Optical characteristics of dissolved organic matter in relation to phytoplankton in Lake Erhai, China

Abstract

Dissolved organic matter (DOM), as the primary form of organic carbon in lakes, is crucial for the lake carbon cycling. As an important component of lake ecosystems, phytoplankton plays a crucial role in carbon fixation. However, we are not yet clear about the contribution of phytoplankton composition to DOM. To clarify this issue, we conducted we conducted continuous monitoring for 6 months in Lake Erhai, a plateau lake in China. Through quantitative detection of phytoplankton and spectral characteristic analysis, four fluorescence components were identified: tryptophan-like (C1), tyrosine-like (C2), fulvic-like (C3), and humic-like (C4). The Fluorescence Index (FI) ranged from 1.70 to 2.54, and the Biogenic Index (BIX) was above 0.8, indicating the DOM in Lake Erhai’s overlying water was predominantly autochthonous. Cyanophyta prevailed in September and November, while Chlorophyta dominated in other months. Phytoplankton diversity was significantly related to DOM concentration that may be related to the difference in the DOM contribution of different phytoplankton. The effect of phytoplankton biomass on C3 and C4 was prominent. Whereas, phytoplankton did not stimulate C1 and C2 significantly, indicating that protein-like may originate from terrestrial input and microbial activity. The composition of phytoplankton significantly affects the DOM composition in Lake Erhai. Therefore, the autochthonous DOM production by phytoplankton warrants further consideration in plateau lake systems.