An official website of the United States government
Abstract An accelerating global rate of sea level rise (SLR), coupled with direct human impacts to coastal watersheds and shorelines, threatens the continued survival of salt marshes. We developed a new landscape‐scale numerical model of salt marsh evolution and applied it to marshes in the Plum Island Estuary (Massachusetts, U.S.A.), a sediment‐deficient system bounded by steep uplands. To capture complexities of vertical accretion across the marsh platform, we employed a novel approach that incorporates spatially variable suspended sediment concentrations and biomass of multiple plant species as functions of elevation and distance from sediment sources. The model predicts a stable areal extent of Plum Island marshes for a variety of SLR scenarios through 2100, where limited marsh drowning is compensated by limited marsh migration into adjacent uplands. Nevertheless, the model predicts widespread conversion of high marsh vegetation to low marsh vegetation, and accretion deficits that indicate eventual marsh drowning. Although sediment‐deficient marshes bounded by steep uplands are considered extremely vulnerable to SLR, our results highlight that marshes with high elevation capital can maintain their areal extent for decades to centuries even under conditions in which they will inevitably drown.
more »
« less
Integrated Modeling of Dynamic Marsh Feedbacks and Evolution Under Sea‐Level Rise in a Mesotidal Estuary (Plum Island, MA, USA)
Abstract Around the world, wetland vulnerability to sea‐level rise (SLR) depends on different factors including tidal regimes, topography, creeks and estuary geometry, sediment availability, vegetation type, etc. The Plum Island estuary (PIE) is a mesotidal wetland system on the east coast of the United States. This research applied a newly updated Hydro‐MEM (integrated hydrodynamic‐marsh) model to assess the impacts of intermediate‐low (50 cm), intermediate (1 m), and intermediate‐high (1.5 m) SLR on marsh evolution by the year 2100. Model advancements include capturing vegetation change, inorganic and below and aboveground organic matter portion of marsh platform accretion, and mudflat creation. Although the results indicate a low vulnerability marsh at the PIE, the vegetation changes from high to low marsh under all SLR scenarios (2%–22%), with the higher bounds belonging to higher rise scenarios. Lower SLR produces more productive marsh (13% gain in high productivity regions), whereas the highest SLR scenario causes increased tidal inundation, which leads to loss in productivity (12% change from high to low productivity regions), generation of mudflats (17% of the domain land), and marsh migration to higher lands. Sensitive nonlinear tidal flow changes, which may be increased or decreased with SLR as a result of mudflat creation, marsh migration, and bottom friction change, emphasize the importance of integrated modeling approaches that include dynamic marsh feedbacks in hydrodynamic modeling and varying hydrodynamic effects on the marsh system.
more »
« less
- Award ID(s):
- 1637630
- PAR ID:
- 10373272
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 58
- Issue:
- 8
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Elevation is a major driver of plant ecology and sediment dynamics in tidal wetlands, so accurate and precise spatial data are essential for assessing wetland vulnerability to sea-level rise and making forecasts. We performed survey-grade elevation and vegetation surveys of the Global Change Research Wetland, a brackish microtidal wetland in the Chesapeake Bay estuary, Maryland (USA), to both intercompare unbiased digital elevation model (DEM) creation techniques and to describe niche partitioning of several common tidal wetland plant species. We identified a tradeoff between scalability and performance in creating unbiased DEMs, with more data intensive methods such as kriging performing better than 3 more scalable methods involving postprocessing of light detection and ranging (LiDAR)-based DEMs. The LiDAR Elevation Correction with Normalized Difference Vegetation Index (LEAN) method provided a compromise between scalability and performance, although it underpredicted variability in elevation. In areas where native plants dominated, the sedge Schoenoplectus americanus occupied more frequently flooded areas (median: 0.22, 95% range: 0.09 to 0.31 m relative to North America Vertical Datum of 1988 [NAVD88]) and the grass Spartina patens, less frequently flooded (0.27, 0.1 to 0.35 m NAVD88). Non-native Phragmites australis dominated at lower elevations more than the native graminoids, but had a wide flooding tolerance, encompassing both their ranges (0.19, −0.05 to 0.36 m NAVD88). The native shrub Iva frutescens also dominated at lower elevations (0.20, 0.04 to 0.30 m NAVD88), despite being previously described as a high marsh species. These analyses not only provide valuable context for the temporally rich but spatially restricted data collected at a single well-studied site, but also provide broad insight into mapping techniques and species zonation.more » « less
-
