Grantee Research Project Results
2006 Progress Report: Linking Impacts of Climate Change to Carbon and Phosphorus Dynamics Along a Salinity Gradient in Tidal Marshes
EPA Grant Number: R832222Title: Linking Impacts of Climate Change to Carbon and Phosphorus Dynamics Along a Salinity Gradient in Tidal Marshes
Investigators: Vile, Melanie A. , Neubauer, Scott C. , Velinsky, D. J.
Current Investigators: Vile, Melanie A. , Neubauer, Scott C. , Weston, Nathaniel
Institution: Academy of Natural Sciences , Villanova University , University of South Carolina at Columbia
Current 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, 2005 through April 13, 2006
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 2 years, we have undertaken an extensive effort to determine the impact of the climate-change induced, salt water intrusion on ecosystem services provided by tidal freshwater marshes (TFMs) 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 SO42- 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.
Progress Summary:
To date, we have implemented all three phases, with implementation of Phase 3 just 3 weeks ago. Phase 1 involved finding suitable field sites 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 (given urbanization pressures and Phragmites invasions, this proved more difficult than we initially thought). We have selected three sites for all three phases of the project and have recently added a fourth site based on the findings from this past field season. Phase 1 also included a laboratory pilot study involving a summer Research Experience for Undergraduates (REU) student. The sites used for the pilot study will not be part of our final set of sites. Phase 2 consists of two components that are ongoing, a laboratory manipulation experiment and field-based gas flux measurements. We have initiated long-term laboratory experiments on cores collected from sites representing the freshwater end-member (i.e., Rancocas Creek) of our salinity gradient. Cores were brought back to the laboratory and subjected to manipulated tidal cycles and salinity (~ 5 ppt) to study the long-term (months to years) impact of salt water intrusion on marsh metabolism. Prior to collecting cores from Rancocas Creek, we ran the manipulation experiment from a different site, Woodbury Creek, and these cores continue to be incubating more than 1 year after collection. We chose to do the experiment with a separate set of cores, because we found that the Woodbury cores might have been exposed to salt at some point in the past, and therefore, the site would not truly represent a freshwater end-member. To complement our laboratory study, we set up field plots this summer at three sites along our established salinity gradient and measured net ecosystem exchange (NEE) over the field season; this portion of the U.S. Environmental Protection Agency (EPA) project served as a summer REU project for a Duke University student (Amanda Foskett). Phase 3 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. Phases 1 and 2 were completed and initiated in 2005 and 2006, respectively. Phase 3 was initiated spring 2007. All three phases will continue until completion of the project.
Summary of Findings
Site Selection. We received our funding at the end of May 2005, and a large portion of the summer had been spent on site selection, experimental design, and method development. 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 United States. The Delaware River is the longest free-flowing (undammed) river east of the Mississippi, 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. In summer 2005, we performed a pilot study using cores from two creeks (Alloway and Manumuskin Creeks) as part of a summer REU project to help us decide on appropriate sites. To date, we have selected a range of 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 analyses of cores collected from Rancocas have verified the lack of salt water intrusion to a depth of 25 cm); Racoon Creek is largely fresh, with salinities ranging from 0 to approximately 0.8 ppt. Stow Creek is our salt water end-member, with salinities ranging from 5–12 ppt. We have set up boardwalks at all three sites, and this spring, we have added another site on the Salem River at Mannington Meadows. Our fourth site is similar to Racoon Creek, which is largely fresh but experiencing slightly higher salt than Racoon Creek during droughts and late summer conditions. At Mannington, we have installed a boardwalk, permanent collars for gas fluxing (Phase 2), and transplanted cores (Phase 3).
