Human land uses enhance sediment denitrification and N<sub>2</sub>O production in Yangtze lakes primarily by influencing lake water quality

Abstract

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.

Within-lake variability and environmental controls of sediment denitrification and associated N2O production in a shallow eutrophic lake

“…The mean net N2O production rate of the sampling sites in the Lake Donghu was 0.32 ng N g -1 h -1 or 157 kg N km -2 year -1 . This value is much greater than the average of 32 Norwegian lakes (68.60 kg N km -2 year -1 ) calculated by McCrackin and Elser (2010), but similar to the value of 20 Yangtze lakes (143 kg N km -2 year -1 ) reported by Liu et al (2015b). It should be noted that N2O may also be produced by nitrification under incomplete anaerobic conditions (Garcı́a-Ruiz et al, 1998), although denitrification is generally recognized as the dominant process for N2O formation.…”

Environmental factors, but not abundance and diversity of nitrifying microorganisms, explain sediment nitrification rates in Yangtze lakes

“…Littoral sites were in general located at water depth less than 2 m, approximately 100-200 m away from the lake shore. 6 At each site, replicate surface sediments were randomly collected within an area about 20 m 2 using a home-made grab sampler and the top 2 cm of sediment was mixed and homogenized to form a composite sample. If submerged vegetation was present in a sampling site, rhizosphere sediments were collected by shaking off sediments that were loosely adhering to the plant roots.…”

“…An insignicant c 2 statistic (P > 0.05) and CFI value > 0.9 indicated that the nal path models provide a reasonable t. 6…”

“…5 High N loading in shallow lakes is generally linked to water eutrophication and several attendant ecological problems, including water quality deterioration, toxic algal blooms, and decline of freshwater biodiversity. 6 The ability and mechanism of shallow lakes to cope with excess N input have attracted much attention in recent decades. [7][8][9] The coupled nitrication-denitrication processes convert ammonium (NH 4 + ) to nitrite (NO 2 À ) and nitrate (NO 3 À )…”

Shifts of the nirS and nirK denitrifiers in different land use types and seasons in the Sanjiang Plain, China

“…Zhao et al found that MC was associated with the denitrifying microbial community. Liu et al reported that MC could regulate denitrification through the influence of oxygen diffusion on microbes directly. Smid et al found that OM could affect denitrification in soil.…”