Effects of Water Velocity and Canopy Morphology on Ammonium Uptake by Seagrass Communities

Abstract

In the research presented here, we examine the effects of water velocity and canopy morphology on rates of nutrient uptake by seagrass communities. Ammonium uptake rates for two types of seagrass communities, Halodule wrightii and Thalassia testudinum, are measured over a range of velocity using a field flume. The field flume allows independent measurements of uptake by communities of natural composition and condition. We compare our results with those estimated using empirically derived engineering equations that describe transport processes to rough surfaces in order to explore the possibility that uptake rates can be predicted from these equations. We also investigate the possibility that the seagrass canopy alters the characteristics of water flow within the community, which is reflected by the friction imposed by the canopy (the friction coefficient) on the moving water. Our results indicate that ammonium uptake by seagrass communities is dependent on water velocity. Further, seagrasses affect characteristics of water flow within the community that are reflected in rates of ammonium uptake. Empirically derived engineering equations used with measured friction coefficients yield expected Stanton numbers (a nondimensional ratio of flux to a surface to advection by a surface) that are within 95% of those measured in the field flume. Thus, the capacity of these communities to remove ammonium from the water column can be predicted using empirically derived engineering equations that describe the transport of chemicals between a fluid and a rough surface.

Prolonged buoyancy and viability of Zostera muelleri Irmisch ex Asch. vegetative fragments indicate a strong dispersal potential

“…Localised flow velocities within the water column also significantly influence acquisition of nutrients by leaves of seagrass species. Higher flow velocities increase nutrient uptake by leaves due to greater vertical exchange (Thomas et al 2000), but under low flow velocity conditions a closing of seagrass canopies may result in a reduction of this process. Under conditions described in the current study where floating vegetative fragments would be continually exposed to flow velocities within the water column, the issue of reduced vertical exchange is negated (Koch & Gust 1999).…”

Restoration of Seagrass Community to Reverse Eutrophication in Estuaries

“…The ecological functions attributed to seagrass communities are strongly related with the environment they inhabit. These plants must overcome many stresses and, by doing so, alter the surrounding abiotic conditions, a capacity known as ecosystem engineering (Jones et al, 1994;Duarte, 2000;Thomas et al, 2000). Thus, seagrasses are considered engineering organisms with significant influence on the struc ture and function of coastal marine ecosystems (Hastings et al, 2007).…”

“…Thus, seagrasses are considered engineering organisms with significant influence on the struc ture and function of coastal marine ecosystems (Hastings et al, 2007). Their structure, above-and belowground, greatly influ ences the water dynamics and consequently dictates every other aspect of the seagrass beds (Thomas et al, 2000;Koch et al, 2006;Peralta et al, 2008). The canopies attenuate water flow favoring sedimentation rates and they can also actively trap particles, whether by passive adherence to the plant or by active filtering by organisms (Jones et al, 1994;Marbà et al, 2006).…”

The attenuation of current‐ and wave‐driven flow within submerged multispecific vegetative canopies

“…In the coastal ocean, such changes ultimately impact benthic and pelagic nutrient cycling (Lemmens et al 1996;Thomas et al 2000;Morris et al 2008). Seagrass communities absorb carbon and nutrients from passing flow (Cornelisen and Thomas 2006;Weitzman et al 2013) and help to break down and recirculate accumulated organic detritus (Williams 1990;Heck et al 2008).…”