龙滩水库溶解无机碳来源及变化特征

河流在碳的运输过程中扮演着重要角色。为探究河流筑坝拦截后龙滩水库溶解无机碳(DIC)的来源和变化特征,于2016年7月和2017年1月采集水样,然后分析了河水DIC及其碳稳定同位素(δ13C)值。研究结果表明:(1)δ13CDIC值具有显著的时空差异,表明两个季节影响DIC的主要因素和DIC的来源并不相同。雨季,DIC及其δ13C主要分布在2.04~4.12 mmol·L^-1和-5.52‰^-2.87‰的范围内;旱季,水体DIC为3.33~4.61 mmol·L^-1,而δ13CDIC显著低于雨季为-15.90‰^-9.12‰。雨季,稀释效应显著降低了DIC浓度,由于水体热分层使得DIC在水柱剖面上差异显著,而旱季由于混合作用的影响,在剖面上差异较低。(2)在雨季,河流δ13CDIC较旱季明显偏正,碳酸盐岩的强烈风化输入大量HCO3-是DIC的主要来源。在旱季,DIC和δ13CDIC成反比关系,δ13CDIC在旱季变得更低,其大部分的DIC来自于土壤CO2输入和原位有机呼吸作用。旱季水体热分层消失,混合作用使得底部具有较低δ13C值的含碳水体上涌,并与表水层混合导致其δ13CDIC值低于雨季。这种季节性模式与自然河流不同,而是与湖泊的季节变化特征更为类似,说明河流拦截蓄水后逐渐湖沼化,并显著影响了DIC的循环。

Sources and Variation Characteristics of Dissolved Inorganic Carbon in Longtan Reservoir,China

Rivers are crucial in the transportation of carbon.In order to determine the composition and variation of dissolved inorganic carbon(DIC)in Longtan Reservoir after damming and interception,water samples were collected in July 2016 and January 2017 respectively,and then the DIC and its stable carbon isotope(δ13C)values were analyzed.The results showed that:(1)Theδ13CDIC values of reservoir had significant temporal and spatial differences,indicating that the main factors and sources of DIC were different during dry and rainy seasons.In rainy season,the DIC andδ13C of reservoir were distributed in the range of 2.04~4.12 mmol·L^-1 and-5.52‰^-2.87‰respectively;in dry season,the DIC of water was3.33~4.61 mmol·L^-1,whileδ13CDIC was significantly lower than that in rainy season,which was-15.90‰^-9.12‰.In rainy season,the diluted effect significantly reduced the concentration of DIC.Because of the thermal stratification of water,the difference of DIC on the water column was significant,while in the dry season,due to the influence of mixing,the difference was lower on the water column.(2)In rainy season,theδ13CDIC of the river was obviously more positive than that in dry season,and the strong weathering of carbonate rocks input a large amount of HCO-3,which was the main source of DIC.In dry season,DIC was inversely proportional toδ13CDIC,andδ13CDIC became lower in the dry season,indicating that most of the DIC came from soil CO2 and situ organic respiration.The thermal stratification of reservoir disappeared in dry season,and the mixing action made the monimolimnion with lowerδ13C value upwelling,and mixing with the epilimnion subsequently resulted in itsδ13CDIC value lower than that in rainy season.This seasonal variation was different from that of natural rivers,but more similar to the seasonal variation of lakes,indicating that the river gradually became limnetic after interception and impoundment,which significantly affected the cycle of DIC.