Effect of best management practice implementation on sediment and phosphorus load reductions at subwatershed and watershed scale using SWAT model

Identification of areas contributing disproportionately high amount of pollutants (i.e., critical source areas (CSAs)) to streams is important to efficiently and effectively target best management practices (BMPs). Process-based models are commonly used to identify CSAs and evaluate the impact of alternative management practices on pollutant load reductions. The objective of this study was to use the Soil and Watershed Assessment Tool (SWAT) to identify CSAs at the subwatershed level and evaluate the impact of alternative BMPs on sediment and total phosphorus (TP) load reductions in the Pleasant Valley watershed (50 km2) in South Central Wisconsin (USA). The Nash-Sutcliffe efficiency, percent bias, and coefficient of determination ranged from 0.58 to 0.71, ? 12.87 to 38.33, and 0.67 to 0.79, respectively, indicating that SWAT was able to predict stream flow, sediment and TP loadings at a monthly time-step with sufficient accuracy. Based on the SWAT simulation results, annual average (2006–2012) sub-watershed yield for sediment and TP ranged from 0.06 to 3.14 tons ha?1 yr?1 and 0.04 to 1.9 kg ha ? 1 yr ? 1, respectively. The croplands were the major source of sediment and TP in this watershed ( Z 84%). Reduction in sediment and TP loading ranged from 66%to 99%at the subwatershed level after conversion of croplands to Conservation Reserve Program (CRP) grasslands in subwatersheds identified as CSAs. On the other hand, reduction in sediment and TP loading with implementation of no-till practices ranged from only 14%to 25%. At the watershed outlet, sediment and TP loading reduction was r 15% after conversion of croplands to CRP grasslands and implementation of no-till practices because only about 8%of the watershed area was targeted for BMPs and/or resuspension of sediment deposited on the stream bed masked the downstream improvements in water quality.     

Impacts of land use and land cover changes on hydrological processes and sediment yield determined using the SWAT model

Land use and land cover (LULC) changes strongly affect local hydrology and sediment yields.The current study focused on a basin in the Brazilian Amazon and had the following three objectives:(1) to perform an effective diagnosis of flow and sediment yield,(2) to evaluate the impacts of LULC changes over the last 40 years on the hydro-sedimentological variables,and (3) to investigate the impacts of the possible trends or breaking points in the flow,surface runoff,and sediment yield series.The Soi...     

Assessment of Climate Change Impact on the Gharesou River Basin Using SWAT Hydrological Model

The evaluation of climate change and its side effects on the hydrological processes of the basin can increasingly help in dealing with the challenges that water resource managers and planners face in future courses. These side effects are investigated using the simulation of hydrological processes with the help of physical rainfall‐runoff model. Hydrological models provide a framework for examining the relationship between climate and water resources. This research aims at the investigation of the effect of climate change on the runoff of Gharesou, which is one of the main branches of the “Karkheh” River in Iran during the periods 2040–2069. To achieve this, the distributed hydrological model Soil and Water Assessment Tool (SWAT) – a model that is sensitive to the changes in land, water, and climate – has been used with the aim of evaluating the impact of climate change on the hydrology of the Gharesou Basin. For this reason, first, the continuous distributed model of rainfall‐runoff SWAT for the period 1971–2000 has been calibrated and validated. Next, with the aim of evaluating the impact of climate change and global warming on the basin hydrology for the period 2040–2069, HadCM3‐AR4 global climate model data under the A2 scenario – from the SRES scenario set‐haves been downscaled. Eventually, the downscaled climate data haves been introduced in the SWAT model, and the future runoff changes have been studied. The results showed that the temperature increases in most of the months, and the precipitation rate exhibits a change in the range of ±30%. Moreover, the produced runoff in this period changes from ?90 to 120% during different months.     

