Factors Governing the Vulnerability of Coastal Marsh Platforms to Sea Level Rise Special Report • Fall 2015 LeeAnn Haaf [email protected] Joshua Moody [email protected] Angela Padeletti [email protected] Danielle Kreeger, PhD [email protected] Erin Reilly [email protected] Martha Maxwell-Doyle [email protected] Funding was provided by the New Jersey Department of Environmental Protection through the National Fish and Wildlife Foundation for Building Ecological Solutions to Coastal Community Hazards. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. government or the National Fish and wildlife Foundation and its funding sources. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Government, or the National Fish and Wildlife Foundation or its funding sources. Suggested citation: Haaf, L., J. Moody, E. Reilly, A. Padeletti, M. Maxwell-Doyle, D. Kreeger. 2015. Factors Governing the Vulnerability of Coastal Marsh Platforms to Sea Level Rise. PDE Report #15-08. Parternship for the Delaware Estuary and the Barnegat Bay Partnership. Cover photograph of high water levels observed while performing condition assessessment in the Dennis Creek watershed; courtesy of the Partnership for the Delaware Estuary 2014. 2 Factors Governing the Vulnerability of Coastal Marsh Platforms to Sea Level Rise INTRODUCTION Coastal wetlands play a crucial role in the maintenance of clean waters. Across the Mid-Atlantic, coastal wetlands are rapidly declining due to anthropogenic alteration, climate change, and sea level rise.1,2 Due to the importance of coastal wetlands, the Partnership for the Delaware Estuary (PDE) and Barnegat Bay Partnership (BBP) consider these habitats a research and conservation priority. To help stem coastal wetland losses in the Delaware and Barnegat Bay Estuaries, PDE and BBP coordinate the Mid-Atlantic Coastal Wetland Assessment (MACWA) with the goal of providing multiple agencies with invaluable monitoring and assessment data on marsh condition, as well as site-specific sources of stress that reduce marsh condition, function and acreage. The goal of this synopsis is to briefly summarize the scientific knowledge on the factors that contribute to vertical losses in brackish and saline marshes of the Mid-Atlantic. Vertical losses, or those driven by platform elevation declines, can be largely attributed to functional impairment. Horizontal loss, also a large contributor to wetland acreage decline, is governed by factors such as edge erosion. This orientation seeks to aid coastal managers and practitioners in understanding the complex array of factors that affect platform (vertical) vulnerabilities of the coastal wetlands in our region. Although guidance on best management protocols and appropriate restoration tactics is beyond the scope of this document, PDE and BBP have previously released reports3 that examine factors of marsh loss, the associated methods for diagnosing marsh condition, and identifying restoration tactics: • Mid-Atlantic Coastal Wetland Assessment (MACWA) reports • Delaware Estuary Living Shoreline Initiative Reports • Marsh Futures Local Restoration Planning Tool • Living Shoreline Monitoring Framework WHAT IS A COASTAL WETLAND? A coastal wetland is any habitat that is subject to tidal action sufficient to sustain hydric (flooded or saturated) soils and support the growth of water loving vegetation (i.e. hydrophytes).4 These include, but are not limited to, salt or brackish marshes, tidal freshwater marshes, bottomland swamps, and sea grass beds. A majority of coastal wetlands within the Mid-Atlantic (particularly NJ, DE, and PA) are coastal marshes.2,5 Coastal marshes are dominated by herbaceous, emergent vascular plants6 and typically occupy elevations between mean sea level and mean high water. 1 Church, J. A., and N. J. White. 2011. Sea-level rise from the late 19th to the early 21st century. Surveys in Geophysics 32(4-5): 585-602. 2 Miller, D., A. Padeletti, D. Kreeger, A. Homsey, R. Tudor, E. Creveling, M. M. DePhilip, C. Pindar. 2012. Chapter 5 - Aquatic Habitats in the Technical Report for the Delaware Estuary & Basin. Partnership for the Delaware Estuary. PDE Report No. 12- 01, pages 119-165. 