Rainfall and drainage basin shape strongly control temporal and spatial variation of dissolved organic matter in a tropical lake.

Dissolved organic matter (DOM) is a central driver of many processes in aquatic environments. Here, we address the issue of spatial and temporal variations in DOM quantity and quality in a deep tropical lake (Brazil). We measure DOC, Chl-a, suspended solids, nutrients and CDOM metrics in surface water samples taken from 21 sampling sites during six campaigns, and we quantify their links with water depth and rainfall estimates. Temporal effects explain between 74.5 and 94.5% of the variance in DOC, SUVA254, aCDOM440, and Chl-a, and all those parameters were influenced by rainfall. In contrast, spatial variations affect more S275-295 and aCDOM254. The contributing drainage area varies spatially in morphology and geometry, and each portion affects a specific part of the lake, resulting in a spatial variation in DOM quantity and quality. Our findings demonstrate the importance of the input of allochthonous DOM (which depends on seasonal rainfall and drainage area shape) to DOM dynamics in a tropical lake. The study area is receiving lower rates of precipitation in recent times, and our results suggest that this may alter the seasonal patterns of input of DOM and nutrients in the lake, with possible impacts on water quality, aquatic biota and ecosystem functioning. [ABSTRACT FROM AUTHOR]