Impact of salmon aquaculture on sediment chemistry and mercury loading

• Main Author: Musclow, Sandy Lee
• Format: Thesis
• Language: English
• Published: McGill University 2005
• Subjects: Agriculture; Fisheries and Aquaculture; Geochemistry; Atlantic salmon
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84063

One of the main environmental impacts of salmon aquaculture activities in the Bay of Fundy is the alteration of sediment chemistry as a result of the large amount of organic waste that accumulates below fish pens. To investigate these impacts, vertical profiles of delta13C, delta 15N, Corg, Corg:Ntot, FeHC1 , MnHCl, Ptot, PHCl, SO4 2-, AVS, Hgtot, and Hgpyrite in sediment cores collected throughout the bay were acquired. These profiles were then used to identify tracers of aquaculture activities and their impact on the redox zonation of the sediment. In addition, representative samples of fish food as well as farmed and wild salmon were analyzed to determine their Hg tot content as well as delta13C, delta15N, Corg, Corg:Ntot. Our results show that, as by-products of salmon aquaculture (e.g., uneaten food, feces, antibiotics, and anti-fouling agents) accumulate in the sediments, their reactive organic carbon content increases and generate a greater oxygen demand. Subsequently, an upwards migration of the oxygen penetration depth and redox boundaries in the sediment column occurs, which is confirmed on the basis of the distribution of redoxsensitive phases (e.g., authigenic metal oxides and AVS) in the sediments. High resolution voltammetric microelectrode measurements show that the FeHCl and MnHCl distributions overestimate the oxygen penetration depth in the sediments. The total phosphorus distribution in the sediment record is shown to be a suitable tracer of marine aquaculture, reflecting the recent history of residual feed and fecal matter accumulation in the sediments. Elevated mercury concentrations in sediments under fish pens are explained by its strong affinity for organic carbon. Although the source of additional Hg has yet to be resolved, as the organic carbon content of the sediments increases in response to the input from fish farming activities, so does the associated Hg. Mercury also partitions strongly to authigenic pyrite in the deeper sulfidic sediments. Of the few farmed Atlantic salmon analyzed, mercury levels were not elevated compared to the concentrations of mercury in the wild salmon captured in two rivers of the Canadian east coast.