Vulnerability of shallow ground water and drinking-water wells to nitrate in the United States: Model of predicted nitrate concentration in U.S. ground water used for drinking (simulation depth 50 meters) -- Input data set for Dunne overland flow (gwava-dw_dun)

This data set represents saturation overland flow estimated by
TOPMODEL, in percent of streamflow, in the conterminous United
States.

The data set was used as an input data layer for a national
model to predict nitrate concentration in ground water used for
drinking.

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 14 data sets (1 output data set and 13
input data sets) associated with the GWAVA-DW model. Full details
of the model development are in Nolan and Hitt (2006).

For inputs to the model, spatial attributes representing 13
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 ground water used for drinking (GWAVA-DW)
> and corresponding input spatial data sets.
> [kg, kilograms; km2, square kilometers.]
>
>Nitrogen Source Factors Data Set Name
> 1 farm fertilizer (kg/hectare) gwava-dw_ffer
> 2 confined manure (kg/hectare) gwava-dw_conf
> 3 orchards/vineyards (percent) gwava-dw_orvi
> 4 population density (people/km2) gwava-dw_popd
>
>Transport to Aquifer Factors
> 5 water input (km2/cm) gwava-dw_wtin
> 6 glacial till (yes/no) gwava-dw_gtil
> 7 semiconsolidated sand aquifers gwava-dw_semc
> (yes/no)
> 8 sandstone and carbonate rocks gwava-dw_sscb
> (yes/no)
> 9 drainage ditch (km2) gwava-dw_ddit
> 10 Hortonian overland flow gwava-dw_hor
> (percent of streamflow)
>
>Attenuation Factors
> 11 fresh surface water withdrawal gwava-dw_swus
> for irrigation (megaliters/day)
> 12 irrigation tailwater recovery (km2) gwava-dw_twre
> 13 Dunne overland flow gwava-dw_dun
> (percent of streamflow)
> 14 well depth (meters) -

"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.

"Water input" is the ratio of the total area of irrigated land
to precipitation, in square kilometers per centimeter.

"Glacial till" is the presence or absence of poorly sorted
glacial till east of the Rocky Mountains.

"Semiconsolidated sand aquifers" is the presence or absence of
semiconsolidated sand aquifers.

"Sandstone and carbonate rocks" is the presence or absence of
sandstone and carbonate rock aquifers.

"Drainage ditch" is the area of National Resources Inventory surface
drainage, field ditch conservation practice, in square kilometers.

"Hortonian overland flow" is infiltration excess overland flow
estimated by TOPMODEL, in percent of streamflow.

"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.

"Dunne overland flow" is saturation overland flow estimated by
TOPMODEL, in percent of streamflow.

"Well depth" is the depth of the well, in meters. Well depth
was not compiled as a spatial data set. Well depth equals 50
meters for the model simulation being presented.

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.

本数据集为美国本土范围内由TOPMODEL模型估算得到的饱和地表径流占径流量的百分比数据。

该数据集曾作为国家级模型的输入数据图层，用于预测饮用水源地下水的硝酸盐浓度。

Nolan与Hitt（2006年）开发了两款国家级模型，用以预测地下水受硝酸盐非点源污染的风险。针对国家级尺度地下水脆弱性评价（Ground-WAter Vulnerability Assessment, GWAVA）所采用的非线性方法，包含表征氮（N）源、迁移及衰减过程的多个模块。

其中一款模型（GWAVA-S）用于预测浅层（通常深度小于5米）、近期补给地下水的硝酸盐污染情况，此类地下水可能被用作饮用水源，也可能不被用作饮用水源。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源中的硝酸盐本底浓度。

本数据集为与GWAVA-DW模型相关的14套数据集之一（含1套输出数据集与13套输入数据集）。该模型开发的完整细节可参见Nolan与Hitt（2006年）的研究成果。

针对该模型的输入数据，研究团队针对美国本土范围内，将表征13项氮负荷、迁移与衰减因子的空间属性整合为栅格数据集（网格单元尺寸为1千米×1千米），详见表1。

>表1 饮用水源地下水硝酸盐非线性回归模型（GWAVA-DW）参数及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-dw_ffer
> 2 圈养畜禽粪便（千克/公顷） gwava-dw_conf
> 3 果园/葡萄园占比（百分比） gwava-dw_orvi
> 4 人口密度（人/平方千米） gwava-dw_popd
>
>含水层迁移因子
> 5 水分输入（平方千米/厘米） gwava-dw_wtin
> 6 冰碛物（有/无） gwava-dw_gtil
> 7 半固结砂岩含水层（有/无） gwava-dw_semc
>
> 8 砂岩与碳酸盐岩含水层（有/无） gwava-dw_sscb
>
> 9 排水沟渠面积（平方千米） gwava-dw_ddit
> 10 霍顿地表径流（占径流量百分比） gwava-dw_hor
>
>
>衰减因子
> 11 灌溉新鲜地表水取水量（兆升/日） gwava-dw_swus
>
> 12 灌溉尾水回收面积（平方千米） gwava-dw_twre
> 13 达尼地表径流（占径流量百分比） gwava-dw_dun
>
> 14 井深（米） -

以下为各参数的详细说明：

“农用化肥”：指1992-2001年间施用在农用土地上的商品化肥年均氮输入量，单位为千克/公顷。
“圈养畜禽粪便”：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。
“果园/葡萄园占比”：指土地覆被分类中果园与葡萄园的占比。
“人口密度”：指1990年街区人口普查区块的人口密度，单位为人/平方千米。
“水分输入”：指灌溉土地总面积与降水量的比值，单位为平方千米/厘米。
“冰碛物”：指落基山脉以东区域是否存在分选性差的冰碛物。
“半固结砂岩含水层”：指区域是否存在半固结砂岩含水层。
“砂岩与碳酸盐岩含水层”：指区域是否存在砂岩与碳酸盐岩含水层。
“排水沟渠”：指《国家资源清查》中地表排水、田间沟渠保护措施对应的面积，单位为平方千米。
“霍顿地表径流”：指由TOPMODEL模型估算得到的超渗地表径流占径流量的百分比。
“灌溉新鲜地表水取水量”：指用于灌溉的新鲜地表水取水量，单位为兆升/日。
“灌溉尾水回收”：指《国家资源清查》中灌溉系统尾水回收保护措施对应的面积，单位为平方千米。
“达尼地表径流”：指由TOPMODEL模型估算得到的饱和地表径流占径流量的百分比。
“井深”：指水井的深度，单位为米。井深未被整合为空间数据集，在本次展示的模型模拟中，井深取值为50米。

参考文献：
Nolan, B.T. 与 Hitt, K.J., 2006年，《美国浅层地下水与饮用水井对硝酸盐污染的脆弱性》，《环境科学与技术》，第40卷第24期，第7834-7840页。