Recovery of a sewage sludge dumping ground. I. Trace metal concentrations in the sediment

Abstract

Sewage sludge has been dumped at sea in the Firth of Clyde, Scotland, for almost 90 yr. Prior to implementation of the Dumping at Sea Act (1974) it was dumped ca 2 km south of the Isle of Bute. Surveys at this site before 1974 showed the accumulation of organic material and metallic contaminants in the sediments. The present study describes the geographical distribution of trace metal concentrations in both surface and subsurface sediments in 1985. Trace metal concentrations in surface sediments were much lower than those reported while dumping was in progress. Marked elevations in trace metal concentrations were found w~t h depth in the sediments. A tentative trace metal budget for this disused disposal site is presented. About a quarter to a half of the input metals were retained in the sediment.

Seafloor ecological functioning over two decades of organic enrichment

“…One reason proposed for the slow recovery of deoxygenated zones is the accumulation of carbon in the sediments. For example, at the pre-1974 disposal site 11 years post-disposal large quantities of TOC were retained in sediments concentrated at depths of 20-60 cm (Moore and Rodger, 1991;Rodger et al, 1991). Organic carbon accumulates in deoxygenated regions due to the lack of macrofaunal bioturbation and slower rate of anaerobic degradation, and this condition may persist for long periods even once it has again become oxygenated (Jessen et al, 2017).…”