by Turtleburp » Thu Jan 31, 2013 10:31 pm
No drains though:
We documented clear and
synchronous threshold declines of 110 of 238 macroinvertebrate taxa in response to low levels
of impervious cover. Approximately 80% of the declining taxa did so between ;0.5% and 2%
impervious cover, whereas the last 20% declined sporadically from ;2% to 25% impervious
cover. Synchrony of individual responses resulted in distinct community-level thresholds
ranging from 0.68% (mountains), 1.28% (piedmont), and 0.96% (coastal plain) impervious
cover. Upper limits (95% confidence intervals) of community thresholds were ,2% cover in all
regions. Within distinct physiographic classes, higher-gradient, smaller catchments required
less impervious cover than lower gradient, larger catchments to elicit community thresholds.
Relatively few taxa showed positive responses to increasing impervious cover, and those that
did gradually increased in frequency and abundance, approximating a linear cumulative
distribution. The sharp, synchronous declines of numerous taxa established a consistent
threshold response at exceptionally low levels of catchment urbanization, and uncertainty
regarding the estimation of impervious cover from satellite data was mitigated by several
corroborating lines of evidence. We suggest that threshold responses of communities to urban
and other novel environmental gradients may be more prevalent than currently recognized.
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