Seed bank and vegetation of a constructed reservoir

Vegetation development in constructed wetlands may be accelerated by planting aquatic and emergent species, especially when wetland seed banks are not initially present. Environmental patchiness of convoluted shorelines may enhance or retard establishment of planted or natural vegetation. Development of the seed bank may be influenced both by planting patterns and by shoreline convolutions. To determine if seed bank composition differed among locations, sediment cores were removed from coves, points, and straights, and from planted and unplanted regions of the shoreline of L-Lake, on the Savannah River Site near Aiken, South Carolina. This reservoir was built in 1985; portions of the shoreline were planted in 1987; and samples were taken in 1992. Sets of cores were taken from areas with water depths up to 1 m, the permanent waterline, and 1 m above water on the shore to determine the effects of hydrology on seed bank composition. Of the 136 seed bank taxa, only 33% were well represented and 35-46% occurred only once. Water depth was the primary influence on seed bank composition. Points, coves, and straights differed in species richness over water depths but did not differ in number of germinable seeds over depths, nor did locations differ in species richness or number of plants at the waterline. Planting vegetation in L-Lake did not significantly influence the seed bank; only 10% of taxa in the seed bank were planted in 1987. Of all taxa recorded, 56% were only in the seed bank, 22% were only in the vegetation, and 13% were in both the seed bank and the vegetation.