[Temporal and spatial variation of water nutrient level after exogenous nutrient input].

In order to study the spatial and temporal variations of nitrogen (N) and phosphorous (P) nutrition in artificial wetlands after a single exogenous nutrient input, 6 mosaic communities of 7 plant species were set up in a cement channel in the greenhouse. After the addition of N and P nutritional solutions, the concentrations of dissolved total nitrogen (DTN), dissolved total phosphorous (DTP), ammonia nitrogen (NH4(+)-N), nitrate nitrogen (NO3(-) -N) and nitrite nitrogen (NO2(-) -N) in the surface, middle, and bottom layers of the bulk water were determined regularly within 22 days. The results show that: (1) the water depth and measuring date have significant effects on nutritional contents while the type of plant communities have no such an influence; (2) the diffusion of nutrient from surface to the middle water layers is relatively slow, which costs 6 days under the current experimental condition; (3) in the bottom water layer, nutritional concentrations had no significant changes except for NO2-N, thus the exogenous nutrient input mainly affects the nutrient contents of surface and middle-level bulk water; (4) DTP and NH4(+) -N contents gradually decline to similar levels that before the nutritional input event until the end of experimental period, though DTN and NO3(-) -N content decrease much more slowly; (5) the fact that NO2(-) -N contents rise in water layers of all depths demonstrates that nitrification and denitrification in the process of N circulation are enhanced. It is concluded that exogenous nutrient inputs not only harm aquatic ecosystems but also directly threat human health.