Seasonal trends in the distribution and abundance of benthic insects in a south central Texas pond as related to their emergence

Abstract

A study was conducted at Postoak Lake (.75 surface hectares), Brazos County, Texas between April of 1971 and May of 1973 to evaluate the changes in numbers and biomass of benthic and emergent insects throughout two annual cycles in response to various ecological parameters. A total of 676 benthic samples was taken at two-week intervals at 13 stations, and a total of 4,020 emergent samples was taken at 12 stations for the two-year period. Benthic sampling techniques were selective for dipterans, particularly chironomids and Chaoborus sp., and for ephemerids (Caenis sp. and Hexagenia sp.). Although the floating pyramidal emergent traps collected some ephemerids, these results were not considered to be quantitatively significant. The data for the chironomids and Chaoborus sp., however, provided useful estimates of lakewide exports of biomass through emergence. The highest total standing crop biomass for the sampled benthos at any one time during the two-year period was slightly over 14 kilograms per hectare (dry weight) on January 28, 1972. During the two-year sampling period, the lake lost over 32.8 kilograms per hectare biomass (dry weight) to emerging insects, with almost 76% of this being due to Chaoborus sp. emergence. An artificial fertilization treatment was applied near the beginning of the first annual cycle of the study. Although increased turbidity from watershed disturbance affected the second annual cycle, higher benthic mean weights for most species following the fertilization treatment suggest that artificial enrichment of the aquatic system had a positive influence on the benthic macroorganisms.