EMERGENCE OF AQUATIC INSECTS FROM 2 HABITATS IN A SMALL WETLAND OF THE SOUTHEASTERN USA - TEMPORAL PATTERNS OF NUMBERS AND BIOMASS

Emergence of aquatic insects from freshwater systems can provide infor mation that is useful from both taxon-specific and ecosystem perspecti ves. Although numerous studies of emergence have been conducted in hig h-latitude systems, relatively few studies have been done in warm-wate r systems, particularly in wetlands, where multiple generations and lo ng emergence periods are likely. We used emergence traps in a small be aver-impounded wetland in the southeastern USA to measure density and biomass of emerging insects, and deposition basins to measure adult re turn and potential export from the system. We focused on 2 major habit ats of the wetland: a shallow (0-1.0 m) vegetated zone dominated by th e white water-lily Nymphaea odorata and a deeper (>1 m) open-water zon e, insects (primarily Chironomidae) emerged from the Nymphaea zone thr oughout the year, but peaked in April at 205 individuals . m(-2) . d(- 1) and then declined from mid June to November to 20-50 . m(-2) . d(-1 ). Emergence from November through January was <10 . m(-2). d(-1), Ins ects (primarily Chironomidae) did not begin emerging from the open-wat er zone until late March, but continued emerging through November. Ann ual emergence in the Nymphaea zone of 16,128 individuals/m(2) and 2.39 g dry mass/m(2) was significantly higher than 4374/m(2) and 0.59 g/m( 2) in the open-water zone. Tanytarsini (primarily Tanytarsus) chironom ids accounted for >33% of the emergent biomass in the Nymphaea zone, w hereas Chaoborus punctipennis and Cladopelma sp. accounted for 19% and 21% of the emergent biomass, respectively, from the open-water zone. The emerging densities and biomasses of at least 6 taxa were significa ntly higher in the Nymphaea zone than in the open-water zone, and only Chaoborus was higher in the open water. Depositional trapping showed that deposition of adult insects in the aquatic environment averaged 2 5% of emerging numbers and biomass. The mayfly Caenis diminuta was com mon in deposition traps (1253 individuals . m(-2) . y(-1), but avoided emergence traps. Both emergent and depositional trapping appeared nec essary to quantify terrestrial activities of aquatic insects. Future c omparisons of emergence and deposition data with larval production in the wetland will enable us to determine the fraction of production tha t is represented by emergence and the fraction that returns to the aqu atic environment.