Chironomidae: Linking Biodiversity and Bioassessment II
Presiding: S Gresens, Towson University; D R Francis, Department of Geosciences, University of Massachusetts
NB22C-01 INVITED 10:30h
Integrating Studies on Chironomid (Diptera) Biological Diversity and Biological Assessment in the Selenge River Watershed, Mongolia
Biological assessment of Chironomidae (Diptera) from eight affluent streams of Lake Hovsgol, Mongolia is combined with diversity survey data from the Hovsgol region. The streams were sampled twice monthly from June through August of 2002 following methods modified from the U.S. EPA Rapid Bioassessment Protocol. All data were combined and analyzed against physical and habitat data by hierarchical cluster analysis. Physical and habitat features of the streams and their watersheds varied little with the exception of substrate and cattle density. Streams in Borsog valley with the lowest density of cattle also had the lowest diversity and abundance of chironomids; whereas Shagnuul gol, which flows through the valley with the highest density of cattle had much higher abundance and diversity and a very unique chironomid assemblage composed of Trichotanypus sp., Derotanypus sibiricus Kruglova and Chernovskij, Potthastia longimani group, and Acricotopus sp. The results of this study are compared to diversity data for the region. This study has resulted in seven new records of chironomids for Mongolia. However, previous qualitative and semi-quantitative sampling of some of the same sites produced markedly different chironomid communities. It is concluded that diversity and ecological sampling are both necessary for biological assessment.
NB22C-02 INVITED 10:45h
Effects of Road De-icing Salts in Constructed Wetlands
In November 2003, a 4-lane highway and 6 mitigation wetlands were opened across the Penn State campus, Erie, Pennsylvania. Road runoff overflows into 1 wetland (T3), and another (R3) receives salt spray and plowed snow. I have logged conductivity and temperature hourly at the sediment-water interface in R3 and T3 since January 2004, and I measure conductivity, temperature, and chironomid density biweekly in all 6 wetlands. Salinity in the wetlands that receive no salt is 0 psu. Biweekly checks of conductivity grossly underestimated winter salinities in T3 and R3. Between January and March 2004, salinity was >5 psu 5 times in R3, and >10 psu 6 times and >30 psu twice in T3. Flushing rates were similar in both wetlands, but time constants were significantly greater in T3 than R3. Salinities returned to 0 psu in both wetlands in May. Chironomid density was significantly lower in T3 than in all other wetlands in summer and autumn, long after salinities at the sediment-water interface returned to 0. Thus, chironomid densities indicated persistent biological effects of de-icers even when measurable salinities were 0 psu. Winter 2005 data show decreasing chironomid density in T3, whereas densities are increasing in the other wetlands.
NB22C-03 INVITED 11:00h
Rapid Recovery of Chironomidae (Diptera) in Little Mill Creek (Kansas, U.S.A.) After the Decommissioning of a Waste Water Treatment Plant
In June 1995 the Lenexa Waste Water Treatment Plant was decommissioned, providing an opportunity to study recovery of Chironomidae community structure in Little Mill Creek. Using pupal exuviae, weekly changes in the species richness and composition of Chironomidae emerging upstream and downstream of the effluent outfall was evaluated from two weeks before decommissioning to eight weeks post-decommissioning. Chironomidae emergence was clearly different between upstream and downstream sites both before and shortly after effluent input ceased. Before decommissioning, sites immediately downstream of the effluent had low species richness and were dominated by Chironomus riparius (Meigen) and other tolerant taxa, with some recovery at sites farther downstream. Two weeks after decommissioning, only sites immediately downstream of the former effluent were clearly impacted, but effects were reduced compared to pre-recovery collections. At five weeks post-decommissioning, species richness was only slightly lower at the sites immediately downstream of the former effluent and the composition of common species (i.e., >5% of relative abundance) was similar between upstream and downstream sites. Rapid recovery of chironomid emergence below the sewage effluent likely resulted from both colonization of drifting larvae from upstream sources and adult dispersal and oviposition, indicating rapid responses in emergence as water quality conditions improved.
NB22C-04 11:15h
Chironomid assemblages along environmental gradients in New York City's drinking water tributaries, New York, USA.
Chironomidae are diverse and abundant in streams and rivers and are often included in water quality and pollution evaluations. We examined distribution patterns of chironomid genera from 60 sites in the 2 regions (East and West of the Hudson River) that are the source of New York City's drinking water. These watersheds range from forested to urbanized. Average midge density ranged from 3320-68813/m2 across all sites, and a total of 75 genera were identified over 3 years. Orthocladius and Cricotopus were the most abundant genera in both regions. Tanytarsus and Sublettea were also abundant in the West whereas Micropsectra and Eukiefferiella were abundant in the East. Multivariate analyses suggest that midge assemblages differed along land cover gradients. Nonmetric Multidimensional Scaling explained 73% of the spatial variation in chironomid assemblages from the western region, and 86% of the spatial variation from the eastern region. Western axes were correlated with population density and total roads in the watershed, percent cropland and farmsteads, and numerous other variables associated with agriculture and development. Eastern axes were correlated with wastewater treatment plant discharge, chlorophyll, total roads, and transportation land cover. Some genera-specific abundance responses were associated with certain land cover gradients.
NB22C-05 11:30h
Do the Choices for Field, Lab, and Data Analysis Methods Affect the Site Assessments in Biomonitoring Programs?
Broad differences remain in the field, lab, and data analysis methods used for bioassessment programs across local, state, national, and international boundaries. Recent calls for direct comparisons among these methods have begun to be fulfilled, including performance-based evaluations, but such comparisons remain limited to a handful of studies. Here, we present the results from our research on 3 intensive methods currently used by California bioassessment groups. These 3 methods were simultaneously used to collect and process samples from the same 40 streams in the eastern Sierra Nevada. The resulting data from each method were then analyzed using both multi-metric IBI and RIVPACS-type multivariate predictive models. Although the field and lab methods differed with respect to replication (1, 3, or 5 composite samples per stream), level of identification (family vs. genus for Chironomidae), and number of individuals processed per site (500 vs. 900 vs. 1500), all field/lab protocols clearly discriminated between independently identified reference and impaired streams. Furthermore, both the multimetric IBI analyses and the RIVPACS-type models produced effective separation of the reference sites from the impaired sites for all field/lab methodologies. These results suggest that alternative methodologies are interchangeable and could complement one another. Thus, the decisions among methods may hinge on objectives, costs, interpretability, and ease of use rather than ability to detect impairment.