外源磷对高原湖滨湿地沉积物砷形态转化及生物有效性的影响机制

Nowadays, plateau lakeshore wetland which are facing double environmental risk both from eutrophication and arsenic contamination is becoming a hot spot as the feature of limitation of recharging sources and long period of changing water of Plateau Lake and the outstanding pollution retention ability of lakeshore wetland. The researchers begin to focus on the effects of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic in plateau lakeshore wetland. However, the existing researches could not explain the effects of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic in plateau lakeshore wetland. In the proposal, the lakeshore wetland sediments with different arsenic contamination extent are selected as the research objects, and we intend to solve the following two scientific problems: (1) To explore the mechanisms controlling the effects of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic in lakeshore wetland; (2) To identify the key controlling micro-environmental factors which dominates the effect of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic in lakeshore wetland. To achieve our goal, we would choose lakeshore wetlands sediments with different arsenic contamination extent and carry out the field monitoring experiment, upon which we could ascertain the distribution status of arsenic speciation and also the range of micro-environmental factors. Based on these original data, we would carry out the indoor simulation experiment by using the diffusive gradient in the thin-film (DGT) technique as a tool, to make it clear that the influencing rule of speciation and concentration of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic. Furthermore, we would explore the mechanism which dominates the effects of exogenous phosphorus on the speciation transformation and bioavailability of sediment arsenic through systematical analyzing the speciation and concentration distribution of arsenic and phosphorus both in sediment and pore water and the characterization results of arsenic and phosphorus speciation distribution from senior spectrum characterization (X-ray absorption spectrum). Finally, we would carry out the micro-environmental factors controlling experiments through single-factor parallel and multi-factor orthogonal manners to identify the key micro-environmental factors and their range of thresholds which drive both the speciation transformation from relatively active speciation to inert one and the bioavailability decreasing of sediment arsenic. The results of this research could provide scientific basis for precisely evaluating the ecological risk of arsenic contamination sediment in plateau lakeshore wetland under the influence of exogenous phosphorus.

面临富营养化及砷污染双重风险的高原湖滨湿地成为研究热点，外源磷对湖滨湿地沉积物砷形态转化及生物有效性的影响值得关注。本项目以不同砷污染程度的湖滨湿地沉积物为研究对象，拟解决以下两个科学问题：（1）探明外源磷影响湖滨湿地沉积物砷形态转化和生物有效性的机制；（2）识别外源磷影响湖滨湿地沉积物砷形态转化和生物有效性的关键调控微环境因子。本项目在野外监测探明砷形态分布规律及微环境因子范围的基础上，通过室内模拟实验并借助梯度扩散薄膜（DGT）技术，弄清外源磷形态和浓度对砷形态转化及生物有效性的影响规律；结合砷、磷在沉积物和孔隙水的浓度及高级谱学（X射线吸收光谱）表征的形态分布结果，系统揭示外源磷的影响机制；通过控制微环境因子的单因子平行和多因子正交实验，识别砷形态向惰性转化，生物有效性降低的关键微环境因子阈值范围。研究结果可为准确评价外源磷影响下的砷污染高原湖滨湿地沉积物的生态风险提供科学依据。

采用室内试验的手段揭示湖滨湿地沉积物中砷和磷的相互作用机制及影响调控因素，旨在为准确评估阳宗海沉积物中砷和磷的潜在风险提供基础数据，主要研究结果显示：.（1）沉积物中砷和磷的活性态及含量对其吸附磷的能力有重要影响，高活性成分的比例越大影响越大；沉积物中弱酸提取态砷、可还原态砷及上覆水-pH对沉积物吸附磷有重要贡献；上覆水磷浓度的升高能促进沉积物砷的释放，污染风险增加。磷的输入能显著增加沉积物中总磷的含量，生态风险也随之增加；.（2）磷浓度为0~20 mg/L时，底层总磷增加量大于表层总磷增加量，磷浓度40~100 mg/L时，表层总磷增加量大于底层总磷增加量；磷浓度大于60 mg/L时，表层沉积物和底层沉积物总磷均为较高风险；上覆水中磷浓度的增加能够显著的改变沉积物中总磷的浓度，磷浓度达到20 mg/L，沉积物总磷达到中度污染水平。磷浓度达到40 mg/L，沉积物总磷达到重度污染水平；上覆水中磷对沉积物总磷的浓度有重要贡献。磷的进入能够促使表层沉积物中砷的释放，能使沉积物总砷的浓度低于土壤环境质量标准值，降低砷的环境风险，沉积物对于污染物的蓄积具有重要意义；.（3）随着磷的输入，活性态磷的比值越来越大，表层沉积物的活性比均值为2.35，底层沉积物的活性比均值为2.69；底层沉积物的活性态增量要大于表层沉积物。磷的输入能改变底泥中各结合态砷的比例，随着实验时间的延长，底泥活性态砷明显增加；风险评价编码法评价结果表明：随着实验时间的延长和磷浓度的增加，沉积物中弱酸提取态砷占比均低于1%，可以判定为低风险；.（4）砷浓度的处理及处理时间的能改变沉积物中各形态砷和磷的占比，随着砷处理浓度的升高，沉积物非活性态磷向活性态磷转化，沉积物活性砷逐渐向残渣态转化。随着磷浓度的升高，不用浓度砷沉积物中砷的释放量均呈现上升趋势。.5）小于200 mg/kg As处理会一定程度促进细菌丰富度，使群落结构复杂多样；随着As处理浓度的升高，微生物丰富度呈下降趋势，群落结构趋于简单。土壤微生物对于As污染有较为敏感的响应。砷形态对于底泥中微生物存在较强的影响，其中影响程度较高的是非专性吸附态砷（F1）和弱结晶水合铁铝氧化物结合态砷（F3）。