Digital data sets compiled by the U.S. Geological Survey were used as input for a collection of Spatially Referenced Regressions On Watershed (SPARROW) attributes for the Chesapeake Bay region including parts of Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, and the District of Columbia. These regressions use a nonlinear statistical approach to relate nutrient sources and land-surface characteristics to nutrient loads of streams throughout the Chesapeake Bay watershed. A digital segmented-watershed network serves as the primary framework for spatially referencing nutrient-source and land-surface characteristic data within a geographic information system.
Flow direction and flow accumulation generated from a 30-meter cell-size Digital Elevation Model and attributes from 1:500,000-scale stream data were used to generate stream and watershed networks. Spatial data sets representing nutrient inputs of total nitrogen and total phosphorus from the early 1990's were created and compiled from numerous sources. Data include atmospheric deposition, septic systems, point-source locations, land use, land cover, and agricultural sources such as commercial fertilizer and manure. Some land-surface characteristic data sets representing factors that affect the transport of nutrients also were compiled. Data sets include land use, land cover, average-annual precipitation and temperature, slope, hydrogeomorphic regions, 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 SPARROW. Stream-nutrient load estimates for 132 sampling sites representing the early 1990's (103 for total nitrogen and 121 for total phosphorus) serve as the dependent variables for the regressions. These estimates were used to calibrate models of total nitrogen and total phosphorus depicting 1992 land-surface conditions. Examples of model predictions consist of stream-nutrient load and source percentages contributed locally to each stream reach, as well as percentages of the load that reach Chesapeake Bay.
The data set NTN92_G represents atmospheric wet deposition of nitrate used with SPARROW for the early 1990's (Version 2.0)in the Chesapeake Bay watershed.
The spatial data set NTN92_g was created and used by the USGS specifically to estimate atmospheric wet deposition of nitrate by watershed segments in the application of SPARROW representing the early 1990's time period (Version 2.0) in the Chesapeake Bay watershed. Revised and updated digital spatial data sets will be created and distributed as planned enhancements and applications for SPARROW are completed.
Any use of trade, product, or firm names is for descriptive purposes
only and does not imply endorsement by the U.S. Government.
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.
Data was compiled at a National level. Three stations were moved beyond the U.S. boundary, so all of the continental U.S. was contained. Three data points were added off the coast of Texas and Washington and average values of existing stations were used for these sites. Sites in Alaska, Hawaii, and Puerto Rico were not included. Two sites in Pennsylvaina that are very close, but have different deposition values, were averaged and treated as one site.
Linear spatial interpolation of NADP data for 169 point measurements
within the United States provided 1992 mean wet-deposition
atmospheric estimates for nitrate (Smith and others, 1997). The
latitude and longitude coordinates of the monitoring stations were
used to create a point data set of the sampling sites attributed
with the 1992 mean deposition value. Deposition values for stations
00391520 and 00394200 were averaged because of their close
proximity. New data points off the coasts of Florida, Texas,
California and Washington were added and averages of sites near
these locations were used. This was done to ensure the entire
continental U.S. would be represented with dopositional estimates.
This process did not affect estimates in the eastern third of the
country.
The point data set was then converted into a Triangulated Irregular
Network (TIN) using 30 meters as a weed tolerance and 10 meters as
the proximal tolerance in the CREATETIN command.
The TIN was converted into a 900-meter cell-size grid using the
TINLATICE command and the quintic option. The area within the
Chesapeake Bay region was extracted.
Units were converted from kg/km2/yr to kg/ha/yr by dividing the value
of the GRID by 100.00137.
Data represents 1992 wet deposition values of nitrate
in the Chesapeake Bay region. The spatial data does not
contain an attribute table. The value represents the
deposition estimate in kg/ha/yr for that GRID cell.
ATDEP92.MEAN: - ASCII text file of mean deposition values
by SPARROW watershed segment.
To be used with SPARROW Segmented Watershed Network
E2RF1## - E2RF1## or unique SPARROW reach identification, Version II.
MEAN - Mean atmospheric deposition, in kilograms per hectare per year
kg/ha/yr
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.
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