北京密云水库流域水体夏季DOC和DIC质量浓度及同位素组成初探

Concentration and Carbon Isotope Composition of DOC and DIC in the Miyun Reservoir Watershed in Summer

为丰富水库水体碳循环研究,有效地从源头控制饮用水源水营养盐输入.以北京境内密云水库及其主要入库河流(密云水库流域水体,包括白河干支流、潮河干支流和密云水库)为研究对象,京密引水渠水体为参比,对比分析了夏季不同水体溶解性有机碳和溶解性无机碳的质量浓度水平及碳同位素组成.结果表明,密云水库流域水体夏季溶解性有机碳(DOC)质量浓度的总体变化范围是1.07~5.19 mg·L^-1,平均值是2.61 mg·L^-1;δ13CDOC值变化范围为-27.4‰^-24.3‰,平均值为-25.8‰.入库河流夏季DOC主要来自土壤有机质,密云水库夏季DOC主要来自陆源C3植物,内源物质对流域水体DOC同样有一定贡献,水位升高导致库滨带淹水可能是密云水库DOC偏高的重要原因.研究区域水体夏季δ13CDIC值变化范围为^-12.6‰^-5.75‰,平均值为-9.44‰,土壤CO2溶解碳酸盐岩过程是河流溶解性无机碳(DIC)的主要贡献者,且DIC明显被水生生物的光合作用所利用.密云水库溶解性碳(DOC和DIC)浓度显著高于京密引水渠水体(P<0.01),两种水体碳素浓度、组分可能存在差异.总体上,除个别点位外,密云水库流域水体夏季DOC受人类生活源影响较小,DIC转化为DOC可能同样是夏季库区水体DOC的潜在来源.

This study aims to complement existing research on the carbon cycle of water in reservoirs,for the effective control of nutrient input in drinking water.The content and isotopic compositions of water dissolved organic carbon(DOC)and dissolved inorganic carbon(DIC)from the Miyun Reservoir watershed in Beijing were studied,and water from the Jingmi diversion canal was also studied as a baseline reference.The results showed that the content of DOC in the Miyun Reservoir watershed in summer varied from 1.07 to 5.19 mg·L-1,with an average value of 2.61 mg·L-1.DOC in tributaries was lower than that of most rivers in China and globally,while DOC in reservoirs,particularly in Miyun Reservoir,was high.The high water level might be the main reason for the high DOC in the Miyun Reservoir.In summer,theδ13CDOC in the Miyun Reservoir watershed ranged from-27.4‰to-24.3‰,with an average value of-25.8‰.Results from the isotopic analysis showed that the water in the Miyun Reservoir watershed was less affected by human sources,with the exception of some points.In summer,DOC in tributaries and in the Miyun Reservoir was mainly derived from soil organic matter and terrestrial C3 plants.In addition,endogenous substances also contributed to DOC in the watershed.DOC concentration increased along the Chao and Bai Rivers,and DOC from soil erosion and human sources was higher in the Chao River.Theδ13CDIC in the study area varied from-12.6‰to 5.75‰,with a mean value of-9.44‰.The weathering of carbonate rocks accounted for the major river DIC,and DIC had been clearly assimilated by the phytoplankton by photosynthesis.DOC and DIC in the Miyun Reservoir were significantly higher than in the Jingmi diversion canal(P<0.01),and theδ13CDIC in the Miyun Reservoir showed a clear positive deviation.This indicated that there were differences in carbon concentration and components in the two kinds of water,which might affect the denitrification capacity of the water in the Miyun Reservoir after mixing.In general,the dissolved carbon in the water of the Miyun Reservoir watershed is less affected by human sources.The conversion of DIC to DOC may also be a potential source of DOC in the study area.