River input and algae growth together determine the composition of dissolved organic matter in the large Lake Taihu

Dissolved organic matter (DOM) is ubiquitous in lakes and is essential for maintaining lake ecosystem health, and river input and algae growth are important DOM sources for eutrophic lakes impacted by rainfalls and human activities. Based on the simultaneous monitoring data of the typical eutrophic Lake Taihu and its surrounding rivers, China, this study investigated the combined effects of both processes on the spatiotemporal variations in DOM composition. The results indicated that river input appeared to have important influences. The northwest rivers appeared to contribute a substantial amount of terrigenous humus and tyrosine, resulting in elevated dissolved organic carbon (DOC) concentration in the western Lake Taihu (5.39 ± 1.86 mg/L). However, heavy rainfalls in summer diluted DOM contents in the Tiaoxi River, leading to low DOC values in the southern Lake Taihu (6.26 ± 0.72 mg/L). In addition, algae growth in lake might produce a notable quantity of endogenous tryptophan. Namely, river input and algae growth should jointly drive DOM dynamics in the Lake Taihu and cause DOC concentration to reach a peak of 7.45 ± 1.44 mg/L in summer. These findings highlight the need to consider the joint influence of river input and algae growth so as to better monitor and manage lake organic pollution.