不同发育程度土壤矿物风化过程化学计量关系及模型建立

Human activities bring about large amount of H+ entering into soil. Soil acidification rate is increasingly becomes the critical indicator in assessing the sustainable use of soil resource and agricultural development as well as environmental protection. However, while proton accelerates mineral weathering, weathering buffers soil acidification so it is hard to discriminate these two processes due to their coupling interactions, which causes difficulty in determining soil acidification accurately. Our previous study shows a promising way is to identify the contribution of weathering and acidification on proton consumption based on the stoichiometry of mineral weathering in nature and the flux of element cycling. This project will focus on the study stoichiometry of mineral weathering of typical soils with different weathering degree derived from granite and basalt. The soil samples will be collected from a series of soil profiles from south to north China. The key step is to wash the adsorbed base cations from soil colloid completely. Then the treated soil samples will be leached by different pH buffered acid rain. This study tries to illustrate the leading factors on stoichiometry of mineral weathering among soil properties and pH of simulated acid rain. Furthermore, we will develop a universal model on stoichiometry of mineral weathering based on all important affecting factors. Thus the different soil buffing potential to H+ will be assessed across the country. The results of this study will serve a more reliable soil acidification assessment and prediction.

人类活动导致大量的外源质子（H+）进入土壤，土壤酸化程度和速率成为评估土壤、农业和环境可持续发展的重要依据。由于酸输入促进风化，风化缓冲酸化，二者相耦合，不易区分，因此酸化速率不易观测和准确估算。过去研究表明准确定量矿物风化过程的化学计量关系，并结合元素循环通量是区分风化和酸化消耗H+的有效途径。本研究拟采集具有不同风化特征的花岗岩和玄武岩两种主要的硅酸盐岩发育土壤，在我国自南向北分别采集具有不同风化程度的系列风化剖面，通过洗脱土壤吸附的盐基离子，在消除阳离子交换影响的基础上，采用模拟不同pH酸雨的淋溶实验，测定不同风化程度土壤矿物风化过程的化学计量关系，结合土壤的物理、化学和矿物学特性，探索自然土壤矿物风化计量关系的主导因素，建立通用的硅酸盐矿物风化计量关系模型，明确我国不同区域土壤对酸的缓冲潜能，为评价与预测我国土壤在酸沉降和农业利用影响下的酸化速率提供可靠的科学依据。

土壤矿物风化计量关系直接影响土壤酸化速率的准确估算，自然土壤含有多种处于不同风化程度的矿物，如何准确获得土壤矿物风化过程中盐基离子（BC，K+、Na+、Ca2+、Mg2+）和硅（Si）释放量的化学计量关系（BC:Si）是当前需要解决的科学问题。本研究选取了玄武岩风化系列、花岗岩风化系列、云母片岩、片麻岩和安山岩不同母质发育的土壤剖面以及全国100个代表性表层土壤，通过洗脱土壤吸附盐基离子后，采用模拟酸雨淋溶的方法，测定了土壤矿物风化过程的BC:Si值。获得了我国主要硅酸盐发育土壤的盐基离子与硅的风化计量关系，明确了同一母质不同风化程度和不同母质发育土壤BC:Si值的差异。建立了土壤交换性盐基离子洗脱过程的最小洗盐次数模型，提高了盐基洗脱效率。结合土壤基本特性分析，筛选了BC:Si值的主控因素，建立了涵盖土壤矿物学性质、物理性质和化学性质的6个主要因子的BC:Si值预测模型。该模型涵盖了我国主要的土壤酸化区域、硅酸盐母质类型、不同风化程度、土壤类型和土地利用类型。通过精度验证，该模型具有一定的普适性，可为大范围BC:Si值的有效获取提供方法，为全国土壤酸化速率的估算和土壤酸缓冲性能评价提供重要的数据支撑。