Grantee Research Project Results

2008 Progress Report: Linking Impacts of Climate Change to Carbon and Phosphorus Dynamics Along a Salinity Gradient in Tidal Marshes

EPA Grant Number: R832222
Title: Linking Impacts of Climate Change to Carbon and Phosphorus Dynamics Along a Salinity Gradient in Tidal Marshes
Investigators: Vile, Melanie A. , Neubauer, Scott C. , Weston, Nathaniel
Institution: Villanova University , University of South Carolina at Columbia
EPA Project Officer: Chung, Serena
Project Period: April 14, 2005 through April 13, 2008 (Extended to April 13, 2010)
Project Period Covered by this Report: April 14, 2008 through April 13,2009
Project Amount: $705,211
RFA: Effects of Climate Change on Ecosystem Services Provided by Coral Reefs and Tidal Marshes (2004) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Water , Ecological Indicators/Assessment/Restoration , Climate Change , Watersheds

Objective:

Over the past three years, we have undertaken an extensive effort to determine the impact of climate-change induced, salt-water intrusion on ecosystem services provided by tidal freshwater marshes in the Delaware Estuary. Our goal was to implement a novel, three-phase approach to determine changes in tidal marsh metabolism (e.g., CO₂, N₂O, and CH₄ gas fluxes and SO₄^2-reduction), C and P sequestration (sediment deposition and burial), and changes in rates of organic matter decomposition at sites along a low-salinity transitional gradient in the Delaware Estuary. All project phases and goals have been initiated and we are on track with regard to deliverables.

To date we have implemented all three phases of the proposed project with two complete field seasons of data for field components and one full year of data collection for the lab experiment. Phase 1 involved finding suitable field sites in the spring and summer of 2005 by making appropriate biological (vegetation) and chemical (e.g., salinity) determinations. We spent several months scouting out tributaries of the Delaware estuary that had appropriate salinity levels and vegetation (which incidentally given urbanization pressures, and Phragmites invasions proved more difficult than we initially thought it would be). We have established 4 sites for all three Phases of the project. Phase 2 consisted of two components: a laboratory manipulation experiment and field-based gas flux measurements. We have initiated two long-term laboratory experiments on cores collected from sites representing the freshwater end-member (i.e., Woodbury and Rancocas Creek) of our salinity gradient (Both Lab studies are completed, and a manuscript is soon to be submitted to the peer-reviewed journal, Limnology & Oceanography; see attached manuscript). To complement our lab study, we set up field plots in 2007 at three sites along our established salinity gradient, and measured net ecosystem production (NEE) over the field season; this portion of the EPA project served as a 2007 summer REU project for a Duke University student (Amanda Foskett). Phase 3 was initiated in 2007, and involves a large-scale field manipulation (reciprocal transplanting of cores as a space for time substitution) to examine longer-term, ecosystem-level responses of marshes to elevated salinity. Since April 2007, we have measured Net Ecosystem Exchange (the balance in C production and consumption), monthly and in some cases bi-monthly, over the duration of the field season, for two seasons in both permanent and reciprocally transplanted plots). All three phases will continue through spring of 2009.

Across all three phases, in both lab and field experiments, we are beginning to understand the response of Tidal Freshwater Marshes (TFMs) to climate change and salt water intrusion. The balance between marsh accretion and subsidence, and ultimately the ability of TFMs to outpace rising sea levels involves a complex interaction of the processes that drive plant production, microbial decomposition, sediment deposition and, ultimately, marsh accretion. The results of our work suggest that salt water intrusion will increase microbial decomposition and, together with declines in plant production, may put TFMs at risk of permanent inundation and create a positive feedback to the global C cycle.

Progress Summary:

Field Sites
The Delaware River basin covers approximately 33,061 km² in DE PA, NJ and NY, and is one of the most populated and ecologically important areas of the mid-Atlantic region in the U.S. The Delaware River is the longest free-flowing [un­dammed] river east of the Mississippi, and extends 530 km from the confluence of its east and west branches in New York, and is a tidal estuary for 190 km before entering the Atlantic Ocean at the mouth of Delaware Bay. The Delaware River Basin is highly urbanized, especially the tidal portion. We have established four sites in the tidal portion of the Delaware River (Figure 1). Rancocas Creek is our freshwater end-member receiving no salt for the duration of the growing season and beyond (pore water analysis of cores collected from Rancocas have verified the lack of salt water intrusion to a depth of 25 cm, Racoon Creek is largely fresh, salinities ranging from 0 to ~ 0.8 ppt, and Salem in Mannington Meadows receives salinity in the range of 1-5 ppt. Stow Creek is our salt water end-member with salinities ranging from 5 -12 ppt. We have set up boardwalks at all four sites, permanent square collars for gas fluxing (0.5 m x 0.5 m; Figure 2 left), and transplanted cores with collars that measure (30 cm in diameter; Figure 2 right). The transplanted cores were collected from Rancocas in 2007, and transplanted to each of the four sites (back transplanted to Rancocas, Raccoon, Salem, and Stow).

Fig.2. Picture illustrating permanent square collars In the field (left) and transplanted cores (right).

