农田降雨径流污染模型探讨——以上海郊区农田氮素污染模型为例

农田降雨径流污染是非点源污染研究中的一个重要问题 ,估算其发生负荷的难度很大。通过对农田降雨径流污染模型结构的理解和适当简化不可直接建模的部分 ,对农田非点源污染物输出的重要环节———降雨径流和污染物迁移进行了模拟。根据实测资料对SCS法的部分参数作了修正 ,使小块农田的降雨径流关系适合上海的区域自然地理条件 ;采用比较完善的径流试验资料建立了相应的径流单位线 ;并利用水流流速与固体颗粒被冲刷强度的关系 ,选择合适的试验资料 ,分析得到了径流过程与氮素流失浓度的相关关系 ,从而建立了以修正的SCS法、径流单位线和径流过程与氮素流失浓度的关系为基础的农田降雨径流污染模型。在具备较长系列降雨量资料的条件下 ,该模型确定了不同降雨量频率代表年份上海郊区农田氮素的年流失量     

红壤丘陵区小流域典型土地利用的面源氮磷输出特征

科学识别不同土地利用方式下的径流污染输出特征是治理流域面源污染的前提.以南方红壤丘陵地区小流域为例,野外实地观测对比了不同降雨特征下林地、种植用地和建设用地的水文过程和面源污染物输出过程.结果表明,土地利用方式影响着地表径流的水文水质过程,典型降雨下3类用地类型产流时间及产流累积雨量的特征为：建设用地（9 min,2.0 mm）、种植用地（35 min,11.4 mm）和林地（108 min,24.0 mm）;而3种用地类型的总悬浮物（TSS）、总氮（TN）和总磷（TP）的污染物浓度、形态、氮磷比变化及输出强度等污染输出过程特征也呈现明显差异.典型降雨下不同用地类型具有相似的污染输出阶段,径流初期的TSS、TN和TP质量浓度均偏高,之后逐步趋于稳定;产流过程的前30 min贡献TSS、TN及TP负荷的范围均在23%~43%之间.年尺度下,各用地类型对TN和TP负荷的贡献率及单位面积负荷比存在明显差异,表现为种植用地污染负荷贡献最高（57%和45%）,而建设用地单位面积负荷比最高（9.50~12.50）.结果亦表明小流域面源污染关键源区的分布具有时空动态变化特征,由汇水单元内的用地类型组成和年降雨特征等综合决定;随着次降雨量的增加,主要贡献源由建设用地向种植用地动态转变,治理时需要根据关键源区的分布特征及下垫面产流过程规律进行针对性生态拦截.     

Coupling PCSWMM and WASP to Evaluate Green Stormwater Infrastructure Impacts to Storm Sediment Loads in an Urban Watershed

We coupled rainfall–runoff and instream water quality models to evaluate total suspended solids (TSS) in Wissahickon Creek, a mid‐sized urban stream near Philadelphia, Pennsylvania. Using stormwater runoff and instream field data, we calibrated the model at a subdaily scale and focused on storm responses. We demonstrate that treating event mean concentrations as a calibration parameter rather than a fixed input can substantially improve model performance. Urban stormwater TSS concentrations vary widely in time and space and are difficult to represent simply. Suspended and deposited sediment pose independent stressors to stream biota and model results suggest that both currently impair stream health in Wissahickon Creek. Retrofitting existing detention basins to prioritize infiltration reduced instream TSS loads by 20%, suggesting that infiltration mitigates sediment more effectively than detention. Infiltrating stormwater from 30% of the watershed reduced instream TSS loads by 47% and cut the frequency of TSS exceeding 100 mg/L by half. Settled loads and the frequency of high TSS values were reduced by a smaller fraction than suspended loads and duration at high TSS values. A widely distributed network of infiltration‐focused projects is an effective stormwater management strategy to mitigate sediment stress. Coupling rainfall–runoff and water quality models is an important way to integrate watershed‐wide impacts and evaluate how management directly affects urban stream health.     

