Effects of water hyacinth (Eichhornia crassipes) on release of nitrogen and phosphorus from sediment of Lake Dianchi
水葫芦对滇池底泥氮磷营养盐释放的影响

To evaluate the effects of water hyacinth (Eichhornia crassipes) on release of nitrogen and phosphorus from sediment, a 25-day laboratory experiment was carried out. The sediment was taken from Lake Dianchi and was covered by water with water hyacinth as treatments and by water only as controls. Released nutrients such as ammonia, nitrate and dissolved total nitrogen, orthophosphate from the sediment were compared between treatments and controls. Results showed that dissolved oxygen and pH significantly decreased and orthophosphate significantly increased in treatments compared to controls (P<0.05). During the first two days of the experiment, ammonia and dissolved total nitrogen in treatments were significantly (P<0.05) higher than in controls. However, from the fifth day forward, the results were inversed. The average release rates of nitrogen and phosphorus were calculated based on the concentrations of nitrogen and phosphorus in overlying water and total contents of nitrogen and phosphorus absorbed by water hyacinth. The results showed that water hyacinth accelerated the release rates of nitrogen and phosphorus from the sediment. The release rates of nitrogen and phosphorus released were 5.3~170.2 and 1.5~21.6 times higher in treatments than in controls respectively.