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The sediment and river stability changes assessed by the RLA, RRISSC
and PLA methodologies are primarily physical changes.
However, the consequences of such physical changes are directly
related to potential impairment of aquatic biological communities
and functions as well. Changes in river stability such as
aggradation, degradation, enlargement and stream type alteration
affect habitats (e.g., reducing pool volume and frequency)
and food chains (e.g., eliminating or reducing intolerant
fish or invertebrate taxa), just to name a few.
Limiting factor analyses are used to assess habitat loss due to river instability and/or excess sediment such as relations of holding cover, in stream/overhead cover, water temperature, dissolved oxygen, and benthic invertebrates. Biological monitoring information associated with stream condition, such as diversity indices, population dynamics, age class distribution, spawning and rearing habitat and many more attributes, can be stratified by stream type and by stream stability to control and reduce within-class variability. Biological monitoring should follow similar approaches for stratification based on the diverse nature of streams and their natural variability. Good ambient monitoring designs and use of reference condition concepts that are physical (i.e., fluvial geomorphic) as well as biological set the stage for well-informed monitoring at the single-stream scale. Many emerging methods for stream biomonitoring are contrasting observed species assemblages with expected species assemblages (developed with the reference data) in an O/E ratio that approaches a value of 1 in the best cases of stream recovery.
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