Chironomidae: Linking Biodiversity and Bioassessment III Posters
Presiding: S Gresens, Towson University; D R Francis, Department of Geosciences, University of Massachusetts
NB33D-01 1330h
Chironomids (Insecta: Diptera) as Indicators of Ecological Status in Lakes
Benthic communities are used in biological assessment and monitoring in lakes. Chironomids are considered indicators of oxygen level and trophic state. The taxocoenosis of 42 Italian lakes with different volume, depth, annual minimum hypolimnetic oxygen concentration, transparency and phosphorous concentration were investigated. Larvae were collected with a Petersen grab at different depths, pupal exuviae with a drift net near the outlet of lakes and adults with a sweep net along the shore. 334 species were identified: 41 Tanypodinae, 17 Diamesinae, 3 Prodiamesinae, 118 Orthocladiinae, 155 Chironominae (61 Tanytarsini, 93 Chironomini and 1 Pseudochironomini). Drift samples included many more taxa than grab samples, adult samples often included terrestrial species. Lake Garda, Como and Maggiore were the richest in species (78, 72 and 66 respectively), as expected because of their large size. Species richness did not result as good indicator: both oligotrophic (Monate 52 species, Toblino 33) and eutrophic lakes (Annone 57, Pusiano 42) were characterized by similar species numbers. Different species were more suitable indicators of oxygen concentration rather than of nutrients. A comparison of different lakes is preliminary because of: 1. different morphometric and trophic conditions; 2. different sampling effort; 3. lack of knowledge of species optima and tolerance.
NB33D-02 1330h
Biodiversity of Chironomidae at the North Temperate Lakes LTER Site
The National Science Foundation has established a network of Long Term Ecological Research (LTER) sites to enhance research at large spatial scales, extended temporal scales, and to facilitate intersite comparisons of system structure and processes. Present knowledge of Chironomidae community structure at LTER sites is insufficient to accomplish these goals. Our project objectives are to determine species composition of Chironomidae in a wide variety of aquatic habitats at LTERs, describe all undescribed species/life stage associations, determine the temporal seasonality of emergence and develop a data base of species by habitat and emergence times. Our methods include light trapping and sweep netting for adults, dip-netting and hand-picking wood/aquatic vegetation for larvae, collecting surface-floating pupal exuviae, and rearing to associate life stages. Our initial focus on the North Temperate Lakes LTER in Wisconsin and has documented 80 genera (representing > 125 species, including 18 undescribed species and/or unknown life stages) from 11 lakes, 5 streams and 2 bogs. Taxa include species with larvae that are: epiphytic, endophytic, xylophagic, phoretic on mollusks or other aquatic insects, specialized to feed on freshwater sponges, predators of black fly pupae, and those occurring in hyporheic zones, marginal semi-aquatic habitats or terrestrial soils.
http://www.entomology.umn.edu/midge/NSFGrant.htm
NB33D-03 1330h
Community Structure of Chironomidae (Midges) in Two Brazilian Rivers in Relation to Contrasting Land Uses
We investigated whether the conversion of riparian land use from indigenous forest to pasture is associated with changes in midge community composition in two South Brasilian rivers. Our study was conducted in the main rivers (Sao Jose dos Dourados 6th order; Aguapei 7th order) of two catchments in Sao Paulo State. Both catchments are dominated by agricultural ecosystems but retain substantial patches of native riparian forest in certain areas. Replicated artificial substrates (baskets filled with clay rocks) were exposed in forested and pasture reaches in both rivers. Both land uses had to be present for at least 500m along both river banks, and the riparian forest had to be at least 50m wide. In each river, six baskets per reach type were sampled after a colonization period of 44 days, and all Chironomidae in these samples were sorted and identified to genus level (a total of 3399 individuals belonging to 28 different taxa). As expected, land use affected midge communities. Total midge density was significantly higher in pasture reaches than in forested reaches. By contrast, midge taxon richness was higher at the forested reaches. These results show the importance of native riparian forests for preserving aquatic biodiversity in Brasilian rivers.
NB33D-04 1330h
Chironomidae From a Sewage Treatment Station of Southern Brazil
As the great number of insects living and reproducing at a municipal sewage treatment station located in Piracicaba City and the fear about how dangerous it could be for human healthy, a study was conduct to identify the taxa presented there and to analyze their community structure using stable isotopes. The Chironomidae identification was performed on specific level. The sewage treatment station is a man-made wetland system, situated 30m nearby the Piracicaba River. It treats the sewage from an urban area with 3000 inhabitants. The sewage discharge varies from 133 to 186L/s/ha. The samples were taken on the ending of the rainy season with a D-frame net. The material was washed (210mm mesh size), sorted and preserved in 70% alcohol. Chironomidae had a low participation in the community, with 14.9% of the specimens. Goeldichironomus serratus (47.8% from total Chironomidae), G. holoprasinus (43.5%) and Chironomus decorus (8.7%) were identified. Those species are worldwide recognized as pollution-resistant, used as indicators of environmental water quality. The wetland studied showed low dissolved oxygen (1.5mg/L) on the sampling period and the presence of those Chironomidae species should be expected. The low diversity and high dominance are common features for those impacted environments.
NB33D-05 1330h
Importance of DOC From Terrestrial Sources in Supporting Benthic Production in Arctic Lakes.
A prevailing paradigm in limnology has been that benthic organisms derive most of their food from pelagic productivity. However, chironomids are known to utilize dissolved organic carbon (DOC) via the microbial food web, and much DOC is derived from terrestrial sources. We tested whether supplements of various DOC and particulate organic carbon (POC) sources would support growth in Chironomus from arctic lakes. Eight treatments with five replicates were administered to Chironomus growing in sediment core microcosms over a twenty-four day period. Growth rates were calculated and stable isotope analysis of Chironomus Δ13C data was performed. An overall ANOVA and a Tukey-Kramer's test were performed on the data. The stable isotope data established that Chironomus assimilated carbon from both pelagic algal-derived DOC and from benthic algae. However, only the terrestrial DOC supplement supported significantly positive growth. The terrestrial particulate detritus treatment showed lowest growth. We conclude that DOC-based production is important in supporting benthic food webs, and that much of this may be derived from terrestrial sources.