Abstract: Evaluating eutrophication in lake wetland and seasonal and spatial change of interception function is important for assessing lake water quality, analyzing pollution sources, reducing lake eutrophication, and facilitating wetland sustainability. Here, we measured the concentrations of total phosphorus (TP) and total nitrogen (TN) in 32 water samples respectively collected in April (the end of dry season) and October (the end of rainy season) 2019 from Xihu wetland landscapes in Dali, with criteria of retention capability and eutrophication composite index (PI). We evaluated the eutrophication level and retention effect. The results showed that the concentrations of TP and TN in farmland water were the highest among all kinds of water. The eutrophication level of wetland was higher in dry season than that in rainy season, which was the highest in farmland water (PI=3.45) among all the wetland types. Furthermore, farmland area had the highest level of landscape division (PI=3.35). Agricultural cultivation was a major cause of eutrophication in this region. The interception amount of TP and TN in lakeside wetlands was the highest (0.04 vs. 1.38 mg·L^-1), implying an obvious purification function. Due to the large inputs of phosphorus and nitrogen and the limited elevational variation, the retention effect on TP and TN was less effective, which thus caused the eutrophication of Dali Xihu Lake. Our results provide a reference for the control of eutrophication in Dali Xihu Lake wetlands and ecological protection to Erhai Lake.

Key words: Dali Xihu Lake, total phosphorus, total nitrogen, eutrophication, water quality evaluation, retention.