Microphytobenthos in Shallow Arctic Lakes: Fine-Scale Depth Distribution of Chlorophyll a, Radiocarbon Assimilation, Irradiance, and Dissolved O

• Published in: Arctic, antarctic, and alpine research antarctic, and alpine research, 2013-05, Vol.45 (2), p.285-295
• Main Authors: Whalen, Stephen C, Lofton, Dendy D, McGowan, Gabriel E, Strohm, Amy
• Format: Article
• Language: English
• ISSN: 1523-0430
• DOI: 10.1657/1938-4246-45.2.285

We compared in three shallow Alaskan Arctic lakes physical properties of bulk sediment and the fine-scale (1 mm increments to 20 mm sediment depth) vertical distribution of dissolved O sub(2), scalar irradiance, chlorophyll a, and radiocarbon assimilation by microphytobenthos to better understand the structural and functional significance of this community. Sediments showed water contents of 86-98%, and dry bulk densities of 0.012-0.146 g cm super(-3), depending on depth. Chlorophyll a displayed no clear vertical pattern, suggesting mixing of surface layers and showed lakewise averages of 5.1-23.7 mu g cm super(-3). Sediments were oxic to 1.5-5.5 mm and showed attenuation coefficients of 1.17-2.07 mm super(-1) for photon scalar irradiance. Photosynthetic activity was localized near the sediment surface, as 57-81% of H super(14)CO super(-) sub(3) added to intact cores was recovered in the 0-2 mm zone. Only 26-44% of the chlorophyll a in vertical profiles was sited in the euphoric zone, but microphytobenthos in underlying, aphotic sediments immediately photosynthesized at or near rates for the surface sediment when artificially irradiated. Area-based chlorophyll a in the euphotic plus photosynthetically capable aphotic microphytobenthos was 62-105 times higher than that of the phytoplankton, pointing to the potential importance of benthic autotrophs to Arctic lake food webs.