Non-point source-driven carbon and nutrient loading to Ganga River (India)

This study was designed to test whether the atmospheric deposition (AD) significantly influences gross primary productivity (GPP) and dissolved organic carbon (DOC) build-up in the Ganga River. We collected data for three consecutive years (2012–2014) along with 37 km river stretch with respect to AD-input of carbon, nutrients, and surface runoff chemistry to relate changes in the river water. We found strong linkages among carbon and nutrients in AD, surface runoff and in the river. The concentration of DOC in the river was highest in the rainy season while those of dissolved inorganic nitrogen and dissolved reactive phosphorus were highest in winter. Spatio-temporal changes in DOC indicated dependence on point- and non-point sources and within-system DOC build-up. The GPP in the river increased consistently over time and significantly correlated with AD-N (R^2?=?0.96, p?<?.001) and AD-P (R^2?=?0.97, p?<?.001). Basin level extrapolation showed that the Ganga River Basin receives 1.81?Tg organic-C, 2.77 Tg reactive-N, and 130?Gg reactive-P annually through atmospheric deposition. Non-point source contributions of carbon and nutrients to the river were substantially higher than those of point sources. The study has relevance for regional scale carbon and nutrient budgeting and action plans for integrated river basin management.     

Pesticides in stormwater runoff−A mini review

• The sources and pathways of pesticides into stormwater runoff were diverse. • Factors affecting pesticides in stormwater runoff were critically reviewed. • Pesticides mitigation strategies were included in this review. • The current knowledge gap of the pesticides in stormwater runoff was identified. Recently, scientific interest has grown in harvesting and treating stormwater for potable water use, in order to combat the serious global water scarcity issue. In this context, pesticides have been identified as the key knowledge gap as far as reusing stormwater is concerned. This paper reviewed the presence of pesticides in stormwater runoff in both rural and urban areas. Specifically, the sources of pesticide contamination and possible pathways were investigated in this review. Influential factors affecting pesticides in stormwater runoff were critically identified as: 1) characteristics of precipitation, 2) properties of pesticide, 3) patterns of pesticides use, and 4) properties of application surface. The available pesticide mitigation strategies including best management practice (BMP), low impact development (LID), green infrastructure (GI) and sponge city (SC) were also included in this paper. In the future, large-scale multi-catchment studies that directly evaluate pesticide concentrations in both urban and rural stormwater runoff will be of great importance for the development of effective pesticides treatment approaches and stormwater harvesting strategies.     

STANDARDIZATION OF PEAK-VOLUME TRANSFORMATIONS1

ABSTRACT: A general treatment of logarithmic transformations and standardization of peak flows on powers of direct runoff is given. Interpretation is offered in this regard for several recent works. There is no basis in reason and no justification in practice for the power standardization. All power standardizations may be calculated from the original relationship.     

NUTRIENT CONTENT OF CROP CANOPY THROUGHFALL PRECIPITATION IN EASTERN SOUTH DAKOTA1

ABSTRACT: Nutrient contents of canopy throughfall precipitation (TFP) from fertilized and unfertilized crops were analyzed and compared to determine the importance of fertilization on this source of nutrients in runoff. Continuous barley, corn, oats, rye, and wheat plots, that had been unfertilized since 1941 and divided and half fertilized since 1959, were studied. TFP soluble PO₄, total PO₄, and soluble K amounts were usually larger from fertilized plots in comparison to unfertilized ones but the differences usually were not significant. NH₄-N and NO₃-N may have been adsorbed from precipitation by corn canopies.     

Impact of Vegetative Cover on Runoff and Soil Erosion at Hillslope Scale in Lanjaron, Spain

