AEI prepress abstract   -  DOI: https://doi.org/10.3354/aei00490

ABSTRACT: This ex situ study utilised oxygen microprofiling and whole core incubations to investigate potential changes in oxygenation of cohesive sediments resulting from offshore fin-fish farming. We examined oxygen conditions in sediments subjected to potential moderate depositional loads (1.1, 2.2, 3.2 g C m^-2 d^-1) of organic farm particles from mariculture expected to settle in dispersive environments. White biofilms formed over particulates that accumulated on the sediment surface after 7 d of at least 2.2 g C m^-2 d^-1. Diffusive oxygen uptake (DOU) rates were estimated from sediment microprofiles taken in cores following total oxygen uptake (TOU) determination from whole core incubations. DOU closely aligned with TOU (DOU:TOU ≈ 1) in cores where biofilms did not develop on the sediment surface (<1.1 g C m^-2 d^-1); however, the development of biofilms reduced DOU:TOU (<1), suggesting the biofilms were responsible for non-diffusive contributions to TOU. It was speculated that ‘vents’ in the biofilms may have enhanced the solute exchange rates in those cores. Despite the biofilms enhancing the benthic TOU, biofilms minimally impacted oxygen penetration depth in sediments immediately next to biofilms, with oxygen penetration shallowing from ~3.6 mm in unenriched cores to ~2.5 mm in sediments adjacent to biofilms. Instead, the patchy accumulation of organic farm particles and development of biofilms on the sediment surface suggests a potential enhancement of structural heterogeneity and availability of organic carbon for higher trophic consumers in an otherwise organically deplete system.