Climate mediated nitrogen and carbon dynamics in a tropical watershed

Climate variability may impact the biosphere's ability to assimilate and store important elements such as nitrogen and carbon. Here we present biogeochemical evidence from the sediments of a large tropical lake indicating that lake level has varied significantly in response to glacial cycles over the late Pleistocene. These abrupt fluctuations in lake level have been accompanied by remarkable shifts in ecosystem state. During prolonged glacial intervals the lake remained in a stable nitrogen limited state; however, during interglacial intervals nitrogen availability increased by a factor of 3 to 10 resulting in a factor 10 to 20 increase in organic carbon content. A biogeochemical model of the watershed identified changes in surface area to volume as a key determinant of atmospheric nitrogen supply and ultimately carbon assimilation. These findings suggest that morphometric properties may be helpful indicators in predicting the response of aquatic ecosystems to future climate scenarios.