Strategy for management of lake-catchment system integrated with natural and anthropogenic factors in China

Lake eutrophication that has caused severe damages to aquatic ecosystems is a hot issue in the field of water pollution control, so analyzing its process and driving mechanism is of great significance. In this study, we detected its major driving factors based on an observed dataset and assessed the impacts of these factors. Firstly, empirical econometric models were used to ascertain the Per capita GDP and the percentage of impervious surface, which are significantly related with the eutrophication level. Eutrophication is slightly affected by anthropogenic disturbance, but is negatively related to the supply coefficient. Secondly, all driving factors are divided into two categories, including the stresses caused by human activities and the comprehensive health status, which are expressed as the two coordinate axes of an indicator-matrix. Thirdly, lake classification, which is a decision-making tool for management and control of eutrophication, suggests a breakdown in communication between researchers and water managers. Finally, corresponding management strategies are recommended, and the classification system can be used to simplify management by grouping lakes that may be managed by similar strategies. The classification management may enlighten and guide the appropriate policy implementation for lake eutrophication management.     

生态补水对白洋淀流域地表水和地下水水化学特征的影响

生态补水是维持和改善白洋淀生态环境的重要途径.为研究生态补水对白洋淀水环境的影响,分别在补水前与补水后采集淀水、河水及地下水样品,分析区域地表水和地下水水化学特征.结果表明：（1）白洋淀补水前、后地表水与地下水的水化学组成中Na⁺为主要阳离子,补水后阴离子以HCO₃^-为主,淀区南部地表水电导率高;补水后地表水与地下水Ca²⁺、Mg²⁺和HCO₃^-浓度显著增加,水体电导率降低.（2）补水前地下水为Na-HCO₃型水,地表水主要为Na-Cl·SO₄及Na-Cl·HCO₃类型;补水后地表水与浅层地下水向Ca·Mg-HCO₃型演化,深层地下水水化学类型基本保持不变.（3）生态补水使白洋淀水位升高,淀区水面积增大,缓解了水资源短缺的问题;同时也使浅层地下水水化学组成发生改变,而深层地下水暂未受到影响.生态补水后,受稀释和混合作用的影响,水体Na⁺、Cl^-和SO₄^2-浓度显著下降,Ca²⁺、Mg²⁺及HCO₃^-浓度增加.在白洋淀生态补水中应"先治污,后补水",以减少补水过程中污染物向淀区的运移,还应注意区域地下水位上升过程中的阳离子交换及水岩相互作用,为合理调配生态补水及改善白洋淀生态环境提供科学依据.     

基于改进SWAT模型的灌溉—施肥—耕作对乌梁素海流域营养物负荷及作物产量的影响

不合理的灌溉、施肥和耕作是导致乌梁素海流域农业面源污染的主要根源,乌梁素海作为我国北方地区重要的生态安全屏障,多年来面临着湖泊水环境污染、水生态退化等问题,科学开展湖泊水环境综合治理首先要解决流域内农业面源污染问题.研究通过修改土壤水平衡、溶质平衡、地下水平衡和作物生长等模块对SWAT 2012原始版本进行改进,并采用改进的SWAT模型构建了乌梁素海流域分布式水文模型,利用实测径流、硝态氮与总磷排放量、地下水埋深以及作物产量校正和验证模型.基于现状情景,以玉米、葵花和小麦3种主要作物为研究对象,设置了削减灌水量、施肥量及调整耕作方式3种农田管理情景.基于改进SWAT模型不同情景的模拟结果,计算分析各管理情景下的硝态氮与总磷负荷及对各作物产量的影响.结果表明,改进SWAT模型具有良好的模拟效果.不同作物削减5%夏灌水量增产最多达8.41%～10.32%,削减10%秋浇水量均明显减少硝态氮和总磷负荷.不同作物营养物负荷均随着氮磷施肥削减比例的增大呈现逐渐降低的趋势,但下降曲线逐渐趋于平缓;各作物产量随氮磷施肥削减比例的增加呈先增加后减少的趋势,其中玉米、小麦氮磷施肥削减比例达20%时产量开...     

