Prediction and validation of flow-dependent uptake of ammonium over a seagrass-hardbottom community in Florida Bay

Abstract

Hydrodynamic surveys and field flume experiments were carried out to characterize water flow and measure nutrient uptake over a shallow hardbottom flat sparsely colonized by seagrasses, a complex community type commonly found along corridors linking Florida Bay and the Florida reef tract. Acoustic Doppler velocimeter profiles collected in tide-driven flows revealed benthic hydrodynamic conditions indicative of disturbed boundary layer flow; attenuation of flow near the benthos and measures of bottom friction were considerably less than observed in densely colonized seagrass beds. Mass-transfer coefficients (S) for ammonium, predicted using velocity data and estimates of bottom friction, ranged between 0. . Values of S measured using a field flume were within the same range as predicted values, validating that ammonium uptake by the community is occurring near the masstransfer limit. Mass-transfer coefficients fell slightly above those previously measured for low-relief coral rubble and below those for dense seagrass canopies, thereby confirming a close link between bottom roughness and mass transfer. Predicted ammonium uptake based on ambient velocity and nutrient concentrations varied considerably over the tidal cycle (range = 0.014 to 0.094 µmol NH 4 m -2 s -1 ) and highlighted the importance of temporal variation in both current velocity and nutrient concentration in driving rates of nutrient uptake. Additional field flume experiments using 15 N-labeled ammonium enabled us to examine flow-dependent uptake for a number of organisms within the complex community. Uptake rates were found to vary among seagrasses, macroalgae, and finger corals, perhaps due to physiological or morphological differences or varying locations within the canopy.

Combined effects of warming and ocean acidification on coral reef Foraminifera Marginopora vertebralis and Heterostegina depressa

“…Velocity of the water flow varied from 4.2-5.2 9 10 -1 m s -1 at the inlet (Ø 0.3 cm) to 3.1-3.8 9 10 -3 m s -1 at the outlet (Ø 3.5 cm). The flow rates between inlet and outlet are in the same range as those measured in situ over dead coral rubble (Williams and Carpenter 1998) and sea grass (Cornelisen and Thomas 2009). Both species kept in the flow-through housings appeared to thrive as indicated by healthy colouration, minimal shell breakage, and the development of firm attachment to the walls of the housings by the pseudopodial network.…”

Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

“…A similar apparatus has been employed successfully in a number of previous studies (Thomas et al 2000, Thomas & Cornelisen 2003, Cornelisen & Thomas 2009). Isotopically labeled nutrients have been used to measure nutrient uptake for individual organisms within a community (Cornelisen & Thomas 2006, Morris et al 2008, to determine the relationship between seagrass and epiphyte nutrient uptake (McRoy & Goering 1974, Lepoint et al 2007, and to trace distribution of nutrients among community components (Koop et al 2001, Cornelisen & Thomas 2006, Gribsholt et al 2006).…”

“…spp., and Penicillus spp. ), and sponges (Cornelisen & Thomas 2009). Encrusting organisms colonize the vertical extent of the seagrass blades.…”

“…Experiments were conducted in late June 2007 on Old Sweat Bank (hereafter OSB, 24°48.99' N, 80°52.1' W), a shallow carbonate bank (< 2 m depth) located between Long Key and Conch Key, approximately 2 km offshore on the Florida Bay side of the Florida Keys (Cornelisen & Thomas 2009). Natural, tidally driven velocities at the site range up to 0.50 m s −1 (Wang 1998), and the bank is also subject to wind-driven surface waves sourced from both the ocean and the bay direction.…”

Photosynthetic oxygen flux by Macrocystis pyrifera: a mass transfer model with experimental validation

“…Previous efforts to model photosynthetic flux using mass transfer theory have assumed fully turbulent flow conditions and used empirical constants to adjust for disagreements between field measurements and model predictions (e.g. Koch 1994, Falter et al 2004, Cornelisen & Thomas 2009. Although this may be justified for applications in habitats such as coral reefs, measured velocities in the interior of moderate-sized Macrocystis pyrifera forests have been reported between 0.1 and 5 cm s -1 (Gaylord et al 2007, Fram et al 2008), corresponding to laminar or transitional flow conditions.…”