Human land uses enhance sediment denitrification and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O production in Yangtze lakes primarily by influencing lake water quality

W. Liu,Z. Xiong,Z. Wang,L. Yao,G. Liu

doi:10.5194/bg-12-6059-2015

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.

Highlights

As a global environmental issue, land use change has numerous consequences, ranging from changes in global climate to local water quality (Foley et al, 2005)
The highest total carbon (TC) and Total nitrogen (TN) concentrations in water were found in Lake Makouhu (31.40 mg L−1) and Lake Yiaihu (2.87 mg L−1), respectively (Table S2)
Among water quality and sediment characteristics, dissolved oxygen (DO), NO−3, NH+4, TN and Sediment total nitrogen (STN) were significantly correlated with the percentage of human-dominated land uses (HDL) (Table 2)

Summary

Introduction

As a global environmental issue, land use change has numerous consequences, ranging from changes in global climate to local water quality (Foley et al, 2005). Conversion of natural land use (e.g., forests and wetlands) to human land use (e.g., cropland and urban areas) releases large quantities of pollutants, including nitrogen, and has widespread effects on biodiversity and ecological function of lakes, rivers and other water bodies (Müller et al, 1998). Lake water quality has deteriorated worldwide due to increasing point- and nonpointsource pollution in watersheds (Nielsen et al, 2012; Baron et al, 2013). The percentage of Chinese lakes classified as eutrophic has rapidly increased from 41 % in 1980 to 85 % in 2005 (Liu et al, 2010). The effects of watershed land uses on lake water quality are well-documented (Liu et al, 2012; Nielsen et al, 2012). Relatively few studies have reported the relationship between watershed land uses and lake sediment characteristics, and their results are inconsistent (Müller et al, 1998; Bruesewitz et al, 2011)

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