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Coastal & Estuarine Science News (CESN)

Coastal and Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries and Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bi-monthly basis.

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2023 Issue 2

Table of Contents

Is Large-Scale Environmental Restoration Possible?

Recommendations from hundreds of Gulf of Mexico projects

Over the last decade, more than 300 environmental restoration projects have been funded by fines and penalties from the Deepwater Horizon oil spill, providing an unprecedented opportunity to demonstrate large-scale environmental recovery. A recent National Academies report, a consensus of 10 committee members over the course of 18 months, addressed the monitoring and assessment of the cumulative effects of Gulf of Mexico restoration projects. They found that gaps in data collection, issues with data accessibility, and a lack of synthesis and analysis are hindering the ability of coastal scientists and managers to examine the impacts of the many restoration efforts on the overall ecosystem health of the Gulf.

To address the challenges of obtaining the long-term and accessible environmental trend data needed for both restoration planning and synthesis, the committee made a series of key recommendations for these programs going forward. First, sustained, consistent monitoring of priority areas and periodic assessments of the long-term data are urgently needed. It’s also crucial to synthesize available data on both successful and unsuccessful restoration projects conducted to-date to inform the design of future projects. They also called for an assessment of the cumulative effects. From a programmatic perspective, the committee recommended that steps be taken to ensure data availability through the utilization or establishment of freely accessible data repositories, and that mechanisms that support cross-state and Gulf-wide collaboration among researchers, resource managers, and practitioners should be evaluated. Finally, they recommended that an adaptive management strategy should be collaboratively developed and put in place to ensure that the program continues beyond the current funding initiatives.

The committee members are cautiously optimistic that—with a mid-course assessment and quick, corrective actions—quantifiable progress toward large-scale environmental recovery can be made.

Source: Greening, H.S. et al. 2022. Assessing the Effectiveness of Large‑Scale Environmental Restoration: Challenges and Opportunities. Estuaries and Coasts. DOI: 10.1007/s12237-022-01149-8

How Surge Barriers Change Estuary Dynamics

Modeling the impacts of flow alterations to sediment dynamics in the Hudson

Gated storm surge barriers are increasingly being considered for the protection of populated areas near estuaries. Although the gates are opened to allow for tidal exchange during non-stormy periods, the permanent infrastructure associated with these structures can significantly alter conditions inside the estuary—affecting the tides, the salinity dynamics, and the resuspension, transport, and accumulation of sediment. To examine the potential impacts of surge barriers on estuarine sediment dynamics, a model simulation was conducted using a range of river discharge and tidal forcing conditions for a potential surge barrier near the mouth of the Hudson River estuary.

According to the model, channel areas near the gates can expect to experience increased tidal velocities and bottom stresses, resulting in erosion and coarsening of the bed. The enhanced flows will also increase turbulent mixing, which will reduce local salinity stratification and mobilize sediments, potentially adding contaminants to the water column. Meanwhile, the main body of the estuary away from the gates would experience a decrease in tidal amplitude, increased trapping of sediment from the watershed, increased stratification, and a landward shift in the salinity intrusion. There would also be a reduction in bottom stress, which would lead to reduced turbidity in the water column, and, subsequently, increased light penetration. In eutrophic estuaries, this could raise the potential for harmful algal blooms.

In the Hudson, modest suspended sediment reductions with the barrier are not expected to have major impacts on algal blooms or on delivery of sediment to adjacent marshes. However, barriers may have more substantial impacts on sediment dynamics in estuaries with lower background concentrations or those that are dependent on sediment input from the seaward direction.

Source: Ralston, D.K. 2023. Changes in Estuarine Sediment Dynamics with a Storm Surge Barrier. Estuaries and Coasts. DOI: 10.1007/s12237-023-01172-3

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TLP: Techniques, Limitations, and Potential

Can thin–layer sediment placement enhance marsh resilience?

Thin–layer sediment placement (TLP) was originally devised as a way to dispose of dredged material by placing sediment in adjacent intertidal areas, but those additional layers of sediment can potentially be used as a coastal management tool to increase the elevation of tidal marshes. This could help restore eroded marshes or confer resilience against sea-level rise. However, guidance is scarce on the use of TLP in the context of marsh restoration and resilience. To address this, over a dozen researchers conducted a coordinated, standardized experiment across eight National Estuarine Research Reserves on the east and west coasts of the U.S. spanning a broad range of geomorphic and hydrologic conditions. At each site, sediment layers of varying thicknesses were added to experimental plots in both low marsh (such as mudflats) and high marsh areas. Elevation and vegetation conditions were measured for three years in treatment plots in comparison to both control plots (located in the same area) and reference plots, which were located in areas with the target elevation and vegetation.

Overall, the elevation of sediment addition plots increased and resembled that of target reference plots; despite declines over time, elevation remained higher than controls during the study period. Revegetation was generally rapid following sediment addition, and after three years, vegetation cover in TLP plots was similar to that of control plots at most sites. Initially, colonization by marsh plants was slower in plots with thicker sediment layers, though because this difference largely disappeared, the authors recommend thicker layers for combating accelerated sea-level rise.

However, vegetation cover in TLP plots remained lower than that of reference plots and did not shift to the target vegetation in high marsh areas. These results indicate that more than three years is needed for the full benefits of increased elevation to accrue, and the goal of achieving reference marsh conditions would be achieved slowly—if at all. Although TLP holds promise as a climate adaptation strategy, a longer timeline is needed to determine whether it can achieve management goals.

Source: Raposa, K.B. et al. 2023. Evaluating Thin–Layer Sediment Placement as a Tool for Enhancing Tidal Marsh Resilience: a Coordinated Experiment Across Eight US National Estuarine Research Reserves. Estuaries and Coasts. DOI: 10.1007/s12237-022-01161-y

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The Cryptic Invasion of Non-Native Cattails

Recognizing invasive Typha in a British Columbia estuary

The early detection of invasive species is critical for minimizing impacts on native ecosystems. Non-native narrow-leaved cattail (Typha angustifolia) has been detected in the Pacific Northwest in recent decades, but their degree of establishment, as well as that of hybrid cattail (Typha × glauca), remain unknown. In wetlands across North America, these species have shown the ability to displace native plant communities and drive changes in community structure. Understanding their current distribution and future risk of expansion would help determine optimal management strategies.

Using a combination of spectral analysis and species distribution modeling, researchers examined the threat of non-native cattails to tidal marsh ecosystems in British Columbia’s Fraser River Estuary. To their surprise, the team found that these invaders are widespread in the estuary, and their distributions will likely increase over time. Furthermore, though never formally recorded in the estuary, T. × glauca appears to be the most abundant species. The resemblance of the invaders to native cattail likely inhibited their detection for decades—highlighting the vulnerability of urban estuaries to cryptic invasions. The model also looked at site suitability (ability to establish and persist) and susceptibility (risk of colonization when suitable). According to their predictions, 29% and 20% of the estuary has moderate or high suitability and susceptibility probabilities, respectively.  

Given the extent of this invasion, containment and eradication across the estuary are unlikely. For future management, the study authors recommend prioritizing the monitoring and eradicating of invasive cattails in areas of high cultural and ecological value. Cryptic invasions will only be overcome by “decrypting” these species through research (including genetic studies), monitoring, public outreach, (ideally) proactively investigating potential threats before they become established, and responding to invasions in a timely way.

Source: Stewart, D. et al. 2023. Undetected but Widespread: the Cryptic Invasion of Non-Native Cattail (Typha) in a Pacific Northwest Estuary. Estuaries and Coasts. DOI: 10.1007/s12237-023-01171-4

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