雅砻江下游梯级筑坝对河流生源物质性质和输出的改变机制研究

The formation and evolution of ecosystems on the earth surface are controlled by the migration and transformation of substances on the earth surface. The changes of hydrological regime, nutrients transformation and export fluxes caused by cascade damming on the river significantly impact the ecosystems in estuaries, inshore and ocean. The lower reach of the Yalongjiang River with enriched hydraulic power will be slected in this study. The samples of rock, soil, riverine suspended matter, surface water (including rain, snow, riverine water and reservoir water) and underground water will be systematically sampled. The organic carbon content, mineral assemblage, major elements contents, carbon stable isotopic composition, phytoplankton contents will be measured. Averaged vegetation coverage and primary production in the drainage basin will be obtained through remote sensing method. The contributions from different sources to the riverine nutrients will be estimated in terms of the “random forest” method and the conventional mass-balance method. The cumulative altering effects of the cascade dammimg on the driving force of the riverine C and Si coupling cycle and on the erosion driving mechanism within the lower basin will be quantified by carbon isotopic tracing technique and element ratios. The purpose of this study will be to provide the foundation data for discussing coupling changes between terrestrial ecosystems and marine ecosystems and “Future Earth”.

地球表层物质的迁移、转化制约着地球生态系统的形成和发展。河流梯级筑坝改变河流水文情势进而改变河流生源物质的性质和输出通量，影响河口、近岸带和海洋生态系统的健康。本研究选择我国水能资源丰富的雅砻江下游河段，系统地采集流域内岩石、土壤、河流悬移质、地表水（雨水（雪）、河流水、水库水）和地下水等样品；测试分析样品的有机碳含量、矿物组成、主要元素含量、碳稳定同位素组成和浮游植物含量；采用遥感方法获取流域内平均植被覆盖率和植物生产力；运用随机森林算法和传统的质量平衡法估算不同源对河流生源物质的贡献；采用碳同位素示踪技术和元素比值法量化识别雅砻江下游梯级筑坝对河流C、Si耦合循环驱动力改变的累积效应和对流域侵蚀动力系统的改变。本项研究可为陆地-海洋生态系统耦合变化研究和“未来地球计划”研究提供基础数据。

为探讨河流梯级筑坝对河流生源物质性质和输出的改变机制，分别于2018年、2019年1月和7月自雅砻江河口至锦屏一级水库采集地表水样品166个，雨水样品6个，悬浮颗粒物样品12个；选择草地、稀树灌丛草地、杂木林、新银合欢林、针阔混交林、云南松林、宽谷草地、玉米地、芒果林和苹果等10个代表性群落，采集土壤样品60个。测量水样品的离子（包括K+、Na+、Ca2+、Mg2+、Cl-、NO3-、SO42-、HCO3-含量和溶解性硅（DSi））含量、溶解有机碳（DOC）和溶解无机碳（DIC）、DIC稳定同位素组成（δ13CDIC）、颗粒有机碳（POC）含量、土壤常量元素、总碳（TC）、有机碳（SOC）和δ13CSOC等指标，运用显著性分析、相关分析、回归分析和随机森林模型处理数据。研究得出：.（1）雅砻江下游梯级筑坝每年滞留POC、DOC和DIC分别为314.43×106 kg、88.72×106 kg和2588.50×106 kg，滞留率分别为93.04%、54.99%和58.14%；梯级筑坝导致POC所占比例从锦屏一级水库入库的6.88%下降至河口的1.13%。雅砻江下游梯级水库有机碳的循环效率（29.09%）高于全球水库的估算值。雅砻江下游梯级筑坝每年滞留Si 120.65×106 kg，其中65.48%为生物硅（BSi）；梯级筑坝对DSi和BSi滞留率分别为19.72%和84.57%，雅砻江下游梯级水库Si的循环效率（43.05%）低于全球水库的估算值（62%）。.(2) 联合使用DSi:HCO3-比值和δ13CDIC可以有效示踪梯级筑坝对C-Si耦合循环过程的改变；运用随机森林模型分析得出水体滞留时间、水温、入库流量、溶解氧含量、叶绿素a含量是改变DSi:HCO3-比值的主要因子。构建雅砻江下游梯级筑坝对河流C-Si生物地球化学循环的概念模型。