Variation trend of nitrogen and phosphorus in Lake Caohai, Guizhou Province, China, during 2014–2024

Lake Caohai, a tectonic karst wetland, has been found to be contaminated with elevated nutrient levels. Understanding the long-term dynamics of nitrogen and phosphorus in Lake Caohai is essential for improving water quality. This study examined the vertical distribution of sediment-bound total nitrogen (TN) and total phosphorus (TP), along with water quality trends from 2014 to 2024. The trend of decreasing sediment-bound TN and TP with depth in Lake Caohai confirmed the anthropogenic factors. Excess sediment-bound TN in the upper layers exerts an adverse effect on the aquatic environment. Concurrent increases in waterborne NH 4 + , and TN over the studied period showed the progressive eutrophication in Lake Caohai. Waterborne TN and NH 4 + were slightly higher during the dry period than the abundant period, whereas the lowest water transparency occurred during the abundant period. Nitrogen and phosphorus dynamics in Lake Caohai are attributed to both external nutrient inputs and internal loading from sediments. It is essential to reduce external nutrient inflows from the Caohai watershed while also mitigating internal nutrient release from lake sediments.