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 locations 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.
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 SEPTIC90 represents septic system information used in the application of the SPARROW models for the early 1990's time period (Version 2.0)in the Chesapeake Bay watershed. Each block group polygon is attributed with a unique census block group identification number, and 1990 estimates of total nitrogen from septic systems per block group.
The spatial data set SEPTIC90 was created and used by the USGS specifically to estimate total nitrogen loads 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.
1990 Census data was used to determine the number of people on septic
and other non-sewer systems by census block groups (polygon). An
average per capita load for nitrogen was calculated for each block
group polygon by summing the number of people on septic and other
non-sewer systems within that polygon, then multiplied by a mean value
of 4.24036 kg/person/year (NCRI, 1995).
load = (#people_septic + #people_non-sewer) * 4.24036 kg/person/year
Several polygons contained the same block group identification number,
while possessing different housing census information. A frequency
operation was performed to sum the total amount of load (TN) per
block group identification number.
SEPTIC.PAT: - Polygon attribute table
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 AREA 8 18 F 5
9 PERIMETER 8 18 F 5
17 SEPTIC# 4 5 B -
21 SEPTIC-ID 4 5 B -
25 BLKGRP 12 12 C -
37 TN 8 18 F 6 KG
** REDEFINED ITEMS **
25 FIPS 5 5 I -
25 STATE 2 2 I -
27 COUNTY 3 3 I -
1 AREA Polygon area, meters, system assigned
9 PERIMETER Polygon perimeter, meters, system assigned
17 SEPTIC# Internal identification number
21 SEPTIC-ID Used defined identification number
25 BLKGRP Census Block group identification number
37 TN Total nitrogen estimates (kg) from septic
** REDEFINED ITEMS **
25 FIPS Federal
25 STATE State
27 COUNTY County
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 Tue Feb 20 10:33:57 2001