A comparative investigation of the effects of south Louisiana crude oil on the vegetation of fresh, brackish and salt marshes

The impact of south Louisiana crude oil on the dominant vegetation, Spartina alterniflora, Spartina patens and Sagittaria lancifolia, of three types of coastal wetlands, salt, brackish and freshwater marshes, respectively, was studied. In the greenhouse, south Louisiana crude oil was applied to natural marsh sods at rates of 0, 4, 8, 16 and 24 l m−2. The photosynthetic rate of S. patens significantly decreased with increasing oil dosage after 1 month of oil application, while the photosynthetic rate of S. alterniflora was not significantly reduced by oil application until 3 months. The photosynthetic rate of S. lancifolia was not detrimentally affected by the oil treatments. Four months after oil application, live above-ground biomass production was significantly reduced at higher oil dosages for S. patens, was not affected in S. alterniflora, while S. lancifolia exhibited significantly higher total biomass at 24 l m−2 compared to the controls. The year following oil application, no regrowth of S. patens and S. alterniflora occurred at oil levels above 8 l m−2. In contrast, the regrowth of above-ground biomass of S. lancifolia increased with increasing oil dosage and resulted in monospecific communities at 16 and 24 l m−2. Furthermore, the residual oil in the soil greatly differed among the three marsh-types, with the highest concentrations in the S. patens soil sods and the lowest concentrations in S. alterniflora soil sods. This difference in oil residue among the marsh-types was mainly due to differences in soil organic content. The sensitivity of these marsh-types to south Louisiana crude oil increased in the following order: S. lancifolia, S. alterniflora and S. patens.