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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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November 2021

Table of Contents

Catch My Drift: Stakeholder-driven Hydrodynamic Modeling

Addressing fecal coliform transport in shellfishing areas

Despite the large economic losses, shellfish areas like clam flats must be closed when there’s a risk of fecal coliform contamination. Although understandable from a public health standpoint, these closures can be unnecessarily conservative due to a lack of detailed information on the amount of time that water remains in a given area, also known as the residence time. A group of researchers in Maine took a “sustainability science” approach to address this issue in collaboration with the soft-shell clamming community in the Medomak River estuary.

The researchers and stakeholders (clammers, municipal managers, and other community members) co-designed a study that involved releasing inexpensive drifter buckets to assess wind and flow patterns in economically valuable clamming areas. Sets of three drifters with GPS trackers were released from stakeholder-identified points during maximum ebb or maximum flood current speed, and they were retrieved 12 to 24 hours later. These observations were then used in a hydrodynamic model to resolve the influence of wind, tidal currents, and bathymetry on water exchange between the main channel and adjacent mudflats. The results showed that residence times in adjacent areas could vary considerably, which has implications for how long an area may need to be closed before it is safe to resume shellfishing. The group has identified a number of follow-up actions from this study, including collecting more information on wind speed and direction and reexamining sampling strategies for bacteria-laden waters.

Although this study was specifically aimed at producing locally relevant knowledge for clammers in Maine, it shows the value of sustainability science. This approach involves aligning research problems with stakeholder questions, understanding user preferences for involvement, discussing progress regularly and making adjustments as needed, co-producing knowledge, and making conscious changes to promote equity within the process.

Source: Hillyer, G.V. et al. 2021. Using a Stakeholder‑Engaged Approach to Understand and Address Bacterial Transport on Soft‑Shell Clam Flats. Estuaries and Coasts. DOI: 10.1007/s12237-021-00997-0

How Drones Help Manage the Coast

Nine applications and a few limitations of UAVs

Uncrewed aerial vehicles (UAVs), or drones, are used for everything from infrastructure inspection to package deliveries, and they’re an increasingly important tool for coastal researchers and decision-makers. A team of researchers in Ireland reviewed nearly 100 references on UAVs, with a focus on applications that could contribute to integrated coastal zone management activities. The applications can be categorized into nine areas, listed below with examples.

1. Habitat Mapping, and Biological and Natural Resource Assessment: aiding conservation studies and managing human-wildlife interactions (this was the most common application of UAVs)
2. Ecological Monitoring: surveying whales, turtles, and seabirds
3. Environmental Law Enforcement and Compliance: investigating illegal fishing and other shoreline development violations
4. Pollution Management: monitoring marine debris and harmful algal blooms
5. Heritage Sites: conducting archaeological surveys and documenting submerged sites
6. Emergency Response: detecting people and wildlife and delivering life-saving equipment
7. Disaster Assessment: estimating damages from oil spills, storms, and other coastal disasters
8. Planning and Development: evaluating the effectiveness of coastal interventions
9. Tourism: creating virtual tours to lessen anthropogenic impacts on the environment

Although UAVs can deliver high-quality data over larger areas than ground surveys, a number of practical and technological challenges remain—from battery life constraints to processing time to image interpretation. There is also a need to standardize methods and establish a set of best practices for users. Finally, compliance with local regulations as well as privacy and data protection must also be considered. However, UAVs are here to stay and have the ability to deliver relevant data for evidence-based decision making.

Source: Kandrot, S. et al. 2021. Applications of Uncrewed Aerial Vehicles (UAV) Technology to Support Integrated Coastal Zone Management and the UN Sustainable Development Goals at the Coast. Estuaries and Coasts. DOI: 10.1007/s12237-021-01001-5

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Should Coastal Defenses Be Moved Landward?

Increasing the buffer zone could help prevent flooding

One of the many implications of rising sea levels is an anticipated increase in the cost of maintaining seawalls as a result of increased flooding in low-lying coastal areas. An adaptation strategy that may help reduce these costs is known as managed realignment (MR)—the landward relocation of sea defenses, followed by the breaching of the old seaward line of defense. This fosters the creation (or recreation) of coastal wetlands, which act as buffer zones to help sustainably manage flood and erosion risks and achieve nature-based coastal protection.

To advance our understanding of managed realignment, researchers developed a model based on one of the largest MR sites in Europe: Freiston Shore on the east coast of England, where 66 hectares of new intertidal and shallow water habitats were restored by breaching the seaward dike at three locations in 2002. They used the model to explore the relationship between surge height and surge attenuation under different scenarios of MR width and area—from 900 meters and 118 hectares to 1500 meters and 205 hectares. They also assessed the effects of reduced vegetation cover using Freiston Shore’s actual MR specifications in comparison with the hypothetical scenario with the largest MR width.

According to their analysis, the current MR configuration of Freiston Shore is too small to effectively attenuate storm surges with return periods of more than 10 years, even with full vegetation cover. However, the largest hypothetical MR width evaluated did result in substantially higher attenuation rates, suggesting that at the open coast only very large MR schemes can effectively reduce coastal flood risk. And because water levels are lower farther inland, constructing and maintaining new landward dikes can be relatively inexpensive compared to the cost of maintaining the original dikes and seawalls.

Source: Kiesel, J. et al. 2021. Can Managed Realignment Buffer Extreme Surges? The Relationship Between Marsh Width, Vegetation Cover and Surge Attenuation. Estuaries and Coasts. DOI:10.1007/s12237-021-00984-5

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How Does Flooding Influence Nesting Success?

Studying waterbird survival in Louisiana

In places where rising sea levels and subsidence impact the success of colonial nesting waterbirds, dredged materials could help increase the elevation of breeding islands and prevent their nests from being inundated. To help inform proposed restoration efforts on Louisiana’s low-lying Rabbit Island, a team of researchers monitored the survival of eggs and chicks in 652 nests weekly in 2017 and 2018. The team also recorded the nests’ elevation and initiation, and they assessed the frequency of inundation events using water loggers.

As expected, flooding was the primary cause of nest failure for most of the birds. However, the effect of flooding on nesting success varied depending on nesting strategy and the timing of nest initiation and storm events. Tricolored herons and roseate spoonbills, which built nesting platforms in vegetation above the ground, were less susceptible to flooding than brown pelicans and Forster’s terns, who nest on the ground. Pelicans nested first and had the longest nesting season each year. Terns, however, nested later in the season; this meant they missed earlier storms, but young chicks were in the nest during the most severe storms.

This study was done in an area without mammalian predators, allowing researchers to isolate flood risk as a threat. Although these findings suggest that raising elevation will increase nest survival, there are trade-offs to consider. Periodic flooding keeps invasive fire ants at bay and minimizes cover of woody vegetation, which has been linked to an increase in mammalian predators like raccoons. In fact, observations on adjacent dredge spoil islands suggest that raising the elevation more than one meter will increase the establishment of woody vegetation. Ultimately, losing occasional years to flooding may have less impact on population trends for these long-lived waterbirds than living in flood-free areas that get taken over by predators. This topic requires more research, but it may be that for low-lying islands, minor increases in elevation are the way to go.

Source: Ritenour, K. et al. 2021. Factors Affecting Nest Success of Colonial Nesting Waterbirds in Southwest Louisiana. Estuaries and Coasts. DOI: 10.1007/s12237-021-00993-4

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