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 2020

Getting a high-level view of coastal habitats
Betting on bivalves?
Using cars to count coastal visitors
Mending salt marshes from the bottom-up

Getting a high-level view of coastal habitats
How aerial surveys of submersed aquatic vegetation show broader trends

Submersed aquatic vegetation (SAV) is a vital shallow-water habitat worldwide, as well as one that is facing a host of stressors: from damage by boat propellers, dredging, fishing and aquacultural activity, to the effects of nutrient loading and climate change. Yet SAV’s sensitivity also makes it a powerful indicator of broader ecosystem health. Understanding long term trends in SAV coverage can help researchers track environmental change — and the best way to do that, a recent review paper suggests, is to get a higher perspective.

Using 33 years of SAV coverage collected through aerial surveys in the Chesapeake Bay, the paper provides eight applications that demonstrate the value of long-term SAV aerial coverage data and how it can be used to take action to prevent or reverse damage. These examples include research into how external forces affect the health of SAV, such as how point nutrient source loading, shoreline armoring, aquaculture and commercial fisheries each interact with, and impact, SAV populations. They also include research on how the presence of SAV beds can improve water quality. In one notable example, a study of a large SAV bed showed that this vegetation significantly decreased local nitrogen concentrations, which led to more resilience against storm turbidity and damage.

The authors also detail how managers can use these maps to set goals for SAV restoration, and to then assess the success of restoration efforts. Overall, these examples highlight the value of such annual large-scale monitoring, especially as new technologies enable aerial surveys like these to be run more frequently, at a higher resolution, and at a decreasing cost.

Source: Orth, R.J. et al. 2019. Long-term Annual Annual Aerial Surveys of Submersed Aquatic Vegetation (SAV) Support science, Management, and Restoration. Estuaries and Coasts. DOI: 10.1007/s12237-019-00651-w

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Betting on bivalves?
The ecological and economic benefits of nitrogen removal by oysters

One potential solution to the ongoing challenge of coastal eutrophication is to use shellfish to remove nitrogen in concert with land-based nutrient management. In New Hampshire’s Great Bay Piscataqua River Estuary, researchers used a local-scale model to test how oysters could contribute to nitrogen removal and eutrophication mitigation.

This research used a model of Eastern oyster (Crassostrea virginica) cultivation created to estimate nitrogen removal in Long Island Sound. The model was populated with data from a five-year monitoring program in the Great Bay Piscataqua estuary and used to estimate how much nitrogen was removed by farmed oysters: 0.072 metric tons per acre, per year, which scales up to 0.61 metric tons per year. If licensed aquaculture was expanded to the maximum possible area, the researchers estimated that oysters could remove a total of 2.35 metric tons of nitrogen per year.

When potential nitrogen removal provided by restoring oyster reefs was included, the benefit was even higher, providing approximately three times the nutrient removal of aquaculture. Based on these results, the authors recommend implementing both expanded aquaculture and nitrogen reef restoration for maximum nitrogen removal. This provides an economic value as well as an ecological one, as the oysters’ presence would remove nitrogen that could cause broader economic woes. Based on this avoided-cost valuation, the model estimates the value of nitrogen removal to be $105,000 for current oyster areas, and a $405,000 value if aquaculture were expanded. Combined with reef restoration, the maximum value was $461,000 for current areas and $760,000 with expansion.

Source: Bricker, S.B. et al. 2019. Bioextractive Removal of Nitrogen by Oysters in Great Bay Piscataqua River Estuary, New Hampshire, USA. Estuaries and Coasts. DOI: 10.1007/s12237-019-00661-8

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Using cars to count coastal visitors
Quantifying recreation within an estuary

It is often difficult to estimate human recreational use of estuaries. Researchers working in the Three Bays estuary system, on the south shore of Cape Cod, developed a practical, observation-based sampling approach to quantify recreational use. This system was designed to be cost-effective, rapid, and to avoid the inaccuracies of traditional surveys, which have been found to overestimate visitation and may not account for the many varied recreational uses that estuaries provide.

Over seven separate days in the summer of 2017, a field team counted the number of parked cars at 11 randomly-selected public access points (beaches, boat ramps, boat landings, and docks) for the Cape Cod Bays system. Simultaneously, a second field team spent the entire day at the entrance to the same 11 sites, and counted the number of visitors that entered and exited the site throughout the day. The team found that when periodic car counts were taken within the time period between 11 A.M. and 4:30 P.M., the estimates were within 44% of actual daily visitation. The most precise estimates came from counts between 2:00 and 2:59 P.M.

There are limitations to the car-counting model, including the fact that it does not capture brief visits, or the many visitors that may enter these sites by foot or by bike. Visitation to these public access points is also very site-specific, and therefore likely cannot be translated wholesale to other estuarine systems. However, this framework provides a valuable set of methods and recommendations for other researchers conducting similar work, especially as coastal managers consider how changes in water quality may change the number of recreational users to an estuary.

Source: Mulvaney, K.M. et al. 2019. Quantifying Recreational Use of an Estuary: A Case Study of Three Bays, Cape Cod, USA. Estuaries and Coasts. DOI: 10.1007/s12237-019-00610-5

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Mending salt marshes from the bottom-up
Overturning the effects of ditching

Whether dating back to 19th-century salt hay farming or mosquito control efforts in the 1900s, ditches are perhaps the most recognizable human alteration of eastern salt marsh habitats. Research has since found that ditching not only has little effect on mosquito populations, but also damages the health of salt marsh ecosystems, causing them to subside. Yet there may be a new solution: Tests conducted in the Great Marsh, in northern Massachusetts, suggest a method of repairing these ditches using vegetation and the marsh’s existing hydrology.

In the fall of 2014, researchers mowed and dried perennial grasses from around nine small test ditches, then loosely raked the dried hay, packed it lightly into the ditch, and secured it with twine and stakes. They repeated this again in fall 2015. By the summer of 2017, the treated ditches were significantly shallower than untreated controls, with depths decreasing by an average of 18 centimeters. They also had 20% more smooth cordgrass (Spartina alterniflora) cover than controls.

It is too soon to tell whether these ditches will continue to rebuild and re-vegetate without continued cycles of this treatment. However, the impact of this experimental method is much lower than other techniques, like ditch plugging or filling, which can disrupt existing hydrologic processes. Instead, the test strategy takes advantage of these processes, with water flow helping the packed hay capture sediment and stimulating the re-colonization of cordgrass. As subsiding marshes leave neighboring lands and communities vulnerable to flooding and sea level rise, learning more about strategies like these may be vital in giving marsh habitats a much-needed lift.

Source: Burdick, D.M et al. 2019. Mitigating the Legacy Effects of Ditching in a New England Salt Marsh. Estuaries and Coasts. DOI: 10.1007/s12237-019-00656-5

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Getting a high-level view of coastal habitats