降雨事件对不同流域背景河流DOM组成及入海通量的影响

Impacts of storm event on DOM composition and flux in two Jiulong Tributaries with different watershed features

通过调查2014年7月"麦德姆"台风影响期间福建九龙江北溪(流域以林地为主)和西溪(农业流域和城市背景)下游定点站DOM的时间序列,测定样品的DOC含量及其吸收光谱和三维荧光光谱,以评估不同流域背景对河流DOM动力学降雨响应的差异性,并为流域-河口系统的一体化管理提供重要参考。降雨期间,两条河流DOC浓度、吸收系数aCDOM(350)以及总荧光强度均随径流量升高而增大,并在水位下降期持续增加,且西溪增加量明显高于北溪,说明受人类活动扰动大的流域河流有机质对暴雨事件的响应更为灵敏;北溪和西溪的SUVA254分别显示出增大和减小的相反变化趋势,表明林地背景的流域主要冲刷芳香度高的DOM到河流,农业和城市背景则相反;降雨期西溪对九龙江DOM入海通量的贡献率高于北溪,与基流期北溪贡献率占主导恰巧相反,这种碳通量的逆转表明暴雨事件会放大人类活动对下游河口生态环境的影响。

Watershed features have great impacts on river DOM composition and flux. In this study, temporal variations in DOM of the North（dominated by forestland）and West（dominated by farmland and urban area）Jiulong River were investigated during the typhoon＂Matmo＂in July, 2014. The DOM was characterized by DOC, absorption spectroscopy, and fluorescence excitation emission matrix spectroscopy（EEMs）analysis. The DOC concentration, absorption coefficient aCDO（350）and total DOM fluorescence intensity of both rivers increased significantly in both rising and falling hydrograph during the storm event. However, DOM abundance in the West River showed a much greater increase than that in the North River, suggesting more sensitivity of river DOM to rainstorm events in the watershed with greater anthropogenic perturbation. The specific absorption coefficient（SUVA254）of CDOM showed different variation tends between the North and West River,indicating that river DOM in forest-dominant watershed had high aromaticity and average molecular weight. The West River showed higher fluxes of DOM than the North River during storm event, which was opposite to that under the base flow condition. This reversion in DOM export flux suggested that storm event could amplify the influence of human activities in the watershed on the receiving estuarine ecosystems.The present findings are of great significance for the integrated management of coupled river-estuary system.