Abstract
AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:337-357 (2019) - DOI: https://doi.org/10.3354/aei00317 Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes David R. Plew* National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch 8440, New Zealand *Corresponding author: david.plew@niwa.co.nz ABSTRACT: Benthic oxygen fluxes were measured in situ using the eddy covariance method at 2 Chinook salmon farms located in the New Zealand Marlborough Sounds in 29-35 m depth and compared to sediment nutrient (C, N and P) and sulphide concentrations. Observations from 3 sites at a high-flow location (near-bed RMS velocities of 0.11 to 0.17 m s-1) showed oxygen fluxes increasing with sediment enrichment. Mean ± SE oxygen fluxes of -102 ± 4 mmol O2 m-2 d-1 were observed immediately adjacent the farm. Higher fluxes were observed at 120 m from the farm (-53 mmol O2 m-2 d-1) than at 50 m (-48 mmol O2 m-2 d-1), consistent with higher sediment nutrient concentrations at the more distant site, and reflecting the effect of currents on deposition patterns. Ratios of C, N and P in sediments indicated a reduction of N mineralisation rates as sediment enrichment increased. The low-flow site (near-bed RMS velocities of 0.033 m s-1) had similar oxygen fluxes (-108 ± 9 mmol O2 m-2 d-1) to the high-flow site closest to the farm, but sediments were more highly enriched with high sulphide concentrations. Oxygen fluxes at the low-flow site were close to the estimated maximum potential flux that could be achieved under the ambient hydrodynamic conditions. Less than 0.2% of surface PAR reached the sediments, and no evidence of benthic primary production was observed at any of the sites. By incorporating ambient hydrodynamic conditions, eddy covariance has the potential to obtain true in situ benthic oxygen fluxes, giving greater insight into aquaculture-environmental interactions. KEY WORDS: Aquaculture · Benthic impacts · Oxygen flux · Organic enrichment · Eddy covariance · Salmon Full text in pdf format PreviousNextCite this article as: Plew DR (2019) Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes. Aquacult Environ Interact 11:337-357. https://doi.org/10.3354/aei00317 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: July 11, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.
Highlights
Deposition of organic material beneath finfish farms is a major concern for the ecological health of the seabed (Brown et al 1987, Hargrave et al 1993, Findlay et al 1995)
Velocities at Site L appear to be less correlated with tides
As measured oxygen fluxes approached maximum potential flux rates predicted by surface renewal models, sediment samples showed accumulation of C, N and P and increases in free sulphides
Summary
Deposition of organic material beneath finfish farms is a major concern for the ecological health of the seabed (Brown et al 1987, Hargrave et al 1993, Findlay et al 1995). While the demand for oxygen increases with the concentration of organic matter in the sediments, the supply of oxygen is restricted by the rate it can be transported across the diffusive boundary layer either by diffusion or through turbulent bursting events (Hondzo 1998, Glud 2008, O’Connor & Hondzo 2008, Grant & Marusic 2011, Sulpis et al 2019) The thickness of this layer, and potential rates of transport through this layer, depends on the nature and roughness of the substrate (Dade 1993, Røy et al 2002), and on the intensity of near-bed turbulence (Hondzo 1998, Lorke et al 2003) and the action of bioturbation and bio-irrigation (Svensson & Leonardson 1996, Pischedda et al 2008). Assessing benthic impacts using benthic oxygen fluxes requires that measurements are conducted in such a way that captures the in situ hydrodynamic conditions and spatial heterogeneity
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