Lithium-Normalized Zinc and Copper Concentrations in Sediments as Measures of Trace Metal Enrichment due to Salmon Aquaculture

Abstract

The results of metal analyses carried out on surficial sediment samples collected in the coastal waters of southwest New Brunswick and the Broughton Archipelago in British Columbia have been used to investigate the use of heavy metals as tracers of salmon farm wastes. New Brunswick in particular has seen rapid expansion of open cage salmon aquaculture in recent years. While techniques have been developed to identify benthic impacts directly beneath the cages, no method has been developed to determine the fate of dispersed wastes. We show that Zn and Cu, two elements associated with aquaculture operations, can be used to identify farm wastes in sediments at some distance from the cage sites. Geochemical normalization for grain size is needed in order to see the small tracer signals. Excess Zn and Cu levels are found in the sediment at varying distances from the salmon cages in depositional areas in southwest New Brunswick and in the Broughton Archipelago. Evidence that links these observations to salmon aquaculture development is described.