Abstract
Sediment transport in coastal regions is regulated by the interaction of river discharge, wind, waves, and tides, yet the role of vegetation in this interaction is not well understood. Here, we evaluated these variables using multiple acoustic and optical sensors deployed for 30–60 days in spring and summer/fall 2015 at upstream and downstream stations in Mike Island, a deltaic island within the Wax Lake Delta, LA, USA. During a flooding stage, semidiurnal and diurnal tidal impact was minimal on an adjacent river channel, but significant in Mike Island where vegetation biomass was low and wave influence was greater downstream. During summer/fall, a “vegetated channel” constricted the water flow, decreasing current speeds from ~13 cm/s upstream to nearly zero downstream. Synchrony between the upstream and downstream water levels in spring (R2 = 0.91) decreased in summer/fall (R2 = 0.84) due to dense vegetation, which also reduced the wave heights from 3–20 cm (spring) to nearly 0 cm (summer/fall). Spatial and temporal differences in total inorganic nitrogen and orthophosphate concentrations in the overlying and sediment porewater were evident as result of vegetation growth and expansion during summer/fall. This study provides key hourly/daily data and information needed to improve the parameterization of biophysical models in coastal wetland restoration projects.
Highlights
The Mississippi River delta plain is a complex and dynamic environment, regulated by the influx of water, sediment, nutrients and carbon from the Mississippi and Atchafalaya Rivers [1]
It is possible that some optical noise in the optical backscatter sensor (OBS) data from Mike3 was due to vegetation growth and/or floating organic matter
We summarize our results using a conceptual model to illustrate the relative impact of river discharge and wind patterns on hydrodynamic drivers interacting with vegetation presence on Mike Island in 2015 (Figure 11A)
Summary
The Mississippi River delta plain is a complex and dynamic environment, regulated by the influx of water, sediment, nutrients and carbon from the Mississippi and Atchafalaya Rivers [1]. Sediment diversions in Louisiana use a combination of new channels and structures to divert sediment and freshwater from the Mississippi and Atchafalaya Rivers into adjacent basins to build new land and slow down land loss. The success of these projects heavily depends on both the presence of vegetation and plant–sediment interactions controlling sediment trapping efficiency to gain elevation and build land. When artificial planting is used in combination with natural wetland creation or sediment diversions, vegetation can potentially uptake nutrients, slow down velocity, trap mud, Water 2020, 12, 2072; doi:10.3390/w12072072 www.mdpi.com/journal/water
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