Comparative influence of resuspended glacial sediment on physicochemical characteristics and primary production in two arctic lakes

Abstract

We compared physicochemical properties and rates of phytoplankton and epipelic primary production in two shallow lakes in the Alaskan arctic on eight occasions over three years. The two morphometrically similar lakes lacked defined inlets and had a mean depth of 2.2 m. The lakes differed with respect to glacial influence. Lake GTH 112 was continuously turbid due to resuspension of glacial silt from the lake bed, while GTH 114 showed higher clarity as it was situated on coarser glacial drift. The two lakes contrasted sharply in euphotic zone nutrient concentrations. Soluble reactive phosphorus, NO3−-N and NH4+-N concentrations averaged 0.17, 2.5 and 12.6 μM, respectively, in GTH 112, but were generally at or below the detection limit of 0.05 μM in GTH 114. Reduced light limited the ability of phytoplankton in GTH 112 to use the increased nutrients, and volume-based rates of phytoplankton primary production were similar between lakes. High turbidity in GTH 112 decreased the average percentage of total lake volume and sediment surface within the euphotic zone to 63% and 47%, respectively, compared with values of 88% and 85%, respectively, for GTH 114. Consequently, the average whole lake (phytoplankton plus epipelic) primary production rate in GTH 112 (8.5 mmol m−2 d−1) was significantly lower than the mean rate (12.3 mmol m−2 d−1) for GTH 114. The increase in turbidity affected benthic and pelagic habitats proportionately, as epipelon accounted for about 25% of total whole lake primary production in both lakes.