Modelling the mud surface temperature on intertidal flats to investigate the spatio-temporal dynamics of the benthic microalgal photosynthetic capacity

Abstract

The mud surface temperature (MST) of an ~ntertidal mudflat in Marennes-Oleron Bay (France) and the biomass-specific photosynthetic capacity (P:,,) of benthic microalgae were modelled to investigate their spatio-temporal dynamics. Simulations were performed over 2 different periods during and after the microphytobenthos spring bloom (April and June, respectively) and under 2 different tidal conditions (spring and neap tides). The deterministic MST model is based on thermodynamic processes. Comparison at different periods between measured data series and sirnulations clearly establishes the reliability of the model, thus allowing extrapolations over time and space. The spatio-temporal dynamics of MST is primarily controlled by the immersion-emersion alternation combined with the solar cycle, with a strong influence of the phase difference in their respective oscillations: the highest MSTs are achieved in summer in the highest parts of the mudflat, when spring low tide occurs at midday. Three relevant time scales characterize the MST dynamics: long-term (seasonal cycle), medium-term (lunar cycle) and short-term (solar and tidal cycles). Within that framework, the response of P:,, to changes in MST depends upon To,,, the optimum temperature for photosynthesis (To,, = 25°C all year round). In April, when the MST values are below To,,, P : , , varies exponentially with MST at short time scales. Conversely, in June, when the range of MST partially exceeds To,,, P:,, is inhibited on most of the mudflat surface area (up to 75%). This thermo-inhibition is highest in summer, when low tide occurs at midday.

Effect of tidal flat on seawater temperature variation in the southwest coast of Korea

“…[31] The sensible heat transfer is given by Businger [1973], Stathers et al [1988], and Guarini et al [1997] …”

“…Heat exchange between tidal flats and seawater has previously been investigated [e.g., Harrison and Phizacklea, 1985;Harrison, 1985]. In particular, heat exchange between tidal flats and seawater due to tidal currents has been shown to produce short-term variability in seawater temperature [Harrison and Phizacklea, 1985;Vugts and Zimmerman, 1985;Guarini et al, 1997;Kim and Cho, 2009]. Harrison [1985] calculated heat exchange between tidal flats and seawater from heat content changes based on observed variations in sediment temperatures at four depths (25, 75, 200, and 280 mm).…”

“…Prediction of the sediment temperature over the entire tidal flat area is fundamental in estimating the heat flux between tidal flats and seawater. The tidal flat sediment temperature was predicted by Guarini et al [1997] in Marennes-Oléron Bay along the French Atlantic coast, using the seawater temperature calculated via a hydrodynamic model. They predicted the surface sediment temperature from the heat exchange between the tidal flat and atmosphere or seawater, in order to estimate the photosynthetic capacity of the benthic micro algal community.…”

Heat flux across the surface of a macrotidal flat in southwest Korea

“…[31] The sensible heat transfer on a tidal flat surface is given by [Businger, 1973;Stathers et al, 1988;Guarini et al, 1997]:…”

“…Variation in seawater temperature can influence local ecosystems [Tang et al, 2003] and weather [Cho et al, 2000]. Accurate estimation of the heat exchange between the tidal flat, seawater and atmosphere is not only important for understanding local biological and physical systems, but essential in investigating macrotidal flat processes [Guarini et al, 1997].…”