天山南坡开都河水中钙的来源解析研究

Calcium was the essential elemental in active of life and main elemental of rock-forming mineral, Calcium carbonate formation and transformation determines the coupled of carbon cycle and calcium cycle. Huge amounts of Soil inorganic carbon (SIC) and carbon pool in groundwater in arid and semi-arid regions, however, the origination of calcium in inorganic carbon of arid regions was unclear until now. We carry out field trials in Kaidu river catchment on arid regions. We were determined calcium and its stable calcium isotopes in rock, soil, dry and wet deposition and Kaidu river water samples in Kaidu river catchment. Study the distribution of calcium and its isotopes in Kaidu river catchment and explore the seasonal dynamics of calcium/strontium and its stable isotopes in Kaidu river. The composition and presentation of calcium ion in Kaidu river was distinguished by the stable carbon isotope mass balance principle. Combined with the calcium and its stable calcium isotopes in Ca-silicate, carbonate and dry and wet deposition, to explore its effect on the formation and transformation of calcium ion in Kaidu river. The results will improve precise calculated inorganic carbon potential sequestration in soil, lake and river and provide foundation for calcium cycle biogeochemical ecosystem in arid regions.

钙是生命活动的必需元素和造岩矿物主量元素，碳酸盐形成转化决定了碳循环与钙循环是耦合的。干旱区、半干旱区土壤无机碳和地下水水体中无机碳数量巨大，但是干旱区无机碳中钙的来源问题至今尚未清楚。本研究拟选择干旱区天山南坡开都河流域展开，通过对开都河流域岩石、土壤、干湿沉降和开都河水进行钙及其稳定性钙同位素分析，明确开都河流域钙含量及其稳定性同位素分布特征；探明开都河水中钙、锶离子含量及其同位素季节变化特征。根据钙质硅酸盐、方解石、干湿沉降样品和开度河水中钙锶同位素值，依据同位素质量平衡原理，计算开都河水中钙来源比例，量化钙质硅酸盐、方解石和干湿沉降对开都河水中钙的贡献量。并结合钙质硅酸盐、方解石和干湿沉降样品钙含量及同位素特征，探明开都河流域钙及其稳定性同位素转移变化机理。本研究结果将为干旱区生态系统钙生物地球化学循环研究奠定基础，同时为干旱区土壤、湖泊、河流区域估算固碳潜力提供依据。

本项目通过对开都河流域岩石矿物、土壤和河水中理化指标和钙锶含量及其同位素测定分析，结合稳定性钙同位素二源混合模型计算，探究开都河水中钙的来源及贡献区分研究。研究发现开都河水pH值大部分超过8.0，呈现碱性特征，上、中、下游pH总体变化不明显。开都河水中阳离子以Ca2+、阴离子以HCO3-为主，占阴、阳离子总量的近80%。农田和草地土壤总碳平均含量分别为50.0±9.3gkg-1和124.2±42.2gkg-1，土壤有机碳平均含量分别为8.1±2.9gkg-1和50.6±33.2gkg-1，土壤无机碳平均含量分别为41.9±8.6gkg-1和84.3±27.8gkg-1。草地土壤总碳、土壤有机碳和土壤无机碳含量高于农田土壤，呈极显著差异（p<0.01）。开都河流域农田土壤CO2浓度呈现单峰变化特征，变化范围从800ppm—3200PPm，在七、八月份达到最大值。土壤地表CO2通量从三月到六月持续增加，最大至7.5 gCm-2d-1，在钙加秸秆处理表现出急剧下降趋势。四个处理土壤温度敏感度Q10值在秸秆和钙加秸秆处理高，为1.62和1.79，对照和钙处理低，为1.38。开都河流域锶87Sr/86Sr同位素值大小范围在0.7100—0.7270。开都河流域碳酸岩矿物87Sr/86Sr值低于硅酸岩矿物，硅酸岩和碳酸岩矿物87Sr/86Sr平均值分别为0.7164和0.7150。开都河流域碳酸岩矿物δ44/42Ca值低于硅酸岩矿物，硅酸岩和碳酸岩矿物矿物δ44/42Ca平均值分别为0.71和0.37。总体来看，开都河水中钙离子来源主要为硅酸岩矿物分解，占比80%以上，夏季硅酸岩矿物钙对河水中来源比春季稍低一些，春季和夏季硅酸岩对开都河水中钙的来源比例分别占比86.80%和79.14%，碳酸岩占比分比为13.20%和20.59%。春冬和夏秋季开都河2011-2018年开都河水中年均钙流量分别为7.36±1.60×104t和12.52±1.58×104t，硅酸岩和碳酸岩来源钙年均流量分别为16.33±2.06×104t和3.55±0.45×104t。研究结果为进一步阐明干旱区无机碳汇来源提供理论依据和技术支撑。