季节性冻融区磷在退耕还湿土壤团聚体滞留-释放的机制研究

Riparian wetlands, the aquatic–terrestrial ecotone, had large impact on the transfer of chemical materials between water and sediments. In recent years,converting croplands to wetlands was an important practice to wetland restoration in China. Due to intense agricultural activities, large amounts of insoluble inorganic phosphorus (P) from fertilizer were accumulated in topsoils. Therefore, during the wetlands restoration process, phosphorus released from soil maybe reduce the purification capacity of wetlands, and then increase the risk of phosphorus transfer into river water. In Northeast China, drying-wetting rotation, freezing-thawing and soil organic material contents had remarkble influence on wetland soil aggregate structure, thus resulting in the variations in soil P retention and release. However, the mechanism of above mentioned phenomenon is still not identified, thus the following work should be done in this project. First, aggregates structure and phosphorus species will be analyzed and the factors influencing the phosphorus distribution will be determined during restoring process. Second, for identification of phosphorus loss risk in the restored wetlands, potential release capacity of phosphorus bound in different soil aggregate will be assessed and release flux of phosphorus will be estimated in different recovery water level. At last, the phosphorus distribution in the soil - water interface will be quantitatively analyzed during the process of transforming P pollution source into sink in the wetland soil using TEM-EDS, XANES and 31P NMR. Furthermore, the influence of soil aggregates structure on the phosphorus retention and release will be determined in micro-scale. The research results will be useful for mitigating the potential soil phosphorus loss in the restored wetlands from cultivated land in the seasonal freezing-thawing regions.

退耕还湿是增加湿地面积的重要途径。由于农业垦殖活动，磷以无机难溶态在土壤表层累积；恢复为湿地后，环境因子的改变使湿地磷不断进行着外源净化-内源释放的过程转化。东北地区受干湿交替、冻融作用和有机质增加等因素的影响，土壤团聚体结构改变剧烈，土壤对磷的滞留-释放能力受团聚体结构的影响显著，而该影响机制目前尚不明确。本项目拟以土壤团聚体为基本单元，剖析湿地恢复过程中土壤团聚体结构及结合磷形态的变化，识别影响团聚体中磷分布的驱动因子；评估不同结构团聚体结合磷的释放潜力，进而估算不同恢复水位下磷的释放通量；综合扫描电镜能谱（TEM-EDS）、X 射线吸收近边结构光谱（XANES）和核磁共振31P NMR等现代技术定量分析磷在湿地土-水界面的分布特征，在微观尺度上揭示土壤团聚体对湿地土壤磷滞留-释放过程的影响机制。研究成果为识别和降低季节性冻融区退耕还湿土壤磷潜在流失风险提供理论支持和技术指导。

东北地区受干湿交替、冻融作用和有机质增加等因素的影响，土壤团聚体结构改变剧烈，土壤对磷的滞留-释放能力受团聚体结构的影响显著，而该影响机制目前尚不明确。本研究以土壤团聚体为基本单元，分析不同退耕年限（退耕年限：1、2、3、5、13和19年）土壤团聚体结构及结合磷形态的变化。研究发现：恢复湿地土壤团聚体稳定性均高于农田，且随湿地恢复年限的延长呈先升高后降低趋势。湿地恢复0-5年内，细粒径团聚体（<0.25 mm）先胶结成粗团聚体，然后又破碎成细粒径团聚体，直至第5年团聚体结构达到相对稳定水平；> 1 mm和0.25-1 mm粒径团聚体对磷的固持能力随湿地恢复年限的延长呈先降低后升高趋势，而0.053-0.25 mm和< 0.053 mm粒径团聚体对磷的固持能力则持续降低。湿地恢复初期，Fe.Al-P和Hu-P的释放风险相对较高，特别是三江平原雨季（6-8月份）需重点关注磷释放风险。.冻融循环造成恢复湿地土壤团聚体磷形态的再分配，土壤团聚体有机碳的降低是磷组分在团聚体中迁移的关键影响因素（解释量为39.6%）。冻融循环作用加速了土壤磷素的矿化过程，饱和含水量处理降低磷的移动性，从而降低了磷释放风险。干湿交替过程造成有效磷含量下降，潜在移动态磷含量增加，不稳定无机磷的含量向有机磷转化。不同干旱程度导致恢复湿地土壤磷的移动性和矿化过程不同，正常降雨和极端干旱情况下增加了土壤磷的潜在移动风险，但磷的矿化过程并没有受到明显的影响，中等干旱情况下加快了磷的矿化过程。冻融循环和干湿交替作用能够加剧恢复湿地初期土壤磷素的不稳定性，在深秋和早春，应增加湿地淹水，降低磷的释放风险。.本项目在微观尺度上揭示土壤团聚体对湿地土壤磷滞留-释放过程的影响机制，研究成果为识别和降低季节性冻融区退耕还湿土壤磷潜在流失风险提供理论支持和技术指导。发表论文10篇，培养学生3名。