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 tnnye_v3 represents a segmented-watershed network attributed with total nitrogen yield estimates from SPARROW for the late 1990s time period for all sources and each source individually in the Chesapeake Bay watershed (Version 3.0).
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).
These data provide a useful tool for determining the spatial distribution of nutrient sources and their potential for delivery into the Chesapeake Bay.
Three types of nutrient estimates predicted by SPARROW for total
nitrogen and total phosphorus representing the late 1990s are
presented by segmented watershed as yields in kg/ha (kilograms per
hectare). These estimates, incremental, delivered, and total,
represent stream-nutrient loads from all nutrient sources evaluated
by the models. Nutrient sources include atmospheric deposition, point
sources, land use and land cover, and commercial fertilizer and manure
application. Nutrient estimates are presented as contributions from
all sources combined and from each source individually.
Incremental yield (load per area), which represents the local
generation of nutrients, is the amount of nutrient that is generated
locally (independent of upstream load) and contributed to the
downstream end of each stream reach. Each stream reach and associated
watershed is treated as an independent unit, quantifying the amount
of nutrient generated. (fig. 14-20). Delivered yield (load per area)
is the amount of nutrient that is generated locally for each stream
reach and weighted by the amount of in-stream loss that would occur
with transport from the reach to Chesapeake Bay. The cumulative loss
of nutrients from generation to delivery to the Bay is dependent on
the traveltime and instream-loss rate of each individual reach
(fig. 21-27). Total yield (load per area) is the amount of nutrient
including upstream load contributed to each stream reach (fig 28-34).
These estimates are calculated by stream reach (E3RF1), and account
for all potential sources cumulatively and individually (Preston and
Brakebill, 1999). These data, in conjunction with the segmented-
watershed network, provide a useful tool for determining the spatial
distribution of nutrient sources and their potential for delivery into
the Chesapeake Bay.
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.
TNWS_V3.VAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 VALUE 4 10 B -
5 COUNT 4 10 B -
9 E3RF1 4 5 B -
13 IYTOT 8 18 F 12
21 IYPNT 8 18 F 12
29 IYURB 8 18 F 12
37 IYATM 8 18 F 12
45 IYAGR 8 18 F 12
53 IYFRT 8 18 F 12
61 IYMAN 8 18 F 12
69 DYTOT 8 18 F 12
77 DYPNT 8 18 F 12
85 DYURB 8 18 F 12
93 DYATM 8 18 F 12
101 DYAGR 8 18 F 12
109 DYFRT 8 18 F 12
117 DYMAN 8 18 F 12
125 TOTTOT 8 18 F 12
133 TOTPNT 8 18 F 12
141 TOTURB 8 18 F 12
149 TOTATM 8 18 F 12
157 TOTAGR 8 18 F 12
165 TOTFRT 8 18 F 12
173 TOTMAN 8 18 F 12
VALUE - Unique reach identification number (same as E3RF1)
COUNT - Number of cells containing the same VALUE
E3RF1 - Unique reach identification number
IYTOT - Incremental yield estimates of total nitrogen from all
sources
IYPNT - Incremental yield estimates of total nitrogen from point
sources
IYURB - Incremental yield estimates of total nitrogen from urban
sources
IYATM - Incremental yield estimates of total nitrogen from
atmospheric sources
IYAGR - Incremental yield estimates of total nitrogen from
agricultural sources
IYFRT - Incremental yield estimates of total nitrogen from
commercial fertilizer
IYMAN - Incremental yield estimates of total nitrogen from manure
DYTOT - Delivered yield estimates of total nitrogen from all sources
DYPNT - Delivered yield estimates of total nitrogen from point
sources
DYURB - Delivered yield estimates of total nitrogen from urban
sources
DYATM - Delivered yield estimates of total nitrogen from
atmospheric sources
DYAGR - Delivered yield estimates of total nitrogen from
agricultural sources
DYFRT - Delivered yield estimates of total nitrogen from
commercial fertilizer
DYMAN - Delivered yield estimates of total nitrogen from manure
TOTTOT - Total yield estimates of total nitrogen from all sources
TOTPNT - Total yield estimates of total nitrogen from point sources
TOTURB - Total yield estimates of total nitrogen from urban sources
TOTATM - Total yield estimates of total nitrogen from atmospheric
sources
TOTAGR - Total yield estimates of total nitrogen from agricultural
sources
TOTFRT - Total yield estimates of total nitrogen from commercial
fertilizer
TOTMAN - Total yield estimates of total nitrogen from manure
* ALL Yield estimates in Kilograms per Hectare per year (kg/ha/yr)
Associated files
tnws_v3_dat.txt - delimited ASCII text file of attributes above
TNWS_v3.dat - INFO file of attributes above
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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