Author: Margot  Sepp,  Researcher (Estonian University of Life Sciences)

Description:
Dissolved organic matter (DOM) plays an important role in the biogeochemistry of lake ecosystems. The main sources of DOM are allochthonous inputs from the catchment and autochthonous, in-lake production. We investigated variation in DOM quantity and quality among and within 11 Estonian lakes for five years (2015-2019) relative to environmental conditions (e.g., precipitation) and internal processes (e.g., primary production). DOM quantity was measured as dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM), the latter representing catchment-derived DOM. The quality of DOM (i.e., molecular weight and aromaticity) was characterized using different spectral parameters based on absorbance and fluorescence measurements. DOM quantity and quality were diverse in the studied lakes; e.g., DOC ranged from 3.9 to 53.0 mg/L and varied temporally within the lakes. DOC and CDOM were strongly correlated (Spearman’s r = 0.95, n = 220), indicating that DOM originated predominantly from the catchment. Temporal variation was overall similar in several lakes, illustrating the primary role of external drivers. However, in oligotrophic lakes with low inputs from the catchment or highly productive lakes, DOM quantity was driven by internal processing; DOC increased with the relative contribution of autochthonous DOM (supported by a concurrent increase in chlorophyll a). Understanding the relative roles of environmental conditions and internal processes driving DOM variation will help predict responses of lake DOM to climate change and effects on the global carbon cycle.

Category: Scientific Program Abstract > Special Session > CS14 Dissolved organic matter - DOC, DON, DOP, fDOM, cDOM