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2018 September

Table of Contents

Three Decades of Change in a Long Island Sound Embayment
How Will Climate Change Affect Exposure to Vibrio
A New Standard for Greenhouse Gas Accounting
Quantifying Shoreline Movement Along Segments of Florida’s Coast

Indicators of declining ecosystem health reflect problems at multiple scales

Norwalk Harbor, an estuarine embayment in Long Island Sound, faces a number of challenges, including dense development, shoreline hardening, and the input of treated sewage. A recent study looked at how the harbor’s ecosystem has changed since the 1980s and what that might mean for the future.

Researchers drew on a dataset that included weekly measurements of water temperature, salinity, and dissolved oxygen taken at multiple sites around the bay from May to September in 1987–2016, as well as samples of the demersal fish population (fish living near the bottom) collected regularly via trawls from 1990–1994 and 2002–2016. Water temperature and salinity both increased over the study’s timespan, while dissolved oxygen decreased and hypoxia events became more frequent. The number of fish caught per trawl declined over time, with more nets coming up empty. Although overall species richness remained the same, some northerly species associated with cold water became less common.

Demersal fish can be important indicators of estuary health, and the study’s authors believe that their findings reflect the effects of both climate change and ongoing local water quality issues. As water temperatures continue to increase and cold-water fish retreat north, the establishment of species adapted for warmer water in the area may be stalled by other water quality issues such as the changes in dissolved oxygen and salinity. Additionally, hypoxia is likely to become more and more of a problem—warmer water holds less oxygen and can increase stratification in the water column, leaving less oxygen available near the bottom, where demersal fish live. The declining health of the Norwalk Harbor ecosystem is tied to environmental challenges from the local to the global scale, and management actions at all levels will be needed to turn things around.

Source: Crosby, S.C., N.L. Cantatore, L.M. Smith, J.R. Cooper, P.J. Fraboni, and R.B. Harris. 2018. Three Decades of Change in Demersal Fish and Water Quality in a Long Island Sound Embayment. Estuaries and Coasts. DOI: 10.1007/s12237-018-0414-

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How Will Climate Change Affect Exposure to Vibrio?
Salinity, not temperature, may have the greatest effect on the pathogen in the Southeast

Vibrio are a genus of bacteria found in shellfish in estuaries around the world. The incidence of Vibrio in the U.S. is on the rise, which is cause for concern, as many are human pathogens. The distribution of Vibrio is largely determined by temperature and salinity, and past research suggests that the observed increase is due to warmer temperatures driven by climate change. However, the authors of a new study wanted to determine how increasing salinity due to sea level rise at upstream sites is likely to influence the future incidence of Vibrio vulnificus in Southeastern estuaries.

Researchers monitored environmental conditions and Vibrio incidence monthly from April to October 2012 at nine sites in South Carolina’s Winyah Bay estuary and developed a model to predict how climate change may affect Vibrio in the area. Their results confirmed previous reports of the optimal salinity range for V. vulnificus growth (approximately 5–19). They also found that salinity changes from sea level rise may actually have a greater effect than temperature on exposure risk in the estuary. Under a scenario in which local waters rise by approximately 0.9 meters, Vibrio incidence is predicted to increase by 290%.

If salinity changes due to sea level rise have a stronger impact on Vibrio incidence than previously recognized, this may increase the risk of human exposure to this pathogen in the future. Complex, interacting factors affect the distribution of Vibrio species worldwide, and more research is needed to understand future human public health risks that may arise due to climate change.

Source: Deeb, R., D. Tufford, G.I. Scott, J.G. Moore, and K. Dow. 2018. Impact of Climate Change on Vibrio vulnificus Abundance and Exposure Risk. Estuaries and Coasts. DOI: 10.1007/s12237-018-0424-5

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A New Standard for Greenhouse Gas Accounting
Methodology offers potential carbon credit funding for wetland restoration

The restoration of coastal wetlands has the potential to sequester large amounts of carbon. If this benefit can be quantified, carbon credits offer a potential source of funding for tidal wetland restoration. A new methodology developed for the Verified Carbon Standard (VCS) provides guidance for accounting for changes in greenhouse gas emissions that result from restoration, making carbon credit funding more feasible than ever.

The methodology considers emissions of carbon dioxide, methane, and nitrous oxide, and compares estimated emissions for a baseline scenario with that of a proposed restoration project in order to calculate the overall change in greenhouse gas flux. It takes a range of factors into account, including soil carbon sequestration, allochthonous carbon, erosion, and the use of prescribed fire, and offers a variety of methods to estimate the greenhouse gas flux from each—values derived from literature, models and proxies, field-collected data, etc. Projects also must consider “additionality” (whether they create additional greenhouse gas benefits beyond what would happen in the absence of funding) and “leakage” (whether a project leads to increase in emissions or decrease in removals outside of the project area).

The goal of the VCS methodology is to be as flexible and as feasible to implement as possible while maintaining scientific rigor. A variety of knowledge gaps remain, such as the need for better estimates of methane emissions from fresh and brackish tidal wetlands, carbon oxidation rates following drainage of mineral tidal wetland soils, and the effects of prescribed fire on soil carbon stocks. However, the VCS approach complements currently available systems of greenhouse gas accounting for tidal wetland systems and provides a potential way to generate carbon credit funding for restoration.

Source: Needelman, B.A., I.M. Emmer, S. Emmett-Mattox, S. Crooks, J.P. Megonigal, D. Myers, M.P.J. Oreska, and K. McGlathery. 2018. The Science and Policy of the Verified Carbon Standard Methodology for Tidal Wetland and Seagrass Restoration. Estuaries and Coasts. DOI: 10.1007/s12237-018-0429-0

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Quantifying Shoreline Movement Along Segments of Florida’s Coast
New software shows intensifying rates of shoreline change

Shorelines are in constant motion, moving back and forth in response to storms, changes in sedimentation and sea level, and human activities such as dredging. A recent study used a new software tool, Jackson’s “Analyzing Moving Boundaries Using R” or AMBUR, to evaluate shoreline change along segments of two of Florida’s barrier islands, one on the Gulf coast and one on the Atlantic coast.

AMBUR offers an advantage over previous methods of quantifying shoreline change in that it can be applied even to irregularly shaped shorelines. For this study, researchers used historical maps and aerial photographs from a range of sources to evaluate shoreline change trends over both the long and short term. Overall, the Gulf coast island experienced a mean annual retreat of approximately 0.62 meters per year from 1856 to 2015. The Atlantic coast island, on the other hand, had a net advance of approximately 0.22 meters per year from 1873 to 2014.

Rates of shoreline change increased considerably when more recent time periods were evaluated. The Gulf coast island saw a mean annual retreat of approximately 5.49 meters per year between 1994 and 2015, possibly due to a cluster of hurricanes and tropical storms that impacted the area during this period and may have increased local erosion. In contrast, the Atlantic coast island showed a seaward advance of 4.72 meters per year between 1999 and 2014 despite the increase in storms, which may be the result of the stabilizing effects of structural armoring and beach renourishment.

As this study demonstrates, shorelines are affected by many factors, and what happens in one location may not predict what occurs elsewhere. The AMBUR program is proving to be a useful tool for evaluating changing shorelines and understanding how they are affected by both natural processes and human activities. Source: Sankar, R.D., J.F. Donoghue, and S.A. Kish. 2018. Mapping Shoreline Variability of Two Barrier-Island Segments along the Florida Coast. Estuaries and Coasts. DOI: 10.1007/s12237-018-0426-3

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