Implementing a nonlinear groundwater module in the soil and water assessment tool (SWAT)

The Soil and Water Assessment Tool (SWAT) is widely used in modeling water quantity and quality. In the original SWAT, groundwater flow is calculated using a linear‐reservoir model, with outflow proportional to storage. However, observations show that this assumption is not always applicable; for example, macropores in Karst formations would seriously affect the groundwater behavior. A nonlinear groundwater algorithm was introduced in a new version of the SWAT model, called ISWAT. The Shenandoah Valley area in the Eastern U.S., which includes a number of geologic formations including Karst, was selected to test the modified ISWAT model. Parameter ESTimation (PEST) was coupled with ISWAT to auto‐calibrate the nonlinear parameter values. Ten years of record at 15 stream gauges were used to calibrate the model. The nonlinear ISWAT, statistically and visually, performed better in stream discharge estimation especially during baseflow recession and low‐flow periods. This indicated that the nonlinear algorithm can better represent groundwater behavior. The coupled ISWAT‐PEST approach can be used in future stream discharge simulation. Copyright © 2013 John Wiley & Sons, Ltd.     

SWAT model application and prediction uncertainty analysis in the Lake Tana Basin,Ethiopia

Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. Many years of mismanagement, wetland losses due to urban encroachment and population growth, and droughts are causing its rapid deterioration. The main objective of this study was to assess the performance and applicability of the soil water assessment tool (SWAT) model for prediction of streamflow in the Lake Tana Basin, so that the influence of topography, land use, soil and climatic condition on the hydrology of Lake Tana Basin can be well examined. The physically based SWAT model was calibrated and validated for four tributaries of Lake Tana. Sequential uncertainty fitting (SUFI‐2), parameter solution (ParaSol) and generalized likelihood uncertainty estimation (GLUE) calibration and uncertainty analysis methods were compared and used for the set‐up of the SWAT model. The model evaluation statistics for streamflows prediction shows that there is a good agreement between the measured and simulated flows that was verified by coefficients of determination and Nash Sutcliffe efficiency greater than 0·5. The hydrological water balance analysis of the basin indicated that baseflow is an important component of the total discharge within the study area that contributes more than the surface runoff. More than 60% of losses in the watershed are through evapotranspiration. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil Budget,Net Export,and Potential Sinks of Nitrogen in the Lower Oglio River Watershed (Northern Italy)

A nitrogen mass balance, realized for the lower Oglio River basin (Po River Plain, northern Italy), suggested an elevated impact of agricultural activities in this watershed. Livestock manure, synthetic fertilizers, biological fixation, atmospheric deposition, and wastewater sludge contributed 51, 34, 12, 2, and 1% of total N (TN) input, respectively (basin average 450 kg N ha^?1 arable land (AL) year^?1, overall input 100 115 t N year^?1). Crop uptake, ammonia volatilization and denitrification in soils contributed 65, 21, and 14%, respectively, of TN output (basin average 270 kg N ha^?1 AL year^?1, overall output 60 060 t N year^?1). N inputs exceeded outputs by 40 056 t N year^?1, resulting in a basin average surplus of about 180 kg N ha^?1 AL year^?1. About 34% of the N surplus was exported annually from the basin while the remaining amount (about 26 800 t N year^?1) underwent other unaccounted for processes within the watershed. The relevance of nitrogen removal via denitrification in aquatic compartments within the watershed was evaluated. Denitrification in the secondary drainage network can represent a relevant nitrogen sink due to great linear extension (over 12 500 km), with estimated nitrogen loss up to 8500 t N year^?1. Denitrification in the riverbed and in perifluvial wetlands have the potential to remove only a small fraction of the nitrogen surplus (<3%). Evidence suggests the relevance of groundwater as a site of nitrogen accumulation.     

