地壳风化速率研究综述

地壳风化速率研究的理论基础是质量守恒原理和溶液与矿物反应动力学法则。元素在风化过程中的行为受多种因素控制,主要包括基岩风化量、大气沉降量、径流量、生物的输出数量和人为输入量（如施肥）。硅酸盐矿物化学风化过程中,矿物与溶液之间总的化学反应速率是单个反应速率之和,其中涉及到 3个关键参数,即：酸中和能力（ANC）、基本阳离子/无机铝（BC/Al无机）比值和临界负荷（CL）。风化速率的研究主要采用四种方法,即PROFILE模型、基本阳离子损耗、元素输入-输出指数和Sr同位素比值等。PROFILE模型是一个稳定态的综合土壤化学模型,矿物的分解速率、矿物的暴露表面积、土壤水饱和度和土壤层厚度决定着该矿物的风化速率,总的风化速率为各种矿物的风化速率之和。元素损耗,主要是基本阳离子（Ca、Na、K和Mg）的损耗,假设Ti、 Zr和Nb在成土过程中含量稳定并不参与风化反应,那么对于给定的土壤层,化学风化损耗的基本阳离子可以通过比较土层与成土母质之间元素组成的差异来计算。输入-输出指数的假设前提是研究的流域处于稳定状态,一般认为输入指数是大气沉降,输出指数是河流搬运溶解部分、悬浮的非岩屑成因部分和生物营养净吸收部分。Sr同位素在生物和化学作用过程中并不分馏,不同生态系统阳离子场中Sr同位素组成是大气和矿物风化来源的Sr的混合物。

REVIEW ON WEATHERING RATES IN THE CRUST WEATHERING SYSTEM

Weathering rates play a significant role in the evolution of geochemistry of the Earth's surface and region environments. The basic theories of calculation of weathering rates are the mass balance and the law of reactions between solutions and minerals. The behavior of the element in weathering is influenced by many factors including weathering of bedrock, atmospheric precipitation, runoff of water, export of biomass and anthropogenic inputs(such as fertilization). Chemical reactions between minerals and solutions contribute to the base cation release rate due to chemical weathering of silicate minerals, and the total specific rate of reaction will be the sum of the rates of the individual reactions. Three key parameters of reactions between solutions and minerals are Acidic Neutral Capacities(ANC). Base Cation/Aluminium ratio(BC/A)and Critical Loads(CL).Methods of calculation of weathering rates mainly include①PROFILE modeling; ②basic cation depletion; ③input-output budget; and ④Stronium isotope ratio. The PROFILE modeling is a steady-stated and integrated soil chemistry model. Weathering rate of a mineral is controlled by dissolvable rate of the mineral, exposed surface area of the mineral. soil moisture saturation and soil layer thickness, and the total weathering rate is obtained by adding the contributions from all minerals. The element depletion is mostly the depletion of base cation such as Ca, Na, K and Mg. In the calculation of weathering rate, it's assumed that Ti,Zr or Nb is resistant, and thus Ti,Zr or Nb is considered to be immobile during weathering. Weathering rate is calculated as the difference between outputs and inputs, provided that the study area is in steady state. In general, the input is considered as the contribution from precipitation, while the output is calculated as the sum of ①river-transported dissolved fraction; ②river-transported suspended non-detrital fraction; and ③biotic nutrient net uptake. It is suggested that Sr isotope is not fractionated during biotic and chemical processes, and Sr isotopic compositions in different ecosystem exchangeable-cation pools ar
e mixtures derived from mineral weathering reactions and atmospheric aerosol.