwater model (MODFLOW) and applied to simulate stream flow, sediment, and nutrients discharges. The results revealed that the model successfully predicted hourly stream flow, sediment, and nutrients concentrations in the study watershed and that the model could be further used to evaluate BMP scenarios. This is the first attempt to quantify the impacts of multiple agricultural mitigation measures on long-term water quality for sediment, nitrate, and phosphate at an hourly resolution. From the model results, the land cover conversion and mulching scenarios achieved a significant reduction in sediment, followed by the cover crop, alternative tillage, and filter strip scenarios. Moreover, conversion of all summer sugarcane to pasture farmland and fertilizer control scenarios gave the superior reduction in nitrate load, while other scenarios were minimally effective. On the other hand, most of the scenarios significantly achieved the reduction of phosphate load. The results further indicated that the BMPs recommended in this study are appropriately combined scenarios, which achieved the significant reduction in all NPS loads. Although this study revealed some effective mitigation measures to improve the water quality in the study watershed, actual implementation of correct ones may be practically challenging unless other environmental and economic risks (e.g. the increase of other pollutants and reduction in agricultural productivity) are also taken into considerations. [ABSTRACT FROM AUTHOR]

Highlights • Systematically calibrating and validating both hydrological and water quality model. • Using satellite imagery to detect possible tail water recovery system in study watershed. • Using reservoir function in SWAT to simulate tail water recovery ponds grouped by sub-basins in watershed wide. • Using management schedule function in SWAT with dynamic analysis of crop rotation scenario. Abstract For an agricultural watershed, best management practice (BMP) is a conservational way to prevent non-point source pollution and soil and water loss. Three BMPs, including tail water recovery pond, conservational tillage, and crop rotation, were evaluated in order to demonstrate the impacts of BMPs on water quality and quantity. Satellite imagery was used to estimate potential tailwater recovery ponds in this study. The Soil and Water Assessment Tool (SWAT) was applied to evaluate BMPs. Results showed that the use of conservational tillage reduced cumulative sediment, total nitrogen (TN), and total phosphorus (TP) yields. In the crop rotation scenario analysis, it was found that sediment and flow were not sensitive to crop rotation management. The corn-soybean rotation scenario had higher TN and lower TP yields than those of the continuous corn scenario. Continuous soybean scenario showed the lowest TN and low TP yields, which may because of the higher nitrogen fertilization demands, greater crop yield, and greater residue of corn than soybean crop. Based on the SWAT model simulation results, the tailwater ponds can reduce sediment yield and improve groundwater storage. [ABSTRACT FROM AUTHOR]

Intensive tillage (IT) in potato crops is considered as one of the main non-point sources (NPS) of local water eutrophication in the Fuquene Lake of Colombia. Therefore, the local government has invested in several programs aiming at the adoption of principles of conservation tillage (CT) which would allow for developing and applying the agricultural best management practices (BMPs). The complexity of hydrological and geological heterogeneity makes the degree of benefit that CT has in different locations uncertain. In this study, the Soil and Water Assessment Tool (SWAT) was used to assess the impacts of changing IT for CT on nitrogen (N ) and phosphorus ( P ) losses in surface water runoff from the potato crop in the Fuquene watershed. This is done at field and watershed levels. A two-year study quantified the changes in surface water runoff pollutants for three potato crop cycles under the traditional IT practice and CT practice - which included reducing tillage, green manure, and permanent soil cover - at twelve runoff plots installed in the Fuquene watershed ( Quintero and Comerford, 2013 ). This information was used to build, calibrate and validate the SWAT model. The results suggest that CT for the Fuquene watershed can be reduced up to 26% of the sediment yield and 11% of the surface runoff compared with IT, which means an overall reduction of load. The main CT effect on nutrient losses in runoff is an increase in the total N and P (2% to 18% respectively) compared to IT. However, the results at watershed level showed different patterns from those obtained at field level. Despite the model uncertainties, the results show a possibility of using hydrological models to assess the effectiveness of various field management practices in agriculture. [ABSTRACT FROM AUTHOR]

