黄山酸雨区花岗岩临界带土壤Ca收支的锶同位素示踪

Mount Huangshan is a famous Global Geopark which is situated in the south of Anhui Province. It is characterized by its lofty and peculiar peaks, green and straight pines, jagged rocks of grotesque shapes, wide and imposing cloud sea. The erosion there, however, is intensive due to its peculiar granite tectonics and climatic conditions, and led to a fragile eco-geo-environment. With the increasing the industrialization of the surrounding areas around the Mt Huangshan, acid rain has become a serious issue in the region. The increasing frequencies of acid rain are found by the weathering monitoring station in the GuangmingDing in the Mt. Huangshan in the past decade. One of key factors that acid rain caused the decline of forest ecosystems is that acid rain can strengthen the loss of nutrients, especially calcium. Acid rain can change the characteristics of calcium biogeochemical cycle: bring calcium to be depleted from ecosystem, reduces the bioavailable calcium in base cation pool in soil and increases soil acidification. Therefore, the acid rain occurred in the Mt. Huangshan will inevitably increase the water loss and soil erosion and the loss of nutrients, in turn, the deterioration of fragile eco-geo-environment there. As a world-famous landscape, the protection of the geo-ecosystem should be an important issue and an urgent demand for the State and the local government. .In this research, we select the calcium as a model element to investigate the impact on nutrient cycles of forest ecosystem from the acid rain in the Mt. Huangshan. We aim to explore the calcium cycle in the granitic "Earth's Critical Zone", which is necessary for our understanding fully and systematically the calcium transport under condition of acid rain in the Mt. Huangshan. We plan to select several regolith profiles in the Mt. Huangshan that are similar to the CZO (Critical Zone Observation) seed sites. We use strontium isotope tracers, biogeochemical and hydrochemical methods, coupled field observation and indoor experiments of simulated acid rain to investigate the sources, content, geochemical distribution and the mass of loss of calcium of soil in the Critical Zone in the Mt.Huangshan under condition of acid rain. Research goals of the project are to quantificationally determine the weathering and atmospheric contributions of calcium and its loss in the Critical Zone, identify the effects of acid rain on distribution of calcium in soil exchangeable complex. We hope that this research will help us to learn the geochemical processes affecting calcium cycles in the granitic Earth's Critical Zone, and determine the tolerance loss of calcium in the granitic forest ecosystem in the Mt.Huangshan, so as to provide scientific support to improvement of vulnerable eco-geo-environment and development of the regional economy in a sustained and coordinated way there.

在世界地质公园安徽黄山花岗岩森林生态系统小流域内，选择典型地球临界带，以其上土壤中的Ca元素为研究对象，以Ca离子在临界带上输入/出为主线，运用锶同位素示踪、生物地球化学及水文地球化学等手段，结合野外监测和室内酸雨模拟实验，研究酸雨背景下黄山花岗岩临界带土壤中Ca的风化贡献、大气输入贡献和流失通量；研究酸雨对临界带上Ca的转运及其在土壤中赋存和淋失的影响。揭示酸雨背景下黄山花岗岩森林生态系统林矿质养分Ca的来源和Ca的允许流失量。为黄山花岗岩临界带生源要素循环规律的研究补充基础数据，也为黄山地质生态环境保护和可持续发展服务。

黄山是世界地质公园。陡峭的花岗岩地貌加上酸雨频发将会引发该地区水土和矿质养分流失。本研究选择世界地质公园黄山作为研究对象，运用元素、碳锶同位素地球化学及环境科学等手段，探讨酸雨背景下黄山北部花岗岩临界带流域化学风化过程，揭示酸雨对化学风化过程以及盐基离子释放的影响；辨识花岗岩临界带流域溶解态Ca的来源，确立其流失通量；分析花岗岩临界带土壤剖面Ca的释放速率，确立其与流失通量之间的收支平衡关系；辨识花岗岩临界带典型植物中Ca的来源，分析其潜在的收支平衡风险。将有助于进一步理解酸雨与人类活动介入下黄山花岗岩临界带流域化学风化过程和营养离子Ca的循环，为黄山生态环境保护提供基础数据。取得的主要结果如下：.（1）酸雨背景下，黄山花岗岩临界带流域水化学组成主要受控于岩石（硅酸盐岩以及小面积或微量分布的碳酸盐岩化）化学风化输入和大气降水输入。结果表明，黄山低温山地气候控制下的硅酸岩盐化学风化速率较低；.（2）花岗岩临界带流域的化学风化过程主要以碳酸溶解过程为主，但酸雨中或黄铁矿氧化形成的硫酸和硝酸也参与了反应。结果说明，人类活动尤其工业烟气及汽车尾气等改变了黄山花岗岩临界带化学风化单一模式，并加速了化学风化速率，影响了对大气CO2的消耗；.（3）锶同位素示踪证据表明黄山花岗岩临界带流域地表径流中的Ca离子主要来自于大气输入和碳酸盐岩化学风化贡献，硅酸盐岩（黄山主峰花岗岩及外围沉积岩）贡献较少；其结果与流域水化学组成分析的结果一致。说明大气输入与微量碳酸盐岩对硅酸盐岩森林生态系统Ca离子养分的输入有着重要的贡献；.（4）初步分析结果表明，花岗岩临界带流域平均土壤剖面（含非花岗岩的硅酸盐岩土壤剖面）Ca元素长期风化速率大于流域源于硅酸盐岩的Ca流失通量，然而纯花岗岩临界带土壤剖面的Ca元素长期风化速率则小于流域源于硅酸盐岩的Ca流失通量，说明黄山花岗岩核心景区森林生态系统中花岗岩化学风化释放的Ca难以与流失的Ca达到平衡；.（5）主、微量元素地球化学以及锶同位素证据表明，黄山花岗岩临界带代表性植物马尾松所需的Ca离子养分主要来自于大气输入和土壤有机质层，降水贡献随着土壤层深度增加而增加。表明降水对该森林生态系统Ca供应有着重要作用。然而近50年的黄山降雨数据表明，该地区降雨量呈递减趋势，加上高频率的酸雨背景，意味着黄山花岗岩景区生态系统Ca养分收支存在着输入不抵流失的风险。