How does vegetation affect sedimentation on tidal marshes? Investigating particle capture and hydrodynamic controls on biologically mediated sedimentation

Abstract

[1] Plants are known to enhance sedimentation on intertidal marshes. It is unclear, however, if the dominant mechanism of enhanced sedimentation is direct organic sedimentation, particle capture by plant stems, or enhanced settling due to a reduction in turbulent kinetic energy within flows through the plant canopy. Here we combine several previously reported laboratory studies with an 18 year record of salt marsh macrophyte characteristics to quantify these mechanisms. In dense stands of Spartina alterniflora (with projected plant areas per unit volume of >10 m −1 ) and rapid flows (>0.4 m s −1 ), we find that the fraction of sedimentation from particle capture can instantaneously exceed 70%. In most marshes dominated by Spartina alterniflora, however, we find particle settling, rather than capture, will account for the majority of inorganic sedimentation. We examine a previously reported 2 mm yr −1 increase in accretion rate following a fertilization experiment in South Carolina. Prior studies at the site have ruled out organic sedimentation as the cause of this increased accretion. We apply our newly developed models of particle capture and effective settling velocity to the fertilized and control sites and find that virtually all (>99%) of the increase in accretion rates can be attributed to enhanced settling brought about by reduced turbulent kinetic energy in the fertilized canopy. Our newly developed models of biologically mediated sedimentation are broadly applicable and can be applied to marshes where data relating biomass to stem diameter and projected plant area are available.Citation: Mudd, S. M., A. D'Alpaos, and J. T. Morris (2010), How does vegetation affect sedimentation on tidal marshes? Investigating particle capture and hydrodynamic controls on biologically mediated sedimentation,

Sediment and carbon deposition vary among vegetation assemblages in a coastal salt marsh

“…3), which may have otherwise been exported during tidal recession, and (2) the capture of mineral particles on plant stems (Morris et al, 2002;Mudd et al, 2004). Dense salt marsh vegetation also has the capacity to enhance sedimentation by reducing the turbulent energy of inundating waters, with Mudd et al (2010) demonstrating that this phenomenon was responsible for virtually all of the sedimentation increase observed when standing plant biomass of Spartina alterniflora was artificially increased. The high short-term litter deposition rates we observed during neap tides (Fig.…”

“…Baustian et al, 2012;Mudd et al, 2010Mudd et al, , 2009Nyman et al, 2006). Generally, these studies have shown that the presence of vegetation may have a significant positive influence on surface accretion through (1) accumulating organic matter and (2) facilitating sediment trapping (Morris et al, 2002;Mudd et al, 2010;Nyman et al, 2006).…”

The secret gardener: vegetation and the emergence of biogeomorphic patterns in tidal environments

“…The trapping flux is here neglected, following Marani et al [3] and Mudd et al [27], who showed that particle settling largely dominates inorganic sediment deposition for flow velocities commonly observed in tidal marshes, i.e. less than 0.05 m s −1 in microtidal environments (i.e.…”

“…vegetation adapted to living in the hypersaline and hypoxic marsh soils [10,24], which affects inorganic deposition (by increasing flow energy dissipation, reducing the turbulent kinetic energy and by direct trapping, e.g. [25][26][27]), produces organic soil (e.g. [4,28,29]) and reduces erosion (by damping wind waves and stabilizing the sediment, e.g.…”

Unsupervised detection of salt marsh platforms: a topographic method

“…For instance, elevation determines flooding frequency and therefore influences pioneer vegetation encroachment (Hu et al, 2015), which in turn affects vertical accretion through inorganic sediment capture (Pennings et al, 2005;Mudd et al, 2004Mudd et al, , 2010. Individual plants also react to elevation by modifying their root to shoot length ratios, generating feedbacks between organic material build-up and sediment capture 15 (Mudd et al, 2009).…”