东平湖菹草腐烂分解及其对水环境的影响

于2011年6月-7月在现场采用网袋法研究了东平湖沉水植物菹草的分解失重和营养元素的变化动态.结果表明,菹草在0～14d腐烂分解较快,40 d可分解约80％的生物量,年残留率为5.0％,与一次指数模型相比,二次指数模型Wt/W0 =0.785e-0.386t +0.215e-0.004t(R2=0.876)能更好的描述菹草分解失重动态.菹草残留物中各营养元素的损失与干重衰减不同步,C、N、S含量在1～20 d内表现为上升,20～30 d显著下降,30～40 d略有增加但变化较小;P含量在1～6 d显著下降,随后呈缓慢上升趋势.菹草各营养元素的累积释放率变化规律基本一致,均在14 d和25 d达到峰值,在腐烂初期(0～8d)表现为P＞S＞C＞N,8d后(10～40 d)表现为P＞C＞S＞N.各营养元素的释放主要集中在菹草腐烂分解的前期(0～ 14 d),初步估算东平湖内该期间C、N、S、P的释放量约为12510 t、1187 t、147 t和235 t,相当于水中C、N、S、P分别增加约29.9、2.84、0.35、0.56 mg·L-1,易造成水体的“二次污染”.东平湖菹草年残留量约为2090t(干重),约占东平湖沉积通量的0.6％,对湖泊的填平作用较小.

Decomposition of Potamogeton crispus and its effect on the aquatic environment of Dongping Lake

The mass loss of Potamogeton crispus during 40 days of its decomposition and the dynamics of nutrient elements (C, N, S and P) in the litter were studied from June to July in 2011 by litterbag method. The results showed that Potamogeton crispus decomposed rapidly in first 14 days. About 80% of the biomass (dry weight) was lost after 40 days and 95% after 365 days. Compared with the single exponential model W_t/W₀=e^-0.157t (R²=0.402), the double exponential model W_t/W₀=0.785e^-0.386t+0.215e^-0.004t (R²=0.876) could describe the mass loss more accurately. The loss of the nutrient elements in litter was not synchronized with dry mass losing. The content of C, N and S in litter generally increased during the first 20 days, then decreased obviously from the 20th day to 30th day and then increased slowly from the 30th day to 40th day. The content of P in litter reduced by 73.3% in the first 6 days and then increased very slowly. The accumulative release rates (ARR) of C, N, S and P had a similar change, and had two peaks in the 14th day and 25th day, respectively. The values of ARR were in the order of P>S>C>N in the initial stage of decomposition (0~8 days), and P>C>S>N on 10~40 days. According to the change of ARR, it could be inferred that the release of nutrient elements was mainly occurred in the early period (0~14 days) of the decomposition. The total release amount of C, N, S and P in this stage (0~14 days) was about 12510 t, 1187 t, 147 t and 235 t, respectively, which was equivalent to the increase of 29.9 mg·L^-1 (C), 2.84 mg·L^-1 (N), 0.35 mg·L^-1 (S) and 0.56 mg·L^-1 (P) in the overlying water. This could cause the secondary pollution of water body. The annual residual amount of Potamogeton crispus was about 2090t (dry weight), and it only accounted for 0.6% of annual depositive flux of Dongping Lake, indicating less impact on sedimentary of Dongping Lake.