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, Sp artina alterniflora, Spartina patens and Sagittaria lancifolia, of thr ee types of coastal wetlands, salt, brackish and freshwater marshes, r espectively, 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 pho tosynthetic rate of S. alterniflora was not significantly reduced by o il application until 3 months. The photosynthetic rate of S. lancifoli a was not detrimentally affected by the oil treatments. Four months af ter oil application, Live above-ground biomass production was signific antly reduced at higher oil dosages for S. patens, was not affected in S, alterniflora, while S, lancifolia exhibited significantly higher t otal biomass at 24 l m(-2) compared to the controls. The year followin g oil application, no regrowth of S. patens and S. alterniflora occurr ed at oil levels above 8 l m(-2), In contrast, the regrowth of above-g round biomass of S. lancifolia increased with dosage and resulted incr easing oil monospecific communities at Furthermore, the residual oil i n the soil greatly differed among the three marsh-types, with the high est concentrations in the S. patens soil sods and the lowest concentra tions in S, alterniflora soil sods. This difference in oil residue amo ng the marsh-types was mainly due to differences in soil organic conte nt, The sensitivity of these marsh-types to south Louisiana crude oil increased in the following order: S. lancifolia, S. alterniflora and S . patens.