COS 18-6
Mechanisms of nutrients enclosure inside benthic microbial mats in Antarctic oligotrophic lakes by combination approach of observation data and theoretical study

Tuesday, August 12, 2014: 9:50 AM
Beavis, Sheraton Hotel
Yukiko Tanabe, Waseda Institute for advanced study, Waseda University, Tokyo, Japan
Akiko Mizuno, Hydropheric Atmospheric Research Center, Nagoya University, Nagoya, Japan

The most of water bodies of freshwater lakes in Antarctica are considered to be nutrients limited. Although the lake water are oligotrophic in Antarctic freshwater lakes, the interstitial water of benthic microbial mats surface were 3-220 times higher in ammonium concentrations and 2-102 times higher in phosphate than the lake water. The nutrient concentrations of the interstitial water in Antarctic lakes are either equaling or surpassing that of temperate eutrophic lakes. Also, the nutrient concentrations of the interstitial water have a wide range of variations although lake waters are similar concentrations among the lakes in Antarctica. Then, it is hypothesized that there are any mechanisms the nutrients hardly discharged from lakebeds to water column such like nutrients enclosure. To reveal the mechanisms, we used vertical profiles of the silicate and ammonium concentration inside benthic mats collected from 17 Antarctic oligotrophic lakes, and examined 3 factors considered as controlling nutrients enclosure by model study. The first is turbulence on the boundary layer between mat and water, the second is viscosity of the mats, the third is uptake by phytobenthos.


To confirm the effect of turbulence, we examined that correlation between the both nutrient concentrations affected by the lake surface area and the maximum water depth using generalized linear model and AIC model selection. Then it was revealed that the lake area and the maximum depth have no effect on the correlation because a simplest model without the both variables was selected by each of the criteria AIC. It indicates that the turbulence are thought to be negligible. Next, we established two diffusion models to represent dynamics of silicate and ammonium in water column and the mat on the vertical axis. The model was used to investigate the distribution pattern of nutrient concentration by molecular diffusion affected by mat viscosity and biological consumption, and was compared with observation data. The silicate model showed a wide range of variations of viscosity, and the viscosity values depending on each lake were obtained. The kinetics of the ammonium uptake by phototrophs were obtained by applying the viscosity of each lake to the ammonium model, then this indicated that the phytobenthos surely take in ammonium in the mat surfaces and the uptake kinetics are largely varied in each lake. Our study suggests that a mechanism of nutrients enclosure inside benthic mats in oligotrophic lakes is caused by viscosity of the mats and uptake by phototrophs.