城市景观湖泊不同时间尺度CH4通量特征及影响因素分析——以南京市莫愁湖为例

Characterization of CH 4 fluxes in urban landscape lakes at different time scales and analysis of influencing factors-A case of Lake Mochou in Nanjing City

城市景观湖泊对温室气体的收支发挥着重要作用。本文以南京市莫愁湖为研究对象,采用静态箱—温室气体分析仪法实时监测湖泊水—气界面CH_(4)通量,分析湖泊主要温室气体CH_(4)在日尺度和季节尺度上因冒泡和扩散排放方式不同对其通量的影响,探究影响湖泊CH_(4)通量的因素。结果表明:(1)在日尺度上,四季24 h内CH_(4)均呈排放状态,受白天冒泡影响,四季CH_(4)总通量均存在白天高于夜间的日变化特征。(2)在季节尺度上,莫愁湖CH_(4)排放通量呈现显著的时空异质性,受冒泡通量的影响夏季CH_(4)通量明显高于春、秋、冬三季;B区的CH_(4)总通量(6.04 nmol/(m^(2)·s))显著高于A区(3.82 nmol/(m^(2)·s)),水体的营养化程度和离岸距离是空间变化的主要影响因素。A、B两区CH_(4)排放夏季以冒泡排放为主,春、秋、冬以扩散排放为主。(3)在日尺度上,CH_(4)通量受气温、水温、辐射和风速等气象要素影响,与水质参数间的关系不显著;在季节尺度上,CH_(4)通量与温度(气温、水温)、水体营养盐水平、叶绿素a浓度及富营养化程度的时间变化相一致,也随着水体透明度、pH和氧化还原电位的减小而呈增加的趋势。本研究为准确估算城市湖泊CH_(4)排放量提供重要的数据基础。

Urban lakes play an important role in the balance of greenhouse gases.In this paper,we took Lake Mochou in Nanjing as the research object,and used the static box-greenhouse gas analyzer method to monitor the CH_(4)flux at the water-gas interface of the lake in real time,to analyze the influence of CH_(4),the main greenhouse gas of the lake,on its flux at the daily and seasonal scales due to the different emission modes of bubbling and diffusion,and to explore the factors influencing the fluxes of CH_(4)in the lake.The results showed that:(1)on the daily scale,CH_(4)was emitted during 24h in all seasons,and the total CH_(4)fluxes in all seasons were influenced by bubbling during the daytime,which was higher than that in the nighttime.(2)On the seasonal scale,the CH_(4)emission fluxes in Lake Mochou showed significant spatial and temporal heterogeneity,and the CH_(4)fluxes in summer were significantly higher than those in spring,autumn and winter due to the bubbling fluxes;the total CH_(4)fluxes in area B(6.04 nmol/(m^(2)·s))were significantly higher than those in area A(3.82 nmol/(m^(2)·s)),and the nutrient level of the water body and the distance to the shoreline were the main factors for the spatial variations.CH_(4)emissions in A and B were dominated by bubbling emissions in summer and diffuse emissions in spring,autumn and winter.(3)On the daily scale,CH_(4)fluxes were influenced by meteorological elements such as air temperature,water temperature,radiation and wind speed,and the relationship with water quality parameters was not significant;on the seasonal scale,CH_(4)fluxes were consistent with temporal changes in temperature(air temperature and water temperature),nutrient levels in the water column,chlorophyll-a content and the degree of eutrophication,and also tended to increase with decreases in water clarity,pH,and redox potential.This study provides an important database for accurate estimation of CH_(4)emissions from urban lakes.