Short-term dissolved oxygen patterns in sub-tropical mangroves

Knight, Jon M., Griffin, Lachlan, Dale, Pat E.R., and Sheaves, Marcus (2013) Short-term dissolved oxygen patterns in sub-tropical mangroves. Estuarine, Coastal and Shelf Science, 131. pp. 290-296.

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Mangrove forests in subtropical areas are highly heterogeneous environments, influenced by diverse physical structures and tidal flushing regimes. An important component of tidal water is the concentration of dissolved oxygen (DO), as it affects aquatic organisms such as fish (directly: respiration and behaviour) and immature mosquitoes (directly: trigger for egg-hatch; indirectly: fish predation of larvae). Changes in DO may be important over relatively small time scales such as minutes and days, but, at such scales it has received little investigation. The aim of this study was to address this knowledge gap, monitoring DO at small time intervals (1 min) over tidal flooding events (hours – days) in two contrasting subtropical mangrove systems. These represented a range of mangrove tidal hydrology: a well-connected fringing mangrove forest in south-east Queensland and a more complex mangrove basin forest in northern New South Wales with impeded tidal connections.

The results indicated that patterns of DO varied diurnally and by mangrove system. In the fringing forest, where the substrate was exposed before and after flooding, the highest mean DO concentration was during the day, followed by evening, with pre-dawn the lowest (6.8, 6.5 and 6.1 mg/l, respectively). DO patterns differed by tide stage and time of day with falling DO especially during late evening and pre-dawn as tides ebbed. In the mangrove basin forest the pattern was reversed, but also depended on the distance the tide had travelled across the basin. Before tidal incursion, standing water in the basin was anoxic (DO 0 mg/l). As tidal water flooded into the systems there was a greater increase in DO closer to the tide source than further away, with a DO concentration of 7.6 mg/l compared to 5.4 mg/l.

The observations were interpreted in the light of processes and potential impacts on aquatic organisms (fish and immature mosquitoes). The most significant observation was that in the mangrove basin DO concentrations suitable for aquatic organisms (such as fish) persisted for only a relatively small period during the tide (∼1 h), with hypoxic conditions for the remainder. This combination of conditions is favourable to immature mosquitoes.

Item ID: 28406
Item Type: Article (Research - C1)
ISSN: 1096-0015
Keywords: water quality; coastal wetland; Avicennia marina; Aedes vigilax; mosquito; mangrove basin; eastern Australia
Funders: Griffith University/James Cook University, Collaborative Grants Scheme, 2012, Mosquito and Arbovirus Research Committee, 2011 Griffith University Research Infrastructure Program grant
Date Deposited: 09 Aug 2013 05:46
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 100%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments @ 60%
96 ENVIRONMENT > 9609 Land and Water Management > 960903 Coastal and Estuarine Water Management @ 20%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960802 Coastal and Estuarine Flora, Fauna and Biodiversity @ 20%
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