The Soil and Water Assessment Tool with downscaled weather data generated using the MarkSim weather file generator was used to evaluate the impact of long-term conservation practice implementation on runoff, sediment, atrazine, nitrogen (N) and phosphorus (P) losses in an agricultural watershed located in northeastern Indiana. As part of the Conservation Effects Assessment Project, evaluation of these conservation practices is required to provide insight on how their implementation is benefiting the environment. The results indicate that individual conservation practices were effective in reducing a particular pollutant load, but combined practices were more effective in reducing multiple pollutant loads simultaneously. Of the individual best management practices (BMPs) assessed, no-till was the most effective in reducing multiple pollutant loads (reduced surface runoff by an average of 25%, sediment by 46%, atrazine by 46%, total N by 9%, soluble P by 16%, and total P by 29%). When BMPs were combined, pollutant load reductions were increased significantly (at α = 0.05) for all pollutants, both under baseline and future climate scenarios. The reductions in runoff and pollutant loads for each decade of future climate ranged from 15 to 25% for surface runoff, 32–68% for sediment loss, 37–60% for atrazine loss, 5–13% for soluble N loss, 12–35% for total N loss, 9–41% for soluble P loss, and 33–60% for total P loss. [ABSTRACT FROM AUTHOR]

This study is to evaluate the reduction of high level nonpoint source (NPS) pollution discharges in Haean highland agricultural catchment (62.8 km 2 ) by applying best management practices (BMPs) of vegetation filter strip installation (VFS), fertilizer control (FC), and rice straw mulching (RSM) in uplands above 600 m of elevation using SWAT (Soil and Water Assessment Tool). From the modeling results, the VFS BMP showed the best performance to reduce sediment (SS) of 16.0% for 1 m strip width up to 34.8% for 5 m strip width and total phosphorus (T-P) discharge loads of 5.1% to 21.3% from highland crop areas. The FC BMP showed the discharge loads reduction of 4.9% for 10% fertilizer reduction up to 16.4% for 30% fertilizer reduction. The RSM BMP results showed the sediment reduction of 3.0% for 6.0% runoff reduction up to 14.1% for 17.0% runoff reduction and T-P reduction of 1.3% for 6.0% runoff reduction up to 6.8% for 17.0% runoff reduction by showing negative effect of total nitrogen (T-N) up to −3.7% for 12.0% runoff reduction. However, because of the difficulties to install vegetation filter strip by farmers unwillingness in South Korea, the BMPs combination of fertilizer reduction and rice straw mulching (FC + RSM) was suggested as an executable BMP to obtain positive removal efficiency for all nutrient discharge loads. The FC + RSM BMP showed sediment, T-P, and T-N reductions up to 9.7%, 8.1%, and 9.2% respectively. [ABSTRACT FROM AUTHOR]