Abstract The fluxes of dissolved organic carbon (DOC) through tidal marsh‐influenced estuaries remain poorly quantified and have been identified as a missing component in carbon‐cycle models. The extreme variability inherent to these ecosystems of the land‐ocean interface challenge our ability to capture DOC‐concentration dynamics and to calculate accurate DOC fluxes. In situ discrete and continuous measurements provide high‐quality estimates of DOC concentration, but these strategies are constrained spatially and temporally and can be costly to operate. Here, field measurements and high‐spatial‐resolution remote sensing were used to train and validate a predictive model of DOC‐concentration distributions in the Plum Island Estuary (PIE), a mesotidal saltmarsh‐influenced estuary in Massachusetts. A large set of field measurements collected between 2017 and 2023 was used to develop and validate an empirical algorithm to retrieve DOC concentration with a ±15% uncertainty from Sentinel‐2 imagery. Implementation on 141 useable images produced a 6‐year time series (2017–2023) of DOC distributions along the thalweg. Analysis of the time series helped identify river discharge, tidal water level (WL), and a marsh enhanced vegetation index 2 as predictors of DOC distribution in the estuary, and facilitated the training and validation of a simple model estimating the distribution. This simple model was able to predict DOC along the PIE thalweg within ±16% of the in situ measurements. Implementation for three years (2020–2022) illustrated how this type of remote‐sensing‐informed models can be coupled with the outputs hydrodynamic models to calculate DOC fluxes in tidal marsh‐influenced estuaries and estimate DOC export to the coastal ocean.more » « less
-
Abstract High tide floods (HTFs) are minor, shallow flooding events whose frequency has increased due to relative sea‐level rise (SLR) and secular changes in tides. Here we isolate and examine the role of historical landscape change (geomorphology, land cover) and SLR on tides and HTF frequency in an urbanized lagoonal estuary: Jamaica Bay, New York. The approach involves data archeology, historical (1870s) map digitization, as well as numerical modeling of the bay. Numerical simulations indicate that a century of landscape alterations (e.g., inlet deepening and widening, channel deepening, and wetland reclamation) increased the mean tidal range at the head of the bay by about 20%. The observed historical shift from the attenuation to amplification of semidiurnal tides is primarily associated with reduced tidal damping at the inlet and increased tidal reflection. The 18% decrease in surface area exerts a minor influence. A 1‐year (2020) water level simulation is used to evaluate the effects of both SLR and altered morphology on the annual number of HTFs. Results show that of 15 “minor flood” events in 2020, only one would have occurred without SLR and two without landscape changes since the 1870s. Spectral and transfer function analyses of water level reveal frequency‐dependent fingerprints of landscape change, with a significant decrease in damping for high‐frequency surges and tides (6–18 hr time scale). By contrast, SLR produced only minor effects on frequency‐dependent amplification. Nonetheless, the geomorphic influence on the dynamical response significantly increases the vulnerability of the system to SLR, particularly high‐tide flooding.more » « less
-
Abstract Sea level rise (SLR) is threatening coastal marshes, leading to large‐scale marsh loss in several micro‐tidal systems. Early recognition of marsh vulnerability to SLR is critical in these systems to aid managers to take appropriate restoration or mitigation measures. However, it is not clear if current marsh vulnerability indicators correctly assess long‐term stability of the marsh system. In this study, two indicators of marsh stress were studied: (i) the skewness of the marsh elevation distribution, and (ii) the abundance of codominant species in mixtures. We combined high‐precision elevation measurements (GPS), LiDAR imagery, vegetation surveys and water level measurements to study these indicators in an organogenic micro‐tidal system (Blackwater River, Maryland, USA), where large‐scale historical conversion from marshes to shallow ponds resulted in a gradient of increasing marsh loss. The two indicators reveal increasingly stressed marshes along the marsh loss gradient, but suggest that the field site with the most marsh loss seems to experience less stress. For the latter site, previous research indicates that wind waves generated on interior marsh ponds contribute to lateral erosion of surrounding marsh edges and hence marsh loss. The eroded marsh sediment might temporarily provide the remaining marshes with the necessary sediment to keep up with relative SLR. However, this is only a short‐term alleviation, as lateral marsh edge erosion and sediment export lead to severe marsh loss in the long term. Our findings indicate that marsh elevation skewness and the abundance of codominant species in mixtures can be used to supplement existing marsh stress indicators, but that additional indices such as fetch length and the sediment budget should be included to account for lateral marsh erosion and sediment export and to correctly assess long‐term stability of micro‐tidal marshes. © 2020 John Wiley & Sons, Ltd.more » « less
