Vulnerability of shallow ground water and drinking-water wells to nitrate in the United States: Model of predicted nitrate concentration in shallow, recently recharged ground water -- Input data set for drainage ditch (gwava-s_ddit)

This data set represents the area of National Resources Inventory surface drainage, field ditch conservation practice, in square kilometers, in the conterminous United States. The data set was used as an input data layer for a national model to predict nitrate concentration in shallow ground water. Nolan and Hitt (2006) developed two national models to predict contamination of ground water by nonpoint sources of nitrate. The nonlinear approach to national-scale Ground-WAter Vulnerability Assessment (GWAVA) uses components representing nitrogen (N) sources, transport, and attenuation. One model (GWAVA-S) predicts nitrate contamination of shallow (typically less than 5 meters deep), recently recharged ground water, which may or may not be used for drinking. The other (GWAVA-DW) predicts ambient nitrate concentration in deeper supplies used for drinking. This data set is one of 17 data sets (1 output data set and 16 input data sets) associated with the GWAVA-S model. Full details of the model development are in Nolan and Hitt (2006). For inputs to the model, spatial attributes representing 16 nitrogen loading and transport and attenuation factors were compiled as raster data sets (1-km by 1-km grid cell size) for the conterminous United States (see table 1). >Table 1.-- Parameters of nonlinear regression model for nitrate in shallow > ground water (GWAVA-S) and corresponding input spatial data sets. > [kg, kilograms; km2, square kilometers.] > >Nitrogen Source Factors Data Set Name > 1 farm fertilizer (kg/hectare) gwava-s_ffer > 2 confined manure (kg/hectare) gwava-s_conf > 3 orchards/vineyards (percent) gwava-s_orvi > 4 population density (people/km2) gwava-s_popd > 5 cropland/pasture/fallow (percent) gwava-s_crpa > >Transport to Aquifer Factors > 6 water input (km2/cm) gwava-s_wtin > 7 carbonate rocks (yes/no) gwava-s_crox > 8 basalt and volcanic rocks (yes/no) gwava-s_vrox > 9 drainage ditch (km2) gwava-s_ddit > 10 slope (percent x 1000) gwava-s_slop > 11 glacial till (yes/no) gwava-s_gtil > 12 clay sediment (percent x 1000) gwava-s_clay > >Attenuation Factors > 13 fresh surface water withdrawal gwava-s_swus > for irrigation (megaliters/day) > 14 irrigation tailwater recovery (km2) gwava-s_twre > 15 histosol soil type (percent) gwava-s_hist > 16 wetlands (percent) gwava-s_wetl "Farm fertilizer" is the average annual nitrogen input from commercial fertilizer applied to agricultural lands, 1992-2001, in kilograms per hectare. "Confined manure" is the average annual nitrogen input from confined animal manure, 1992 and 1997, in kilograms per hectare. "Orchards/vineyards" is the percent of orchards/vineyards land cover classification. "Population density" is 1990 block group population density, in people per square kilometer. "Cropland/pasture/fallow" is the percent of cropland/pasture/fallow land cover classifications. "Water input" is the ratio of the total area of irrigated land to precipitation, in square kilometers per centimeter. "Carbonate rocks" is the presence