PARENT SESSION
Oral Session # 94: Pathogens, Toxins, and Disease III.
Presiding: C Duffie
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 200.

Aquatic community metabolism: Effects of toxic chemicals in microcosms.

Taub , Frieda ^*,1, ¹ University of Washington, Seattle, WA, USA

ABSTRACT- Just as the oxygen consumption of an animal can be used to estimate energy expended, community metabolism can be estimated (based on the heat of combustion of organic material as ca. 14 kJ per gram O₂). Net Ecosystem Production (NEP), the net energy gain (net photosynthesis) minus (night respiration) reflects the net daily energy change. I demonstrate that NEP is a more useful measure than P:R ratio for microcosms treated with three toxic chemicals. Streptomycin, an antibiotic and selective algicide reduced net photosynthesis for more than a month; yet, P:R ratios were almost always near 1 because R decreased a similar amount. Malathion, an insecticide, temporarily eliminated Daphnia; net photosynthesis was increased during the absence of grazers, but P:R ratios were almost always near 1, since R was high when P was high. CuSO₄, both a selective algicide and a zooplankton toxicant, had a range of effects depending on concentration; low CuSO₄ concentrations eliminated grazers and sensitive algae but allowed insensitive algae to bloom; at higher CuSO₄ concentrations, most algae as well as grazers were eliminated, and net photosynthesis was reduced; still P:R ratios were usually close to 1. NEP and accumulated NEP were more useful in understanding the trophic interactions and demonstrating statistical differences from controls.

Key words: net ecosystem production, community metabolism, ecotoxicology, standardized aquatic microcosm