Monitoring water quality in river systems vary regionally, this makes it unfeasible to have a constant standard of which all rivers are measured. In this case, the EPA proposed the Index of Biotic Integrity(IBI), to serve as a continuing assessment of our nation's water systems, by which our impact on environments could be identified, comparatively, through the years.
The IBI is a measure of an ecosystem's "ability to support and maintain a balanced, integrated, and adaptive community of organisms...having a species composition, diversity and functional organization comparable to those of natural habitats within a region"(Karr, J. R. and D. R. Dudley).
Biotic integrity could be equated to environmental prosperity, measured through the complexity and diversity of the native biotic populations.

The major determinates of the IBI level are human-induced, as illustrated by and IBI's standard, the Biological Condition Gradient(BCG). The BCG offers classification for measuring freshwater biota in response to human disturbance. The extreme alterations in an ecosystem yield extreme alterations in populations densities. Nearly all rivers and streams have been influenced or 'modified by direct and indirect human activity' (Baron, Jill S.)

As defined by the USGS:
"Direct activities that have altered aquatic ecosystems include: habitat destruction and fragmentation; dams, diversions, channelizations, and groundwater pumping that alter flow patterns, erosion activities, thermal regimes, and species migration routes; point and non-point introduction of a wide array of organic chemicals, toxic metals, and fertilizers such nitrogen and phosphorous; alteration of thermal regimes through damming, point source inputs of hot water, or riparian vegetation alteration; introduction of non-native plant and animal species; and over-harvesting.
Indirect effects occur from land use change within watersheds, and long-range transport and deposition of acid and metal pollutants."


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