3 See the Partnership for the Delaware Estuary’s website: http://www.delawareestuary.org/ 4 New Jersey Coastal Wetland Protection Act. N.J. STAT. ANN: 13:18-1 to 13:9A-10; Clean Water Act (33 U.S.C. Section 125) 5 U.S. Fish and Wildlife Service. Accessed October 2015. <http://www.fws.gov/wetlands/Documents%5CMid-Atlantic-Wetlands- A-Disappearing-Natural-Treasure.pdf> 6 U.S. Environmental Protection Agency. Accessed October 2015. <http://water.epa.gov/type/wetlands/marsh.cfm> 3 WHAT IS MARSH CONDITION? Marshes provide many services to coastal communities: they support habitat for local fisheries; provide storm and flood protection;7 and sequester carbon and nitrogen.8 Such services are derived from dynamic, coalescing processes which are the foundation of a functioning marsh. The services provided by marshes scale with marsh functions, which are reduced when condition is reduced. Degradation of condition typically precedes marsh acreage decline. Therefore, it is vital to assess condition and associated functions, not just acreage. Marsh functionality can be compromised by natural or anthropogenic alterations to the environment. The effects of these alterations are often described by marsh condition, vulnerability, and resilience. To deduce which management or restoration practices are warranted for a site, it is critical to discern the marsh’s a) current condition b) underlying causes of impairment, c) future vulnerabilities, and d) the future trajectory of marsh condition or resilience with no intervention. Condition Condition is the cumulative effect of multiple impacts or disturbances on marsh health. The interacting physical, chemical and biological factors affecting marsh condition may include nutrient concentrations, competition with invasive plants, or herbivory. Additionally, anthropogenic activities and management practices may alter water levels, sediment supplies, nutrient regimes, and migration potentials. The evaluation of marsh condition requires the assessment of physical and biological indices that describe levels of impairment or gauge performance of ecosystem services and functions. Marsh condition is described as poor or good; impaired or healthy.9 Vulnerability Vulnerability is the susceptibility to decreased function driven by a specific impact. It is helpful to understand that vulnerability is stressor-specific and future-focused,10 whereas condition reflects the integrated effect from all stressors. For example, a marsh in good condition may be vulnerable to future impact from intensifying boat wakes, increasing nutrient loads, insufficient sediment supply, or greater frequency of severe weather events. Resilience Resilience is the long term ability of a marsh to sustain or regain performance and functionality in the face of multiple vulnerabilities.11,12 Resilience can also be thought of as the expected ability of a marsh to persist with good condition and function over time. 7 Arkema, K. K., G. Guannel, G. Verutes, S. A. Wood, A. Geurry, M. Ruckelshaus, P. Kareiva, M. Lacayo, J. M. Silver. 2013. Coastal habitats shield people and property from sea-level rise and storms. Nature Climate Change Letters, DOI:10.1038/ NCLIMATE1944. 8 Costanza, R., R. D’Arge, R. de Groot, S. Farberk, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R. V. O’Neill, J. Paruelo, R. G. Raskin, P. Suttonkk, M. Van Den Belt. 1997. The value of the world’s ecosystem services and natural capital. Nature, 387(6630): 253-260. 9 Turner, R. E., E. M. Swenson, C. S. Milan, J. M. Lee, T. A. Oswald. 2004. Below ground biomass in healthy and impaired salt marshes. Ecological Research, 19: 29-35. 10 Cahoon, Donald R., et al. 2006. Coastal wetland vulnerability to relative sea-level rise: wetland elevation trends and process controls. Wetlands and natural resource management. Springer Berlin Heidelberg, 271-292. 11 Holling, C. S. 1973. Resilience and stability of ecological systems. Annual Review of Ecological Systems, 4: 1-23. 12 D’Alpaos, A., S. M. Mudd, L. Carniello. 2011. Dynamic response of marshes to perturbations in suspended sediment concentrations and rates of relative sea level rise. Journal of Geophysical Research, 116: F04020. 4 INSIGHT REVIEW marshes to survive accelerating rates of sea-level rise6,20. Similar feedbacks Threshold rates of sea-level rise between flooding, plant growth and sub-surface expansion operate in Despite robust ecogeomorphic feedbacks that stabilize tidal wetlands, the root zone, generating highly organic soils that persist for thousands observations of wetland deterioration in places such as the Mississippi of years19,21,26 (Box 1). Together, these eco-geomorphic interactions sug- River Delta indicate that there are limits to the feedbacks that preserve gest that more extensive flooding associated with sea-level rise should wetlands within the intertidal zone. An emerging idea is that marshes be accompanied by enhanced accretion. Indeed, vertical accretion rates survive increasing rates of sea-level rise by becoming lower in the tidal approximately tripled in several marshes surrounding Long Island, New zone, which allows them to build elevations at progressively faster rates York, in response to