Disaggregation rates of salmon feces and microbial inoculation of sediments: new insight for particle dispersion modelers

The flow of organic waste into the environment from large-capacity fish farms, and its consequences for the marine ecosystem, is a contentious issue. Our ability to manage and mitigate the effects can be improved by enhancing our ability to predict dispersal and distribution of waste, and by better understanding the mechanisms that drive ecological perturbation. This study examines the fate of individual particles in controlled chambers, designed to simulate contrasting receiving environments, and the ensuing physical, chemical, and microbial changes. Fecal particles that landed on impacted sediments broke down twice as fast as those on natural sediments and were effectively removed from the system after 160 h, which was attributed to microbe- and fauna-mediated decomposition. Particles in turbulent water disaggregated rapidly into numerous smaller particles, which persisted for >200 h. These smaller particles have fundamentally different physical properties, which, when included in dispersion models, increase the predicted horizontal dispersion and flux rates at distances >1 km and the potential for overlapping effects between farms. Microbial inoculation of the sediment from waste particles was limited, but evident, especially for natural sediments, which were significantly altered from a single introduction of fecal pellets at a density of 288 to 481 m -2 . Therefore, waste-dispersion models may be improved by the inclusion of particle breakdown stages with associated size-specific behavioral dynamics and benthic impact-specific sediment consolidation times. Further consideration should be given to the potential for the microbiome of the receiving environment to be altered by extraneous sources, both near and far field.