典型风化背景下硅循环及其对土壤酸化速率的影响

Acidification is an important aspect of soil development in acid deposition area. However, soil acidification rate is difficult to be determined in a short period because of soil buffering capability. The biogeochemical cycling of silicon (Si) is closely related to weathering and leaching, so is coupled with soil acidification process and affecting its rate. This project aims to establish a method to estimate soil acidification rate based on the biogeochemical balance of Si and other elements in a typical granite watershed located in the subtropical area. The stoichiometric relations of Si and base cations during mineral weathering in the main soil type in the watersheds will be studied through simulated experiment. This study will illustrate the contribution of mineral weathering to soil acidification buffering.

在酸沉降影响地区，酸化是土壤重要的演变方向。但由于土壤的缓冲性能，短期内难以监测到土壤的酸化速率。硅的生物地球化学循环与风化和淋溶密切相关，对酸化速率有重要影响。本研究拟以亚热带地区典型花岗岩小流域为研究单元，模拟流域内主要土壤类型中混合矿物风化释放硅和盐基离子的化学计量关系，结合对大气沉降和径流输出的化学组成的多年观测数据，明确矿物风化对酸缓冲的贡献，建立基于硅循环的土壤酸化速率定量估算方法。

酸化是我国热带和亚热带土壤演变的主要趋势。在日益严重的酸沉降情况下，准确估算土壤的酸化速率对我国南方土壤的可持续发展非常重要。本研究以位于亚热带花岗岩发育的流域为单元，系统地观测了流域内H+、硅和盐基离子的输入输出平衡，表明我国亚热带地区酸沉降严重，除了降雨直接输入的H+以外，大气沉降输入的NH4+和SO2在土壤中转化产生的H+甚至超过降雨直接输入的量。虽然目前土壤已经酸化，但是仍然具有较强的缓冲作用，能够完全消耗外界输入的H+，保持径流水不被酸化。这包括风化和阳离子交换的贡献，其中阳离子交换带来土壤的酸化。在硅酸盐地区，利用流域中硅、盐基离子和H+的风化计量关系和输入输出平衡是估算土壤酸化速率较为有效的方法，亚热带花岗岩年轻土壤的酸化速率为702 mol ha-1 yr-1，比单纯的元素平衡估算方法更加准确。