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INDICATORS OF HYDROLOGIC PERMANENCE IN HEADWATER STREAMS
Citation:
FRITZ, K. M. INDICATORS OF HYDROLOGIC PERMANENCE IN HEADWATER STREAMS. Presented at SWIMS Conference, Chicago, IL, January 30 - February 01, 2007.
Impact/Purpose:
The goal of this research is to develop methods and indicators that are useful for evaluating the condition of aquatic communities, for assessing the restoration of aquatic communities in response to mitigation and best management practices, and for determining the exposure of aquatic communities to different classes of stressors (i.e., pesticides, sedimentation, habitat alteration).
Description:
Headwater intermittent streams lie at the aquatic-terrestrial interface and represent much of our nation's stream miles. Recent court cases concerning the definition of jurisdictional waters under the Clean Water Act have illuminated a need to better understand the characteristics and function of temporary streams. The objective of our study was to identify physical and biological indicators of hydrologic permanence in forested headwater streams. A total of 113 reaches from 31 streams across 6 EPA Regions were sampled over three years. Physical habitat indicators were identified using stepwise discriminant analyses and classification and regression tree analysis. Reaches surveyed by USEPA Regional partners were held as a validation dataset for discriminant models. Perennial, intermittent, and ephemeral reaches were distinguished based on physical habitat characteristics. Drainage area, bankfull width, and the North Carolina Division of Water Quality's Stream Identification Form (modified to exclude hydrology metrics) were the most consistent measures distinguishing ephemeral from perennial reaches. Other physical characteristics (e.g., entrenchment ratio, valley slope) were most useful in discriminating intermittent from perennial reaches; however, these variables were less consistent between years. Discriminant models correctly classified 75-88% of ephemeral reaches, but only 35-50% of intermittent and 14-36% of perennial sites from the validation dataset. Five bryophyte families were identified as indicators of hydrologic permanence. The number of bryophyte taxa at ephemeral sites was significantly higher than at perennials while intermittent sites were intermediate. Invertebrate assemblages differed between perennial and intermittent reaches; however, physiographic region appears to be a stronger factor governing assemblage composition. Although further analyses are needed, these preliminary findings suggest that both physical and biological characteristics of stream reaches can be useful as regional indicators of hydrologic permanence in headwater streams.