Quantitative evaluation of best management practice (BMP) effectiveness can help stakeholders to make better watershed management decisions. However, such evaluations are always challenging as they require complex algorithms to simulate the relevant hydrological processes, crop growth and the corresponding pollutant transport pathways in order to evaluate potential BMPs and select the best one for the specific field conditions. In this study, a web-based interface (CalBMP) was developed to predict BMP effectiveness in California, focusing on pesticide modeling at the field scale. With built-in databases for soil, weather, crop, pesticides, and BMPs, users can run simulations for baseline and BMP scenarios using their site-specific field conditions by simply providing the field information, such as zip code, soil, crop management, and pesticide application data. CalBMP uses PRZM5 + , a USEPA model, to simulate pesticide transport and fate at the field edge. The CalBMP simulations were validated based on measurements from an alfalfa field study. The results indicated that the CalBMP interface could reasonably simulate the runoff and adsorbed pesticide loss leaving the field with default parameters from previously known field parameters or public databases. CalBMP underestimated sediment erosion, possibly due to uncertainties in field measurements or inaccurate simulation of the temporal distribution of flood irrigation. CalBMP is likely to underestimate pesticides with greater solubility, such as diuron, because PRZM5 + uses the simplified instantaneous equilibrium sorption model. In addition, a strawberry field study was adopted to demonstrate the capability of the CalBMP interface for simulating BMP effectiveness (pesticide reduction percentage in the main pathways) with easy-to-understand graphs and tables. The results indicated that users can easily compare and review the results from multiple scenarios, which could facilitate the decision-making process for mitigating the amount of active ingredient bifenthrin leaving the field. The CalBMP tool provides useful information on pesticide runoff potential and BMP selection at the field scale. With increasingly stringent regulations for water quality protection, CalBMP will add to the growers' toolbox for minimizing the environmental impacts from their inevitable pesticide usage. [Display omitted] • An online best management practice (BMP) modeling tool was developed and validated. • It could help stakeholders identify water quality risks from pesticide use. • It is open access and greatly aid in BMP selection to reduce pesticide runoff. [ABSTRACT FROM AUTHOR]

In this study, an innovative method to generate spatially-distributed data sets on land management and terraces based on sparse field data for a steep-sloping catchment in the Three Gorges Region in China is introduced and tested using the eco-hydrological model SWAT. The generation of such data sets is necessary for the development and evaluation of Best Management Practices (BMP) towards a reduction of high inputs of sediment and nutrients in water bodies. It is hypothesized that the inclusion of land management as well as terraces in the eco-hydrological modelling approach are individually as well as combined able to increase the model efficiency regarding streamflow and sediment. The results of the study show that the field data sets on land management and terraces can be used to generate useful SWAT input data sets to represent management and conservation practices and the model results are plausible. The effect of land management and terraces on streamflow is identified to be rather small. At the same time a strong effect of the inclusion of the terrace dataset on sediment yields can be observed, which can be seen as an improvement of the process representation within the model. By introducing the new method the study contributes to an improved representation of land management and terraces in data-scarce study regions in eco-hydrological models. At the same time the study confirms the importance of the consideration of BMPs in eco-hydrological modelling, especially towards the representation of the dynamics of sediment and sediment-bound substances. [ABSTRACT FROM AUTHOR]

A 2-year study was conducted to explore the impact of current and alternative best management practices (BMPs) of irrigation and fertigation on nitrate (NO 3 − ) leaching below the root zone. Using a fully randomized complete block design, three fertigation strategies were compared: current BMP with and without accounting for NO 3 − -N in irrigation-water, and a high frequency fertigation treatment with low-N concentration applications. Temporal changes in water content, pore water NO 3 − concentrations and soil water potential were monitored within and below the root zone to a soil depth of 3 m at eight sites in an almond and a pistachio orchard. NO 3 − concentrations below the root zone ranged from <1 mg L −1 to more than 2400 mg L −1 (almond), and up to 11,000 (pistachio) mg L −1 , with mean concentrations of 326 and 4631 mg L −1 , respectively. Within the fertigation cycle, fertilizer injection at the end of an irrigation event generally resulted in lower NO 3 − losses below the root zone compared with fertilizer injection midway through the irrigation. Pre-bloom and post-harvest flood irrigation in the almond orchard caused deep soil wetting and flushing of NO 3 − below the root zone, threatening groundwater quality. Statistical analysis using principal component analysis, Chi-squared Automatic Interaction Detector and the Artificial Neural Network showed that most of the deep soil NO 3 − concentration variability could not be explained by irrigation duration, fertigation timing or local variations in soil physical characteristics. However, mass balance estimates for water and N indicated the annual orchard average N loss could be estimated based on eight monitoring sites in spite of the inherent spatial variations in soil properties and the spatiotemporal variations in water and NO 3 − applications. The study indicated that reduction of N losses at the orchard scale would require alternative fertigation and irrigation practices, including better control of fertigation amounts and irrigation duration. [ABSTRACT FROM AUTHOR]

