Characterization of the trophic transfer and fate of methylmercury in the food web of Zhalong Wetland, Northeastern China.

The transfer and fate of methylmercury (MeHg) in typical components, such as sediment, sediment-inhabiting animals, pelagic fish, and three large waterfowls, namely, red-crowned crane (Grus japonensis), mallard (Anas platyrhynchos), and oriental stork (Ciconia boyciana), of the ecosystem in China's Zhalong Wetland were examined using equivalence-based mass balance model. The biomagnification degree of MeHg increased on the species at the high trophic level of the system. Hence, elevated MeHg concentration (3.2 μg g-1, dry weight) was detected in the endangered G. japonensis. The accumulation of the organometal generally followed the decreasing order of oriental stork (carnivore) > mallard (omnivore) > red-crowned crane (omnivore). The predicted results of MeHg at each node of the food web were generally in accordance with the measured values (F = 0.09, P = 0.78), implying that the model is suitable for the prediction of MeHg fate in the inland aquatic system. According to the model, the respiration for the species at low trophic strata was the key input source of MeHg, but ingestion played an important role for MeHg intake in the species at the high trophic position in the food web. Metabolism was a crucial pathway of MeHg loss for the top predators in the ecosystem.