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 -- Model output data set (gwava-s_out)

This data set represents predicted nitrate concentration in
shallow, recently recharged ground water, in milligrams per
liter, in the conterminous United States, and was generated by a
national nonlinear regression model based on 16 input
parameters.

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 a national map of nitrate concentration (in
milligrams/liter) in shallow, recently recharged ground water as
predicted by the GWAVA-S model. The data set is one of 17
spatial 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).

This data set represents the model output, which is depicted in
figure 2 of Nolan and Hitt (2006) that shows predicted nitrate
concentration in milligrams per liter in shallow, recently
recharged ground water. The model results can be used to
indicate areas of the Nation that may be vulnerable to nitrate
contamination.

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.