[Effects of sodium hypochlorite on structure and function of pond microcosms]

To study the influence of sodium hypochlorite on destruction and restoration of simulated pond ecosystems.

Six pond microcosms were established to simulate aquatic ecosystems. 0, 1, 2.5, 5.0, 10.0 and 20.0 mg/L of sodium hypochlorite were put in these simulated pond microcosms every 24 h for 13 days and followed by observation for 10 days. The values of chlorine residual, total bacteria count, chlorophyll-a and total productivity were detected regularly.

Chlorine residual increased continuously with the increase of doses and time course. Content of chlorophyll-a, total productivity negatively correlated with dose of sodium hypochlorite. 1.0 mg/L and 2.5 mg/L of sodium hypochlorite promoted the growth of bacteria, but 5.0 mg/L, 10.0 mg/L and 20.00 mg/L of sodium hypochlorite could kill bacteria effectively. Under low doses of sodium hypochlorite (1.0, 2.5 and 5.0 mg/L), there were no influence on microcosms' restoration, but the high doses (10.0 mg/L and 20.0 mg/L) could severely damage the microcosms.

According to the tendency of chlorophyll-a and total productivity, structure and function of every pond microcosm could be changed by sodium hypochlorite in this test condition, the influence was reversible under the doses of 1.0, 2.5 and 5.0 mg/L, but microcosms could not be restored under the doses of 10.0 mg/L and 20.0 mg/L.