| Due to suffering from both land and ocean impact, the physical and chemical reactions are complicated in estuarine wetland and bay. Moreover, these areas are affected by persistent organic pollutant discharged from human activities, which make the environment very vulnerability. Thus, the study of biogeochemistry in these areas is very important and emergency. In this research, the PAHs distributions in surface sediments from estuary are studied in Yangtze estuary and Mississippi river estuary, the PAHs transport among different interfaces are also studied in Nueces delta, Chongming Dongtan wetland and Mission-Aransas reserve, respectively. The PAHs accumulation in zooplankton is studied in North Gulf of Mexico as well.The PAHs concentrations in tidal marsh from Yangtze river estuary range from252.2to627.0ng g-1, which range from39.4to177.5ng g-1in river plume sediments. The PAHs concentration is higher in tidal marsh than river plume and higher in southern marsh than northern marsh. The PAHs concentrations in surface sediments from Mississippi river estuary range from174.5～990.9ng g-1which are the highest i river plume and oil spill station. The PAHs concentrations decrease from estuary to ocean in both two areas. In term of PAHs compositions,3～4rings PAHs are dominate in both two areas, accounting for more than60%. The5～6rings PAHs decrease with the sampling location far from estuary. The PAHs in two areas are suggested both from combustion by source analysis. However, the PAHs in Yangtze river estuary are from coal or biomass combustion, while those are from petroleum combustion in Mississippi river estuary. This is consistent with the energy consume in these two areas. There is no significant correlation between PAHs and TOC in this study, but the distance between sediments and pollution source, hydrodynamic force and deposition affect PAHs distribution in estuary area. Although the PAHs concentrations are lower than EFL, they may still harmful to the ecosystem. Rapid released PAHs from sediments are more bioavailable, thus, the PAHs behave between sediments and water is studied. The results show the dry-wet cycle would affect PAHs distribution between water and sediments. Phe, Flua and Pyr were released preferentially into the water phase from sediments after dried-wet cycles. The results also indicate drying would change the structure of SOM, which may cause the rapid release of PAHs. The results also show large particles are easier to release PAHs than fine particles, and pctrogenic source PAHs are easier to release than pyrolysis PAHs. The sorption-desorption experiments show different impact of drying on aged and fresh PAHs. Aged PAHs may enter into the interior of hydrophobic part in SOM. Drying may expose these groups or decrease the force between SOM and these groups, which may increase PAHs rapid release. However, the fresh PAHs may be absorbed on the surface or the microspores in SOM, drying may make the microspores or3D structure of SOM collapse, which seal the PAHs in SOM and inhibit PAHs rapid release.The study on PAHs transfer between sediments and plants show that the PAHs concentrations in rhizospheric sediments are from56.8-102.4ng g-1, which are lower than those in surface sediments with plants(112.4～136.2ng g-1) and higher than tho in surface sediments without plants(38.7～109.9ng g-1). This indicates the PAHs would transfer between sediments and plants. The PAHs concentrations in the issues range from51.9～181.2ng g-1, which increase from bottom to top in plants except Spartina. The similar PAHs compositions in each issue suggest the same mechanism of PAHs distribution in the issues. The significant correlation is found between PAHs concentration in leaves and PAHs concentration in surface sediments, as well as between PAHs concentration in roots and PAHs concentration in rhizospheric sediments. This means the PAHs in surface sediments may come from falling leaves and the PAHs in roots may come from rhizospheric sediments. Low molecule weight PAHs are dominate in both sediments and plants issues, but the sediments contain more high molecule weight PAHs than plants. The source analysis indicates the PAHs in sediments are form pyrolysis, but the PAHs in plants are from mixture of pyrolysis and petrogenic, indicating that the plants could accumulate PAHs by root absorb and atmospheric deposition. The difference in PAHs compositions between sediments and plants found by PCA suggests different sources. RCFs indicate low-medium molecule weight PAHs are easier to accumulate in plants than high molecule weight PAHs. Further analysis suggests the RCFs are correlation with Kow.The PAHs transfer between sediments and crabs is compared between Chong ming dongtan wetland and Mission-Aransas nature reserve. The PAHs concentrations in crabs range from37.3～103.4ng g-1, suggesting PAHs would accumulation is stable in the crabs and not affected by PAHs concentrations in sediments. The PAHs concentrations are different in female and male crabs due to the different growth cycles. In winter and spring, the PAHs concentration in female crab is lower, while it is opposite in autumn and summer. BAFs suggest the low molecule weight PAHs are easier to accumulate in crab but high molecule weight PAHs are not. The source analysis indicates the PAHs in sediments are from pyrolysis while the PAHs in crabs are from petroluem, which means the crab may mainly take up PAHs from water. The PAHs are more readily to accumulate in the crab from Dongtan wetland than that from Mission Aransas, indicating the PAHs accumulation in the crabs is correlation with the growth cycles and feeding behaves.The PAHs transfer between water and aquatic organism show that the PAHs concentrations are30.8ng L-1in water,492.0ng g-1in suspension particles,366.6ng g-1in plankton and100ng g-1in fish, respectively. There is no magnification with the trophic level, however, we do observe the PAHs dilute with trophic level by TMF. In organisms,2～3rings PAHs are dominate, accounting for more than60%,4rings PAHs could be detected in all organisms, however,5～6rings PAHs can be detected only in few samples. The results indicate the PAHs would accumulate in high level organisms.Because the PAHs would be accumulated in zooplankton, the mechanism of PAHs accumulation in zooplankton is studied in North Gulf of Mexico. The average PAHs concentrations in zooplankton increase first then decrease with the location far from estuary. The good correlation is found between lipid and PAHs concentrations in ocean but not in estuary, which indicate the complicated mechanism of PAHs associate with zooplankton in estuary. The PAHs in different size fraction zooplankton range from200to900ng g-1, with highest in500-1000μm size fraction, which contain Tunicata more than other size fractions. This suggests Tunicata may have higher accumulation ability than other species. Crude oil incubation experiments show the Copepods would accumulate more4rings PAHs than low molecule weight PAHs. The results also indicate the zooplankton accumulate PAHs by both sorption and ingestion. |
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