In this research, an interval-fuzzy possibilistic programming (IFPP) method was developed by integrating interval parameter programming (IPP), fuzzy possibilistic programming (FPP), and a fuzzy expected value equation within a general optimization framework. The developed IFPP method can not only effectively address uncertainties presented in terms of crisp intervals and fuzzy-boundary intervals in both the objective function and constraints, but it can also improve the traditional fuzzy mathematical programming by choosing the credibility degree of constraints based on the decision maker’s preference and avoiding complicated intermediate models with high computational efficiency. The developed method was applied to identify optimal placements for best management practices (BMPs) to control nutrient pollution in the Baoxianghe River watershed in China, in which a GIS-aided export coefficient model (ECM) was employed to estimate the phosphorus loads from a nonpoint source (NPS). The optimization results showed that the hybrid approach could be used to generate a series of implementation levels for BMPs under multiple credibility levels, ensuring that the NPS phosphorus loads discharged into rivers reduce to an allowable level and considering a proper balance between expected system costs and risks of violating the constraints. Relaxing the sub-basin discharge permits suggests a global discharge permit for the entire watershed, which may allow managers to shift BMP implementation among sub-basins to meet the overall discharge permit at a lower cost. [ABSTRACT FROM AUTHOR]

Highlights: [•] Agro-hydrological modeling to quantify agricultural change on nutrient cycle. [•] Historical BMPs and natural strips have a low impact on nutrient loss. [•] Systematic CC implementation maintain nitrate stream concentration below 50mgl−1. [•] Nutrient loss reduction varies from year to year with CC. [•] Nutrient loss reduction is constant in time for natural strips implementation/straw management options. [Copyright &y& Elsevier]

Highlights: [•] SWAT-IRRIG model is used to test best management practices (BMPs) on irrigation return flows and phosphorus load. [•] Combination of BMPs gives better results than individual BMPs. [•] The best scenario is optimum irrigation, conservation tillage and reduced P use. [•] This scenario resulted in the highest increase of sunflower and barley gross margin. [•] The highest increase of corn and alfalfa gross margin was not reached. [Copyright &y& Elsevier]

Abstract: Agricultural non-point source pollution (ANSP) is considered a major contributor to local water degradation in the Three Gorges Reservoir Area (TGRA) of China. The Xiangxi River, which is a first level anabranch of the Yangtze River, was selected for investigation of the effectiveness of selected best management measures (BMPs) to alleviate water pollution through analysis of several scenarios by SWAT (Soil and Water Assessment Tool). Specifically, changes in land use, fertilizer management and tillage management measures were simulated in SWAT because they were shown to be the primary factors influencing non-point source (NPS) pollution in the Xiangxi River watershed. The results revealed that when farmland was returned to forests, both runoff and NPS pollution loads showed a clear downward trend and the NPS pollution loads in the Xiangxi River watershed decreased by 20% or more when compared with the status of 2007. Furthermore, conservation tillage and contour farming can help reduce runoff by 15.99% and 9.16%, total nitrogen (TN) by 8.99% and 8%, and total phosphorus (TP) by 7% and 5%, respectively. Conservation tillage has a greater effect in controlling the losses of soil, water and nutrients than contour farming. Based on the fertilizer conditions of 2007, changing the fertilizer application resulted in little change in local runoff; however, for NPS pollution loads, various forms of nitrogen (N) and phosphorus (P) pollution loads were directly proportional to the amount of chemical fertilizer applied. Overall, the results of this study can facilitate development of environmental friendly land use plans by local managers, and enable farmers to manage agriculture and fertilizer more efficiently, ultimately achieve the goal of reduce water pollution. [Copyright &y& Elsevier]