Figure 1. Delaware Estuary: Field Sites
Summer 2005
In June and July 2005, Ashley Smyth collected cores from two TFMs that we selected as potentially good sites to determine the relationship between SO4-2 and CO2 production by manipulating sulfate concentrations under controlled conditions in the laboratory in freshwater sediments. We manipulated salinity levels for 2 weeks, and measured CO2 fluxes over the 2-week period. CO2 fluxes did not differ significantly under light (117 ± 9.7 mmol m-2 da-1) versus dark conditions (112 ± 9.8 mmol m-2 da-1), nor did CO2 differ in control/oligohaline reference (126 ± 10 mmol m-2 da-1) and salinity-amended (125 ± 12 mmol m-2 da-1) cores from Manumuskin and Alloway Creek (data not shown), suggesting that a longer time frame is needed to resolve the importance of photosynthetic algae/plants and the rate of sulfate diffusion into the sediment column in regulating C fluxes. Subsequent to salinity amendment and gas flux measurements, each core was sectioned into 2 to 4 cm depth increments, and sediment solid-phase C and S were measured. Sediment was dried, ground, and run on a CE Flash 1112 Elemental Analyzer. The oligohaline reference site also had significantly lower sediment C and significantly higher sediment S than the TFM (data not shown).
Summer 2006
Weston has made considerable progress in initiating the long-term, salinity-manipulation laboratory experiment (Part 1 of Phase 2) that we plan to run for 2 years. We have approximately 14 months of CO2 and CH4 flux measurements from control and salinity-amended cores in the laboratory manipulation experiment (Figure 2; note only 240 days of data are shown). In spring 2006, we initiated a larger and more sophisticated laboratory salinity-amendment experiment, where we are measuring CO2 fluxes from cores collected at a different TFM site and amended with salinity via scheduled tidal cycles (we have approximately 6 months of data thus far; data not shown). Results suggest that more than a 6- month period is needed to see CO2 fluxes diverge between control and salinity-amended treatments. This finding has important implications for microbial populations and what controls their abundance, population, and community dynamics. 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.
Figure 2. Laboratory Experiment: Long-term CO2 Flux Rates
Weston has incorporated a new component of the project (not initially proposed in the EPA grant) that links process-based biogeochemical rates with quantitative determinations of key functional genes for sulfate reducers and methanogens. We submitted a grant to the National Science Foundation (NSF) to cover funding for this aspect of the project, but the proposal was declined. Weston and Vile have revised the proposal and have resubmitted to the NSF in January 2007; we expect to hear about funding in June. Preliminary data collected by Weston are promising. 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), and denitrifiers (nitrite reductase, nir). Population sizes were determined using quantitative PCR (qPCR) techniques, and community composition was determined by selective cloning and sequencing. Weston extracted DNA from freshwater and saline marsh sediments, functional genes were PCR amplified using functional gene-specific primers, and dsrAB and mcrA products of appropriate size were obtained. Qualitatively, we found more mcrA functional gene products in freshwater sites and more dsrAB in saline sites (Figure 3).
Figure 3.
Amanda Foskett helped out with summer field fluxes in 2006. We installed boardwalks and permanent collars at Rancocas, Racoon and Stow Creek. We measured NEE in July and August, and we found the sites followed a pattern of highest NEE at Stow Creek, the highest salinity site, and least at Rancocas, our freshwater site). We plan to implement an extensive field sampling campaign for the summer of 2007 beginning in March through November (weather permitting). In addition to CO2 fluxes, we will also measure CH4 and N2O fluxes from all sites.
Next Steps
Currently, the laboratory experiment involves cores incubated without plants and in the dark under controlled temperatures (Figure 4). Cores are hooked up to infrared gas analyzers (IGAs) to measure instantaneous CO2 fluxes. We plan to incorporate plants and/or diatoms with a light regime. We are beginning our field-based flux measurements using Plexiglas chambers also coupled to IRGA’s for C fluxes. We plan to sample both the laboratory experiment and field experiment (permanent collars and transplanted cores) intensively this field season. Results will provide us a quantitative estimate of how ecosystem services of TFMs will respond to increasing salt water intrusion in the Delaware Estuary.
Figure 4.
Journal Articles:
No journal articles submitted with this report: View all 20 publications for this projectSupplemental Keywords:
ecosystem, aquatic, habitat, environmental chemistry, biology, geology, ecology, hydrology, genetics, limnology climate models, northeast, Atlantic coast, mid-Atlantic, 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 chemistryProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.