Purpose

The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes.

Materials and methods

Greenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis.

Results and discussion

Sewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO₂ diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH₄ and N₂O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO₂, CH₄ and N₂O diffusive fluxes at the sewage-draining river sediment–water interface were − 123.26 ± 233.78 μmol m⁻² h⁻¹, 1.88 ± 6.89 μmol m⁻² h⁻¹ and 1505.03 ± 2388.46 nmol m⁻² h⁻¹, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N₂O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO₂ and the source of CH₄ and N₂O. There were positive correlations among the CO₂, CH₄ and N₂O diffusive fluxes. The main influencing factor for CO₂ and N₂O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH₄ diffusive fluxes were the Eh of the sediment and the NH₄⁺-N of the overlying water.

Conclusions

River sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.

中文翻译：

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排污河底沙-水界面的温室气体扩散通量

目的

这项研究的目的是分析排污河和天然河流的沉积物-水界面处温室气体扩散通量的时空变化，并研究造成温室气体扩散通量变化的因素。

材料和方法

通过实验室培养实验，研究了天津市（海河流域）河流在沉积物-水界面的温室气体扩散通量，时间分别为2014年7月和10月以及2015年1月和2015年4月。通过Spearman相关分析和多元逐步回归分析，评估了环境变量对温室气体扩散通量的影响。

结果和讨论

与自然河流相比，排污河受到人类排污的污染更为严重。沉积物-水界面的温室气体扩散通量表现出明显的时空变化。CO ₂扩散通量的平均绝对值随春季>冬季>秋季>夏季而季节性变化，而CH ₄和N ₂ O扩散通量的平均绝对值在夏季和冬季均较高，在秋季和冬季均较低。弹簧。的CO的年平均值₂，CH ₄和N _2个O不连到污水排水河流沉积物-水界面扩散通量分别为- 123.26±233.78微摩尔米^-2  ħ ^-1，1.88±6.89微摩尔米⁻²  h ^-1和1505.03±2388.46 nmol m ^-2  h ^-1，分别是天然河道沉积物-水界面的1.22、4.37和134.50倍。排污河和天然河中N ₂ O扩散通量的空间变化最为明显。通常，河流污染越严重，温室气体的扩散通量就越大。平均全年，河流沉积物是CO的水槽₂和CH的源极₄和N ₂ O.有所述CO之间的正相关₂，CH ₄和N ₂O扩散通量。CO ₂和N ₂ O扩散通量的主要影响因素是上覆水的水温。但是，CH ₄扩散通量的关键因素是沉积物的Eh和上覆水的NH ₄ ⁺ -N。

结论

河流沉积物可以是温室气体的汇，也可以是温室气体的来源，它们在不同的污染水平和不同的季节而变化。人的污水排放极大地影响了城市河流的碳和氮循环。