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Coastal & Estuarine Science News (CESN)

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

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2017 March

Contents

How do Floodgates Rate?
Sediment Loading and Coral Reef Ecosystem Services
Sculpins, Oysters Impaired by Hypoxia
For New England Coastal Marshes, the Future is Here


How do Floodgates Rate?

Storm surge barriers have worked well in some low-lying cities. Would they work in Chesapeake Bay?

Climate change will likely bring increased intensity of coastal storms, resulting in more frequent and serious flooding in many areas. Some low-lying cities, like Rotterdam and New Orleans, have built storm surge barriers – essentially gates that keep the water out – to reduce flood damage, but there may be an ecological cost to these structures. Could floodgates work to protect the Chesapeake Bay region? What impacts might they have on the hydrodynamics and ecology of the bay?

A team of researchers used a numerical modeling approach to examine the impacts of two tide gate installation scenarios on hydrodynamics and circulation in the Chesapeake: one in which tide barriers are placed on both the northern and southern shores of the bay near its mouth (leaving a large channel between them) and one which includes an additional central section of barrier between the two shore-associated barriers. They also examined a scenario in which tidal energy was reduced at the mouth of the bay with no barrier in place. The presence of the storm surge barriers significantly reduced tidal range, vertical mixing, horizontal exchange, and bottom water inflow in the bay, and increased stratification. While the floodgates led to longer residence time for water within the bay, overall estuarine flow did not change significantly. Similar but less severe effects were observed for the scenario in which tidal energy was reduced with no tide gates in place. These hydrodynamic impacts could lead to significant ecological changes, including reduction of salt marsh habitat in the bay, increases in hypoxia in bottom waters, and increases in nutrient retention. The authors note that the impacts of these barriers in a partially-mixed estuary such as the Chesapeake will differ from those in the well-mixed estuaries where such barriers already exist.

Source: Du, J., J. Shen, D. M. Bilkovic, C. H. Hershner, and M. Sisson. 2017. A numerical modeling approach to predict the effect of a storm surge barrier on hydrodynamics and long-term transport processes in a partially mixed estuary. Estuaries and Coasts 40(2): 387-403. DOI: 10.1007/s12237-016-0175-0


 

Sediment Loading and Coral Reef Ecosystem Services

What coral reefs can do for us may depend on how much sediment they receive 

Coral reefs provide much more than homes for colorful fish: they provide storm surge protection for coastal communities, support coastal economies via recreational fishing and tourism, and are hotbeds for potential discovery of pharmaceuticals. Terrestrial sediment runoff ranks high as a stressor for coral reefs, and could impact the ecosystem services they provide. A research project in Puerto Rico, home to some of the most threatened reefs in the Caribbean, examined how provision of a range of types of ecosystem services was related to levels of sediment delivery into the coastal zone. The authors used 28 ecological production functions sorted into five general categories (shoreline protection, fisheries, etc.) to translate maps of coral reef conditions into predictions of ecosystem service metrics, and then evaluated whether those services are affected by sediment delivery. They found that higher sediment delivery was associated with a reduction in coral reef ecosystem services, although some services associated with more inshore habitats (mangrove stands, seagrass beds) were enhanced. This result suggests that tradeoffs may need to be considered when making coastal management decisions: what is good for reefs might have multiple benefits for coastal communities as well, but might not be as beneficial for other habitats. The approach used here, in which data from multiple sources were used to shed light on ecological functions, could potentially be applied in other coastal communities.

Source: Orlando, J. L. and S. H. Yee. 2016. Linking terrigenous sediment delivery to declines in coral reef ecosystem services. Estuaries and Coasts (September 2016). DOI: 10.1007/s12237-016-0167-0.


 

 

Sculpins, Oysters Impaired by Hypoxia

Hypoxia can stress even stress-tolerant estuarine species in Elkhorn Slough

Elkhorn Slough, one of the largest estuaries in California, sits in the middle of a major agricultural area and is subject to high nutrient loading and resulting eutrophication and hypoxia. Contributing to the estuary’s water quality problems are a number of dikes and other water control structures that restrict tidally-driven mixing. Researchers recently conducted an in situ transplant experiment in which two stress-tolerant species, staghorn sculpin and Olympia oyster, were caged at sites with restricted and full tidal exchange, representing a range of levels of dissolved oxygen (means of 4.68-8.80 mg/L) to examine impacts of water quality on mortality and growth.

Results confirmed that sites with restricted tidal exchange experienced more frequent and severe hypoxia. The duration and severity of hypoxia were negatively correlated with fish survival: at the three most severely hypoxic sites, all sculpin were dead after the first week. Although oyster survival was high at all sites, growth almost entirely ceased at the hypoxic sites.

One unique aspect of this study is that it examined impacts of water quality in the field rather than under controlled conditions in the laboratory. The authors emphasize that such studies can be invaluable for illustrating how organisms respond to real-world conditions where multiple stressors often interact. Field manipulations such as this provide concrete evidence of the negative impacts of water quality degradation, which can be useful for both educating stakeholders and informing management actions.

Source: Jeppesen, R., M. Rodriguez, J. Rinde, J. Haskins, B. Hughes, L. Mehner, and K. Wasson. 2016. Effects of hypoxia on fish survival and oyster growth in a highly eutrophic estuary. Estuaries and Coasts (September 2016). DOI: 10.1007/s12237-016-0169-y.


 

For New England Coastal Marshes, the Future is Here

Journal special issue examines the science and management of marsh loss in southern New England

Sea level rise is drowning salt marshes world-wide, but nowhere more than in southern New England, where rates of sea level rise have been as much as 50% higher than global averages. A

confluence of rising seas, low sediment input for marsh accretion, and a lack of available space for upland migration, has led to significant marsh loss in the region. A special issue of Estuaries and Coasts emerged from an April 2014 workshop on this topic. The issue includes papers ranging from historic analyses of vegetation loss to explorations of potential management responses.

This article, which is an introduction to the special issue, provides an overview of the topic and the papers that follow. Evidence for marsh loss in the region includes declines in high marsh taxa, loss of other vegetation species, and overall marsh retreat. Potential adaptation actions include raising marsh elevations through thin-layer sediment additions; installing living shoreline to stabilize against erosion; improving drainage to better support growth of some species; removing dams to increase sediment supply; and planning for landward marsh migration. These observations and suggestions are relevant well beyond New England, as marsh loss is occurring in many areas.

Source: Watson, E. B., K. B. Raposa, J. C. Carey, C. Wigand, and R. S. Warren. 2016. Anthropocene survival of southern New England’s salt marshes. September 2016. DOI: 10.1007/s12237-016-0166-1.