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Sea Level Rise – Where Do We Go From Here?

David J. Yozzo, Ph.D.

The occurrence and destructive aftermath of Hurricane Sandy, which struck New Jersey’s central/southern coast in 2012, certainly captured the attention of those who live, work and recreate along shorelines. For proponents and practitioners of ecosystem restoration projects, especially coastal wetlands, the effects of Sandy were striking.

Coastal resiliency planning and sea level rise became a major concern after the destructive effects of Hurricane Sandy

Coastal resiliency planning and sea level rise became a major concern after the destructive effects of Hurricane Sandy. Photo by Dr. David Yozzo.

While it has been recognized for decades that restored coastal wetlands are subject to adaptive modification as a result of stochastic processes, such as storm events and vessel traffic, the design of these systems has not always benefitted from forecasting the effects of sea level rise (SLR) on tidal flooding regimes and storm events over anticipated project lifetimes (i.e. 50+ years). Resource management agencies and coastal ecologists often question the value of investing considerable time, money and labor into restoring habitats at the dynamic water’s edge – will these ecosystems and the ecological and social benefits they provide persist for sufficient durations given current SLR forecasts? How should current thinking with regard to design elevations, planting schemes, and proximity to adjacent natural and engineered habitats be modified to compensate for SLR impacts, especially within estuaries surrounded by dense residential, industrial, and commercial infrastructure?

The Impacts of Rising Seas

Centuries of shoreline development and realignment have left New Jersey and other coastal land forms in jeopardy of inundation and ecological habitat loss

Centuries of shoreline development and realignment have left New Jersey and other coastal land forms in jeopardy of inundation and ecological habitat loss.

The primary impact of sea level rise on coastal environments and infrastructure is the direct loss of land and habitat from inundation. A secondary impact is the migration of coastal landforms inland (retreat). In an urban setting such as the New York/New Jersey metropolitan area, the likelihood of coastal retreat is severely restricted from centuries of shoreline development and re-alignment. An additional impact of climate change and sea level rise is the effect of increased salinity associated with rising coastal waters, ultimately resulting in the conversion of freshwater tidal wetlands to brackish salt marshes in the upper reaches of estuaries.

Piermont Marsh, lower Hudson River – common reed (Phragmites australis) is believed to have provided a defense from storm surge damage to nearby homes and other coastal infrastructure during Hurricane Sandy.

Piermont Marsh, lower Hudson River – Common reed (Phragmites australis) is believed to have provided a defense from storm surge damage to nearby homes and other coastal infrastructure during Hurricane Sandy.

Presently, the rate of sea level rise in the Hudson-Raritan Estuary (HRE) is approximately 2.7 mm/year, which exceeds the global average of 1.8 mm/year (IPCC, 2014, Needelman et al. 2012). The higher observed average rate of sea-level rise in this region is partially the result of post-glacial rebound. This exacerbates the amount of observed wetland/shoreline subsidence attributed to eustatic sea-level rise (i.e., that brought about by an increase in the volume of the world’s oceans, because of the thermal expansion) (Hartig et al. 2002). Along with increases in mean sea level, storm intensity and frequency are also predicted to increase. A shift in storm intensity towards Polar regions is anticipated under future climate change scenarios, with more frequent and damaging storms expected to occur in the north Atlantic (NWF 2011). These processes are complementary, as an increase in mean sea level will exacerbate the surge effects associated with more intense and frequent coastal storms.

Coastal Resiliency Planning

An important factor that is often ignored in forecasting the response of coastal wetlands to sea level rise is tidal range, which varies considerably along the world’s coastlines. Estuarine and coastal habitats characterized by a micro-tidal regime (tidal range of less than 2 meters) (i.e., the Gulf of Mexico) may experience the greatest effects of sea level rise, as native plant and animal communities are not accustomed to large fluctuations in inundation frequency and depth. In contrast, macro-tidal systems (4+ meter tidal range), such as the Puget Sound region of Washington or estuaries along Maine’s coast, are expected to exhibit a considerable degree of resilience to changes in sea level, as the plant and animal communities present in these systems are adapted to wide fluctuations in tides and current regimes. Meso-tidal estuaries, for example the Hudson–Raritan Estuary, are likely to exhibit a moderate degree of resilience in comparison to micro- or macro-tidal systems (Needelman et al. 2012).

Piermont Marsh, lower Hudson River – common reed (Phragmites australis) is believed to have provided a defense from storm surge damage to nearby homes and other coastal infrastructure during Hurricane Sandy.

Ribbed mussel (Guekenisa demissa) and salt marsh cordgrass (Spartina alterniflora) matrix behind dilapidated wooden cribbing in Jamaica Bay, NY. Both species function as ecosystem engineers to stabilize coastal sediments.

An additional source of uncertainty in attempting to predict the effects of climate change and sea level rise on coastal habitats within the Hudson-Raritan Estuary (and elsewhere) is the occurrence of non-linear response patterns (Needelman et al. 2012). Often, impacts to wetlands and other coastal habitats are not necessarily observed until a disturbance threshold is reached. This may explain the rapid and recent loss of salt marsh islands in Jamaica Bay, New York, a lagoon-type estuary subjected to dredging, coastal development, and wastewater inputs for several decades before exhibiting tangible degradation. Once the impact threshold was reached, perhaps in the late 1990s, the system reached a tipping point, and degradation became readily discernible. In the future, Jamaica Bay will likely continue to experience rapid erosion and/or subsidence of wetlands in the face of rising sea level. In contrast, wetlands associated with a continuous source of sediments from river drainage basins (i.e., Raritan River wetlands) may persist for a much longer duration before reaching disturbance thresholds.

Non-linear responses in coastal systems are not well-studied and future restoration programs in the Hudson-Raritan Estuary would benefit substantially from a better understanding of ecological tipping points and disturbance thresholds, especially with regard to enhancing resiliency in the face of climate change impacts.

The second edition of this two part blog series will provide an overview of ongoing restoration and management initiatives in response to SLR within the Hudson-Raritan Estuary, including living shoreline approaches, managed retreat, and the beneficial use of dredged material in coastal habitat restoration programs.

References

Hartig, E.K, V. Gornitz, A. Kolker, F. Mushacke, and D. Fallon. 2002. Anthropogenic and climate change impacts on salt marshes of Jamaica Bay, New York City. Wetlands 22:71-89.

IPCC. 2014. Climate Change 2014. Synthesis Report. An Assessment of the Intergovernmental Panel on Climate Change.

Needelman, B.A., S. Crooks, C.A. Shumway, J.G. Titus, R.Takacs, and J.E. Hawkes. 2012. Restore-Adapt-Mitigate: Responding to Climate Change Through Coastal Habitat Restoration. B.A. Needelman, J. Benoit, S. Bosak, and C. Lyons (eds.). Restore America’s Estuaries, Washington D.C., pp. 1-63.

NWF 2011. Practical Guidance for Coastal Climate-Smart Conservation Projects in the Northeast: Case Examples for Coastal Impoundments and Living Shorelines. National Wildlife Federation.

About the Author

Dave YozzoDr. David Yozzo is an estuarine ecologist with over 20 years of experience in academics, government, and the private sector. His professional and research expertise includes community ecology of tidal and freshwater wetlands, ecosystem functional assessment, and coastal/freshwater habitat restoration.

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