| Biogeochemical research was conducted in the Delaware Inland Bays from 2001 to 2004 to understand the effects of seasonal anoxia on fish kills and algal community structure distribution. Eutrophication and poor flushing produced seasonal anoxia in Torquay Canal and Bald Eagle Creek, tributaries of the Delaware Inland Bays. Subaqueous mud from these tributaries was used for housing development during the 1960s which created a dozen holes. The normal water depth is 2 m whereas the holes are 5.5 m. Fish kills occurred in these areas in 2000 and 2003--4. By using solid-state gold/amalgam microelectrodes, dissolved O2 and H2S were measured in situ to document seasonal anoxia. Temperature, salinity, pH, nutrients, Chl a, algal community structure, Fe, Mn and S species were analyzed to understand biogeochemical processes.; The water column stratified from May to September in all holes every year. O2 was saturated in surface waters but not detectable in bottom waters. Over 1 mM H2S was measured in bottom waters. Storm events mixed the water column releasing H2S to surface water. H 2S appears to be the primary cause for fish kills in these tributaries. Seasonal anoxia in the Delaware Inland Bays is a potential threat to fish and shellfish and promotes harmful algal blooms. High concentrations of H 2S, NH4+ and PO43- were produced from organic matter decomposition and iron (oxy)hydroxides reduction in bottom waters during summer. Diatoms occurred when O2 was measured in bottom waters, whereas dinoflagellates and flagellates dominated in surface, interface and bottom waters during seasonal anoxia. Seasonal anoxia caused shifts of phytoplankton community structure and promoted harmful algal blooms.; Fe was the dominant metal in the oxidation and precipitation of H 2S in this ecosystem. In situ voltammetry detected FeSaq (molecular clusters) which are reactive, and led to FeS precipitation. Sulfide was oxidized by Fe in a catalytic cycle to form S8, which reached 30 muM total S(0) at the interface. Therefore, iron redox chemistry prevented H2S from releasing to surface waters during stable weather conditions; however, when storms came, physical mixing disrupted the Fe catalytic cycle releasing H2S to surface waters. |
