煤矿开采沉陷区水域沉积物中磷迁移转化的动力学机制研究

Extensive subsidence and flooding of agricultural land have been caused by the coal mine activities in China. As a result, the cultivation ecosystem has been transformed to freshwater ecosystem. It is of great significance to the freshwater ecosystem if the nutrient contained in subsided agricultural soils was released to the overlying water. "Human stress-response of freshwater system" will be the keynote scientific topic of this research project. And the behavior of phosphorus "forced by organic matter input and controlled by surrounding solution" in the soils/sediments were proposed as a theoretical model according to the results of preliminary work.. .The center of research work will be the interaction between soils/sediments and its surrounding solution, considering two important forms of phosphorus. One is the transport and transformation processes of Fe-P forced by the organic degradation. The other is the controlling of carbonate equilibrium on Ca-P transport. Considering the change of local hydro-geochemistry, lab-scale experimental apparatus will be designed to obtain the pore water information of soils/sediments, which could indicate the important processes and mechanisms related to phosphorus behavior. Our goal is to estimate the potential and ecological effect of phosphorus releasing from the sediments to overlying water under the two conditions of natural development or heavy human stress on the freshwater system. This research would give an important scientific perspective for understanding this unique system originated from the subsided land.

煤矿开采造成广泛的土地沉陷，潜水位较高的地方则形成大面积沉陷区水域，陆生农田生态系统向水生态系统转化，农业土壤/沉积物中营养元素迁移对水域生态系统营养平衡意义重大。本项目围绕沉陷区"人为活动胁迫-水域生态系统响应"的核心科学问题展开，依据前期工作基础提出土壤/沉积物磷迁移的"有机质输入驱动-环境溶液控制-生态系统响应"的动力学模式。以"土壤/沉积物-环境溶液"相互作用为中心，研究两种重要形态磷的迁移转化过程：（1）有机质分解驱动的Fe-P迁移转化过程；（2）溶液碳酸盐平衡体系控制的Ca-P迁移转化过程。研究以区域水文地质条件为背景，设计室内模拟控制实验，通过环境溶液体系来表征磷迁移相关的重要生物地化过程。沉陷区水域在自然演化和强人为活动两种不同胁迫模式下，土壤/沉积物释磷对水域营养状况的影响及生态环境效应是本项目研究目标所在，本项目研究成果将为沉陷区水域生态环境保护提供关键性的理论基础。

本项目以煤矿开采沉陷生态环境效应为主题，主要研究两淮矿区农田沉陷覆水条件下土壤/沉积物磷（P）赋存形态与分布规律、迁移转化过程与动力学机制、相关生态环境效应等3方面内容。项目重要研究结果包括：.（1）沉陷区水生态环境特征：淮南、淮北沉陷区水域均为碳酸盐缓冲体系控制的弱碱性水体，淮北矿区水体碱度和离子含量均高于淮南矿区。保持自然状态的水域呈“轻度富营养”状态，而受人为活动影响较大的水域已经过度至“中度富营养化”水平，沉陷区水域初级生产总体上体现出P限制的特点。.（2）土壤/沉积物P赋存形态特征和分布规律：纵向剖面上层次差异明显，自表层而下，沉积物中有机质（OM）、总氮（TN）、总磷（TP）、铁氧化物（Feo）等理化指标浓度呈逐渐递减的趋势。淮南矿区Fe/Al结合态P所占比率较大，BD-P和NaOH-P占TP百分比率之和超过50%，而淮北矿区钙结合态磷（HCl-P）占TP百分比率高达70%。.（3）土壤/沉积物中P迁移转化的动力学机制：淮南矿区沉积物P内源负荷潜能主要取决于Fe、Al化合物，而淮北矿区则主要受当地Ca质土壤的影响，Kopáček（2005）经验比率模型适用于淮南矿区P内源负荷风险判别。农田沉陷覆水条件下土壤中Fe2+向沉积物表层迁移，并重新氧化后形成非晶质氧化物而强烈影响P的迁移，而P自身向表层迁移性较弱。淮南矿区覆水土壤中Al：Fe＜3：1，而Al：P＞20：1，P内源负荷风险较小，在外源污染负荷较高的条件下，富集在表层沉积物中的P浓度显著升高，改变了Fe、Al、P的比率结构，厌氧条件下内源负荷风险加大。.（4）水质保护目标及营养盐调控关键阈值：不同水量调蓄和污染负荷模式下，沉陷区水域水体TP浓度分别能够保持在Ⅲ类（≤0.05 mg/L）、Ⅳ（≤0.10 mg/L）和Ⅴ（≤0.20 mg/L）水平范围，其中淮北矿区重要水源地可以执行Ⅲ类水质标准，淮南矿区主要水域可以执行Ⅳ类水质标准，在保证水生态环境健康的同时保持较高的渔业生产潜力。.项目研究成果为两淮沉陷区水质管理和生态环境修复提供了关键性的理论基础。