The seasonal distribution of macrobenthos and sediments chronically impacted by oil/gas field produced water

Typescript (photocopy).Little is known about how climatic events (i.e., heavy rain, drought, etc.) inhibit or enhance movement of petroleum hydrocarbon laden sediments in estaurine systems and how this in turn effects the macrobenthic populations exposed to them. Seventeen collection stations were established and monitored at New Bayou, Texas, a small gradient estuary which receives petroleum products via oil/gas field produced water discharge. Hydrographic, geologic and biotic samples were taken monthly from each station during a period of reduced rainfall (May 1980 - April 1981) and during a period of heavy rainfall and subsequent bayou flushing (May 1981 - August 1981). Both temperature and dissolved oxygen data taken during the study followed patterns typical for the area. Salinity values increased into the polyhaline range at near-bay stations during the reduced rain period, while upper bayou stations remained within the oligohaline range. A rapid decrease in salinity was noted at all stations following bayou flushing. Sediment grain sizes along the bayou were generally in the silty-clay range from May 1980 to April 1981, and were altered into the clayey-silt range with the onset of bayou flushing. Sediment hydrocarbons concentrations were highest (11.4 mg/g dry sediment) around the produced water discharge site and lowest at near-bay stations (0.2 mg/g dry sediment). Bayou flushing resuspended the hydrocarbon laden sediments and carried them downstream and out of the system. Ninety-six macrobenthic species (91,594 individuals) were collected during the study. General effects from produced water discharge on macrobenthic populations followed the classical pattern outlined by other research. A sediment hydrocarbon concentration of 2.5 mg/g dry sediment was found to reflect the average value needed to depress population abundances. Both abundance and diversity values were lowest at central stations near the discharge site. Bayou flushing significantly altered the community composition along the bayou. Freshwater species invaded stations further downstream, and the previous ubiquitous species component was pushed downstream towards the higher salinities. Percent composition of the polychaetes decreased while insect percent composition increased. An influx of adult organisms was noted at the central stations after hydrocarbon laden sediments were removed, but no true community was ever established