Roles of Terrestrial Carbon Subsidies to Aquatic Community Metabolism in Mountain Lake Ecosystems

Abstract

Terrestrial–aquatic linkages of Japanese mountain lake ecosystems were examined to identify terrestrial carbon input into mountain lakes and the importance of the allochthonous carbon for the ecosystem metabolism of aquatic food webs therein. Stable carbon isotope analyses revealed that the flux of terrestrial dissolved organic matter from the surrounding catchments was relatively larger in smaller lakes with higher drainage ratios and tended to predominate carbon cycling in the epilimnetic water of such lakes. However, the metabolic balance of epilimnetic lake waters was net autotrophic or approximately in balance between gross primary production (GPP) and community respiration (CR) rates, suggesting that allochthonous organic matter generally subsidizes benthic and hypolimnetic communities. Empirical models established based on these observed GPP and CR values predict that climate change may increase carbon flows from both autochthonous and allochthonous pathways in epilimnetic communities of unproductive mountain lakes, directly through the functional dependence of community metabolism on the projected temperature rise and indirectly through the increased supply of terrestrial organic matter.