Human land uses enhance sediment denitrification and N₂O production in Yangtze lakes primarily by influencing lake water quality

Abstract. Sediment denitrification in lakes alleviates the effects of eutrophication through the removal of nitrogen to the atmosphere as N₂O and N₂. However, N₂O contributes notably to the greenhouse effect and global warming. Human land uses (e.g. agricultural and urban areas) strongly affect lake water quality and sediment characteristics, which, in turn, may regulate lake sediment denitrification and N₂O production. In this study, we investigated sediment denitrification and N₂O production and their relationships to within-lake variables and watershed land uses in 20 lakes from the Yangtze River basin in China. The results indicated that both lake water quality and sediment characteristics were significantly influenced by watershed land uses. N₂O production rates increased with increasing background denitrification rates. Background denitrification and N₂O production rates were positively related to water nitrogen concentrations but were not significantly correlated with sediment characteristics and plant community structure. A significant positive relationship was observed between background denitrification rate and percentage of human-dominated land uses (HDL) in watersheds. Structural equation modelling revealed that the indirect effects of HDL on sediment denitrification and N₂O production in Yangtze lakes were mediated primarily through lake water quality. Our findings also suggest that although sediments in Yangtze lakes can remove large quantities of nitrogen through denitrification, they may also be an important source of N₂O, especially in lakes with high nitrogen content.