Spatial-Scale Effects on Relative Importance of Physical Habitat Predictors of Stream Health |
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Authors: | Emmanuel A Frimpong Trent M Sutton Bernard A Engel Thomas P Simon |
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Institution: | (1) Department of Forestry and Natural Resources, Purdue University, 715 W. State Street, West Lafayette, Indiana 47907, USA;(2) Department of Agricultural and Biological Engineering, Purdue University, 225 S. University Street, West Lafayette, Indiana 47907, USA;(3) US Fish and Wildlife Service, Bloomington Field Office, 620 S. Walker Street, Bloomington, Indiana 47403, USA |
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Abstract: | A common theme in recent landscape studies is the comparison of riparian and watershed land use as predictors of stream health.
The objective of this study was to compare the performance of reach-scale habitat and remotely assessed watershed-scale habitat
as predictors of stream health over varying spatial extents. Stream health was measured with scores on a fish index of biotic
integrity (IBI) using data from 95 stream reaches in the Eastern Corn Belt Plain (ECBP) ecoregion of Indiana. Watersheds hierarchically
nested within the ecoregion were used to regroup sampling locations to represent varying spatial extents. Reach habitat was
represented by metrics of a qualitative habitat evaluation index, whereas watershed variables were represented by riparian
forest, geomorphology, and hydrologic indices. The importance of reach- versus watershed-scale variables was measured by multiple
regression model adjusted-R2 and best subset comparisons in the general linear statistical framework. Watershed models had adjusted-R2 ranging from 0.25 to 0.93 and reach models had adjusted-R2 ranging from 0.09 to 0.86. Better-fitting models were associated with smaller spatial extents. Watershed models explained
about 15% more variation in IBI scores than reach models on average. Variety of surficial geology contributed to decline in
model predictive power. Results should be interpreted bearing in mind that reach habitat was qualitatively measured and only
fish assemblages were used to measure stream health. Riparian forest and length-slope (LS) factor were the most important
watershed-scale variables and mostly positively correlated with IBI scores, whereas substrate and riffle-pool quality were
the important reach-scale variables in the ECBP. |
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Keywords: | Scale Habitat Predictive models Stream health Biotic integrity Fish |
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