Benthic primary production in two perennially ice-covered Antarctic lakes:patterns of biomass accumulation with a model of community metabolism

A mathematical model was used to simulate interannual patterns of biomass a ccumulation within benthic microbial mats of two Antarctic lakes. Lakes Hoa re and Vanda are in the Dry Valley region of Southern Victoria Land, and ar e both perennially ice covered. The model combines experimentally derived o bservations of light/photosynthesis relationships and rates of respiration of mats from a range of depths in these lakes, with data on incident radiat ion and the optical properties of the ice and water column. The model was u sed to estimate daily and annual production and, using measured carbon cont ent, the potential vertical accumulation of the mats over a year. An annual pattern of photosynthesis was predicted far both lakes, with net productio n from October to February and net respiration at other times. Predicted ra tes and patterns of net photosynthesis were remarkably similar in the two l akes, despite differences in light climate: the ice of Lake Hoare transmits 1-4% incident radiation, whereas that of Lake Vanda transmits up to 20%. M aximum daily rates of 15-20 mug carbon cm(-2) were predicted to occur at ap proximately 10 m depth in both lakes. Maximum annual rates of carbon fixati on (at 10-12 m depth) in both lakes were c. 1.2 mg carbon cm(-2) equating t o approximately 0.1-4 mm vertical accumulation of mat each pear. Experiment al studies of microbial mats in the lakes revealed horizontal laminations o f similar thickness to model estimates, supporting the hypothesis that thes e were annual layers. Differences between model estimates and observations were found in deeper water in Lake Vanda, where considerably more material accumulated than was predicted.