Soil loss and surface runoff patterns over a four-year period (1997–2000) were studied in erosion plots from three hillslopes under different vegetative covers (Rosmarinus officinalis, Triticum aestivum and natural-spontaneous vegetation) in Lanjaron (Alpujarras) on the south flank of the Sierra Nevada of southeast Spain. The erosion plots were located on the hillslopes at 35.5% incline, at 1,480 m in altitude and with 41.8 m² (21 m×1.9 m) in area. The vegetative covers were tested for effectiveness in controlling the surface runoff and soil loss production. The highest runoff and erosion values, ranging from 114.1 to 1.7 mmyr^–1 and from 14,564.3 to 6.6 kgha^–1yr^–1, respectively, over the entire study period, were measured under the Triticum aestivum. In the Rosmarinus officinalis, runoff ranged from 7.9 to 1.3 mmyr^–1 and erosion from 156.4 to 2.3 kgha^–1yr^–1, while on the hillslope under natural-spontaneous vegetation, runoff ranged from 4.4 to 0.9 mmyr^–1 and erosion from 322.3 to 2.2 kgha^–1yr^–1. According to the results the vegetative covers of Rosmarinus officinalis and natural-spontaneous vegetation reduced the soil losses by 99 and 98%, with respect to the Triticum aestivum, and the runoff losses by 94 and 96%, respectively. Also, the Rosmarinus officinalis and natural-spontaneous plants influenced infiltration by intercepting much of the rainfall water respect to the Triticum aestivum. Monitoring allowed more direct linkages to be made between management practices and their impacts on runoff and soil erosion, thereby enabling to identify problems and take appropriate preventive measures to improve the management practices.     

Regional scale flood modeling using NEXRAD rainfall, GIS, and HEC-HMS/RAS: a case study for the San Antonio River Basin Summer 2002 storm event

This paper develops a framework for regional scale flood modeling that integrates NEXRAD Level III rainfall, GIS, and a hydrological model (HEC-HMS/RAS). The San Antonio River Basin (about 4000 square miles, 10,000 km2) in Central Texas, USA, is the domain of the study because it is a region subject to frequent occurrences of severe flash flooding. A major flood in the summer of 2002 is chosen as a case to examine the modeling framework. The model consists of a rainfall-runoff model (HEC-HMS) that converts precipitation excess to overland flow and channel runoff, as well as a hydraulic model (HEC-RAS) that models unsteady state flow through the river channel network based on the HEC-HMS-derived hydrographs. HEC-HMS is run on a 4 x 4 km grid in the domain, a resolution consistent with the resolution of NEXRAD rainfall taken from the local river authority. Watershed parameters are calibrated manually to produce a good simulation of discharge at 12 subbasins. With the calibrated discharge, HEC-RAS is capable of producing floodplain polygons that are comparable to the satellite imagery. The modeling framework presented in this study incorporates a portion of the recently developed GIS tool named Map to Map that has been created on a local scale and extends it to a regional scale. The results of this research will benefit future modeling efforts by providing a tool for hydrological forecasts of flooding on a regional scale. While designed for the San Antonio River Basin, this regional scale model may be used as a prototype for model applications in other areas of the country.     

Evaluation of seasonal scale first flush pollutant loading and implications for urban runoff management

This study investigated how the occurrence and magnitude of first flush events in stormwater may influence the effective management of urban runoff pollution. To facilitate the understanding of the first flush phenomenon on a seasonal scale, the City of San Jose, CA carried out an investigation between May 1997 and April 2000 to characterize concentrations of pollutants in local waterbodies during eight storm events. The purpose of the investigation was twofold: (1) To determine if concentrations of specific constituents in stormwater runoff are elevated during the first substantial storm of the wet season, and (2) To identify the physical and environmental conditions surrounding such events. Concentration data for total and dissolved metals, pesticides, polyaromatic hydrocarbons, anions, total suspended solids, total organic carbon, conductivity, gasoline and diesel, and volatile and semi-volatile organics were collected at over 25 sites. Monitoring data analysis focused on identifying physical and environmental conditions yielding increased levels of pollutants during the first substantial storms of the rainy season compared to other storm events. Quantitative analysis focused on metals and anions because most observations for other constituents were below detectable levels. The results suggest that first flush phenomena did not occur consistently throughout most of the stations investigated. The results further suggest that there are specific combinations of site and storm conditions that result in a first flush effect with respect to dissolved metals. Based on the results of this and related investigations, implications for urban runoff management are discussed. For example, if dissolved metals are of principal concern, it may be worthwhile to optimize existing control strategies to minimize pollutant loading from storms that are preceded by an extended dry period.