Temporary Waters: Ecological Values, Policy, and Management III
Presiding: K Fritz, U.S. Environmental Protection Agency; B Johnson, U.S. Environmental Protection Agency
NB23B-01 13:30h
Similarities and Differences Between Headwater Streams in the Mountains and Piedmont of North Carolina
Biological sampling has been underway in headwater streams in the North Carolina Piedmont for two years and in Mountain headwater streams for one. Streams in the mountains usually started at springs, whereas most piedmont streams are fed by surface water runoff. Watersheds above springs, both mountain and piedmont, were smaller (mean 4 acres) than surface water streams in both regions (mean 19 acres). While taxa richness at perennial mountain headwater sites was similar (mean 38 taxa/sample) to piedmont perennial sites (mean 35), macroinvertebrate abundance in the mountains (mean 540 organisms/sample) was nearly double the sample abundance in the piedmont (mean 295). In both ecoregions winter/spring peaks in taxa richness and abundance were observed. Intermittent segments in the mountains were rare, but occurred as wet weather springs, while in the piedmont, intermittent segments were stream channels above perennial reaches. In both types, taxa richness and abundance were very low when the channel was dry, but were only slightly below levels found in perennial segments when wet. There were few species confined to intermittent reaches. Most taxa collected in intermittent reaches were also found downstream in perennial reaches, however some groups (e.g. mayflies, caddisflies, odonates, megaloptera) were rarely found in intermittent segments.
NB23B-02 13:45h
Patterns in Biological Communities of Vernal Pools on Cape Cod, USA.
Long-term studies (1995-2003) of vernal pools in the Cape Cod National Seashore, Massachusetts, USA, show a number of patterns in plant and animal communities. Some pools can be identified as discrete "types," - e.g. graminoid, Sphagnum/shrub, - based on plant community composition, and support distinctive macroinvertebrate communities. Year-to-year variation in weather patterns and hydroperiod produces measurable changes in plant community composition in some pools, and these changes are accompanied by parallel changes in fauna. The distributions of some macroinvertebrate species in individual pools are consistent from one year to the next and are correlated with plant community composition and average hydroperiod. The distributions of other species vary with between-year variations in weather patterns and plant community composition.
NB23B-03 14:00h
Assessment of Hydrological Variability on Habitat Stability and Macroinvertebrate Communities in an Intermittent Karst Ozark Stream
Research on the ecological effects of prolonged stream drying in karst systems has lagged far behind studies of continually flowing epigean systems. Macroinvertebrate community responses to hydrological variation in the South Dry-Sac River were examined over six seasons during 2003-2004. Stream permanence was quantified by measures of seasonal discharge, minimum discharge at summer baseflow, wetted riffle area-perimeter, and weekly bankfull percentages. Invertebrate community composition was determined by collecting three samples in each of ten riffles (180 samples) along a 1-km stretch of the stream located along a natural fault line in the Ozarks region of southwestern Missouri. Measures used to describe the invertebrate communities included measures of community composition (invertebrate density, richness, EPT taxa), and a series of diversity and similarity indices. Principal Components Analysis identified hydrological factors over physiochemical measures as being responsible for the greatest proportion of variation in abiotic factors among riffles. ANOVA techniques demonstrated that significant differences in invertebrate response variables existed among riffles when grouped by hydrological rather than seasonal parameters. Finally, a positive and linear relationship was evidenced between invertebrate response measures and riffle permanence. Results are discussed in relation to the role of hydrological variability in determining the biodiversity of karst instream communities.
NB23B-04 14:15h
Recovery of Aquatic Macroinvertebrate Communities From Drought in Georgia Piedmont Headwater Streams.
Drought is an important disturbance in stream ecosystems. From 1998-2002, Georgia suffered a major drought, ending in September 2002, when a tropical storm dumped almost 38 cm of rain. During the drought, many headwater streams experienced reduced flows or dried completely, affording an opportunity to study the recovery of aquatic macroinvertebrate communities. Six headwater streams in protected landscapes of the Georgia Piedmont were selected and paired based on similarities in physical parameters (sandy, bedrock, or mixed substrate). Each pair consisted of a stream that dried completely during the drought and one that retained at least some surface water. Riffles were sampled with a core sampler, runs and pools were sampled with a Hess sampler, and wood was sampled by randomly collecting every fifth piece of at least 5 cm diameter. Sampling occurred every four weeks for the first three months following the September 2002 re-flooding of streams and then every three months until the following November. Cluster analyses were used to assess the relative effects of drought history (dried or continually wet), stream condition, and temporal change.
NB23B-05 14:30h
Do Droughts Have Similar Consequences for Benthic Macroinvertebrate Communities in Similar Streams?
Hydrologic variability due to drying is common in streams, but does a single drought disturbance have similar effects across streams? In 2002, a severe drought occurred during an experiment designed to test the influence of habitat heterogeneity on macroinvertebrate community stability in two New Hampshire streams. I used this "demonic intrusion" to compare the effects of a single drought disturbance on benthic community composition in two similar streams. Prior to the drought, Alder and Loomis Valley Brooks, were very similar in size, discharge, cover, substratum, and community composition. However, following the drought, both univariate and multivariate measures of community composition demonstrated dramatic differences between the two streams with Loomis Valley shifted towards a community dominated by collector/gathering taxa, and Alder Brook dominated by predators, shredding detritivores, grazers, and filter feeders. In both streams, habitat heterogeneity played little or no role in mediating drought effects. Many of the post-drought differences between streams may have resulted from differential hydrologic impacts of the drought: Loomis Valley was without visible surface flow for several weeks, while Alder had reduced but visible surface flow. These results demonstrate that drought effects on benthic macroinvertebrate communities must be considered in a context which incorporates local hydrologic conditions.
NB23B-06 14:45h
Macroinvertebrate Response to Drought in Undisturbed Headwater Streams of Southwest Georgia.
Macroinvertebrates were sampled in four headwater streams for two years (2001-2003) to establish baseline conditions for a study evaluating forestry best management practices. The Palmer Drought Severity Index indicated that the study site experienced a prolonged moderate to severe drought prior to study initiation, with year one of the study characterized as a moderate drought, while year two encompassed drought and initial rainfall recovery. Benthic macroinvertebrates were collected in streams during year one (December 2001/February 2002) and year two (December 2002/February 2003) using a multi-habitat sampling procedure. Individuals were identified to the lowest practical taxonomic level (mostly genus), and metrics including abundance, total number of taxa, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa were calculated. Repeated measures ANOVA identified differences in macroinvertebrate assemblages due to sampling period, with lower values for December 2001 relative to February 2003. Abundance and EPT taxa showed an increasing relationship with average daily flow in successive samples of the study. Initiation of drought conditions prior to the study adversely affected species composition (low numbers of EPT taxa and long lived taxa) and trophic structure (co-dominance of shredders, collectors, and predators).