Final Report: Climate-Linked Alteration of Ecosystem Services in Tidal Salt Marshes of Georgia and Louisiana

EPA Grant Number: R832221
Title: Climate-Linked Alteration of Ecosystem Services in Tidal Salt Marshes of Georgia and Louisiana
Investigators: Hester, Mark W. , Alber, Merryl , Joye, Samantha , Mendelssohn, Irving A.
Institution: University of Louisiana at Lafayette , Louisiana State University - Baton Rouge , University of Georgia
EPA Project Officer: Packard, Benjamin H
Project Period: March 21, 2005 through September 30, 2009
Project Amount: $749,457
RFA: Effects of Climate Change on Ecosystem Services Provided by Coral Reefs and Tidal Marshes (2004) RFA Text |  Recipients Lists
Research Category: Ecosystems , Climate Change , Water , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration , Global Climate Change , Water and Watersheds

Objective:

We examined the alteration of ecosystem services in Georgia and Louisiana, including eutrophication control, carbon sequestration, sustainable habitat, and faunal support, that could result from climate change. Specifically, we investigated how varying levels of Spartina alterniflora stem density, as may result from increased drought severity, generated changes in ecosystem processes and resultant ecosystem services in both microtidal (Louisiana) and macrotidal (Georgia) salt marshes. To this end, we selected areas of salt marsh in Georgia and Louisiana where plant density was impacted by severe drought and installed a large manipulative experiment as described below.
 
Our approach took advantage of severe drought events in salt marshes of both Louisiana and Georgia that resulted in large areas of sudden salt marsh dieback. Within each state, six salt marsh areas (blocks) were identified, each of which contained both dieback areas lacking plants and nearby reference areas where plant density was unaltered. We constructed boardwalks to minimize sampling disturbance and manually transplanted Spartina alterniflora to manipulate plant density as a treatment independent of the drought-induced dieback. We established a mosaic of 48 permanent plots (60 m2 each) in Louisiana and Georgia that spanned a range of Spartina alterniflora plant densities from reference density, to high transplanted plant density, to low transplanted plant density, to bare plots, in which alteration of ecosystem services was assessed via direct measurement of ecosystem processes at several scales by the four collaborating research teams. We quantified aboveground productivity and plant nutrient-use efficiency, belowground productivity and decomposition, marsh accretion and elevation change, sediment biogeochemistry, and invertebrate ecology. Major sampling efforts occurred early during the growing season and in the fall (peak standing crop), with some additional sampling activities occurring as needed to address specific tasks.

Summary/Accomplishments (Outputs/Outcomes):

Experimentally manipulated decreases in S. alterniflora stem density strongly influenced a number of ecosystem processes and the provision of resultant ecosystem services. In Louisiana, bare plots initially lost elevation, whereas high density plots exhibited significantly greater increases in elevation as their lower position in the intertidal facilitated sediment trapping by the vegetation. Therefore, stem density was directly related to the provision of the ecosystem service of habitat sustainability in Louisiana. These findings illustrate the importance of hydrogeomorphic setting as an important modulator of stem density, which in turn effects the ecosystem service of habitat stability. These findings also support the hypothesis that drought impedes the capacity of salt marshes to keep pace with sea-level rise.
 
Microbially mediated processes were highly variable among treatments. However, substantial differences between hydrogeomorphic settings were again noted, particularly in regard to nitrogen fixation, which was greater in Louisiana, and nitrification, which was greater in Georgia. Overall, Louisiana marsh soils appear to function overall as a net source of nitrogen. Soil nitrogen content increased as stem density increased, suggesting greater retention of organic nitrogen compounds with greater abundance of S. alterniflora. Photosynthetic nitrogen-use efficiency increased with S. alterniflora stem density as hypothesized, illustrating a greater net carbon assimilation rate per unit leaf nitrogen at higher stem densities. Although plants growing at high stem densities displayed a slightly lower amount of nitrogen per leaf, this appears more than compensated (in terms of N uptake per area) by the greater density of stems. Thus, overall, S. alterniflora stem density does appear to directly influence the ecosystem service of eutrophication control. Generally, greater numbers of snails, macroinfauna, and meiofauna were found in conjunction with greater S. alterniflora stem densities. However, invertebrate abundance was typically lower in experimentally manipulated plots than in reference plots, demonstrating the importance of mature marsh stem density to maintain faunal habitat provision.

Conclusions:

Spartina alterniflora stem density was shown to contribute significantly to the provision of multiple ecosystem services. Specifically, the ecosystem services of eutrophication control, carbon sequestration, and faunal support were positively influenced by S. alterniflora stem density. Hydrogeomorphic setting was an important modulator of ecosystem processes that can potentially alter the relationship between S. alterniflora stem density and the provision of ecosystem services. Importantly, S. alterniflora stem density was consistently associated with greater aboveground biomass, belowground biomass, and soil organic matter content, all of which are ecosystem processes that translate into the ecosystem services of carbon sequestration and salt marsh sustainability. Increased S. alterniflora stem density was also positively associated with the abundance of snails, macroinfauna and meiofauna, illustrating a greater provision of the ecosystem service of habitat for fauna with increasing S. alterniflora. The potentially long-lasting effects of decreased plant density underscores the importance of making decisions that help to sustain salt marsh habitat in the face of climate change.


Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 27 publications 1 publications in selected types All 1 journal articles
Type Citation Project Document Sources
Journal Article Alber M, Swenson EM, Adamowicz SC, Mendelssohn IA. Salt marsh dieback:an overview of recent events in the US. Estuarine, Coastal and Shelf Science 2008;80(1):1-11. R832221 (2008)
R832221 (Final)
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  • Supplemental Keywords:

    Watersheds, sediments, global climate, marine, estuary, ecological effects, vulnerability, organism, stressor, susceptibility, ecosystem, indicators, restoration, aquatic, habitat, environmental assets, environmental chemistry, biology, ecology, hydrology, zoology, monitoring, analytical, surveys, measurement methods, southeast, Atlantic coast, Gulf coast, EPA Region 6, EPA Region 4., RFA, Scientific Discipline, Air, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, climate change, State, Air Pollution Effects, Aquatic Ecosystem, Monitoring/Modeling, Environmental Monitoring, Ecological Risk Assessment, Atmosphere, environmental measurement, meteorology, climatic influence, global ciruclation model, global change, climate, tidal marsh, Georgia (GA), climate models, ecosystem indicators, Louisiana (LA), aquatic ecosystems, environmental stress, coastal ecosystems, global climate models, coral reef communities, ecological models, climate model, ecosystem stress, sea level rise, Global Climate Change, atmospheric chemistry, climate variability

    Relevant Websites:

    A website for this project is currently under construction at the University of Louisiana at Lafayette at www.coastalplantecologylab.com

    Progress and Final Reports:

    Original Abstract
  • 2005 Progress Report
  • 2006 Progress Report
  • 2007 Progress Report
  • 2008 Progress Report