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Abstract

ABSTRACT: Sediment resuspension is an important factor in controlling the impact of any
localised point source impacts such as salmon farms; at high-flow (dispersive) sites, resuspension
can significantly reduce potential effects. Depositional modelling (DEPOMOD) is widely used to
predict localised seabed impacts and includes an optional flow-related resuspension module. This
study examined the observed impacts at 5 farms with contrasting flow regimes to evaluate the role
of modelled resuspension dynamics in determining impacts. When resuspension was included in
the model, net particle export (i.e. no significant net downward flux of organic material) was predicted
at the most dispersive sites. However, significant seabed effects were observed, suggesting
that although the model outputs were theoretically plausible, they were inconsistent with the
observational data. When the model was run without resuspension, the results were consistent
with the field survey data. This retrospective validation allows a more realistic estimation of the
depositional flux required, suggesting that approximately twice the flux was needed to induce an
effect level at the dispersive sites equivalent to that at the non-dispersive sites. Moderate enrichment
was associated with a flux of ~0.4 and ~1 kg m−2 yr−1, whilst highly enriched conditions
occurred in response to 6 and 13 kg m−2 yr−1, for low and dispersive sites, respectively. This study
shows that the association between current flow, sediment resuspension and ecological impacts is
more complex than presently encapsulated within DEPOMOD. Consequently, where depositional
models are employed at dispersive sites, validation data should be obtained to ensure that the
impacts are accurately predicted.

Item Type:	Article
Authors/Creators:	Keeley, NB and Cromey, CJ and Goodwin, EO and Gibbs, MT and MacLeod, CK
Keywords:	Aquaculture, Benthic, Biodeposition, enrichment, dispersive, depositional, modelling, DEPOMOD, Marlborough Sounds
Journal or Publication Title:	Aquaculture Environment Interactions
ISSN:	1869-215X
DOI / ID Number:	https://doi.org/10.3354/aei00068
Additional Information:	Copyright 2013 The Authors
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