红枫湖、百花湖沉积物全氮、可交换态氮和固定铵的赋存特征

氮是引起湖泊水体富营养化的关键营养元素之一。本次工作从贵州两个重要水库（红枫湖和百花湖）采集了未受扰动的沉积物样品性,分析了分层沉积物样品中的总氮,无机交换性氮和固定铵的含量及垂直剖面分布,研究表明,红枫湖和百花湖沉积物中具有较高的全氮含量,平均含量约为沉积物干重的0.36%～0.40%,其垂直分布在埋藏过程中受到成岩作用改造,沉积物交换性氮在沉积物中的赋存受到全氮含量和埋藏环境的双重控制,红枫湖和百花湖沉积物具有较强的吸持固定铵的能力,沉积物固定铵的绝对含量的平均值分别为434.05mg/kg和416.94mg/kg,分别占全氮的13.53%和12.53%。     

基于SWAT模型的典型农业小流域氮污染时空分布特征及关键源解析

水资源恶化、水体富营养化严重威胁生态环境健康,农业活动所产生的氮是造成水污染的主要原因之一.本研究以句容水库农业流域为研究对象,基于实地监测数据验证了SWAT模型模拟当地氮污染的适用性,并分析了氮素负荷的时空分布特征及其关键源.结果 表明:硝态氮(NO3-N)和总氮(TN)的年均入库量分别为9.98和27.22 t.时...     

Evaluation of River Water Quality Simulations at a Daily Time Step – Experience with SWAT in the Axe Catchment,UK

The Water Framework Directive (WFD) was established for the protection of surface waters (rivers, lakes, transitional and coastal waters) and ground waters in the European Union. The main environmental objective is to achieve and maintain a good status for all waters by the target date of 2015. Models which are able to address the majority of environmental objectives are proposed within the WFD to inform the management changes required to meet current water policy goals. The use of the Soil and Water Assessment Tool (SWAT) catchment model is widespread throughout the world, especially to support river basin management as required by the WFD. This paper provides a critical evaluation of the use of the model by placing model performance in the Axe catchment, UK, in the context of international performance of the model. Within the constraints of the available data, SWAT represents hydrology, sediment and ortho‐phosphorus concentration well for this heterogeneous catchment, but the representation of daily nitrogen concentration dynamics is poor. Temporal aggregation of model outputs from daily to monthly improved the performance metrics for all the river outputs, including nitrate. Wider review of SWAT studies showed widespread reporting of monthly performance metrics within the SWAT studies, despite the model operating at a daily time step. Poor performance for nitrate identified in this current study may be a significant factor in the choice to not report daily results. This demonstrates the importance of ascertaining the reasons for the use of temporal aggregation in modelling studies.     

新疆艾比湖流域地表水丰水期和枯水期水质分异特征及污染源解析

采用2015年艾比湖流域54个采样点的10个地表水水质指标数据,首先利用水质指数模型(WQI)和地统计学方法对流域水质污染情况进行全局评价,然后利用层次聚类法、判别分析法和因子分析法分析艾比湖流域地表水丰水期和枯水期水质分异特征.在水质时空分异特征研究的基础上,利用主成分回归分析法对艾比湖流域水质进行污染源解析.结果表明:艾比湖流域丰水期WQI值介于38~70之间,枯水期WQI值介于31~71之间,艾比湖流域丰水期的地表水水质污染情况比枯水期严重,而艾比湖、博尔塔拉河和精河靠近艾比湖湖区的河道污染程度均比其他河道严重.由聚类分析和判别分析得出艾比湖流域丰水期和枯水期的水质采样点在空间上均被分成A、B两组,A组包括艾比湖湖区西部、奎屯河、古尔图河和四棵树河,B组包括艾比湖湖区东部、精河和博尔塔拉河.艾比湖流域丰水期和枯水期的水体主要受到化学需氧量、溶解氧、氨氮和悬浮物浓度等指标的影响,B组水质污染指标的值相比于A组的值偏高,B组区域内存在高污染企业,艾比湖流域水环境治理工作需主要集中在B组所包括的艾比湖湖区、博尔塔拉河和精河.(4)艾比湖湖区、精河和博尔塔拉河地表水体的污染主要来自于有机物污染和营养物质污染,其次为工矿业污染;而奎屯河、古尔图河、四棵树河地表水体的污染主要来自于有机物污染,其次为营养物质污染,生物污染的影响较为微弱.该研究结果可为艾比湖流域地表水水环境改善和治理提供一定参考.     

