U.S. GEOLOGICAL SURVEY
Water-Resources
Investigations Report 99-4173
Effects of Residential and Agricultural Land Uses on the Chemical Quality of Baseflow of Small Streams in the Croton Watershed,Southeastern New York
By Paul M. Heisig
ABSTRACT
Data on the chemical
quality of baseflow
from 33 small streams
that drain basins of
differing land-use type and intensity
within the Croton watershed were
collected seasonally for 1 year to
identify and characterize the quality
of ground-water contributions to
surface water. The watershed
includes twelve of New York City’s
water-supply reservoirs. Baseflow
samples were collected a minimum
of three days after the most recent
precipitation and were analyzed for
major ions, boron, and nutrients.
Findings —
• Concentrations of selected
chemical constituents in baseflow
were strongly affected by the
predominant land use in a given
basin. Land uses included forested
undeveloped, unsewered residential,
sewered residential, and agricultural
(horse and dairy farms).
• A positive linear relation was
indicated for chloride concentration
in baseflow and the basin’s annual
rate of road-salt application (or
density of two-lane roads). Chloride
concentration exhibits a relatively
stable relation to road-salt
application rate or 2-lane road
density throughout the year.
• Positive linear relations were
indicated for nitrate concentration
in baseflow and the basins
unsewered housing density. Nitrate
is characterized by a different
relation to unsewered housing
density for each season, with the
highest observed nitrate
concentrations during the winter
and the lowest concentrations
during the summer.
• Baseflow nitrate concentrations
in sewered basins, and in unsewered
basins with riparian wetland buffers
between residential development and
the stream, were lower than
concentrations predicted from
unsewered-housing density.
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