Abstract: To explore the spatiotemporal distribution and variation characteristics of different forms of nitrogen in karst wetland of Caohai, Guizhou Province, we collected surface water samples in wet and dry seasons using a grid distribution method, and measured the concentrations of dissolved nitrogen with different forms. The spatial and temporal distribution of the different nitrogen forms were analyzed by using ArcGIS statistical module. The correlation between various forms of nitrogen and environmental factors was analyzed. The results showed that the average concentrations of total nitrogen (TN) in Caohai were (0.96±0.52) mg·L^-1 in the wet season and (0.90±0.71) mg·L^-1 in the dry season, with higher concentrations of TN in the wet period. Moreover, inorganic nitrogen was predominant in the wet period. The sum of NH₄⁺-N and NO₃^--N accounted for 54% of TN, with an average concentration of (0.14±0.08) and (0.38±0.56) mg·L^-1, respectively. The high values of these two forms of nitrogen were distributed in the west area, which was mainly affected by external import. In the dry season, organic nitrogen was the main form. The dissolved organic nitrogen accounted for 49% of TN, with an average concentration of (0.44±0.26) mg L^-1. Furthermore, the high value area appeared in the south area, as the water supply of Caohai decreased in the dry season, coupled with the decline of aquatic organisms and nitrogen release in sediments, which contributed to the release and transformation of nitrogen in water body. Therefore, the seasonal variation of nitrogen forms in Caohai Lake was mainly affected by water environmental changes, exogenous nitrogen input, and endogenous nitrogen release. Pollution control in three rivers entering the lake in Western Caohai should be strengthened in the wet season, while nitrogen release in lake sediments should be controlled in the dry season, to effectively reduce nitrogen concentration in water body of Caohai.

Key words: Caohai Lake, karst wetland, nitrogen form, spatiotemporal distribution, environmental factor.