Effect of oil on recruitment from the seed bank of two tidal freshwater wetlands

The effect of oil spills on the recruitment of freshwater tidal wetland species was determined using soil seed bank samples collected in early March from two New Jersey Delaware River marshes. Samples were exposed to simulated tidal cycles 0 (2 days), 2 and 4 wk after soil was collected; 0 wk samples were treated before germination began. Oil treatment significantly reduced survival to I May (end of study) of Acnida cannabina and Bidens laevis, the dominant species, as well as number of species per sample and height of B. laevis. Total perennial seedlings, present in low numbers, also showed significant reduction with treatment. However, during the course of the study, Peltandra virginica recruitment and survival were not reduced by oil treatment and recruitment of Sagittaria latifolia appeared enhanced. There was no consistent pattern regarding which treatment time produced the greatest effect. Interactions (site, treatment, time) were generally not significant. Because these tidal freshwater wetlands and seed banks are dominated by annuals, reduction in seedling numbers and growth could substantially alter vegetation patterns. Timing of oil spills would be important, but impact would depend on species composition of the seed bank and colonizing vegetation, dispersal of seeds into the site, and germination requirements.