IMPACT OF LIGHT REGIMES ON PRODUCTIVITY PATTERNS OF BENTHIC MICROBIALMATS IN AN ANTARCTIC LAKE - A MODELING STUDY

Filamentous cyanobacteria often dominate benthic microbial communities of antarctic lakes and usually exhibit saturation of photosynthesis a t light intensities similar to 100 mu Einst m(-2) s(-1). Incident ligh t regimes an controlled by ice and snow accumulations overlaying water columns during much of the year. Thus, Light availability to microbia l mats is often below saturation intensity and is strongly influenced by modest changes in climatic factors. A model of net primary producti on for benthic mat communities of the subantarctic Sombre Lake, Signy Island, was developed (1) to evaluate depth-specific productivities of mat communities, (2) to test the relative importances of model parame ters to mat production, and (3) to explore the potential impacts of cl imate change on mat production as manifested through changes in light regime. Simulated rates of net primary production corresponded to obse rvations on a daily basis (similar to 1-4 mu g C fixed mg(-1) ash-free DW of mat d(-1)) but were an order of magnitude lower than estimates of net annual production based on field measurements (less than or equ al to vs. 11-45 g C m(-2) yr(-1), respectively). Close examination sug gested that the simulated values were mon plausible. A detailed sensit ivity analysis of model behavior revealed that variations in the time of ice and snow melt in spring accounted for 40-60% of the total varia tion in model behavior, emphasizing the importance of climatic factors to net primary production of mat communities and the sensitivity of m at production to climate change.