Bioassessment VIII: Lentic and Estuary
Presiding: R S King, Center for Reservoir and Aquatic Systems Research, Department of Biology, Baylor University; M Moeykens, US Environmental Protection Agency
NB52F-01 10:30h
Evaluating Long-Term Trends in Crayfish Populations from acid Sensitive Softwater Lakes in South-Central Ontario (1988-2004).
We evaluated changes in crayfish abundance over time in 17 lakes on the Precambrian Shield with a modified Mann-Kendall trend test. Each year crayfish were sampled in midsummer using baited minnow traps. The lakes support as many as 3 crayfish species (e.g., Cambarus bartoni, Orconectes propinquus, and O. virilis). The trend test indicated significant linear declines in the relative abundances of C. bartoni in 7 of the 8 lakes where they were found. The decline of C. bartoni is unexpected, and somewhat surprising, since C. bartoni is more acid tolerant than the two orconectid species. Perhaps concomitant declines in lake-water calcium concentrations are affecting crayfish populations. The introduction of largemouth and smallmouth bass (Micropterus spp.) has affected crayfish catches in at least one lake. Long-term monitoring of crayfish and the evaluation of changes have allowed us to generate hypotheses regarding the cumulative effects of anthropogenic activities on the biota of lakes in south-central Ontario.
NB52F-02 10:45h
Linking Watershed Land Cover to Ecological Indicators in Streams and Subestuaries of Chesapeake Bay
Estuaries are dynamic, hydrologically open ecosystems. Consequently, it is difficult to identify linkages between the ecological health of estuaries and their watersheds. In 2002 and 2003, we sampled streams and subestuaries of 31 subwatersheds of Chesapeake Bay that spanned gradients in land use ranging from largely forested to highly developed or agricultural. Ecological indicators included water quality, wetland vegetation, benthic macroinvertebrate, bird, and fish assemblages, contaminants in fish, and estuarine optical properties. We observed a consistent linkage between the amount and spatial proximity of developed land and degraded ecological condition in both streams and subestuaries, with many indicators exhibiting threshold responses at similar levels of development in both years. The effect of agriculture was unclear for most indicators except stream nutrient concentrations, which increased with increasing percentage of cropland in watersheds. However, in 2003 (a wet year), markedly higher concentrations of nutrients were observed in agricultural subestuaries than in 2002, suggesting an interaction between watershed landuse and interannual hydrologic flux on estuarine nutrients. Overall, the majority of estuarine indicators responded negatively to development and less to agricultural land uses. Given the trend of urbanization of agricultural lands in coastal areas, our results have important management implications for coastal watersheds.
NB52F-03 11:00h
Changes in Benthic Macroinvertebrate Communities in Relation to Water Chemistry in 17 Lakes in South-Central Ontario, Canada
Benthic macroinvertebrates can be strong indicators of lake conditions, integrating the effects of all physical and chemical aspects of the environment. In lake systems that have been exposed to acid deposition, benthic community structure may be impacted by changes in water chemistry associated with either acidification or subsequent recovery. Multivariate analysis was used to examine temporal changes (from 1988 to 2002) in the benthic macroinvertebrate communities of 17 acid-sensitive lakes to evaluate the relationship between benthic community structure and water chemistry associated with acidification. Over the 15 years, chemical variables were found to explain 45-87% of the total variation in the benthic community. Temporal changes in community structure were most apparent from 1991 to 1999, while chemical parameters explained the greatest amount of variance from 1993 to 1997. During this period, relationships were evident between specific invertebrate groups and a number of chemical parameters, with covariables such as calcium and sodium often explaining significant additional variation. Overall, the correlation between benthic community structure and water chemistry suggests a strong association between temporal changes in the macroinvertebrate community and changes in lake chemistry associated with acidification and gradual recovery.
NB52F-04 11:15h
Macroinvertebrate Community Responses to the Chemical Removal of Phragmites in a Lake Erie Coastal Wetland
The invasive giant reed, Phragmites australis, can quickly form near-monotypic stands in North American wetlands, and as a result, sometimes reduce system biodiversity. However, the effects of Phragmites, and of the glyphosate herbicides used to control it, on trophic structure in benthic communities in these systems are less well known. Our study compares macroinvertebrate, algal, and juvenile fish diversity in replicate 10 x 5 m stands of Typha angustifolia (narrow-leaf cattail), glyphosate-sprayed Phragmites, and unsprayed Phragmites in a Lake Erie coastal wetland in Huron, Ohio. Macroinvertebrate diversity and proportions of functional feeding groups did not differ among stand types. However, overall densities of macroinvertebrates did vary among stands. Snails and larval chironomids and odonates were typically higher in Phragmites than in Typha stands. Interactions between changing water levels, algal densities, and prevailing flow patterns partly explain these outcomes. Ovipositing adult odonates did not prefer a particular stand type. Similarly, captures of juvenile fish did not vary among stands. Our results suggest that Phragmites, at least in small to moderately sized-patches, and herbicide application to these patches, does not detrimentally affect diversity in wetland, benthic communities.