水位波动对浅层地下水系统中磷迁移富集规律的影响研究

Based on the phenomenon of “The enrichment of phosphorus in groundwater was found in water level fluctuation zone of Jianghan Plain”, the scientific hypothesis that the major source of phosphorus in groundwater is attributed to its release from soil or sediment was proposed in this study according to the hydrological changes. According to the scientific proposal “The migration and enrichment of phosphorus in groundwater was driven by water level variation”, the influences of water level fluctuation on the migration and transformation of phosphorus in the unsaturated and aquifer were studied to discover the enrichment of phosphorus in groundwater by combining simulation and field experiments. Especially, the biogeochemistry processes and their spatial and temporal variation characteristics in the unsaturated and the saturated zones were identified during water level changes. The coupled model with multi-processes was established to evaluate quantitatively the influences of changing water level on the release of phosphorus from soil or sediment, which provided a new understanding for the phosphorus cycle in groundwater and a scientific evidence for the prevention and control of water eutrophication.

本研究基于“江汉平原地下水位波动区域地下水中磷富集”现象，从水文变化角度提出“土壤/沉积物中磷的释放可能是地下水中磷的主要来源”的科学假设。针对“水位波动驱动着地下水中磷的迁移富集”这一科学问题，以室内模拟和野外实验相结合的方法，研究江汉平原水位波动对非饱和带-含水层中磷运移、转化机制的影响，揭示水位波动对浅层地下水系统中磷迁移富集的影响机制。重点识别水位波动过程中非饱和带-含水层系统中的生物地球化学过程及其时空变化特征，建立水位波动下浅层地下水系统中磷迁移富集的多过程耦合模型，定量评价水位波动对土壤/沉积物中磷迁移转化过程的影响，为地下水中磷循环提供新认识，并为防治水体富营养化提供科学依据。

地下水作为水环境系统的重要组成部分，与地表水交互作用，直接将氮磷等污染物排入地表水体，成为水体富营养化的重要污染源。该项目依托地下水位波动强烈的江汉平原区域，采用室内模拟与野外观测实验相结合的方法，研究水位波动影响下非饱和带-含水层系统结构时空变异过程中的生物地球化学作用及微生物生态环境效应，揭示水位波动对浅层地下水系统中磷迁移富集的影响机制。结果表明：地下水中磷含量出现明显富集，高达2.0mg/L，且土壤沉积物中有效磷含量高达1114mg/kg，超过了环境阈值而饱和。在高达1.6m季节性水位波动条件下，地下水中高含量磷向地表水排泄，水力传导系数为0.0074~7.302 m/d，其中溶解性磷在沉积物-水界面的扩散通量范围为-0.058-0.180mg/(m2•d)，平均值为0.028mg/(m2•d)。室内模拟实验表明地下水中磷的扩散通量与地下氧化还原环境、水体中磷浓度以及温度等密切相关；野外降雨模拟实验表明包气带磷的释放与土壤类型及土壤磷的饱和度密切相关。一方面，水位波动促使土壤沉积物中铁/锰氧化物和含磷矿物（如蓝铁矿）还原溶解，是导致地下水中磷富集的主要来源；另一方面，水位波动改变了地下水水化学特性（如碱度的变化、pH等），打破了地下水中磷平衡而释放。地下环境中微生物不仅直接参与氧化还原物种的转化，而且影响土壤沉积物中磷矿物的磷释放，从而使其在地下水中富集。研究结果为地下水中磷循环提供了新认识，并为防治水体富营养化提供了科学依据。