Digital data sets were compiled by the U. S. Geological Survey (USGS) and used as input for a collection of Spatially Referenced Regressions On Watershed attributes for the Chesapeake Bay region. These regressions relate streamwater loads to nutrient sources and the factors that affect the transport of these nutrients throughout the watershed. A digital segmented network based on watershed boundaries serves as the primary foundation for spatially referencing total nitrogen and total phosphorus source and land-surface characteristic data sets within a Geographic Information System. Digital data sets of atmospheric wet deposition of nitrate, point-source discharge locations, land cover, and agricultural sources such as fertilizer and manure were created and compiled from numerous sources and represent nitrogen and phosphorus inputs. Some land-surface characteristics representing factors that affect the transport of nutrients include land use, land cover, average annual precipitation and temperature, slope, and soil permeability. Nutrient input and land-surface characteristic data sets merged with the segmented watershed network provide the spatial detail by watershed segment required by the models. Nutrient stream loads were estimated for total nitrogen, total phosphorus, nitrate/nitrite, amonium, phosphate, and total suspended soilds at as many as 109 sites within the Chesapeake Bay watershed. The total nitrogen and total phosphorus load estimates are the dependent variables for the regressions and were used for model calibration. Other nutrient-load estimates may be used for calibration in future applications of the models.
The original USSOILS coverage was originally compiled to support a national model of water quality. The model uses the soil characteristics contained in the STATSGO data base to mediate deliveries of nonpoint source pollution to stream and river segments in the RF1 data base. The National Resource Conservation Service (NRCS) recommends that any maps using NRCS STATSGO data show the source and date, and provide the following statement:
"STATSGO is designed to support regional, multistate, State, and river basin resource planning, management and monitoring."
The PERM data set was modified and used by the USGS in the initial applications of the SPARROW models in the Chesapeake Bay watershed (Version 1.0). The same data was also used with SPARROW models representing version 2.0 (Brakebill and others, 2000) and Version 3.0. The data file perm.mean represents mean soil permeability for the watershed segments generated for version 3.0 applications.
Revised and updated digital spatial data sets will be created and distributed by the USGS as planned enhancements and applications for the SPARROW models are completed.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology. Users are cautioned not to be confused by this terminology. This metadata file should contain enough information to eliminate any confusion caused by the use of ARC/INFO-specific terminology.
The National Resource Conservation Service recommends that the data not be used to describe soil characteristics for regions smaller than a multi-county area.
STATSGO is designed to support regional, multistate, State, and river basin resource planning, management and monitoring.
U.S. Department of Agriculture, National Resource Conservation Service, National Soil Survey Center, 1991, (Revised July 1994.) "State Soil Geographic (STATSGO) Data Base: Data use information," Miscellaneous Publication Number 1492, 110p.
Soil data originating from the State Soil Geographic Data Base (STATSGO) (Schwarz and Alexander, 1995) was acquired from URL <http://water.usgs.gov/nsdi/usgswrd/ussoils.html> for the eastern region of the United States. The data was then clipped using the Chesapeake Bay Watershed boundary originating from USGS 1:250,000 Hydrologic units. The Soil data was then converted into a raster grid format with a cell size of 1-kilometer using Arc/Info's GRID module. The grid was attributed with a numeric value representing the permeability of the soil in inches per hour (in/hr). The permeability value was calculated as a layer- thickness weighted average across soil layers of a simple average of high and low measurements of the soil layer contained in the original STATSGO data set (U.S. Soil Conservation Service, 1994). Details of this calculation can be found in the Process_Step of the metadata found in (Schwarz and Alexander, 1995).
An average permeability was calculated for each SPARROW watershed segment by using the ZONALSTATS function in GRID where the SPARROW watershed segments represent the zonal grid and the permeability grid represented the value grid. This data can be found in the INFO table PREM.MEAN.
PERM.MEAN:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 VALUE 4 10 B -
5 COUNT 4 10 B -
9 MEAN 4 10 F 3
VALUE - Represents ERF1##, or unique reach identification for SPARROW segments
MEAN - Average Soil Permeability in inches per hour
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data.
The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.