Parametric distance weighting of landscape influence on streams |
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Authors: | John Van Sickle Colleen Burch Johnson |
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Institution: | (1) National Health and Environmental Effects Research Laboratory, Western Ecology Division, U.S. Environmental Protection Agency, 200 SW 35th St., Corvallis, OR 97333, USA;(2) Indus Corporation, 200 SW 35th St., Corvallis, OR 97333, USA |
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Abstract: | We present a parametric model for estimating the areas within watersheds whose land use best predicts indicators of stream
ecological condition. We regress a stream response variable on the distance-weighted proportion of watershed area that has
a specific land use, such as agriculture. Distance weighting functions model the declining influence of landscape elements
as a function of their flowpath distances, first to the stream channel (to-stream distance), and then down the channel to
the location at which stream condition was sampled (in-stream distance). Model parameters specify different distance scales
over which to-stream and in-stream influences decline. As an example, we predict an index of biotic integrity (IBI) for the
fish communities in 50 small streams of the Willamette Basin of Oregon, USA, from distance-weighted proportions of agricultural
or urban land use in their watersheds. The weighting functions of best-fitting models (R
2 = 0.57) represent landscape influence on IBI as extending upstream tens of kilometers along the stream channel network, while
declining nearly to zero beyond a distance of 30 m from the channel. Our example shows how parametric distance weighting can
identify the distance scales, and hence the approximate areas within watersheds, for which land use is most strongly associated
with a stream response variable. In addition, distance-weighting parameters offer a simple and direct language for comparing
the scales of landscape influence on streams across different land uses and stream ecosystem components. |
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Keywords: | Land use Stream ecology Flowpath Riparian Watershed Regression modeling Distance weighting |
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