干旱区绿洲开发利用进程中的无机碳汇研究

This study is to aimed at a long-been-neglected phenomenon of the transfer and sequestration of dissolved inorganic carbon in the process of oasis development in arid zone; and to quantify the contribution of land use in arid areas to regional carbon cycle. Basic hypothesis of this study is that the leaching process for soil salinity control is also a process of inorganic carbon leaching, and transferring. Based on this hypothesis, a case study is to be carried out at a typical inland river basin named the Sangong River watershed in Xinjiang province, northwest China. Soil columns are to be used to simulate irrigation and leaching solutions are to be collected at irrigated landscapes, with which the leaching solution volume and inorganic carbon content are to be quantified. After then, land use change and amount of water consumed in irrigated landscape types are to be analyzed based on data from remote sensing image, land use, and water resources combined with field investigation. Through scale conversion, the spatial distribution patterns of inorganic carbon sinks from the leaching process are to be quantified for different periods. The relationship between the amount of dissolved inorganic carbon (DIC) and the oasis development will be studied. Major factors governing the migration of DIC transfer and storage will be determined. After that, the process of this inorganic carbon sink is to be modeled, and the spatial pattern of potentially increased DIC sink is to be established. These results will help us to understand its role in slowing soil CO2 release, and then to evaluate the role of this DIC sink in global carbon cycle.

该申请以长期被忽略的，干旱区绿洲土地开发利用驱动的，可溶性无机碳的迁移存储过程为研究对象，致力于干旱区土地利用诱发的碳汇效应研究。基本科学假设为：土壤盐分淋洗过程实际也是无机碳的淋洗、传输过程。以此假设为基础，以典型的内陆河流域三工河流域为靶区，采用土柱模拟灌溉法和原位灌溉景观取液法相结合的实验手段，确定各灌溉景观类型淋溶水的体积和无机碳的含量。尔后，以遥感影像/土地利用/水资源利用数据为基础，结合现场调查，分析区域土地利用变化和各灌溉景观类型的灌水数量。通过尺度转换，量化不同开发时期淋溶形成的无机碳汇的空间分布格局，进而评估绿洲开发进程中可溶性无机碳汇总量的变化及其影响机制，探明淋溶无机碳迁移存储的规律。在此基础上，模拟灌溉淋溶无机碳汇的形成过程，构建促进可溶性无机碳汇的空间增汇模式，有效认识其在减缓土壤CO2释放中的作用，进而探讨这种碳汇过程在全球碳循环中的地位与作用。

干旱区内陆河流域源于山区的径流，在平原区消耗，为一独立封闭的系统，并且土壤呈现盐碱特性。近年来，人类活动导致的绿洲区域耕地面积扩张已是不容质疑的事实。在这种背景下，在没有灌溉就没有农业的这类地区、盐渍化随灌溉自然发生；而过量灌溉淋洗又为防治耕地盐渍化的主要方式。事实上，土壤盐分淋洗过程实际也是无机碳的淋洗、传输过程。本项目研究了绿洲土地开发利用驱动的，可溶性无机碳的迁移存储过程，重点是干旱区土地利用诱发的无机碳汇效应。土柱模拟灌溉法和原位农田灌溉景观取液法实验结果表明，灌溉淋溶无机碳含量与土壤盐分之间，存在明显的数量相关性。不同作物间，灌溉淋溶无机碳的含量和强度不同。通过碳同位素分析，盐碱土中，有近20%为可溶性无机碳，并且具有短的周转时间和高的聚积速率，用土壤无机碳来表征土壤碳的周转将极大掩盖土壤可溶性无机的贡献现代碳循环的作用。以14C同位素数据，结合内陆水资源特征，证实了该碳汇迁移、存储过程是干旱区盐碱土改良、盐渍化控制的一个伴生过程，当农业灌溉洗盐的同时，无机碳也被淋洗，最终被吸收的大气CO2被封存于沙漠下的咸水层。区域上，灌溉淋溶可溶性无机碳的碳汇强度达20gC－2yr－1，依据全球地下咸水层的分布，初步估计，每年碳汇强度为0.2 Pg C yr－1,这个碳库总量（全球）高达1000亿吨（等同于1000Pg C），是陆地上植物、土壤之外的第三个活动碳库。气象因素、灌溉制度、作物种植结构和土地开垦年限等相互作用影响可溶性无机碳汇的强度，在水资源数量一定的条件下, 若调整种植结构，绿洲区无机碳汇强度显著提高，无机碳汇总量增大。尽管节水灌溉在一定程度上影响了年碳汇数量，但由于节水的实施使得灌溉土地面积的扩大，随洗盐作用，在一定程度上促进了淋溶无机碳汇的数量。研究成果对于认识该无机碳汇在减缓土壤CO2释放和全球碳循环中的的地位与作用具有重要意义。