Coastal Plain Rivers of the Southeastern United States II
Presiding: A Benke, University of Alabama; S W Golladay, Joseph W. Jones Ecological Research Center at Ichauway
NB42D-01 INVITED 10:30h
Correlation of Invertebrate Drift Density and Colonization Density on Submerged Wood During Rising and Falling Water Levels: Efficiency of Colonization
Submerged wood is the major solid substrate available for invertebrate colonization in Coastal Plain rivers, and the quantity of wood submerged varies with discharge. As water level drops, invertebrates enter the drift, potentially to colonize other submerged wood. When water level rises, drifting animals colonize newly inundated habitat. We measured wood colonization and invertebrate drift monthly from February through July in the Sipsey River, Alabama. Samples were taken during rising and falling water levels to test how changes in water level affected rates of drift and colonization, and to determine whether there was a correlation between drift rates and colonization rates. The drift consisted of invertebrates originating from wood and floodplain habitats. No consistent differences in either drift or colonization were correlated with changing water levels. However, there was a strong correlation (0.93) between drift and colonization of wood-dwelling invertebrates. The highest 7-day colonization density was 44,249 animals/m2 of wood surface with a biomass of 1868 mg/m2. Minimum density and biomass were 4325 animals/m2 and 258 mg/m2. Drift of potential colonizers ranged from 4.90 to 1.98 animals/m2/s. Colonization densities calculated from drift rates agreed closely with actual 7-day colonization densities. This indicated that drifting invertebrates efficiently colonized any wood encountered.
NB42D-02 10:45h
Freshwater macroinvertebrate research in western Louisiana: limitations of our knowledge base
Western Louisiana streams and rivers represent relatively uncharted waters with regard to their biota, particularly aquatic macroinvertebrates. Whereas statewide taxonomic surveys have been conducted for several taxa (Dryopid Coleoptera, Odonata, and Plecoptera), peer-reviewed studies on macroinvertebrate communities and their structuring factors are few. We present the findings of three different macroinvertebrate community studies in western Louisiana encompassing 1990-2004. These studies investigated large-scale forest cover removal and localized biotic influences on macroinvertebrate communities. These studies generally were inconclusive with regard to abiotic anthropogenic disturbances; instead, strong seasonal and spatial patterns combined with wide tolerances to stream physio-chemistry appeared to be more important factors. However, strong localized biotic effects did appear to significantly alter macroinvertebrate communities. Further, a paucity of classic shredding organisms was noted in each study suggesting a unique community composition in these streams in comparison to neighboring regions. We believe geologic phenomenon may have acted as an evolutionary filter that produced a macroinvertebrate community generally tolerant of abiotic disturbance, but not as of yet, tolerant to biotic disturbances.
NB42D-03 11:00h
Stream Restoration Effects on an Impaired Benthic Macroinvertebrate Community in a Small Coastal Plain Stream in Johnston County, North Carolina.
Pre- and post-construction benthic macroinvertebrate community data were collected from a recently restored small coastal plain stream in North Carolina. Metrics for comparing two sites, a restoration and a reference reach, included total and EPT taxa richness, total and EPT biotic indices (BIs), and EPT abundance. Initially, the restoration site scored worse than the reference site on every metric and indicated an impaired status for biological integrity, the stream's primary designated use. Two years after restoration, metric values for the restoration site have improved, while those for the reference site remained stable. EPT taxa richness has nearly doubled from 7 to 13 taxa, exceeding that of the reference site. However, BIs at the restoration site, while improving, remain worse than those of the reference site, suggesting that the restoration site community has not yet stabilized. This conclusion is supported by the lesser number of shredders found at the restoration site than the reference site. However, it is anticipated that the restoration shredder population will grow as organic matter input from maturing riparian vegetation increases. These observations suggest that stream restoration can be an effective management tool for restoring biological integrity, as measured by benthic macroinvertebrate communities.
NB42D-04 11:15h
Relationship of Freshwater Mussel Distribution and Species Richness to Local and Regional Scale Variables in South-east Louisiana
The Southeastern United States has the most diverse and imperiled freshwater mussel fauna in the world. The community structure and decline of these assemblages is the result of complex interactions between biotic and abiotic factors, but the local scale of most community studies has failed to elucidate the underlying mechanisms of these interactions. We test the hypothesis that mussel species richness, distribution and abundance are related to a combination of local scale habitat variables and regional scale landscape variables. We used semi-quantitative, timed sampling to census the mussel assemblages of the Tickfaw and Tangipahoa river drainages in south-eastern Louisiana during the spring and summer of 2004. At each site, we recorded the relative abundances of mussels, microhabitat descriptors and GPS coordinates. We then used GIS to determine land use and geological formations within a 100 meter buffer extending 1Km upstream of each site as well as within each sub-basin. Stepwise multiple regression coupled with multivariate descriptive statistics revealed both longitudinal changes in species richness and abundance along rivers, anthropogenic impacts caused by land use, and differences in species richness between sub-basins.