Modelling the contribution of benthic microbial mats to net primary production in Lake Hoare, McMurdo Dry Valleys

Abstract

A model was used to simulate primary production of benthic microbial mats in Lake Hoare, southern Victoria Land, Antarctica, and to compare potential benthic to planktonic production. Photosynthetic and respiratory characteristics of mats from five depths in the lake were extrapolated across depth, surface area and time, to estimate whole-lake, annual net primary production. Variation in under-ice light regimes resulting from changes in ice thickness and transparency, and light extinction in the water column was examined, and an uncertainty analysis of key model parameters performed. Daily mat production estimates were 0.98–37.83 mg C m⁻² d⁻¹, depending on depth and PAR, whereas in situ production of phytoplankton averaged 15% of this. Annual patterns of mat production achieved maximum rates of 15–16 g C m⁻² y⁻¹ at 10 m depth when ≥ 5% of ambient PAR was transmitted through the ice covering the lake; observed transmittance values were usually ≤ 5%. Increasing underwater PAR had little effect above 5–7% transmittance, as photosynthesis became saturated at this level. Uncertainties in estimates of maximum photosynthetic rate (P_max), initial slope of photosynthetic-light response (α) and maximum respiration rate (R_max) explained 72–99% of uncertainty in model behaviour; P_max was increasingly important at high light levels whereas α was more important at low light levels, however R_max exerted the greatest influence under most conditions.