Dissolved and colloidal element transport through the coastal transition zone

Moo Joon Shim


There are several factors (e.g., hurricanes, floodplain, and anthropogenic sources) that could modify trace element behavior through the coastal transition zone (CTZ). However, there is still a lack of information about these variables in affecting trace elements in the CTZ. For this study, water samples were collected in the Pearl River (PR), Bay of St. Louis (BSL), and the Mississippi River plume to study the effects of these factors on trace element. A possible effect of Hurricane Katrina on water quality was examined in the East Pearl River (EPR). Hurricane Katrina could have resulted in increased inputs of organic matter and suspended particulate matter in the EPR and thus affected water quality. However, based on a time series analysis of a number of water quality parameters, there was no significant impact of Katrina on the chemistry of the EPR. Hurricanes Katrina and Rita also caused resuspension of sediments in areas of the Louisiana Shelf near the Mississippi River. This could have resulted in significant changes in trace element behavior such as by injection of reducing sediments or increased scavenging. However, the results indicate there was no significant effect on the dissolved trace elements or nutrients. The role of the floodplain along the EPR as an importer or exporter of trace elements and nutrients was investigated. Based on the results, the EPR floodplain can play role as a source for dissolved (e.g., Fe, Mn, Cd, Co, Ni, Pb, Zn, and SiO3 ) and colloidal (e.g., Fe) elements, mostly during high water periods. Hyporheic input was also suggested to explain the observed increased flux of some elements (e.g., dissolved As, Cr, and Cu) because floodplain sources did not seem able to support the flux. Finally, trace element behavior was compared between the lower PR distributaries and BSL. In the lower PR, natural processes were the main mechanisms to explain trace element distributions, and there was no sign to indicate any local anthropogenic sources. In contrast to the PR distributaries, some elements appeared to be affected by anthropogenic input in BSL. For example, Cs appeared to be from the Ti dioxide refinery.