The cessation of long-term fly-ash dumping: Effects on macrobenthos and sediments

Four decades of continual fly-ash disposal off Northumberland, U.K., ended in December 1992. Quantitative sampling of the sediment and the macrobenthos was undertaken in the Summer 1993 over 27 km2 of seabed covering the Blyth Fly-ash Dumpsite and the surrounding area. The offshore portion of the region surveyed bore only traces of fly-ash particles, waste being confined to the region shallower than 45 m. There, disposals have changed local sedimentary conditions increasing the spatial patchiness of sediment types and altering silt-clay dynamics. Inshore of the dumpsite, substrata affected by long-term tipping have effectively become an artificial reef due to the cementation of the waste. The seabed within the designated dumpsite was still composed of pure fly ash, resulting in macrobenthic densities and species richness markedly lower than control areas, though higher than recorded in a previous survey in 1988. At the dumpsite, between 47 and 66% of the species had only one or two representatives and juveniles made up 47–88% of the individuals. Additional faunal impoverishment occurred where pebbly clinker and aggregates abounded. Nine months after cessation of dumping recovery was essentially dependant on the decrease in the concentration of the waste and will proceed as the gradual fertilization of the sediments occurs.