Physical Control of Sediment Oxygen Uptake During Severe Wind Wave Events in Shallow Coastal Embayments: A Study Case
2Institute of Water Research, University of Granada, Spain
In shallow coastal waters where the sea-bottom is often dominated by soft sediments with low settling velocities, light limitation during wind induced re-suspension events can be a critical factor controlling benthic primary productivity and the dissolved oxygen balance between the water column and the upper sediments.
In this work, we analyze the physical control of the sediment oxygen uptake rate (JO2) during severe wind wave events in a shallow coastal system: the Mar Menor lagoon, in the Mediterranean coast of Spain. For the analysis, we have coupled: (1) a transient 3rd generation wave model, (2) empirical models to estimate the total sediment load and the active sediment region, (3) light attenuation models using the total suspended solids as significant predictor and (4) a 1D transient diffusive-reactive O2 transport model (with Monod consumption kinetics and with a parametric source term for benthic primary production).
Once calibrated and validated, the models have been applied to simulate the JO2 dynamics during a severe wind event (February, 2015) at a shallow control point (0.8m water depth) in the Western coast of the Mar Menor lagoon. The results show that both the vertical O2 distribution and the JO2 are severely affected. In the first stage of the re-suspension event (42mg/l), the JO2 is almost suppressed by increasing the oxic zone in the upper sediments. Once this region becomes anoxic, light attenuation limits the benthic primary production resulting in a significant increase of the sediment O2 uptake until light conditions are completely recovered. Three time scales control the overall O2 water-sediment balance: (1) the event duration, (2) the scale related to the sediment settling velocity and (3) those of the O2 consumption rate.
The seasonal distribution of wind wave re-suspension events affecting locations up to 1m water depth in the Mar Menor lagoon has been characterized using 5 year local wind data. By quantifying the JO2 dynamics during these events, this work contributes to understand their role on the water quality of shallow coastal lagoons and their footprint at seasonal scales. The potential impact of future climate change scenarios and changes in the sediment composition of Mar Menor lagoon will be also discussed.
Acknowledgements: MICINN (project-CTM2011-28984).
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