菹草衰亡腐烂对水质持续性影响试验研究

Experimental study over the continuous effects of decaying Potamogeton crispus on water quality

为研究菹草衰亡残体对水质的持续影响,在铺有10 cm厚底泥的A、B、C、D、E 5个实验桶内添加生物量分别为4 kg/m^2、3 kg/m^2、2kg/m^2、0.8 kg/m^2、0 kg/m^2的处于衰老期的菹草,跟踪监测水质变化情况。结果表明:1)试验开始第10～16 d,各实验桶水体TN、TP、COD_(Mn)都达到峰值,溶解氧(DO)达到谷值,随后TN、TP、COD_(Mn)快速下降,45 d后主要水质指标都明显改善,表明菹草衰亡腐烂对水体的影响时间较短;2)试验后期,A桶内的TN、TP明显高于对照,其他桶与对照差异不大,表明在试验条件下,生物量大于3 kg/m^2的菹草残体腐烂分解会对水体产生比较严重的氮磷污染,生物量小于2 kg/m^2时,其死亡残体腐烂分解对水体营养盐增加较少;3)试验后期A、B、C桶的COD_(Mn)仍然超过Ⅳ类水标准,表明有机质降解比较慢;4)试验后期,除对照外,各实验桶的DO小于5.0 mg/L(Ⅳ类水标准)。

The present paper is aimed at introducing its author＇s experimental study over the accumulating effects of decaying Potamogeton crispus on the water quality. As is well known, Potamogeton crispus, being a wild weed, is easy to over-grow in the water bodies, such as in the eutrophic lakes, like Hongze Lake （Jiangsu）, Xuanwu Lake （Nanjing）, Gucheng Lake （Nanjing）, usually prosperous in Spring and early Summer, forming a great primary productivity and decomposing dead slowly. It may lead to endogenous accumulation of nutrient loads and the ＂yellow water＂ effect in many lakes. Let it alone, the decaying weed may result in the secondary pollution to the water bodies. Looking for its remaining effects on the water quality, we have put 4 kg/m^2, 3 kg/m^2, 2 kg/m^2, 0.8 kg/m^2, 0kg/m^2 of Potamogeton crispus in 5 water buckets（ numbered A - E） with 10 cm thick sediments, respectively, and then track-monitoring the changes of the water. The results of our experiments show that： （ 1 ） The concentration of TN, TP, CODMn may all reach its peak whereas the concentration of DO may. reach the valley when the experiment enters the 10-th to 16-th day. And, subsequently, TN, TP, and CODM, may decrease rapidly, with main water quality indexes improved significantly in 45 days, showing decaying Potamogeton crispus had short-time effects on the water quality; （2） The concentration of TN, TP in A proves greater than CK obviously with little difference between B - D and CK at the later stages of the experiment, showing above 3 kg/m^2 of the biomass of the decaying grass would produce serious nitrogen and phosphorous pollution, whereas that below 3 kg/m^2 may have little influence; （3） At later stages of the experiment, the concentration of CODu, in A - C buckets exceeded class IV water standard, showing that the organic ingredients of the weed tends to decompose slowly; （4） At the later stages of experiment, the concentration of DO in A - D buckets turned to be less than 5.0 mg/L （class 1V water standard）. Thus, it can be concluded that the above described facts are likely to offer some reference to the aquatic plants management.