Marsh Dynamics: Laboratory and Field Investigations of Gas Transport, Wave Attenuation, and Biosolids Amendment
- Author(s): Foster-Martinez, Madeline
- Advisor(s): Variano, Evan
- et al.
Marshes, and tidal salt marshes in particular, are gaining recognition as critical elements in sustainable shoreline protection (Narayan, Beck, Reguero, et al. 2016; Narayan, Beck, Wilson, et al. 2016; Spalding, Ruo, et al. 2014; Spalding, McIvor, et al. 2014). They contribute to coastal resiliency not only by attenuating wave energy in large storms (Gedan et al. 2011; M�oller, Kudella, et al. 2014), but also by maintaining the existence of coastal land (Kirwan et al. 2016), supporting sheries (Boesch & Turner 1984; MacKenzie & Dionne
2008), sequestering carbon (Ouyang & Lee 2014), and removing contaminants (Dhir et al. 2009; Windham et al. 2003). These benets directly contribute to the sustainability of the growing populations in coastal regions (Sutton-Grier, Wowk, et al. 2015). With this
recognition, there are many ongoing projects to preserve existing salt marshes, restore former marshes, and create hybrids of natural and engineered structures (Pontee et al. 2016). These projects require an understanding of the underpinning processes that lead to marsh sustainability. The projects presented in this dissertation are efforts to better understand marsh dynamics. The fist project explores the impact of emergent vegetation on gas flux in marsh surface waters. Wind causes the stems of emergent vegetation to wave back and forth, stirring the water column and facilitating gas exchange. To understand the magnitude of this effect, a gas transfer velocity (k600-value) was measured via laboratory experiments. Measuring this transport pathway contributes to a mechanistic understanding of gas flux and can improve models of climatically important gases. The second project examines wave attenuation
across a salt marsh. Salt marsh vegetation is effective at reducing wave energy. It is important to understand how this attenuation varies. Through field measurements, wave attenuation is explored as a function of hydrodynamic conditions, season, and vegetation
type. The results showed that even fringe marshes, which are common in San Francisco Bay, are effective at reducing wave energy year-round. The last project investigates the viability of using biosolids as an amendment to dredged material in marsh restorations. Biosolids is a reliable and sustainable source of sediment, and more sources of sediment are needed for marsh restoration projects. Both the aboveground and belowground biomass increased when vegetation was grown in soil containing biosolids as compared to only dredged material. Taken together, the three projects discussed here can contribute to improving the success and effciency of marsh restoration and preservation.