or absence of Valley and Ridge carbonate rocks. "Basalt and volcanic rocks" is the presence or absence of basalt and volcanic rocks. "Drainage ditch" is the area of National Resources Inventory surface drainage, field ditch conservation practice, in square kilometers. "Slope" is the soil surface slope, in percent times 1000. "Glacial till" is the presence or absence of poorly sorted glacial till east of the Rocky Mountains. "Clay sediment" is the amount of clay sediment in the soil, in percent times 1000. "Fresh surface water withdrawal for irrigation" is the amount of fresh surface water withdrawal for irrigation, in megaliters per day. "Irrigation tailwater recovery" is the area of National Resources Inventory irrigation system, tailwater recovery conservation practice, in square kilometers. "Histosol soil type" is the amount of histosols soil taxonomic order, in percent. "Wetlands" is the percent of woody wetlands and emergent herbaceous wetlands land cover classifications. Reference cited: Nolan, B.T. and Hitt, K.J., 2006, Vulnerability of shallow ground water and drinking-water wells to nitrate in the United States: Environmental Science and Technology, vol. 40, no. 24, pages 7834-7840.本数据集表征了美国本土范围内，隶属于国家资源清查（National Resources Inventory）的地表排水与田间沟渠防护措施的面积，单位为平方千米。 该数据集曾作为国家级模型的输入数据图层，用于预测浅层地下水中的硝酸盐浓度。 Nolan与Hitt（2006）开发了两款国家级模型，用以预测非点源硝酸盐对地下水的污染。这款面向全国尺度的地下水脆弱性评估（Ground-WAter Vulnerability Assessment, 简称GWAVA）非线性建模方法，整合了氮（N）源、迁移与衰减三类组分。 其中一款模型（GWAVA-S）用于预测浅层（通常深度小于5米）且为近期补给的地下水的硝酸盐污染情况，此类地下水可能被用作饮用水，也可能不被用作饮用水。另一款模型（GWAVA-DW）则用于预测可作为饮用水源的深层地下水中的环境硝酸盐浓度。 本数据集是与GWAVA-S模型相关的17份数据集之一，其中包含1份输出数据集与16份输入数据集。该模型开发的完整细节可参见Nolan与Hitt（2006）的研究。 针对该模型的输入数据，研究人员针对美国本土整合了16项表征氮负荷、迁移与衰减因子的空间属性，并以栅格（raster）数据集（栅格单元尺寸为1千米×1千米）形式存储（详见表1）。 >表1.-- 浅层地下水硝酸盐非线性回归模型（GWAVA-S）参数与对应输入空间数据集 > [kg，千克；km²，平方千米。] > >氮源因子 数据集名称 > 1 农用化肥（千克/公顷） gwava-s_ffer > 2 圈养畜禽粪便（千克/公顷） gwava-s_conf > 3 果园/葡萄园占比（百分比） gwava-s_orvi > 4 人口密度（人/平方千米） gwava-s_popd > 5 农田/牧场/休耕地占比（百分比） gwava-s_crpa > >含水层迁移因子 > 6 水分输入（平方千米/厘米） gwava-s_wtin > 7 碳酸盐岩分布（是/否） gwava-s_crox > 8 玄武岩与火山岩分布（是/否） gwava-s_vrox > 9 排水沟渠面积（平方千米） gwava-s_ddit > 10 坡度（百分比×1000） gwava-s_slop > 11 冰碛物分布（是/否） gwava-s_gtil > 12 黏土沉积物占比（百分比×1000）gwava-s_clay > >衰减因子 > 13 灌溉新鲜地表水取水量 gwava-s_swus > （单位：兆升/天） > 14 灌溉尾水回收面积（平方千米）gwava-s_twre > 15 有机土土壤类型占比（百分比）gwava-s_hist > 16 湿地占比（百分比） gwava-s_wetl "Farm fertilizer" 指1992-2001年间，施用于农用地的商用化肥的年均氮输入量，单位为千克/公顷。 "Confined manure" 指1992年与1997年的圈养畜禽粪便年均氮输入量，单位为千克/公顷。 "Orchards/vineyards" 为土地覆被分类中果园与葡萄园的占比百分比。 "Population density" 为1990年街区组人口密度，单位为人/平方千米。 "Cropland/pasture/fallow" 为土地覆被分类中农田、牧场与休耕地的占比百分比。 "Water input" 为灌溉土地总面积与降水量的比值，单位为平方千米/厘米。 "Carbonate rocks" 指瓦利-岭区碳酸盐岩的分布有无情况。 "Basalt and volcanic rocks" 指玄武岩与火山岩的分布有无情况。 "Drainage ditch" 指隶属于国家资源清查的地表排水与田间沟渠防护措施的面积，单位为平方千米。 "Slope" 为土壤地表坡度，单位为百分比×1000。 "Glacial till" 指落基山脉东部分选性较差的冰碛物的分布有无情况。 "Clay sediment" 为土壤中黏土沉积物的占比，单位为百分比×1000。 "Fresh surface water withdrawal for irrigation" 指用于灌溉的新鲜地表水取水量，单位为兆升/天。 "Irrigation tailwater recovery" 指隶属于国家资源清查的灌溉系统尾水回收防护措施的面积，单位为平方千米。 "Histosol soil type" 为土壤分类学中有机土纲的占比百分比。 "Wetlands" 为土地覆被分类中木本湿地与挺水草本湿地的占比百分比。 引用文献： Nolan, B.T. 与 Hitt, K.J., 2006, 美国浅层地下水与饮用水井对硝酸盐的脆弱性：《环境科学与技术》（Environmental Science and Technology），第40卷，第24期，第7834-7840页。