Empirical observations and numerical modelling of tides, channel morphology, and vegetative effects on accretion in a restored tidal marsh

Abstract

Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine-grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high-resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco-geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood-ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In-situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea-level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience.

Salt Marsh Dynamics in a Period of Accelerated Sea Level Rise

“…Plant productivity is also closely linked to marsh elevation with respect to high tide, tidal range, and sediment supply. Process‐based models coupling geomorphology and biology are therefore crucial tools for understanding salt marsh evolution (Fagherazzi, Fitzgerald, et al, 2013; Fleri et al, 2019).…”

“…Previous work highlights the strong ecogeomorphic feedbacks in these systems (Allen, 2000; Fagherazzi, Fitzgerald, et al, 2013; Kirwan & Megonigal, 2013; Nardin & Edmonds, 2014; Nardin et al, 2016; Temmerman et al, 2005). For example, vegetation influences hydrology, sediment erosion, deposition, and channel morphology (Fleri et al, 2019; Gran & Paola, 2001; Manners et al, 2015; Nepf, 2012). Marsh platform stabilization induced by vegetation can impact the migration of creek meanders, promotes single channelization, and reduces channel width (Simon & Collison, 2002).…”

A threshold‐like effect on the interaction between hydrological connectivity and dominant plant population in tidal marsh wetlands

“…A follow‐up research also reported that the distribution of species and biomass in high salinity areas are affected by hydrological connectivity (Liu et al, 2020; Liu et al, 2020). As several other studies found that the distribution and cover rate of plant species are also influenced by the distribution and morphology of tidal creeks (Fleri, Lera, Gerevini, Staver, & Nardin, 2019; Wu et al, 2020), studies examining the relationship between dominant species population structure and hydrological connectivity remain to be limited.…”

Influence of Rigid Emerged Vegetation in a Channel Bend on Bed Topography and Flow Velocity Field: Laboratory Experiments

“…According to the formation of plants, their mechanical properties and density, as well as their spatial distribution, can greatly affect the flow structure, biotic processes, channel planform and sediment movement in rivers [4,[37][38][39][40][41][42]. The effectiveness of plants as a bed reinforcing measure depends upon the scale and density, as well as the protrusion of plant stems that are partly or fully submerged, the geometric arrangement concerning one another, and their development stage [43,44].…”