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Evaluating Coastal Wetland Vulnerability to Sea Level Rise in Pennsylvania

Tidal wetlands are important ecosystems that provide a number of ecosystem services such as nutrient transformation and removal, carbon sequestration, and habitat for fish and wildlife. Tinicum marsh in John Heinz National Wildlife Refuge is Pennsylvania’s largest and last remaining tidal wetlands. Tinicum is one of nine wetland monitoring sites within the Mid-Atlantic Coastal Wetland Assessment Site-Specific Intensive Monitoring network (MACWA SSIM). MACWA was developed to assess coastal wetland condition in the mid-Atlantic, as there was little information on baseline wetland structure and function as well as how tidal wetlands were responding to climate change including sea-level rise. In order to assess several physical, chemical, and biological parameters that can be used in evaluating wetland structure and function, we developed five central questions:

  1. Are wetlands keeping up with sea level rise?
  2. Are plant zones and plant morphology changing over time?
  3. Is peak above- and below ground biomass changing and how does it contribute to accretion?
  4. Is soil and water chemistry changing over time and is it related to accretion?
  5. Is there a change in faunal abundance over time?

To address these five questions our five specific objectives are to determine:

  1. marsh surface elevation change
  2. above- and below ground plant biomass and surface algal biomass
  3. plant community shifts and faunal presence
  4. soil nutrients, organic matter and carbon content with depth
  5. tidal creek nutrient concentrations.

Overall, initial baseline data suggest that the impact of relative sea-level rise such as an increase in salinity in tidal freshwater wetlands and/or an increase in accretion was not apparent over the first two years. Elevation change and surface accretion did not significantly differ from zero over the first two years, largely due to large temporal fluctuations. Additional years of monitoring are necessary to quantify significant seasonal, inter-annual, and long-term trends in vertical marsh growth. The plant community in Tinicum was dominated by Nuphar lutea with a large increase in Zizania aquatica from 2011 to 2013. Inter-annual biomass dynamics were influenced by the change in dominant species. Above ground biomass of Nuphar lutea averaged 148 ±14 g/m2 in 2011. The high marsh near SET 3 generally had higher biomass averaging 1493 ± 625 g/m2 of live Zizania aquatica in 2013. Below ground, live biomass was greater than that above, averaging >2000 g/m2. Soil organic matter, organic carbon, and nitrogen were similar between years but were two times higher in the high marsh averaging 30, 14, and 0.9%, respectively. Inorganic nutrient concentrations were relatively high with soluble reactive phosphorus the most variable among sampling times. The year of wetland monitoring of the present study allowed us to examine differences among years. Additional monitoring is necessary to evaluate longer-term trends, relationships between variable, and to continue to compare the structure and function of Tinicum marsh to other sites within the MACWA SSIM network.

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