Abstract: The non-point source (NPS) pollution is difficult to manage and control due to its complicated generation and formation. In large scale watersheds, the priority sources areas (PSAs) identification is an important and necessary process for efficient aquatic environmental management. Here, a framework for the PSAs identification and pollution load estimation in PSAs screened for Best Management Practices (BMPs) is proposed. Fujiang Watershed, a branch of Jialingjiang, the upper reach of Yangtze River, was chosen for evaluation of the method proposed here. The entire Fujiang Watershed was divided into 21 subbasins, after which the Agricultural Pollution Potential Index (APPI) was used to identify the PSAs, and a modified runoff coefficient was introduced to mitigate the impact of the rainfall heterogeneity in the process. Next, the identified PSAs were further divided into 34 subbasins, after which quantification of the pollution load was conducted using the Pollution Load (PLOAD) model. The results indicated that there are five subbasins have much higher NPS pollution load intensities, with an average value of 6.05t/km2/year for TN and 0.31t/km2/year for TP. According to the cluster analysis on land use structure, these five subbasins were featured by higher proportion of agricultural land, suggesting a need for better fertilizer application management. The method developed here provided a helpful framework for conducting NPS pollution management in a large watershed. [Copyright &y& Elsevier]

Abstract: Irrigation of pasture enables the intensification of land use, but can also result in increased losses of nitrogen (N) and phosphorus (P). In 2006 an irrigation scheme was introduced into the Kakanui River and Waiareka Creek catchments in North Otago, New Zealand, which has intensified land use, especially dairying. Supplementation of the Waiareka Creek by direct discharge of ‘clean’ irrigation water from a nearby River is practiced to raise the minimum flow. This supplementation is hypothesized to dilute N and P losses associated with increased land use intensification and irrigation return flow. Farm losses of N and P before irrigation were then used as a reference to judge in the Kakanui River, and compare against dilution in the Waiareka Creek, the effectiveness of best management practices (BMPs) to improve water quality in 2010 and 2020. Data for N and P fractions from three sites since the mid 1990s were analysed, and flow adjustments for direct discharge to the Waiareka Creek made. Similar concentrations of N and P fractions in Waiareka Creek before and after irrigation began suggest the current minimum flow of 100Ls−1 is insufficient to improve the nutrient status of the Creek, but does dilute recent intensification, which without dilution would have increased concentrations by 30–400%. In the lower Kakanui catchment, direct discharge does not occur and N and P concentrations increased, while little change occurred in the upper Kakanui catchment. Within each catchment, N and P losses from sheep and beef farms and dairy farms (with and without BMPs) were modelled for 2010 and 2020 and compared against that estimated in 2000. This showed that although substantial decreases could be made by adopting BMPs, the predicted increase in N and P losses (up to 200% by 2020) would require either more rigorous use of existing strategies or additional strategies to improve water quality, over and above dilution which is restricted by a need to minimise the risk of flooding. [Copyright &y& Elsevier]

Abstract: Investigation of the interaction of surface water (SW) and groundwater (GW) is critical in order to determine the effects of best management practices (BMPs) on the entire system of water resources. The objective of this research was to develop a modeling system for considering SW–GW interactions and to demonstrate the applicability of the developed system. A linked modeling approach was selected to consider SW–GW interaction. The dual-simulation scheme was developed to consider different time scales between a newly developed surface model: Dynamic Agricultural Non-point Source Assessment Tool (DANSAT), and existing groundwater models; a three-dimensional finite-difference groundwater flow model (MODFLOW) and a modular three-dimensional transport model (MT3D). A distributed and physically based DANSAT predicts the movement of water and pesticides in runoff and in leachate at a watershed scale. MODFLOW and MT3D simulate groundwater and pesticide movement in the saturated zone. Only the hydrology component of the linked system was evaluated on the QN2 subwatershed in the Nomini Creek watershed located in the Coastal Plain of Virginia mainly due to lack of observed data for MT3D calibration. The same spatial scale was used for both surface and groundwater models while different time scales were used because surface runoff occurs more quickly than groundwater flow. DANSAT and MODFLOW were separately calibrated using the integrated GW approach which uses own lumped baseflow components in DANSAT, and using the steady-state mode in MODFLOW, respectively. Then the linked system was applied to QN2 based on the parameters selected for DANSAT and MODFLOW to simulate time-dependent interactions on the entire system. The linked approach was better than the integrated approach for predicting the temporal trends of monthly runoff by improving the monthly Nash–Sutcliffe efficiency index from 0.53 to 0.60. The proposed linked approach will be useful for evaluating the impacts of agricultural BMPs on the entire SW–GW system by providing spatial distribution and temporal changes in groundwater table elevation and enhancing the reliability of calibrated parameter sets. [Copyright &y& Elsevier]

