2006 BES Annual Meeting Presentation and Poster Abstracts
Mid-summer emergence of chironomid taxa in streams spanning a gradient of watershed urbanization
Co-Authors: Alyson Paul and Susan Gresens
Abstract: Twenty-five Baltimore (Maryland, U.S.A.) area streams were surveyed to determine the response of chironomid communities to environmental changes associated with urbanization. Surface-floating chironomid pupal exuviae were collected on twelve dates in 2002 (a year of severe drought). Concurrent measurements were also made of attached algal biomass, sediment particle size distribution, concentration of sediment-bound metals, and standard water quality parameters, including concentrations of nitrate and total phosphorus. An initial analysis of 15 streams is presented, focusing on emergence during June, of eleven select chironomid genera/species. Canonical Correspondence Analysis was used to quantify the relationships between the pattern of chironomid distribution and environmental variables. The first CCA axis represented 38% of the inertia in the chironomid data, and contrasted the abundance of fine sand and silt sediments, predominant in rural streams with high values (in urban streams) for total phosphorus, maximum algal biomass and sediment-bound zinc and lead. Along the first axis, abundances of Tanytarsus c.f. glabrescens, T. sepp, Micropsectra polita and Rheotanytarsus spp. were associated with rural streams. The second CCA axis, representing 16% of inertia in the biotic data, emphasized the variability among urban streams in concentration of metals, total phosphorus and conductivity. Paratanytarsus nr. inopertus and Cryptochironomus sp. appeared moderately tolerant of eutrophication, but intolerant of high zinc and lead concentrations. The total abundance of Cricotopus was strongly associated those urban sites with the highest concentration of metals, as well as large seasonal blooms of the alga Cladophora.