万峰湖水库溶解性无机碳来源及时空变异特征

Source and spatio-temporal variation characteristics of dissolved inorganic carbon in Wan-fenghu Reservoir,China

溶解性无机碳(DIC)的通量和形式在水生态系统的生物地球化学循环中起关键作用,是碳收支的重要组成部分。通过分析万峰湖水库库区水体理化参数、DIC和稳定碳同位素(δ13C(DIC))特征,揭示了DIC的行为和来源。结果表明:1)在表水层,整个库区pH变化较保守,均呈弱碱性。硝酸盐氮(NO3^--N)有最大变异系数,具有高度的时空变异性。由于稀释效应的存在,电导率(EC)、二氧化碳分压(pCO2)和DIC的最低值均出现在夏季高径流量阶段。在水柱面上,夏季氧化还原电位(Eh)和NO3^--N随水深增加无显著变化,其余指标均变化明显,且在温跃层变异程度最大。两季节的水温(T)、pH和Eh均随水深增加而降低,pCO2则与之相反。EC、总碱度(TA)和DIC在夏季随水深增加而降低,冬季变化梯度较小。两季节的DIC与pH、Eh呈负相关,与EC、pCO2呈正相关。2)夏季DIC为2.66~4.9 mmol·L^-1,而冬季为3.38~4.52 mmol·L^-1。水体热分层期间,DIC和δ13CDIC在温跃层的变化梯度最大,DIC与δ13CDIC在夏季表水层呈正相关。两个季节水柱面上及冬季表水层的DIC和δ13CDIC均呈负相关,但冬季DIC和δ13CDIC值随水深变化趋势不明显。3)夏季δ13CDIC较高,为-7.71‰^-1.38‰,表明碳酸盐矿物的溶解占优势。冬季δ13CDIC为-16.93‰^-9.44‰,显著低于夏季且范围更宽,生物源CO2的输入和有机质矿化是主要来源。δ13CDIC在不同季节和水深均差异显著,一方面是碳的来源不同;另一方面归因于碳来源的相对贡献比例的变化。

The flux and form of dissolved inorganic carbon(DIC),an important part of carbon budget,play a key role in the biogeochemistry of aquatic ecosystem.By analyzing physicochemical parameters and water DIC andδ13CDIC characteristics in Wanfenghu Reservoir,we examined the behavior and source of DIC.In the epilimnion,water pH in the entire reservoir was conservative,being weakly alkaline.Nitrate(NO3--N)had the maximum coefficient of variation and a high spatio-temporal variation.Due to the dilution effect,the lowest values of electrical conductivity(EC),partial pressure of carbon dioxide(pCO2)and DIC appeared during the summer high flow phase.On the water column in summer,redox potential(Eh)and NO3--N did not change with water depth,while other indicators changed significantly,with greatest variation in the thermocline.Water temperature(T),pH and Eh all decreased with increasing water depth in both seasons,while pCO2 showed an opposite trend.Water EC,total alkalinity(TA),and DIC decreased with increa-sing water depth in summer,but with a smaller gradient of change in winter.The DIC in water was negatively correlated with water pH and Eh,while positively correlated with EC and pCO2 in both seasons.2)The concentration of DIC was 2.66-4.9 mmol·L-1 in summer and 3.38-4.52 mmol·L-1 in winter.During the period of thermal stratification,the variation gradients of DIC andδ13CDIC in the thermocline were most significant.DIC was positively correlated withδ13CDIC of epilimnion in summer.DIC was negatively correlated withδ13CDIC in epilimnion in winter and on water column in both summer and winter.However,the variation of DIC andδ13CDIC with water depth was not obvious in winter.3)In summer,δ13CDIC was-7.71‰--1.38‰,indicating that the dissolution of carbonate minerals was dominant.In winter,δ13CDIC was-16.93‰--9.44‰,signifi-cantly lower than that in summer but with a wider range,indicating biological input of CO2 and mineralization of organic matter were the main sources.Theδ13CDIC varied significantly in different seasons and water depths because of differences in carbon sources and changes in the relative contribution proportion of carbon sources.