Interactions of Atlantic salmon in the Pacific northwest environment: II. Organic wastes
Section snippets
Dissolved nutrients in the water column
Salmon excrete 75–90% of their ammonia and ammonium waste across gill epithelia (Gormican, 1989) or in concentrated urea (Persson, 1988, Gowen et al., 1991). Brett and Zala (1975) reported a constant urea excretion rate by sockeye salmon of 2.2 mg N/(kg h). Nitrogen and phosphorus are also dissolved from waste feed and feces during and after descent to bottom sediments. Silvert (1994) suggested that 66–85% of phosphorus in feed is lost in a dissolved form at salmon farms. Johnsen and Wandsvik
Organic enrichment of sediments
Salmon aquaculture in British Columbia grew from a small industry producing less than 2000 MT of Atlantic and Pacific salmon in the early 1980s to 49,700 MT in 1999 (Statistics Canada, 2001). Reviews by Brooks (1996), Winsby et al. (1996), EAO (1997), EVS (2000), and NMFS (2001) describe the benthic response to organic inputs from salmon farms. Considerable information describing benthic effects has been provided by case studies of small farms producing 200–400 MT salmon per cycle in the early
Total volatile solids
There is a diverse literature describing changes in sediment chemistry near salmon farms (Ye et al., 1991, Holmer and Kristensen, 1992, Johnsen et al., 1993, Hargrave et al., 1995, Hargrave et al., 1997, Lu and Wu, 1998, Karakassis et al., 1999). These case studies demonstrated consistent, but variable, increases in sediment carbon under and immediately adjacent to salmon farms. They also suggested that organic biodeposits from fish farming are locally patchy with significant variability in
Predicting biological responses to sedimentation
Plant and animal waste settling onto the seabed is not toxic in and of itself. Therefore, the only relationship that TVS has with infaunal community structure, other than as food, is through its covariance with redox, sulfide, or ammonia concentrations. No literature was found describing the partitioning of the relative effects of oxygen depravation and sulfide toxicity. The toxicity of H2S at high concentrations is unquestioned. Because sulfides are ubiquitous in marine benthic environments,
Chemical and biological remediation of sediments
Chemical and biological recovery of sediments under salmon farms is well documented in the literature by, inter alia, Ritz et al. (1989), Anderson (1992), Mahnken (1993), Brooks (1993b), Lu and Wu (1998), Karakassis et al. (1999), Brooks (2000a), and Crema et al. (2000).
Brooks (2000a) defined two types of remediation:
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Chemical remediation is the reduction of accumulated organic carbon with a concomitant decrease in hydrogen sulfide and an increase in sediment oxygen concentrations under and
Conclusions
This review supports a thesis that, with the exception of a few shallow poorly flushed embayments, the potential for net-pen enhancement of phytoplankton populations is remote, or non-existent. There also appears to be little risk associated with reduced concentrations of DO associated with salmon culture. A greater risk is imposed on the farm by nutrient rich and oxygen deficient waters, which upwell along the northeastern Pacific coastline and periodically advect into farm tenures. Hydrogen
Acknowledgements
The authors would like to thank William T. Fairgrieve, Robert N. Iwamoto, Colin E. Nash, Michael B. Rust, Mark S. Strom, and F. William Waknitz, the other co-authors of this series of papers, who reviewed and commented on this and the other works. The authors also acknowledge the critiques of nine additional reviewers who read the original manuscripts. Their suggestions were much appreciated.
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