The relationship between produced water discharges, and plant biomass and species composition, in three Louisiana marshes

Abstract

Afield analysis of the effect of oil and gas derived produced water discharges on the vegetation of one freshwater and two brackish wetlands in coastal Louisiana was conducted. Aboveground biomass, plant species composition, pH and salinity were measured to determine if the produced water discharge in each marsh was related to differences in plant response. Of the three marshes investigated, only one of the brackish marshes exhibited significantly lower live aboveground biomass at the site receiving produced waters compared to its adjacent reference site. Although interstitial salinities were significantly higher at the treatment site of this brackish marsh, the salinity difference between treatment and reference sites was only 1·5 ppt in a marsh with a mean salinity of 11·9 ppt. This salinity difference should have no discernible biological effect on the brackish species inhabiting this marsh. Also, the differences in species composition between treatment and reference sites of each marsh did not indicate a produced water effect. Thus, at these three produced water discharge sites the dilution of the produced water in the discharge canals, plus the sinking of higher density produced water to canal bottoms (thus making it less available for tidal movement into the marsh), appears to prevent a biologically significant negative impact on the marsh vegetation. Whether this conclusion is valid for other produced water sites needs further evaluation.