Abstract: The Southeast U.S. receives an average of 1300mm annual rainfall, however poor seasonal distribution of rainfall often limits production. Irrigation is used during the growing season to supplement rainfall to sustain profitable crop production. Increased water capture would improve water use efficiency and reduce irrigation requirements. Furrow diking has been proposed as a cost effective management practice that is designed to create a series of storage basins in the furrow between crop rows to catch and retain rainfall and irrigation water. Furrow diking has received much attention in arid and semi-arid regions with mixed results, yet has not been adapted for cotton production in the Southeast U.S. Our objectives were to evaluate the agronomic response and economic feasibility of producing cotton with and without furrow diking in conventional tillage over a range of irrigation rates including no irrigation. Studies were conducted at two research sites each year from 2005 to 2007. Irrigation scheduling was based on Irrigator Pro for Cotton software. The use of furrow diking in these studies periodically reduced water consumption and improved yield and net returns. In 2006 and 2007, when irrigation scheduling was based on soil water status, an average of 76mmha−1 of irrigation water was saved by furrow diking, producing similar cotton yield and net returns. Furrow diking improved cotton yield an average of 171kgha−1 and net return by $245ha−1 over multiple irrigation rates, in 1 of 3 years. We conclude that furrow diking has the capability to reduce irrigation requirements and the costs associated with irrigation when rainfall is periodic and drought is not severe. [Copyright &y& Elsevier]

Abstract: Phosphorus (P) losses from agricultural lands degrade surface waters due to anthropogenic eutrophication. Previous studies focused on plot-to-field scale P loss and reductions from best management practices (BMP''s), little information in intense agricultural catchments has been gathered on the dynamics influencing P beyond the edge of the field. This study was conducted to examine the phosphorus equilibrium between the water column and sediments in three tile fed drainage ditches in Northeast Indiana. Surface water and sediment samples were collected and analyzed for organic carbon (C), particle size and P from sites along three ditches with similar soils and land use at sites within each watershed draining approximately 300 and 1500ha on each ditch. Organic C, silt and clay fractions of the bottom sediments decreased with increasing drainage area. Soluble P concentrations were low in Ditch A, but increased with increasing drainage area (0.02–0.05mg PL-1). Overall, the P concentrations were higher in the Ditches B and C (0.06–0.09mg PL-1). Exchangeable P, P partitioning index and equilibrium P concentrations (EPCo) decreased with increasing drainage area by as much as 95, 93 and 100%, respectively, except in one catchment area with a confined animal feeding operation between sampling points, where ExP and EPCo increased by 4 and 116%, respectively. Aluminum sulfate and calcium carbonate treatment of ditch sediments reduced exchangeable P and sediment EPCo in this study. Results from this study indicated some watershed characteristics, as well as sediment physiochemical properties, affect ditch sediment and water P equilibrium and buffering capacity. Furthermore, this study demonstrated that managers could potentially use chemical treatment of the ditches to increase the temporary retention of P in ditches and maybe reducing sediment P availability. [Copyright &y& Elsevier]