Distribution and source of nutrients and dissolved organic matter in the Dagang river sediments in southeast Hubei, China

Inflowing rivers input many pollutants into lakes, affecting their water quality and ecological health. The contents of total nitrogen (TN), total phosphorus (TP) and organic matter (OM) in the Dagang river, the largest inflowing river of Daye Lake, were measured in 2019 to determine the sediment pollution status. The sediment pollution was evaluated to provide information for pollution source control of the Dagang river and Daye Lake basin. The results showed that: (1) The average TN, TP and OM contents in the Dagang river sediments were 1323.72 mg/kg, 1378.65 mg/kg and 7.20%, respectively. (2) The comprehensive pollution index of the Dagang river was 3.64–4.42, indicating severe pollution at all sampling points. All sites had organic pollution except for DG5 and DG6. (3) The source of the dissolved OM (DOM) was exogenous and endogenous, which FI and BIX were 1.58–1.70 and 0.7–1.51, respectively. The characteristics of endogenous pollution are more obvious. (4) TN was significantly (p < 0.05) and positively correlated with the TP (r = 0.72) and OM (r = 0.87), indicating similar sources of nitrogen (N) and phosphorus (P). N may have been derived from organic N components in the OM. Targeted measures should be implemented to control the nutrient input and reduce nutrient pollution, and the focus should be on OM pollution sources.