Headwater Influences on Downstream Water Quality |
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Authors: | Walter K Dodds Robert M Oakes |
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Institution: | (1) Division of Biology, Kansas State University, Manhattan, KS 66506, USA;(2) Present address: University of Pennsylvania Law School, 3400 Chestnut Street, Philadelphia, PA 19104, USA |
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Abstract: | We investigated the influence of riparian and whole watershed land use as a function of stream size on surface water chemistry
and assessed regional variation in these relationships. Sixty-eight watersheds in four level III U.S. EPA ecoregions in eastern
Kansas were selected as study sites. Riparian land cover and watershed land use were quantified for the entire watershed,
and by Strahler order. Multiple regression analyses using riparian land cover classifications as independent variables explained
among-site variation in water chemistry parameters, particularly total nitrogen (41%), nitrate (61%), and total phosphorus
(63%) concentrations. Whole watershed land use explained slightly less variance, but riparian and whole watershed land use
were so tightly correlated that it was difficult to separate their effects. Water chemistry parameters sampled in downstream
reaches were most closely correlated with riparian land cover adjacent to the smallest (first-order) streams of watersheds
or land use in the entire watershed, with riparian zones immediately upstream of sampling sites offering less explanatory
power as stream size increased. Interestingly, headwater effects were evident even at times when these small streams were
unlikely to be flowing. Relationships were similar among ecoregions, indicating that land use characteristics were most responsible
for water quality variation among watersheds. These findings suggest that nonpoint pollution control strategies should consider
the influence of small upland streams and protection of downstream riparian zones alone is not sufficient to protect water
quality. |
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Keywords: | Water quality Geographic information systems Headwater streams Nonpoint source pollution Riparian zones Watershed management |
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