Impact Assessment of Climate Change and Human Activities on Runoff Variation in Coal Mining Watershed,NW China

Water Resources - The Kuye river watershed is a coal mining watershed in Northwest China. The study analyzed runoff change of year, high flow period and low flow period in the past 60 years based...     

Sediment transport in distributary channels and its export to the pro-deltaic environment in a tidally dominated delta: Fly River, Papua New Guinea

Current metre deployments, suspended sediment measurements and surface sediment samples were collected from three locations within distributary channels of the tidally dominated Fly River delta in southern Papua New Guinea. Net bedload transport vectors and the occurrence of elongate tidal bars indicate that mutually evasive ebb- and flood-dominant transport zones occur in each of the distributary channels. Suspended sediment experiments at two locations show a phase relationship between tidal velocity and sediment concentration such that the net suspended sediment flux is directed seaward. Processes that control the export of fluid muds with concentrations up to 10 g l⁻¹ from the distributary channels across the delta front and onto the pro-delta are assessed in relation to the available data. Peak spring tidal current speeds (measured at 100 cm above the bed) drop off from around 100 cm s⁻¹ within the distributary channels to <50 cm s⁻¹ on the delta front. Gravity-driven, 2-m thick, fluid mud layers generated in the distributary channels are estimated to require at least 35 h to traverse the 20-km-wide, low-gradient (2×10⁻³ degrees) delta front. The velocities of such currents are well below those required for autosuspension. A 1-month time series of suspended sediment concentration and current velocity from the delta front indicates that tidal currents alone are unable to cause significant cross-delta mud transport. Wave-induced resuspension together with tides, storm surge and barotropic return-flow may play a role in maintaining the transport of fine sediment across the delta front, but insufficient data are available at present to make any reliable estimates.     

Soil and onsite nutrient conservation potential of aromatic grasses at field scale under a shifting cultivated,degraded catchment in Eastern Ghats,India

Land degradation due to soil erosion is a global problem, especially on cultivated hill slopes. Economically important aromatic grasses can protect degraded hill slopes more effectively than field crops, but little information is available on their performance. This study quantifies runoff, sediment yield,enrichment ratios of soil and nutrients, and sediment-associated organic carbon and nutrients losses under three aromatic grass species: citronella(Cymbopogon nardus), lemon(Cymbopogon flexuosus), and palmarosa(Cymbopogon martini), compared with a traditional field crop, finger millet(Eleusine coracana)grown at three land slopes(4%, 8%, and 12%). It was observed that the degree of slope and type of grass both significantly influenced runoff generation. Runoff and sediment yield(SY) were significantly higher at 12% slope than at 8% and 4% slopes. Relation between rainfall and runoff were significant for all the grass species(p 0.05). Palmarosa, lemon, and citronella grass reduced the SY by 10, 54, and 60%,respectively, over finger millet. SY was also significantly related to rainfall for all the treatments(p 0.05). The threshold runoff values to produce SY were higher for aromatic grasses compared to finger millet. Enrichment of clay, silt, sand, soil organic carbon(SOC), available nitrogen(N), phosphorus(P) and potassium(K) in the sediment were not significantly different between slopes but differed significantly between aromatic grasses and finger millet. Sediment associated nutrient load varied inversely with SY mainly because of the nutrient dissolution effect of high runoff volume. Annual loss of SOC and nutrients varied from 84.7-156.8 kg ha~(-1) y~(-1) for SOC, 4.38-9.18 kg ha~(-1) y~(-1) for available N, 0.35-0.75 kg ha~(-1) y~(-1) for available P, and 2.22-5.22 kg ha~(-1) y~(-1) for available K, with the lowest values for citronella and highest for finger millet. The study found that the aromatic grasses have greater environmental conservation values than finger millet on steep degraded land.