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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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January 2019

Table of Contents

Breakwater Associated Morphological Changes Increase Estuary Flood Risk
Invertebrates as Indicators in Restored Marshes
Do oyster reefs protect nearby marsh?
Lights Out! Artificial light at night

Breakwater Associated Morphological Changes Increase Estuary Flood Risk
“Ensemble modeling” predicts flood effects in a Portuguese estuary

Accurately predicting the effects of estuary flooding is increasingly critical in the era of climate change, especially in highly urbanized estuaries where human activity has altered local morpho-hydrodynamics. A recent study applied an “ensemble” method—running two or more related but different numerical models and then synthesizing the results into a single solution—to paint a more accurate picture of flood risk in the Douro River estuary on Europe’s Iberian Peninsula.

Past extreme floods on the Douro River washed out the sandbar at the mouth of the estuary. Although this allowed the discharge of excess water and reduced the risk of additional flooding, the loss of the sandbar also created navigational hazards and exposed the lower estuary to greater wave damage. Between 2004 and 2008, a breakwater was constructed to stabilize and protect the estuary banks, improve navigability, and prevent further erosion of the sandbar. This structure changed the river’s hydrodynamic patterns, increasing the area and volume of the sandbar, with potential effects on future river flooding.

Researchers synthesized output from the open TELEMAC-MASCARET and Delft3D models, which are both well-known hydrodynamic software packages widely applied to riverine, coastal, and estuarine areas. Calibration with contemporary non-flooding conditions and historical floods confirmed the models’ accuracy, and that the final solution was improved with the “ensemble” technique. The modeling results reveal that the growth of the estuary sandbar is likely to significantly increase water levels associated with extreme flood events. To minimize flood risk in the future, proper management of upstream reservoirs along the Douro River will be required.

The results of this study demonstrate that ensemble modeling can improve the accuracy of predictions of the effects of extreme events in complex estuarine environments. They also highlight the importance of accounting for human alterations of estuarine hydrodynamics in models to characterize areas of risk, to promote population safety, and to minimize economic losses.

Source: Iglesias, I., S. Venâncio, J.L. Pinho, P. Avilez-Valente, & J.M.P. Vieira. 2018. Two Models Solutions for the Douro Estuary: Flood Risk Assessment and Breakwater Effects. Estuaries and Coasts. DOI: 10.1007/s12237-018-0477-5

Invertebrates as Indicators in Restored Marshes
Periwinkles and amphipods recover at different rates in restored Gulf marshes

Coastal restoration strives to create habitat that replicates the ecosystem services provided by natural systems—but how do coastal managers know when they’ve succeeded? This question has become especially important in the northern Gulf of Mexico as salt marsh restoration efforts continue after the Deepwater Horizon oil spill, and a new paper highlights two marsh invertebrates that can be used as indicators of ecosystem recovery following restoration.

Periwinkle snails and amphipods are indicators of overall marsh health and productivity, facilitating nutrient cycling and providing food for economically important species. Through a literature review, researchers compiled studies on these species from both natural and restored marshes along the Gulf and East coasts. They found that restored marshes typically had periwinkle densities similar to those of reference marshes after about four years; periwinkles have a close association with the marsh grass Spartina alterniflora, and their recovery may depend on habitat suitability and predation levels. For the amphipods the available data was not sufficient to determine the length of time at which recovery would be expected, but amphipod density in restored marshes only averaged about 50% of that in reference marshes. Soil organic matter content and nutrients may take much longer to return to reference conditions than surface vegetation, which could explain the weak recovery of soil-dwelling amphipods.

The authors of the study point out that recovery may also depend on the hydrology of a restored marsh as much as the passage of time—they recommend taking the habitat and accessibility needs of a variety of species into account when designing a restoration project. This study can help inform the continuing efforts to restore marshes damaged by Deepwater Horizon and shows that conducting meta-analyses of data from multiple literature sources can be a powerful tool.

Source: Baumann, M.S., G.F. Fricano, K. Fedeli, C.E. Schlemme, M.C. Christman, & M.V. Carle. 2018. Recovery of Salt Marsh Invertebrates Following Habitat Restoration: Implications for Marsh Restoration in the Northern Gulf of Mexico. DOI: 10.1007/s12237-018-0469-5

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Do oyster reefs protect nearby marsh?
Shallow reefs could shelter low-lying marshes from erosion

Globally, marshlands fringing coastal bays are undergoing significant erosion. Because wave action is the primary driver of this erosion, research has suggested that oyster reefs, like coral reefs, might be effective at decreasing wave energy and slowing the retreat of vital marsh habitat. Yet there has been limited research quantifying just how much protection oyster reefs might offer. Using tide and wave recorders on both sides of human-constructed oyster reefs off Virginia’s Delmarva Peninsula, the authors of a recent study determined that oyster reefs can indeed have a significant effect on wave energy. However, the benefits depended on the depth of the water above the reef.

When a reef’s crest was near the water surface (water depth of 0.5 to 1 meters), the four oyster reefs studied reduced wave heights by an average of 30 to 50 percent on their sheltered sides. However, there was little to no difference in wave height observed when water depth over the reef crest increased to 1 meter or more.

The lack of wave attenuation in deeper water means that oyster reefs would likely offer little protection from high-wind driven storm surges, which would place most reef crests well below 1 meter. Even so, these results offer guidance for the construction of artificial oyster reefs. Reefs constructed at or just below sea level would be most effective at protecting low-lying marshes, particularly from the smaller storms and moderately-sized wind-driven waves that contribute most to marsh erosion.

Source: Wiberg, P.L., S.R. Taube, A.E. Ferguson, M.R. Kremer, M.A. Reidenbach. 2018. Wave Attenuation by Oyster Reefs in Shallow Coastal Bays. DOI: 10.1007/s12237-018-0463-y

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Lights Out! Artificial light at night
Artificial lighting disrupts aquatic life

The bright lights of human life on the coast have a dark side. Situated at the population-dense border between ocean and land, coastal and estuarine ecosystems are likely to be disproportionately affected by artificial lighting at night, or ALAN. This form of light pollution is known to be highly disruptive to many kinds of animals, which use cues from ambient light to drive activity and maintain biological rhythms. In a recent review paper, researchers synthesized how human light pollution at night broadly disturbs coastal and estuarine systems.

The authors provide examples of how both the intensity of ALAN and its color can affect biological processes, such as the production of certain hormones and stress responses, and also alter behaviors, including mating and reproduction, navigation, and migration. The researchers also gave examples of how these observations can be scaled up to the ecosystem level — citing examples such as primary production, and energy flows through food webs — but also point out that this is an important area for future research.

The paper also highlights several management practices that have already seen success in controlling nighttime light pollution, such as limiting the use of ALAN to specific time frames or spectral ranges. Given that nighttime light is projected to increase by roughly six percent each year, understanding the system-specific and ecological impacts of ALAN will be vital to guiding best management practices.

Source: Zapata, M.J., S.M.P. Sullivan, & S.M. Gray. 2018. Artificial Lighting at Night in Estuaries--Implications from Individuals to Ecosystems. DOI: 10.1007/s12237-018-0479-3

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