Dynamics of nutrient and heavy metai release and environmental effect during the decomposition of Potamogeton crispus Linn in Dongping Lake
Dongping Lake is an important reservoir on the eastern route of the South-to-North Water Diversion Project and is a significant water source for the West-to-East Water Transfer Project in Shandong Province.Potamogeton crispus Linn.,the dominant submerged plant in Dongping Lake,plays a crucial role in aquatic ecosystems.To reveal the dynamic changes in nutrient elements(C,N,and P)and heavy metals(Hg,As,Cd,Cu,Cr,and Zn)in the litter,a 170-day decomposition experiment was conducted in situ using the litterbag method.The dynamic release/accumulation of nutrient elements and heavy metals was analyzed,and their environmental effects were assessed using the element accumulation index(AI).The results showed that the residual ratio of dry mass during the decomposition of P.crispus could be simulated using the double exponential model,Wt/W0=0.474e-0081t+0.526e-0001t(R2=0.889),and P.crispus decomposed rapidly during the initial 32 days.The C content in the litter increased slightly from days 0-32 and then decreased,whereas the N content decreased slightly from days 0-4 and then increased significantly.The P content decreased significantly from days 0-4 and then slowly increased,and the content of all heavy metals in the litter increased significantly.During the decomposition of P.crispus C,N,and P were released into the water,whereas heavy metals,except Zn,were enriched in the litter.The Al values of C,N,and P were significantly and positively correlated with the residual ratio(P＜0.01),whereas no significant correlations were found between the Al values of heavy metals and the residual ratio(P＞0.05).Adsorption and microbial activity may be the main causes of heavy metal accumulation in litter.These results indicate that the decomposition of P.crispus in Dongping Lake increases the risk of water eutrophication and endogenous heavy metal pollution.
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