Journal of the North American Benthological Society
Published by: North American Benthological Society
Journal of the North American Benthological Society 27(3):690-704. 2008
doi: 10.1899/07-117.1
Physical indicators of hydrologic permanence in forested headwater streams



National Exposure Research Division, US Environmental Protection Agency, Cincinnati, Ohio 45268 USA
Abstract
Recent court cases have questioned whether all headwater streams are jurisdictional waters under the US Clean Water Act. Rapid field-based indicators of hydrologic permanence are needed for making jurisdictional determinations. Our study objectives were to: 1) identify physical 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 drainage-scale characteristics at 113 sites across 10 study forests in the US. Streams in 4 core forests (61 core sites) were sampled over 2 consecutive years and were used in model construction. Streams in 6 satellite forests (72 satellite sites) were used to validate the models over a broader geographic range. Discriminant function models successfully differentiated hydrologic permanence categories at core sites. Drainage area, the Ohio Environmental Protection Agency Headwater Habitat Evaluation Index (HHEI), and the North Carolina Department of Water Quality Stream Classification 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 across the core forests. The models had mixed results when applied to the validation data set, but did classify correctly 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 Bioassessment Protocol Habitat Assessment, 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. However, data from core sites do indicate that a suite of physical variables can be used successfully to identify hydrologic permanence at regional scales.
Received: September 17, 2007; Accepted: May 16, 2008
Keywords: jurisdictional waters, intermittent, ephemeral, perennial, temporary, rapid habitat assessments, hydrology, geomorphology
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Fig. 3. Tree diagrams from classification trees (CART) for the Ohio Environmental Protection Agency Headwater Habitat Evaluation Index (A), the North Carolina Division of Water Quality Stream Classification index (B), and the US Environmental Protection Agency (EPA) Rapid Bioassessment Protocol (RBP) Habitat Assessment index (C) across hydrologic permanence categories of core and satellite sites. RBP scores are also shown for reference wadeable streams taken from the US EPA Environmental Monitoring and Assessment Program. The number of sites within each category (E = ephemeral, I = intermittent, P = perennial, and W = wadeable) is shown at each node. Cut values associated with explanatory variables are shown at bifurcations and the associated proportion of reduction in error (PRE) is in parentheses.
Fig. 4. Box plots comparing multimetric habitat scores for the Ohio Environmental Protection Agency Headwater Habitat Evaluation Index (HHEI; n = 113) (A), the North Carolina Division of Water Quality Stream Classification index (NCSC; n = 111) (B), and the US Environmental Protection Agency (EPA) Rapid Bioassessment Protocol (RBP) Habitat Assessment index (n = 304) (C) across hydrologic permanence categories of core and satellite study sites. RBP scores also are shown for reference wadeable streams (193 sites) taken from the US EPA Environmental Monitoring and Assessment Program. Dashed lines indicate habitat thresholds derived by associated state agencies to assist in delineating among stream classes. HHEI class 1 = ephemeral streams, class 2 = warm-water perennial and intermittent streams, and class 3 = cold-water perennial streams. Lines inside boxes are means, box ends are quartiles, whiskers show 2 SD, dots show scores >2 SD. Boxes with different lowercase letters are significantly different (p < 0.05, Tukey's post hoc test) within panels.
Table 1. Study locations, hydrologic landscape region (HLR) number (Wolock et al. 2004), study years, number of sites across permanence categories (E = ephemeral, I = intermittent, P = perennial), and annual and summer precipitation ranks for study years. Precipitation ranks (1 = wettest year or summer on record) were derived from nearby National Weather Service stations with daily records >50 y. na = not available (National Weather Service data incomplete), – = not applicable to study periods, * = core study forests.
Table 2. Physical variables measured in forested headwater streams. Wet variables were measures of water presence (during spring) and were used only to discriminate intermittent and perennial sites. Dry variable ranges are listed for all 113 study sites (except for ER [no values for New York sites], NCSCM, and RBPM [no values for New York ephemeral sites]), whereas wet variable ranges are listed only for the 89 intermittent and perennial sites.
Table 3. Tests of discriminant functions for classifying ephemeral, intermittent, and perennial headwater streams. % correct is the percentage of sites that were classified correctly by the model.
Table 4. Correlation coefficients (r) between canonical scores for the discriminant function models and physical variables. Variable abbreviations given in Table 2. Coefficients in bold are significant at p < 0.05. – = variable not in model.





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