Chesapeake Bay restoration efforts are focused on improving water quality, living resources, and ecological habitats by 2010. One aspect of the water-quality restoration is the refinement of strategies designed to implement nutrient-reduction practices within the Bay watershed. These strategies are being refined and implemented by resource managers of the Chesapeake Bay Program (CBP), a partnership comprised of various Federal, State, and local agencies that includes jurisdictions within Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, and the District of Columbia. The U.S. Geological Survey (USGS), an active member of the CBP, provides necessary water-quality information for these Chesapeake Bay nutrient- reduction strategy revisions and evaluations.
The formulation and revision of effective nutrient-reduction strategies requires detailed scientific information and an analytical understanding of the sources, transport, and delivery of nutrients to the Chesapeake Bay. The USGS is supporting these strategies by providing scientific information to resource managers that can help them evaluate and understand these processes. One statistical model available to resource managers is a collection of SPAtially Referenced Regressions On Watershed (SPARROW) attributes, which uses a nonlinear regression approach to relate nutrient sources and watershed characteristics to nutrient loads of streams throughout the Chesapeake Bay watershed. Developed by the USGS, information generated by SPARROW can help resource managers determine the geographical distribution and relative contribution of nutrient sources and the factors that affect their transport to the Bay.
Nutrient source information representing the late 1990s time period was obtained from several agencies and used to create and compile digital spatial datasets of total nitrogen and total phosphorus contributions that served as input sources to the SPARROW models. These data represent atmospheric deposition, point-source locations, land-use, land-cover, and agricultural sources such as commercial fertilizer and manure applications.
Watershed-characteristics datasets representing factors that affect the transport of nutrients also were compiled from previous applications of the SPARROW models in the Chesapeake Bay watershed. Datasets include average-annual precipitation and temperature, slope, soil permeability, and hydrogeomorphic regions.
Nutrient-input and watershed-characteristics datasets representing conditions during the late 1990s were merged with a connected network of stream reaches and watersheds to provide the spatial detail required by SPARROW. Stream-nutrient load estimates for 125 sampling sites (87 for total nitrogen and 103 for total phosphorus) served as the dependent variables for the regressions, and were used to calibrate models of total nitrogen and total phosphorus depicting late 1990s conditions in the Chesapeake Bay watershed.
Spatial data generated for the models can be used to identify the location of nutrient sources, while the models' nutrient estimates can be used to evaluate stream-nutrient load contributed locally by each source evaluated, the amount of local load generated that is transported to the Bay, and the factors that affect the nutrient transport. Applying the SPARROW methodology to late 1990s information completes three time periods (late 1980s, early 1990s, and late 1990s) of viable data that resource managers can use to evaluate the water- quality conditions within the Bay watershed in order to refine restoration goals and nutrient-reduction strategies.
The data set NTN97_G represents estimates of atmospheric wet deposition of nitrate used with SPARROW for the late 1990s (Version 3.0) in the Chesapeake Bay watershed.
The U.S. Geological Survey (USGS) is investigating processes related to nutrient sources and transport through multiple studies designed to provide scientific information to resource managers responsible for the restoration and protection of the Chesapeake Bay and its' watershed. Two main goals of USGS Chesapeake Bay studies related to this report include: (1) enhancing the prediction and monitoring of nutrient delivery to the bay; and (2) disseminating information and enhancing decision-support tools.
This report describes the processes used to create, compile, and obtain the necessary digital spatial datasets generated with a geographic information system (GIS) for the purpose of applying the SPARROW methodology to develop total nitrogen and total phosphorus models in the Chesapeake Bay watershed representing the late 1990s (Version 3.0).
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 late 1990s time period (Version 3.0) in the Chesapeake Bay watershed.
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 ArcInfo format, this metadata file may include some
ArcInfo-specific terminology.
Linear spatial interpolation of National Atmospheric Deposition
Program (NADP) data for 191 point measurements within the
continental United States provided 1997 mean wet-deposition
atmospheric estimates for nitrate (Alexander and others, 2001;
Karl and others, 1990) in kilograms per
hectare per year (kg/ha/yr).
The latitude and longitude coordinates of the monitoring stations
were used to create a spatial data set of the sampling sites
attributed with the 1997 mean deposition value. A Triangulated
Irregular Network (TIN) was calculated by interpolating data values
between the sampling locations.
The area within the Chesapeake Bay region was extracted
and converted into a 1,000-meter grid. This cell size was chosen
because it was well suited to the spatial distribution of the
monitoring stations. Smaller cell sizes did not sufficently improve
the quality of the interpolated information to warrant such a large
data set. The atmospheric-deposition grid then was used with the
segmented-watershed network to calculate a mean-wet deposition
value for each watershed segment.
NTN97_G.txt:
Data represents 1997 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.
ATDEP97.MEAN: - ASCII text file of mean deposition values
by SPARROW watershed segment.
To be used with SPARROW Segmented Watershed Network
E3RF1 - E3RF1 or unique SPARROW reach identification, Version III.
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.
More USGS GIS Data for Water Resources
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