†U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado 80526, United States.
‡U.S. Environmental Protection Agency, National Exposure Research Laboratory, Ecological Exposure Research Division, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, United States.
Environ Sci Technol. 2015 Jul 7;49(13):7762-9. doi: 10.1021/acs.est.5b00911. Epub 2015 Jun 10.
Opposing hypotheses posit that increasing primary productivity should result in either greater or lesser contaminant accumulation in stream food webs. We conducted an experiment to evaluate primary productivity effects on MeHg accumulation in stream consumers. We varied light for 16 artificial streams creating a productivity gradient (oxygen production =0.048-0.71 mg O2 L(-1) d(-1)) among streams. Two-level food webs were established consisting of phytoplankton/filter feeding clam, periphyton/grazing snail, and leaves/shredding amphipod (Hyalella azteca). Phytoplankton and periphyton biomass, along with MeHg removal from the water column, increased significantly with productivity, but MeHg concentrations in these primary producers declined. Methylmercury concentrations in clams and snails also declined with productivity, and consumer concentrations were strongly correlated with MeHg concentrations in primary producers. Heterotroph biomass on leaves, MeHg in leaves, and MeHg in Hyalella were unrelated to stream productivity. Our results support the hypothesis that contaminant bioaccumulation declines with stream primary production via the mechanism of bloom dilution (MeHg burden per cell decreases in algal blooms), extending patterns of contaminant accumulation documented in lakes to lotic systems.
相反的假设认为,增加初级生产力应该导致溪流食物网中污染物的积累增加或减少。我们进行了一项实验,以评估初级生产力对溪流消费者中 MeHg 积累的影响。我们通过在 16 条人工溪流中改变光照,在溪流之间创造了一个生产力梯度(氧气产生量为 0.048-0.71mg O2 L(-1) d(-1))。建立了由浮游植物/滤食蛤、周丛生物/食草蜗牛和叶子/碎甲螨(Hyalella azteca)组成的两级食物网。浮游植物和周丛生物生物量以及水柱中 MeHg 的去除量随生产力显著增加,但这些初级生产者中的 MeHg 浓度下降。蛤和蜗牛中的 MeHg 浓度也随生产力下降,消费者浓度与初级生产者中的 MeHg 浓度密切相关。叶片上的异养生物量、叶片中的 MeHg 以及 Hyalella 中的 MeHg 与溪流生产力无关。我们的结果支持这样一种假设,即污染物的生物积累随溪流初级生产力的增加而减少,这是通过浮游生物繁盛(藻类繁盛时每个细胞中的 MeHg 负担减少)的机制,将污染物积累的模式扩展到湖泊到流水系统。