Dissolved organic carbon dynamics in shallow lakes along a precipitation gradient in Patagonia

MANSILLA FERRO, C.; GARCIA, P.E.; DIÉGUEZ, M.C.

Grand Rapids

Congreso; Joint Aquatic Sciences Meeting 2022 (JASM 2022); 2022

Ecological Society of America

The lateral transport of terrestrial carbon (C), mostly as dissolved organic C (DOC), subsidizes aquatic ecosystems. Changes in precipitation and temperature affect profoundly the terrestrial-aquatic linkages, impacting on biogeochemical pathways. Natural climate gradients allow assessing mechanisms of abiotic control on ecosystem processes, such as the effects of temperature and precipitation on biogeochemical cycles. Here, we studied DOC dynamics in four shallow (Zmax < 20 m) lakes of Andean North Patagonia, located in a bioclimatic gradient characterized by a sharp west to east decrease in precipitation (3000 to 800 mm y-1) and vegetation/soil complexity (forest to grassland) and increasing temperature. Lakes were sampled monthly, assessing POC, DOC, TN and TP, Chlorophyll a, pH, conductivity, etc. Multivariate analysis showed that terrigenous inputs (high humic content and large molecular weight DOC) prevailed in the lakes along the wetter part of the transect, indicating a high hydrological connectivity with the landscape. In all lakes, terrigenous signatures were higher during the spring due to snowmelt and higher precipitation, whereas autochthonous signatures increased during summer. The Climate Forcing Optical Index (CFOI), indicated a larger contribution of terrestrially derived DOM and lower degradation impact in the two shallower lakes (< 6 m) compared to the deeper lakes (< 20 m), which in turn displayed higher internal production and degradation. Our results indicated that inputs of terrestrial C prevail in lake C pools in spring due to increased runoff, and that warming towards summer controls the internal C processing and its incorporation to aquatic production.