土地利用变化对贵州印江喀斯特小流域水体DIC含量及δ^(13)C_(DIC)的影响

Effects of Land Use Change on DIC Contents and δ^(13)C_(DIC) Values of Surface Water in a Small Karst Catchment in Yinjiang County,Guizhou Province

以印江流域水体为研究对象,分别于2014年夏季和冬季采集印江河主干与支流表层水样品,测定并分析其基本物理化学参数、主量离子浓度和溶解性无机碳(DIC)含量及其碳同位素组成(δ^(13)C_(DIC)),结合流域内不同的气候条件和土地利用强度与方式等生态环境条件,对表层水体中DIC的来源及其时空变化特征进行探讨。结果表明:印江河流域表层水p H值呈中性到碱性,水化学组成主要受碳酸盐岩风化的控制,阳离子主要以Ca^(2+)、Mg^(2+)为主,阴离子主要以HCO-3为主,而且主量离子在冬夏季表现出较为显著的差异。印江河流域干、支流水体DIC和主量离子含量向下游总体呈现递增趋势,并随季节呈现夏低冬高的变化趋势,可能与研究区水体上游土地利用强度低而下游存在大量的农耕用地以及当地冬夏季降雨量差异有关。相比之下,印江河流域干流水体δ^(13)C_(DIC)均值为-10.39‰、支流水体δ^(13)C_(DIC)均值为-8.29‰,差异相对显著,反映了作为源头支流水体主要受碳酸盐岩风化影响,支流汇入干流水体过程周边土地利用强度增大、方式多样,影响较为明显。而且该流域干、支流水体δ^(13)C_(DIC)的季节性差异显著,支流水体DIC主要由于水-岩交换在冬季更加富集13C,而干流水体DIC则主要由于生物量效应在夏季相对富集13C,极有可能与当地土地利用强度和方式的季节性变化有关。

Surface water samples were collected from main stream and tributaries of Yinjiang watershed in the summer and winter,2014.Basic physical and chemical parameters as main ions concentration,dissolved inorganic carbon（ DIC） content and their carbon isotopic composition（ δ13CDIC） were studied. Combined with different weather conditions and ecological environment settings,such as land use intensity and patterns in the basin,the sources and temporal-spatial variations of DIC were discussed. Results showed that p H values were between neutral and alkaline. Chemical compositions of surface water were mainly derived from carbonate rock weathering,and Ca2＋and Mg2＋were major cations while HCO-3was preponderant anion. Differences of main ions content were obvious between summer and winter. The contents of DIC and main ions increased from upstream to downstream,and those were lower in the summer than in the winter,which would be due to strong land use intensity in downstream and differences of rainfall between winter and summer.δ13CDIC values of main stream and tributaries were-11. 6‰ and-9. 8‰,respectively,indicating that primary sources of DIC in tributaries were affected by carbonate rock weathering.δ13CDICvalues of main stream and tributaries had significant seasonal difference,as enrichment of 13C value in winter was found in tributaries mainly because of water-rock exchange while opposite phenomenon was found in main stream mainly because of effect of biomass,which most likely related to seasonal changes of local land use intensity and patterns.