城镇快速发展对河流温室气体溶存及扩散通量的影响——以重庆市黑水滩河流域场镇为例

场镇发展是西南山区城镇发展的重要模式,且大部分场镇沿河分布,快速城镇发展给河流水环境及生物地化过程带来了一系列影响,然而其对河流温室气体排放时空格局的影响及机制尚不清楚。选择流域场镇发展特征明显的黑水滩河为研究对象,于2014年9月、12月、2015年3月、6月,对流域内干、支流水体温室气体浓度及扩散通量进行分析,旨在阐明流域场镇式发展下河流温室气体排放时空特征及关键驱动因素。研究结果表明,黑水滩河干、支流水体年均二氧化碳分压(pCO_2)及甲烷(CH_4)、一氧化二氮(N_2O)浓度均处于过饱和状态,是大气温室气体的净排放源;流域内干、支流水体流经不同场镇区前后水体碳、氮、磷及叶绿素a含量均不同程度增加,从上游向下游呈现明显的污染累积;水体溶存pCO_2\\CH_4\\N_2O浓度及扩散通量在不同场镇前后也呈现显著增加的趋势,三种温室气体扩散通量平均增幅分别为25.88%、55.22%、99.64%;河流水体pCO_2与N_2O浓度及通量秋季高于其他季节,CH_4浓度及扩散通量春季最高,秋季次之,夏、冬季最低,温室气体浓度及排放的季节变化主要受温度和降雨格局共同影响。相关分析表明,pCO_2与水温和pH关系密切,而水体CH_4和N_2O浓度与水体碳、氮、磷等生源要素均呈显著的正相关关系,水体CH_4与N_2O浓度对生源要素输入极为敏感,流域场镇发展带来的河流污染负荷的增加可能对水体CH_4与N_2O排放产生明显的激发效应。本研究认为,山区河流流域内沿河串珠状场镇分布对河流水体生源要素及其他理化性质产生累积影响,进而改变了水体温室气体的产生与排放时空格局。

Effects of field towns development on the dissolved and diffusion fluxes of greenhouse gases in Heishuitan River basin, Chongqing

Watershed field town development along the river, an important mode of urban development in mountainous areas in southwest China, has brought a series of environmental problems for river and impacted the riverine biogeochemical process. However, the effect of field towns development on the spatial-temporal pattern of riverine greenhouse gas emissions are not clear. In this study, the Heishuitan river, whose watershed is undergoing rapid town development, was selected to investigate greenhouse gas concentration and diffusion fluxes in the surface water of main stream and its tributaries from September, 2014 to June, 2015. The results showed that annual average of partial pressure of carbon dioxide (pCO₂), methane (CH₄), and nitrous oxide (N₂O) concentrations in the main stream and tributaries were all oversaturated, which indicated that Heishuitan river was the net emission source of atmospheric greenhouse gases. The concentrations of carbon, nitrogen, phosphorus, and chlorophyll a in water increased to different extents before and after it flowed through different towns. This suggests obvious accumulation of pollutants due to the pattern of town distribution in Heishuitan basin. Meanwhile, CO₂, CH₄, and N₂O concentrations and diffusion fluxes from Heishuitan river also showed significant increases before and after different towns with average increase ratio of diffusion fluxes of 25.88%, 55.22%, and 99.64%, respectively. pCO₂ and N₂O concentration were found higher in autumn than in other seasons, while the concentrations and diffusion fluxes of CH₄ was the highest in spring, followed by autumn, the lowest in summer and winter. The seasonal pattern was co-regulated by both water temperature and precipitation pattern. Correlation analysis showed that pCO₂ was closely related to water temperature and pH, while CH₄ and N₂O concentrations were positively correlated with the biological elements such as carbon, nitrogen, and phosphorus, reflecting that the concentration of CH₄ and N₂O in water body of biological elements input was extremely sensitive. The pollution load increase due to the watershed town development may have a significant excitation effect on the CH₄ and N₂O emission from rivers. In this study, the distribution of the beaded field towns along the river in mountainous areas would have cumulative impacts on the river water biogenic element and other physical and chemical properties, thus changing the spatial and temporal pattern of the greenhouse gas generation and emission.