Study
site descriptions and Watershed Characteristics
Land Cover/Use - Population
Density - Point Source Dischargers
Study
sites were separated into two groups: 50 "targeted"
and 10 "integrative" sampling stations. "Targeted"
stations occurred throughout the watersheds on streams of varying
size. "Integrative" stations occurred sufficiently downstream
in a watershed to integrate effects of land use and other factors
on a given project element or task under study over a large portion
of the watershed. In some instances ‘downstream’ distance
was constrained by feasibility of one or more of the
study elements. Several of the specific tasks involved all 60
sites, while a few tasks were only conducted at the integrative
sites. All sampling sites were located using a Trimble GPS Pathfinder™
ProXR receiver unit in Year 2 (2001) of the project. In a few
cases, two site locations are given for a single sampling site.
This is because a site was either re-located from the original
Year 1 location, or sampling for a specific task was not at the
exact location as for the other study tasks.
Land Cover/Use
Land
cover data for sites West of the Hudson
River (WOH - Delaware/Catskill systems) were derived by the
NYC DEP from 1 or 2 Landsat Thematic Mapper (TM) scenes per major
watershed (as defined by the reservoirs) spanning 1992 and 1993.
For sites East of the Hudson River
(EOH – Croton/Kensico systems), land cover data were derived
from five Landsat TM scenes in combination with Landsat Multispectral
Scanner data from two dates, all spanning the period 1987 to 1993.
EOH data were originally from University of Massachusetts but
were modified and distributed by the NYC DEP. Land cover data
were compiled for each study watershed, as defined by the study
site locations, including reservoirs. Watershed
boundaries were derived from an existing NYC DEP coverage of subwatershed
delineations for the region, with some modifications necessary
to match the mouth of a given subwatershed boundary with the location
of a particular study site. Study sites were located using a GPS
as previously described. The EOH land cover grid did not exactly
match the overall EOH delineated watershed boundary coverage.
Therefore, when combining the two data sources, the nonoverlapping
portions resulted in a “no-data” classification affecting
a total of 25 EOH watersheds. The no-data classification ranged
from 0.1 to 9.0% of the total watershed area in these 25 watersheds
with a median value of 0.7%.
Wetlands data were taken from
the U.S. Fish and Wildlife Service’s National Wetlands Inventory
and were processed (including field checks) for the WOH and EOH
regions by the NYC DEP. Wetlands data for the WOH region were
based on high-altitude aerial photography taken between 1982 and
1987; EOH data were based on photography taken between 1984 and
1987. Classification of wetland types was based on Cowardin et
al. (1979). Wetland features were compiled for each study watershed
as described for land cover data. Only the “palustrine”
wetland class – those wetlands commonly referred to as swamp,
marsh, bog, etc., and including small ponds – were compiled
for these study watersheds.
Population Density
Population density data were compiled
from total population counts from the 1990 and 2000 censuses using
census blocks within each county. Census blocks are the smallest
unit for which census data are available (Census 2000 Geographic
terms and concepts; http://www.census.gov/geo/www/census2k.html).
Census 2000 Geographic Census data, including population counts,
were retrieved as Census 2000 TIGER/Line data through the Environmental
Systems Research Institute, Inc. (ESRI) web page at http://www.esri.com/data/download/census2000_tigerline/index.html.
The 1990 census block boundaries were downloaded by county from
the Cornell University Geospatial Information Repository at http://cugir.mannlib.cornell.edu
and the University of Connecticut’s Map and Geographic Information
Center site at http://magic.lib.uconn.edu/.
The 1990 census block population data were downloaded from the
1990 Census LOOKUP page at http://venus.census.gov/cdrom/lookup.
Watershed boundaries were used to determine the portion of each
census block that fell within a given study site watershed. The
fraction of the census block area falling within a given watershed
was multiplied by the total population count for that census block.
This product of fractional census block area and corresponding
population count was summed for all census blocks falling within
a watershed and then divided by the watershed area to arrive at
a watershed population density estimate.
Point Source Dischargers
Surface-water discharging wastewater
treatment plant (hereafter WWTP) monthly mean daily flows were
supplied by the NYC DEP for all State Pollutant Discharge Elimination
System (SPDES)
permitted dischargers in the NYC watershed for 2000-2002. These
outflow data were values reported by WWTP operators on Discharge
Monitoring Reports with estimation occasionally necessary due
to missing values (B. McCann, personal communication). A corresponding
GIS point coverage of WWTP locations was used to determine which
plants were located upstream of our stream and reservoir study
sites. For each reported or measured monthly value, the mean daily
discharge was multiplied by the number of days in the given month.
The resulting total monthly flow volume was summed for all months
with flow data for all sites within a study watershed (as defined
by either a stream or reservoir study site) and divided by watershed
area, providing a relative estimate of the total annual WWTP outflow
across watersheds for each year in the period 2000-2002. Annual
outflow values and the total number of WWTPs within a study watershed
are provided in the site-specific data pages (EOH
or WOH). It should be noted that
not all WWTPs included in the total number of WWTPs have reported
outflow data (primarily due to little or no operation at these
plants).
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