典型农业流域池塘甲烷浓度及扩散排放特征

Dissolved methane concentration and diffusion emission characteristics of ponds in a typical agricultural catchment

为探究农业流域池塘水体CH_(4)动态变化特征,以巢湖北岸典型农业流域——烔炀河流域为研究对象,选取4种不同景观池塘(排污塘、灌溉塘、养殖塘和自然塘),基于为期近1 a的逐月野外调查,探明农业流域不同景观池塘甲烷溶存浓度及其排放特征。结果表明:受人为活动干扰较低的自然塘CH_(4)浓度([(0.41±0.29)μmol·L^(-1)]及其扩散排放通量([(0.54±0.49)mmol·m^(-2)·d^(-1)]相对较低,但农业活动以及生活污水排放等致使流域内养殖塘、排污塘和灌溉塘成为大气CH_(4)的热点排放区域,其扩散排放通量分别是自然塘的6.0、3.0倍和2.2倍。不同景观池塘CH_(4)排放均表现出明显的时间变化,但因受外源碳氮等生源要素累积以及人为活动干扰等影响,其CH_(4)变化特征有所不同。统计分析表明该流域池塘CH_(4)变化总体上受水温、溶解氧和污染负荷(有机质和营养盐等)等因素驱动。综上,烔炀河农村流域池塘水体是大气CH_(4)的显著排放源,年均CH_(4)溶存浓度和扩散排放通量分别为(1.30±0.78)μmol·L^(-1)和(1.64±1.50)mmol·m^(-2)·d^(-1),其中养殖塘具有较高CH_(4)扩散排放通量,在未来研究中需要重点关注。

This study investigated the dynamic variability of CH_(4) in four ponds draining distinct landscapes(sewage pond,irrigation pond,aquaculture pond,and natural pond)in the Tongyang River catchment,a typical agricultural catchment,based on field measurements over the period of 1 a.Results showed that these ponds were hot spots of atmospheric CH_(4) due to agricultural activities and domestic sewage discharge.For comparison,the estimated diffusive CH_(4) emissions in the aquaculture,sewage,and irrigation ponds were 6.0,3.0 times,and 2.2 times higher,respectively,than natural ponds[(0.54±0.49)mmol·m^(-2)·d^(-1)]with less human activity.The CH_(4) varied temporally in the four ponds;however,factors influencing the CH_(4) variability varied between ponds.Generally,the temporal variability of CH_(4) was associated with water temperature,dissolved oxygen concentration,and pollutant loadings(e.g.,organic matter and nutrients).Overall,the mean dissolved CH_(4) concentration in ponds of the agricultural catchment was(1.30±0.78)μmol·L^(-1),and the estimated diffusive CH_(4) emission was(1.64±1.50)mmol·m^(-2)·d^(-1),suggesting that the ponds were a significant source of atmospheric CH_(4).Notably,peak CH_(4) emissions occurred in aquaculture ponds,which should be further investigated in future research.