Distributions And Seasonal Variations Of Arsenic In The Sanggou Bay And Coastal Area Of The Changjiang Estuary

Arsenic is a metalloid element which occurs ubiquitously in nature, and many countries list arsenic as the main inspected pollution in the environment. Since arsenate has similar chemical structure with phosphate and can be assimilated by the phytoplankton when phosphate concentration is quite low, the study of marine biogeochemical cycle arsenic causes widely attentions. The investigations were carried out in the Sanggou Bay and in the coastal area of the Changjiang estuary, where were influenced by significant anthropogenic activities. The concentrations of total dissolved inorganic arsenic (TDIAs,TDIAs=[As3+] + [As5+]), dissolved organic arsenic(DOAs) and total arsenic in the sediments in the Sanggou Bay and the coastal area of the Changjiang estuary, and fluxes of arsenic at the sediment-water interface of the coastal area of the Changjiang estuary were studied. The distributions and seasonal variations of arsenic in the study areas are primarily discussed.The Sanggou Bay locates at the east of the Shandong peninsula and is famous with its strong aquaculture activities. Four cruises were carried out in the Sanggou Bay in April, July, November of 2006 and January of 2007. The average concentrations of the TDIAs are 9.3±1.6 nmol.L-1, 8.3±2.2 nmol.L-1, 18.5±0.6 nmol.L-1 and 17.9±2.0 nmol.L-1, respectively. The concentrations of dissolved organic arsenic are 6.1±0.6 nmol/L,6.1±1.0 nmol/L,4.3±1.9 nmol/L,3.6±2.0 nmol/L, respectively. The average concentrations of total arsenic in the sediments are 7.7±1.5μg.g-1, 9.1±2.2μg.g-1, 9.4±1.2μg.g-1 and 6.8±0.7μg.g-1, respectively. The seasonal variations of TDIAs may be caused by both the biological and hydrological reasons. During the spring and summer, when the kelp and scallop were flourishing, the complementarity of TDIAs from the Yellow Sea was constrained by the aquaculture seriously. Both the reasons resulted in the relative low TDIAs concentrations in the spring and summer. On the contrary, during the fall and winter, when the water exchange ability with the Yellow Sea was increase and the biological absorptions were decreased in the Sanggou Bay, the concentrations of TDIAs were similar with the Yellow Sea. The concentrations of dissolved organic arsenic are higher correspondied to high phytoplankton activities. The concentrations of arsenic in the sediment vary with seasons, higher in the summer and fall while lower in the winter and spring.In June, August and October of 2006, three cruises were carried out in the coastal area of the Changjiang estuary. The distributions and seasonal variations of TDIAs in the coastal area of the Changjiang esuturay and the flux at the interface of sediment-water were investigated. The average concentrations of TDIAs are 11.8±4.7nmol.L-1, 27.9±17.1nmol.L-1 and 19.8±3.0 nmol.L-1, and the dissolved organic arsenic concentrations are 4.3±3.0 nmol/L, 5.2±3.3 nmol/L, 2.2±1.3 nmol/L, respectively. The concentrations of TDIAs were higher in the bottom than the surface in June, and decreased with the distance off the coast. In August, the concentrations of TDIAs were higher in the coastal area and hypoxia area. The concentrations of TDIAs were decreased with the distance off the coast in October. The distributions of TDIAs were influenced by the mixing of different water masses. The vertical profiles of TDIAs were higher in the bottom water. The dissolved organic arsenic distribution was resemble with the chlorophyl a, indicate that the dissolved organic arsenic is drived from the mediation of phytoplankton. The distributions of arsenic in the sediment were decreased with the distance off the coast. The concentration of arsenic was lower in August than June and October. The flux of arsenic at the sediment-water interface was influenced not only by oxic/anoxic environment, but also by the sediment types and other factors (e.g. the TDIAs concentrations in the overlying water and sampling depth of the sediment). The release of arsenic from the sediment water interface may be one reason for the higher concentration of TDIAs in the bottom layer.