TEN YEARS OF SALTMARSH MONITORING—THE CASE HISTORY OF A SOUTHAMPTON WATER SALTMARSH AND A CHANGING REFINERY EFFLUENT DISCHARGE

Abstract

ABSTRACT One of the largest refinery and petrochemical plants in the U.K. has been discharging its effluents into the creek system of a Spartina anglica-dominated saltmarsh in Southampton Water since 1953. This resulted in extensive damage to the marsh system up to 1971. At that time, a program of effluent quality improvement commenced that has resulted first in recolonisation of small areas of damaged marsh followed by extensive recovery. Changes in the marsh vegetation have been studied first by transect surveys in 1969 and 1970 (to assess damage) and subsequently by twice-yearly vegetation mapping resurveys from 1972 to the present. This paper summarises the data from the 10 years of survey. The recovery/recolonisation has continued progressively to the present day, with improvements in effluent quality clearly related to saltmarsh recovery. However, although several annual and perennial marine species have been successful colonisers, the original dominant Spartina anglica has recolonised only poorly. In addition to vegetation mapping, several series of Spartina transplantation experiments have been carried out to precisely define areas of continued effluent impact. These have formed a nucleus for Spartina recolonisation in some parts of the marsh and may well speed up the return of this species in these areas. Using these relatively simple techniques it has been possible to identify differences in toxicity between different outfalls. This has been taken into account in site effluent management policy. Research programmes have recently been extended to include recolonisation of the marsh by intertidal animals and detailed analysis of hydrocarbon contents of sediments over the marsh. Preliminary results from these programmes are described. These additional techniques improve monitoring sensitivity and provide valuable information for interpreting long-term effects of retention of hydrocarbons in sediments. They are designed to monitor continued effluent improvements being undertaken by the refinery.