Human land uses enhance sediment denitrification and Nsub2/subO production in Yangtze lakes primarily by influencing lake water quality

摘要

Sediment denitrification in lakes alleviates the effects of eutrophicationthrough the removal of nitrogen to the atmosphere as N₂O and N₂.However, N₂O contributes notably to the greenhouse effect and globalwarming. Human land uses (e.g. agricultural and urban areas) stronglyaffect lake water quality and sediment characteristics, which, in turn, mayregulate lake sediment denitrification and N₂O production. In thisstudy, we investigated sediment denitrification and N₂O production andtheir relationships to within-lake variables and watershed land uses in 20lakes from the Yangtze River basin in China. The results indicated that bothlake water quality and sediment characteristics were significantlyinfluenced by watershed land uses. N₂O production rates increased withincreasing background denitrification rates. Background denitrification andN₂O production rates were positively related to water nitrogenconcentrations but were not significantly correlated with sedimentcharacteristics and plant community structure. A significant positiverelationship was observed between background denitrification rate andpercentage of human-dominated land uses (HDL) in watersheds. Structuralequation modelling revealed that the indirect effects of HDL on sedimentdenitrification and N₂O production in Yangtze lakes were mediatedprimarily through lake water quality. Our findings also suggest thatalthough sediments in Yangtze lakes can remove large quantities of nitrogenthrough denitrification, they may also be an important source of N₂O,especially in lakes with high nitrogen content.