Sub-lethal effects of coastal petroluem pollution on Spartina alterniflora stem epiphytes

Sub-lethal effects of diesel fuel on N2 fixing Spartina alterniflora stem microbial epiphytes from North Carolina salt marshes were examined to assess impacts of chronic petroleum pollution on the structure and function of this ecologically-important habitat in southeastern US estuaries. Changes in nitrogenase activity (NA), primary productivity, and chlorophyll (Chi ) were assessed following short-term (3 hour) and longterm (4 day) exposures to a range of diesel fuel concentrations (0.87–17,400 ppm). In short-term experiments no effect was observed on Chi values and reductions in NA and primary productivity occurred only following exposure to high concentrations of diesel fuel (>5,000 ppm). Long-term incubations produced reductions in both NA and Chi at diesel fuel concentrations of 87 and 435 ppm. Primary productivity was reduced at additions ≥ 8.7 ppm. Reduction in phototrophy and NA resulting from sublethal concentrations of petroleum pollution may affect biogeochemical cycling and trophodynamics in salt marshes.