Abundant deposits of nutrients inside lakebeds of Antarctic oligotrophic lakes
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Most freshwater lakes in continental Antarctica are in a paradoxical situation as they are in nutrient-poor conditions despite luxuriant vegetation growth covering the entire lakebed. Although the phytobenthos possibly take up nutrients from inside lakebeds, the amount of nutrients and their utilization by these phytobenthos are unclear. Sediment cores were collected from 17 freshwater lakes in East Antarctica, then dissolved inorganic nitrogen (DIN) and phosphate of the lake waters, and the vertical profiles of the interstitial water in the sediment cores were analyzed. Here we revealed that there are abundant nutrients inside lakebeds surface with 3–220 times the amount of DIN and 2–102 times concentration of phosphate than those in lake water, and the nutrient profile inside the sediment suggested that the phytobenthos can utilize the much nutrients from lakebeds. We also show that nitrogen stable isotope ratios of shallower phytobenthos lying on the small amount of nutrients in a lake are similar to that of terrestrial cyanobacteria possessing N2 fixation ability.
KeywordsOligotrophic lakes Sediments Antarctica Polar ecosystems Material cycle Freshwater
This study was supported by a research grant of a project under the Centre for the Promotion of Integrated Sciences (CPIS) of the Graduate University for Advanced Studies (SOKENDAI) and by JSPS KAKENHI Grant Numbers 26310213 and 21810035. The authors acknowledge the members of the 51st and 53rd Japanese Antarctic Research Expedition for their field support, particularly the summer party leaders, Prof. Y. Motoyoshi and Prof. H. Yamagishi, for their logistic support. We also thank Ms. C. Ôuchida and Prof. J. Kanda of Tokyo University of Marine Science and Technology for assistance and for providing the nutrient analysis facilities and Dr. E. Cooper of University of Tromsø for English proofreading.
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