稻蟹共作农田底泥中PAHs释放迁移规律与生物富集机制

Rice-crab culture system is new ecological agriculture model, and considered to achieve both rice and crab. However, the people only focused on the ecological agriculture system and ignored the potential ecological risk of PAHs in sediment of this model at present. The studies on the mechanism of PAHs in sediment release to water, transfer to sediment, and bioaccumulation were scarce. The microcosm system is built to show these mechanisms in rice-crab culture system under combine bioturbation of crab and other macrobenthos in this project. The release dynamic mechanism of PAHs from sediment to water will be carried out by release kinetics. The impact of the DOM from crab on the PAHs absorbing on the surface of sediment will be identified. The mechanism of synergistic effect on the release of PAHs in sediments for different bioturbation types will be discussed. Based on fluorescent tracer technique, the migration of PAHs in sediment by the carrier of sediment particles in sediments will be revealed. The migration of PAHs in different depth sediment under different bioturbation will be explored to show the form mechanism of PAHs source and sink in sediment of rice-crab culture field. The bioaccumulation of PAHs in the crabs, rice and fish in paddy field will be studied.Using SPMD membrane instead of fish, the PAHs content in bioturbation, rice and SPMD will be measured. The biological sediment accumulation factor, rice enrichment coefficient and migration coefficient, and SPMD-accumulation factor will be calculated. The correlation between the enrichment coefficients and physiochemical factors in water and sediment will be fitted and quantified, and thus will show the mechanism of aquatic organisms bioaccumulation of PAHs in both water and sediment by single and combined bioturbation in rice-crab culture system. This study will provide the most important information of theoretical guidance and technical support on the PAHs pollution prevention and controlling, risk reduction in rice-crab culture field.

稻蟹共作是结合水稻种植与蟹类养殖的新型生态农业模式，目前仅专注于生产理论与技术体系建设，而忽视了稻田底泥中多环芳烃PAHs的潜在生态风险，底泥中PAHs向水体释放、底泥迁移以及生物富集的研究匮乏。本项目构建蟹类单独扰动以及蟹与其它底栖动物联合扰动的微宇宙系统，分析底泥中PAHs向水体释放的动力学特征，明确蟹类排放的溶解性有机物DOM对底泥吸附PAHs的影响，揭示联合扰动对底泥中PAHs释放的协同作用机制。基于荧光示踪技术考察底泥颗粒物在底泥中的迁移特征，量化不同深度底泥中PAHs的变化，揭示底泥PAHs迁移所致的源与汇的形成机制。以SPMD膜代替鱼类，测定生物扰动者、水稻、SPMD内PAHs含量；计算生物-底泥积累因子、水稻富集系数与迁移系数、SPMD-沉积物累积因子，拟合量化富集系数与水-底泥理化因子的相关性，揭示系统中PAHs生物富集机制。成果将为降低农田系统PAHs生态风险提供依据。

稻蟹共作是结合水稻种植与蟹类养殖的新型生态农业模式，目前多数研究忽视了稻田底泥中PAHs因生物扰动而释放迁移所造成的潜在生物富集效应。本项目通过构建蟹类以及与其它底栖动物联合扰动的微宇宙系统，进行了相应研究，成果将为降低农田系统PAHs生态风险提供依据。其研究结论阐述如下：. （1）分析底泥PAHs向水体释放的动力学特征结果可知，生物扰动提高了上覆水中DOC和TSS含量，促进底泥颗粒物再悬浮。其中，泥鳅和蟹扰动组中颗粒态菲含量与TSS分别呈弱正相关性和极显著正相关性（p＜0.05）。上覆水中70 %的菲形态主要以颗粒态为主。就底泥中不同浓度蟹类DOM对菲的吸附特征曲线而言，7 mg/L蟹类DOM符合Langmuir模型，35 mg/L蟹类DOM符合Freundlich模型。进一步结合紫外SUV254和SR的数据提出了低浓度蟹类DOM对菲的大分子竞争-增容吸附模型和高浓度DOM小分子对菲的共吸附-累积模型，明确了蟹类DOM对底泥吸附PAHs的影响，揭示了生物扰动对底泥中PAHs释放的协同作用机制。. （2）基于荧光示踪技术考察底泥颗粒物在底泥中的迁移特征结果表明，泥鳅可使荧光物迁移至底泥2-4 cm处，而蟹类最大迁移深度为4-6 cm。就整体而言，蟹类生物扰动系数为Db=23.6×10-3 cm2/d，相比泥鳅Db=0.4×10-3 cm2/d较大。生物扰动作用改变底泥理化性质以及造成底泥颗粒空间位置发生位移，导致各底泥层中菲含量随深度发生变化，揭示了底泥PAHs迁移所致的源与汇的形成机制。. （3）分析各生物介质中PAHs富集含量可知菲在水稻中的浓度为根 (138.7 mg/kg)＞茎(8.39 mg/kg)＞叶(6.47 mg/g)；泥鳅体内菲浓度呈现先上升后下降的变化规律；蟹类体内菲浓度波动较大，在前20d增长迅速；至实验30d结束时，SPMD膜-鱼的浓度为15.15mg/kg。进一步计算其生物富集系数BSAF、BSSAF和BAF值可知，蟹和泥鳅的生物富集能力相比SPMD膜-鱼和水稻的较小，尤其是鱼和水稻对于菲的积累趋势在不同扰动组具有显著差异（p<0.05)。通过拟合量化富集系数与水-底泥理化因子的相关性得出了菲在生物体内的富集程度受上覆水中的菲浓度、TSS和DOC浓度的联合影响，揭示了系统中PAHs生物富集的不同机制。