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 AGLD97 represents a segmented-watershed network attributed with total nitrogen and total phosphorus load estimates from manure and commercial fertilizer sources. This data was evaluated for the SPARROW models representing 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 AGLD97 was specifically created by the USGS to estimate nitrogen and phosphorus loads from agricultural sources by watershed segments in the Chesapeake Bay watershed for the use of the SPARROW models (Version 3.0).
Several datasets representing annual estimates of nutrients from
agricultural sources were evaluated using SPARROW. Animal manure data
compiled by the Natural Resources Conservation Service (NRCS) were
evaluated and included county estimates of annual nutrients from
manure excreted, and annual nutrients recoverable from manure
generated by livestock held in confinement (Kellogg and others, 2000;
Lander and others, 1998). Annual county application rates of manure
spread on various land-uses compiled by the CBP (Palace and others,
1998) were also evaluated. Commercial fertilizer data evaluated
include county estimates of annual nutrients based on fertilizer
sales from the Bureau of Census compiled by the National Water Quality
Assessment (NAWQA) program (D. Lorenz, U.S. Geological Survey, written
commun., 2002) and county fertilizer application rates on various
land-uses compiled by the CBP (Palace and others, 1998).
Using SPARROW version 3.0, the total nitrogen model showed the best
statistical fit using county-based NRCS nutrient estimates of
recoverable manure generated by livestock held in confinement, and
county-based fertilizer estimates compiled by the NAWQA program. The
total phosphorus model showed the best statistical fit using both
manure and fertilizer application estimates generated by the CBP.
NRCS nutrient estimates from livestock manure are based on animal
population numbers by county, derived from the 1997 Agricultural
Census (U.S. Bureau of the Census, 2000). The basic building block of
the estimation process is an animal unit, which represents 1,000
pounds of animal weight, including all beef, dairy, swine, and poultry
animals.
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.
In order to distribute county-based nutrient estimates from
agricultural sources, it was assumed that manure and commercial
fertilizer would be applied to areas classified as both row-crop
and pasture lands (agricultural land) combined. The modified 1997
30-meter land-cover data were used to calculate the total number of
30-meter agricultural cells within each county. County-based
estimates of nutrient load for each source were divided by the
number of agricultural cells within each county. This produced a
nutrient-load estimate for each agricultural cell. Load estimates
for each 30-meter cell then were summed by SPARROW watershed segment
to obtain nutrient-load estimates from commercial fertilizer and
recoverable manure generated by confined livestock for each SPARROW
watershed segment. This process distributed the county load
estimates throughout the agricultural land within a SPARROW
watershed segment.
AGLD97.PAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 AREA 4 12 F 3
5 PERIMETER 4 12 F 3
9 AGLD97# 4 5 B -
13 AGLD97-ID 4 5 B -
17 E3RF1 4 5 B -
21 FN_NAWQA 8 18 F 6
29 FP_CBP 8 18 F 6
37 MN_AVCF 8 18 F 6
45 MP_CBP 8 18 F 6
AGLD97.DAT: - INFO file
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 E3RF1 4 5 B -
5 FN_NAWQA 8 18 F 6
13 FP_CBP 8 18 F 6
21 MN_AVCF 8 18 F 6
29 MP_CBP 8 18 F 6
E3RF1 - Unique reach identification number. Used as common
column to relate to spatial data.
FN_NAWQA - Total nitrogen estimates from commercial fertilizer,
kg/yr, NAWQA.
FP_CBP - Total phosphorus estimates from commercial fertilizer,
kg/yr, CBP
MN_AVCF - Total nitrogen estimates from manure recoverable from
confined units, kg/yr, NRCS.
MP_CBP - Total phosphorus estimates from manure, kg/yr, CBP
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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