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Physical indicators of hydrologic permanence in forested headwater streams
Citation:
FRITZ, K. M., B. R. JOHNSON, AND DAVID M. WALTERS. Physical indicators of hydrologic permanence in forested headwater streams. JOURNAL OF THE NORTH AMERICAN BENTHOLOGICAL SOCIETY. North American Benthological Society, Lawrence, KS, 27(3):690-704, (2008).
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:
Recent court cases have brought headwater streams and their hydrologic permanence into the forefront for regulatory agencies, so rapid field-based indicators of hydrologic permanence in streams are critically needed. Our study objectives were to 1) identify environmental characteristics of forested headwater streams that best distinguish perennial, intermittent, and ephemeral reaches, and 2) assess the applicability of existing rapid field-based tools for classifying hydrologic permanence across a wide geographic range. We surveyed reach- and watershed-scale characteristics at 113 sites across 10 study forests in the United States. Four core forests (61 sites) were sampled over two consecutive years and were used in model construction. The other 72 sites (satellite sites) were used to validate the models over a broader geographic range. Hydrologic permanence categories at core sites were significantly different based on discriminant function models. Drainage area, Ohio Environmental Protection Agency's Headwater Habitat Evaluation Index (HHEI), and North Carolina Department of Water Quality's Stream Classificaton Method (NCSC) were strongly correlated with the discriminant function that separated ephemeral from perennial and intermittent sites. Entrenchment ratio was the most consistent variable discriminating intermittent from perennial sites. The models had mixed results on the validation dataset, but did correctly classify most intermittent and ephemeral sites. Classification trees were used to assess broad regional applicability of existing rapid field-based protocols and to identify important metrics. Scores from the Rapid Habitat Assessment (RHA) protocol, HHEI, and NCSC all clearly distinguished ephemeral from intermittent and perennial sites, but no differences were detected between intermittent and perennial sites across all sites. Data from core sites do however indicate that a suite of environmental variables can be used to successfully identify hydrologic permanence at regional scales.