Invertebrate recolonization of fine-grained beneficial use schemes: An example from the southeast coast of England

Abstract

The disposal of maintenance dredged material con- stitutes one of the most important problems in coastal zone management. To minimise ecological impacts, a number of 'beneficial use' options have developed whereby the material is regarded as a potential resource and used to recharge or recreate intertidal habitats. This paper presents the results of a sampling programme to investigate the macrofaunal recovery rates, and the underlying mechanisms responsible for them, following a beneficial use scheme involving the placement of fine-grained dredged material on a salt marsh in southeast England. Three stations in the recharge area and three reference stations, located within the same salt marsh system, were selected. These stations were sampled prior to recharge (re- charge stations only) then 1 week, 3, 6, 12 and 18 months after the recharge. Sediment redox potentials (1, 2 and 4 cm sedi- ment depths) were also measured on each sampling occasion. The results indicated a rapid recolonization of the fauna typi- cal of the surrounding salt marsh channels. All univariate parameters had recovered after 3 months after the recharge. Active post-juvenile immigration is likely to have been the predominant recovery process. Multivariate data analysis re- vealed that the community structure of the recharge stations, however, did not progress towards those of the reference sites. Natural spatial variability in community structure at the scale of the recharge-reference station distance, and differences in eventual tidal elevations are factors responsible for these differences. The need to carefully assess reference site suit- ability in monitoring beneficial use schemes is discussed.