内源植酸对高原湖滨湿地底泥砷和磷生物有效性的影响机制

The plateau lakeside wetland is of environmental concern due to the dual risk of arsenic (As) pollution and eutrophication. However, the wetland sediments are rich in organic phosphorus (P) (like phytate, the predominant organic phosphorus in soil and sediment), whose effects on As and P transformation especially under various and complex hydrogeology conditions are limited studied. To elucidate the mechanism by which phytate influence sediment As and P transformation as well as the subsequent changes in bioavailability, field in-situ monitoring analysis and indoor simulation experiment under controlled environment are involved in the present project. Besides, single-factor parallelism and multi-factor orthogonality experiments are introduced in the process and mechanism studies. The typical As-contaminated plateau lake wetland Yangzonghai in Yunnan province of China is chosen as the study site. The project focuses on the detailed reaction process and underline mechanism in the endogenous phytate application induced As and P transformation and mobilization in wetland sediments. In addition, the bioavailability of released As and P is estimated via indoor uptake experiment by typical wetland plants (including emerged plant and submerged plant). The aims of the project are to: (1) examine the effect of endogenous phytate on sediment As and P transformation and their subsequent plant uptake and distribution, evaluate their environmental risk, and figure out the most significant phytate speciation and concentration monitoring the transformation process; and (2) evaluate the effect of sediment micro-environment factors (including pH, DOC, Eh, and electrical conductivity) on phytate-mediated As and P transformation and bioavailability variation, focus on the whole reaction process and the underline mechanism, with an aim to identify the most predominant factor in affecting the phytate-induced transformation performance and plant uptake efficiency of sediment As and P. The result and information obtained from the project will help to better evaluate the environmental risk of wetland sediment As and P induced by endogenous phytate in high levels, and provide theoretical and technical supports for environmental risk control, water quality protection and ecological restoration of other similar plateau lakes.

富营养化和砷污染的双重风险加剧了湖泊水环境保护的压力，高原湖滨湿地底泥砷和磷的污染防控是国内外关注的热点问题。本项目以内源植酸为切入点，系统开展其对高原湖滨湿地底泥砷和磷赋存形态转化与植物吸收有效性研究并解决如下两个科学问题：（1）探明内源植酸对底泥砷和磷形态转化及其生物有效性影响机制；（2）明晰湖滨湿地频繁变化的底泥微环境因子对相关过程的影响机制。拟通过野外典型样地的原位监测，初步掌握湖滨湿地底泥内源植酸的时空分布规律和主要微环境因子变化特征；通过开展内源植酸、底泥砷和磷形态转化、湿地植物吸收、底泥微环境因子的单因子平行、多因子正交室内控制模拟试验，逐步筛选出对底泥砷和磷赋存形态转化及植物吸收影响显著的因素，揭示相关过程的机理。研究成果可为准确理解内源植酸对底泥砷和磷生物有效性的影响机制提供理论基础，为其他同类高原湖泊湖滨湿地环境风险控制与生态修复提供依据和支撑。

砷因赋存形态多变和极强的生物蓄积性及高毒性而被广泛关注。磷与砷是同主族化学类似物，具有相似的化学性质和化学行为。磷是植物必须营养元素，亦是引起水体富营养化风险的重要因子。植酸是有机磷的重要组成部分，占比50-80%。植酸通过螯合、置换、酸化等作用强烈影响砷和磷的赋存形态和生物有效性。本项目开展：1）高原湖滨湿地底泥中重金属与磷的总量、分布与形态分析；2）湿地植物砷、磷总量与分布分析；3）植酸对矿物态砷的溶解能力分析；4）碳酸钙对砷生物有效性和砷功能菌群结构的影响4方面研究内容，表明：1）湖滨湿地底泥中As、Cu和Zn含量为740–4081、96–228和869–3331 mg kg–1，As以残渣态为主（>92%），水和碳酸盐结合态占比0.06–0.28%，表明As生物有效性较低。总磷含量为1160-2807 mg kg-1，无机磷含量为164-633 mg kg-1（均值328 mg kg-1），非不稳定型（Oc-P、Ca10-P）含量最高，占比66%；中等不稳定型（Al-P、Fe-P）含量次之，占比23%；不稳定型（Ca8-P、Ca2-P）含量最低，占比11%；2）芦苇As、Zn、Cu含量为44.1–99.4、109–177和12.7–16.4 mg kg–1，转运系数为0.2–1.9，表明主要积累在地下部，富集系数为0.01–0.32，表明芦苇对As、Cu和Zn吸收不显著；3）植酸处理组溶液As浓度（39–82 μM）显著高于柠檬酸（32–63 μM）和草酸（9–66 μM），有机酸:FeAsO4摩尔比=1:1时，植酸溶解39% FeAsO4，表明植酸具有更高的Fe络合能力；4）2、10 g kg–1 Ca使有效态As含量降低54.1%和67.8%。100 mg kg–1 As或10 g kg–1 Ca使As功能菌群物种丰度降低，使arrA和arsC功能菌物种多样性增加，不同As功能菌群结构对As和Ca响应程度存在差异，As表现为arrAarsMarsC，Ca表现为arsMarsCarrA。研究内容可为理解植酸对砷、磷赋存形态转化与释放的影响、过程与作用机制，为降低土壤和沉积物砷、磷污染提供理论依据和技术参考。