Summer 2007 & 2008
Lab Experiment
We have completed the long-term, salinity-manipulation lab experiment that began in 2007. From both control and salinity-amended cores, we have approximately 14 months of CO₂ and CH₄ flux measurements, depth integrated concentrations of chloride, sulfate, dissolved inorganic carbon (DIC), ammonium, dissolved organic carbon (DOC), acetate, sediment organic C and methane, and depth specific rates of sulfate reduction, hydrogenotrophic methanogenesis, and acetoclastic methanogenesis. Results from this experiment demonstrate that salinity intrusion increased rates of both sulfate reduction and, surprisingly, methanogenesis, resulting in increased CO₂ and CH₄ emission (as the product of these decomposition processes) from the TFM sediments undergoing salinity intrusion. This increase in organic matter decomposition and carbon gas emission indicates that the vertical accretion potential of TFM experiencing salinity intrusion may be decreased, with implications for the ability of TFM to keep pace with rising sea levels and feedbacks to the global C cycle. The bulk of these data soon will be submitted as a manuscript to the peer-reviewed journal, Limnology & Oceanography. Please see attached manuscript (Weston et al. L&O submission) for figures and full interpretation.

Field Experiments: Permanent Plots and Transplants
For both the permanent plots (Figure 3) and transplanted cores (Figure 4), we have two complete field seasons of biomass, photosynthetic efficiency, respiration rates, and methane fluxes. These data sets constitute the bulk of the project, and will likely be published as two, perhaps three manuscripts. Not surprisingly, transplants behaved differently than permanent plots early on (2007), especially in terms of biomass, but by the second field season, the native plants had grown into the transplanted cores, which initially contained the dominant vegetation at Rancocas (Pontederia cordata), and behaved more like the host site, biologically and chemically (Figures 3 & 4). By the second year post-transplant, plant species reflected that of the host site and estimates were comparable to those in the permanent plots. We are still working through this summers round of data, but thus far the data are interesting, and will yield at least two more peer-reviewed manuscripts.

Fig.3.

Fig.4.

Microbial Community Composition
The ability of marshes to keep pace with rising sea level depends upon accretion of C, and the accretion and decomposition of C is dependent on which microbes are dominant. This finding has important implications for microbial populations and what controls their abundance, population and community dynamics. To gain a mechanistic understanding of how and why the dominant microbial processes responded in the manner they did in the lab experiment described above (especially as some of the results were unexpected), we wanted to know how the community composition of sulfate reducing and methanogenic microbes responded to salinity intrusion. Over the summer of 2007 and 2008, Tanja Prsa, a senior thesis research student, with funding from the Biology Department added a molecular component to take advantage of, and complement our biogeochemical process rate data to further understand the impact of salinity intrusion on C mineralization pathways in TFM. Key populations of anaerobic microbes mediating the oxidation of organic matter were targeted using functional gene primers: Sulfate Reducers (dissimilatory sulfite reductase, dsrAB), Methanogens (methyl co-enzyme M reductase, mcrA). Population sizes were determined using q-PCR techniques, and community composition was determined by selective cloning and sequencing. Tanja Prsa has used this approach to examine the community composition in the laboratory experiment, and currently is working on the transplanted sediment cores. Ms. Prsa has presented this work at the Society of Wetland Scientists meeting in Washington D.C. this past May 2008. She won honorable mention for best student poster (please see attached poster presentation titled, Prsa SWS 2008).

Future Activities:

Currently the lab continues to flux through the fall with gas samplings throughout October and November. We will implement two additional intensive, core and gas flux samplings, in October 2008 and April 2009 to complete CO₂ and CH₄ flux measurements, depth integrated concentrations of chloride, sulfate, dissolved inorganic carbon (DIC), ammonium, dissolved organic carbon (DOC), acetate, sediment organic C and methane, and depth specific rates of sulfate reduction, hydrogenotrophic methanogenesis, and acetoclastic methanogenesis. These intensive samplings generate a large number of samples that then take months to run on the GC, HPLC and TOC analyzer. If possible, if any funding remains, we would like to measure gas fluxes in the permanent plots next summer to obtain a third year of flux data for the salinity gradient.

Journal Articles:

No journal articles submitted with this report: View all 20 publications for this project

Supplemental Keywords:

Ecosystem, aquatic, habitat, environmental chemistry, biology, geology, ecology, hydrology, genetics, limnology climate models, northeast, Atlantic coast, midatlantic, ecosystem scaling, metabolism, marine, estuary,, RFA, Scientific Discipline, Air, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, climate change, Air Pollution Effects, Chemistry, Monitoring/Modeling, Aquatic Ecosystem, Environmental Monitoring, Terrestrial Ecosystems, Ecological Risk Assessment, Atmosphere, wetlands, urbanization, environmental measurement, meteorology, climatic influence, salinity stress, global change, tidal wetlands, biogeochemcial cycling, salt water intrusion, climate models, ecosystem indicators, aquatic ecosystems, environmental stress, coastal ecosystems, global climate models, phosphorus, coral reef communities, ecological models, climate model, ecosystem stress, carbon supply, Global Climate Change, atmospheric chemistry

Progress and Final Reports:

Original Abstract

2005

2006 Progress Report

2007

Final Report