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 TPNYE represents a segmented-watershed network attributed with total phosphorus yield estimates generated by SPARROW for the early 1990's time period (Version 2.0) in the Chesapeake Bay watershed.
The data set TPNYE contains three types of estimates predicted by SPARROW for total phosphorus representing 1992 land-surface conditions in the Chesapeake Bay watershed. These estimates, incremental, delivered, and total, represent stream-nutrient load predictions presented as yields in kg/ha (kilograms per hectare) by segmented watershed from all phosphorus sources evaluated by the models. Phosphorus sources evaluated include point sources, septic systems, agricultural land, atmospheric deposition, and commercial fertilizer and manure application.
Incremental yield, which represents the local generation of nutrient, is the amount (load per area) of nutrient that is generated locally (independent of upstream load) and contributed to each stream reach. Each stream reach and associated watershed is treated as an independent unit, quantifying the amount of nutrient generated. Delivered yield is the amount (load per area) 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. Total yield is the amount (load per area) of nutrient including upstream load contributed to each stream reach. These estimates are calculated by stream reach (E2RF1##), and account for all potential sources cumulatively (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.
Revised and updated digital spatial data sets will be created and distributed by the USGS 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.
Network Generation.
In order to improve the existing network, a new stream reach network
was created using synthetic stream channels generated from 30-meter
grid-cell digital elevation data. The USGS DEMs, organized by 4
digit hydrologic units, (0205, 0206, 0207, and 0208) were acquired
from preliminary versions of the National Elevation Data Base
(USGS NED, 1999). This elevation data had been projected into an
Albers Equal Area projection and converted into an integer grid
by team members at the USGS EROS Data Center.
Arc/INFO's flow direction function was used to create a flow
direction GRID. Flow accumulation, was then calculated for each
30-meter grid cell within each hydrologic unit.
A synthetic stream network was generated for each unit using a
threshold of 5,000 flow-accumulated cells that will flow into a
single cell (condition > 5,000). The number 5,000 was chosen as a
threshold because it yielded the best results in test areas that
were comparable to the desired final scale of 1:500,000, or
comparable to the modified stream reaches used in Version I of the
SPARROW applications (Brakebill and Preston, 1999).
The synthetic stream network was converted from a raster form to a
vector form (GRIDLINE) and was compared to the National Hydrography
Dataset (NHD) 1:100,000 stream data for positional accuracy
(USGS NHD, 1999). Where the DEM's failed to yield satisfactory
stream networks (typically in flat coastal areas or near wide
rivers, lakes and reservoirs), the NHD vector data was inserted. The
stream data by hydrologic unit was then appended together, forming
one dataset which was tested for connectivity to ensure proper
topology.
The above processes generated more stream reaches than were
necessary to build the segmented network. A Flag in the dataset was
attributed if the existing stream corresponded to the modified
1:500,000 scale stream reaches used in Version I. This "main
channel" was then selected out of the data set to produce a subset
of stream reaches. These reaches were then attributed with the same
unique reach identifier that exists in the Version I stream reach
file (ERF1##). A node was placed at the streamflow sampling
locations and attributed with the USGS station identification number
(STAID). All reaches upstream of a sampling station were assigned a
new unique reach identifier (E2RF1##) between 10000 and 11000 along
with the STAID of the USGS streamflow sampling site. Any reach that
is not associated with a sampling site has the same ERF1## and
E2RF1## value. For any reach that contained an associated sampling
location from Version I, the downstream ERF1## value was used.
E2RF1## now represents the new unique stream-reach identifier for
Version II and is used as a common field identifier.
Shoreline locations of major estuaries within the Chesapeake Bay
watershed were added to the stream data set. Nodes were placed at
arbitrary locations along the shoreline creating new reach segments
and each E2RF1## was calculated with a unique value greater than
80,000. Streamflow and velocity information for these reaches were
then estimated based on various watershed characteristics.
The 30-meter cell-size flow direction raster grid and the new
attributed synthetic reach network were used to generate a 30-meter
cell-size raster grid of watershed boundaries for each stream reach.
This was accomplished by converting the reach network into a
30-meter cell-size raster grid using E2RF1## as a value item.
Contributing drainage areas for all cells with the same E2RF1##
value were determined, using these cells that represent the stream
reach as the lowest points within the watershed. These watershed
boundaries, now containing the same E2RF1## value found in the
stream-reach data set, were converted to a polygon-vector format.
Subsequently, the watershed boundaries could be analyzed within a
grid cell (raster) or polygon (vector) environment using E2RF1## as
a common field, providing an improved network and the framework for
the SPARROW models spatial detail.
tnnye.dbf - data file
SHAPE - Internal value
ID - Internal value
E2RF1__ - represents unique reach identification number
(E2RF1##). Used as common column to relate data
presented in this report.
DYTOT - delivered yield, the amount (load per area) of
phosphorus 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. All sources in kg/ha/yr
IYTOT - incremental yield, the amount (load per area) of
phosphorus generated locally (independent of
upstream load) and contributed to each stream reach
due to all sources in kg/ha/yr
TOTTOT - total yield, the amount (load per area) of
phosphorus including upstream load contributed to
each stream reach due to all sources in kg/ha/yr
TNTP.txt - Associated data file containing both nitrogen
and phosphorus yield estinates. Can be used in
conjunction with segmented watershed network to
display.
TN - Total Nitrogen
TP - Total Phosphorus
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.
Generated by mp version 2.2.5 on Fri Dec 01 15:18:55 2000