Accumulation of periphyton biomass on artificial substrates deployed near a sewage sludge outfall in South Australia

Digested sludge from the Port Adelaide Sewage Treatment Works has been discharged into Gulf St Vincent, a marine embayment in South Australia, since 1978. The outfall was sited in seagrass meadows and four years after it began operating the dominant seagrass species were lost from an area of 365 ha. Discernible effects extended over 1900 ha and the seagrass beds in partially affected areas were characterized by unusually heavy growth of epiphytes. Artificial substrates were used to assess the accumulation of ‘epiphyte’ (periphyton) biomass in areas affected by sludge and at a control site. The greatest accumulation was recorded in the area most affected by sludge, i.e. the area from which all seagrass has been lost. It is suggested that excessive accumulation of epiphytes, resulting from the addition of sludge to the water column, may have contributed to the decline of the original seagrass beds.