GCE-II Question 1: Environmental Forcing
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Research QuestionQ1: What are the long-term patterns of environmental forcing to the coastal zone? OverviewCoastal ecosystems are influenced by the characteristics of the upstream watershed (e.g. land use, slope), by those of the ocean (e.g. wave climate, sea level), and by those of the atmosphere (e.g. temperature, precipitation). Each of these external forcing functions is expected to experience substantial changes over the coming decades due to factors such as climate change, sea level rise, and human alterations of the landscape. In order to understand the effects these external drivers, we need to document their patterns over both time and space. The GCE collects data on local climate (temperature, precipitation, wind speed and direction) and on the water chemistry of the tributaries that discharge into the Altamaha River. We also obtain data from other organizations (NWS, USGS, NOAA and other sources) on river discharge, watershed characteristics, human population demographics, sea level, oceanographic conditions and climate. Research Components
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Research Question BackgroundThe coastal population of Georgia is expected to double in the next 25 years (State of the Coast Report, 2004). This increase in population and accompanying land use change affects downstream water quality: over the past 18 y, Verity (2002; Verity et al., 200x) has documented significant increases in the concentrations of nutrients and chlorophyll a and significant decreases in oxygen concentrations in Georgia coastal waters. Humans can also affect downstream water delivery either directly, via flow diversion, channel modifications, reservoirs and dams, point source discharges; or indirectly, via changes in land cover, which affect the proportion of overland runoff versus groundwater infiltration. Future climate change will also affect freshwater delivery to the coast. Miller and Russell (1992) predicted that the annual average discharge of 25 of the 33 largest rivers of the world would increase under a scenario in which atmospheric CO2 doubled. In the Altamaha River, one commonly used climate change model (the Hadley model) predicts that flow will increase by as much as 55% by the end of the century, whereas the drier, hotter Canadian model predicts that inflow will decrease (Wolock and McCabe 1999; Boesch et al. 2000). Regardless of the directional change in flow, most models agree that there will be an increase in extreme rainfall events and thus increased variability of freshwater runoff in the future. Finally, sea level is inexorably rising along the low-gradient coastal plain environments of the world. Under all model scenarios, the rate of sea-level rise is expected to increase over the coming decades as higher global temperatures accelerate both glacial melting and expansion of ocean and coastal waters (IPCC, 2001). In Georgia, sea level is rising at a rate of 0.3 cm/y (NOAA 2001). Low-lying intertidal areas are particularly sensitive to these changes, as only slight variations in vertical position can affect large parts of the landscape. As the land/water boundary encroaches steadily onto the upland, the increased hydraulic head will cause saltwater to intrude further into coastal aquifers (Michael et al. 2005; Schultz and Ruppel, 2002), changing the quality and quantity of potable groundwater. Rising sea levels will also drive salty surface water further up river, causing fresh and brackish marshes to convert to salt marshes, and will increase the extent of coastal flooding during storm surges from Atlantic hurricanes and Nor'eastern storms. The GCE is monitoring patterns of environmental forcing and the propagation of freshwater to the coastal zone. We also obtain relevant long-term datasets from other organizations. Long-term monitoring serves three purposes. First, it provides a context for short-term studies by documenting contemporaneous environmental conditions. Second, because these data are collected at frequent intervals, they provide information on short-term temporal variation in environmental forcing (e.g., daily, tidal, lunar and seasonal patterns). Third, long-term observations are required to evaluate long-term trends. |
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Atmospheric forcingWeather stationsWe collect data from an array of geographically dispersed weather stations to characterize climatic conditions across the GCE LTER domain. We operate a comprehensive weather station at Marsh Landing on Sapelo Island in collaboration with the Sapelo Island National Estuarine Research Reserve (SINERR), which serves as our primary LTER meteorological station for inter- comparison studies and ClimDB (the LTER network climate database). We also operate a weather station on the mainland at Meridian Landing in cooperation with the U.S. Geological Survey (USGS) and SINERR. High frequency (15 minute) or hourly data from these two stations, respectively, are acquired in near real-time from NOAA (via GOES satellite uplink) and USGS (via microwave transmission) data servers, using the fully automated climate data harvesting system developed by GCE. Long-term daily weather data from National Weather Service COOP stations operated at the UGA Marine Institute on Sapelo Island and in Brunswick, Baxley, Jesup and Glennville, Georgia are also regularly acquired to provide long-term regional records of temperature and precipitation. We also use weather data collected by the NOAA National Buoy Data Center Gray's Reef buoy to provide a long term record of climate observations representing oceanic boundary conditions of the GCE study area. Atmospheric depositionAtmospheric wet and dry deposition are measured at Marsh Landing by a collaboration between NADP and SINERR (NADP Station GA33). Weekly measurements are made of Hydrogen (acidity as pH), sulfate, nitrate, ammonium, chloride, base cations (such as calcium, magnesium, potassium, sodium). Oceanographic forcingSea levelSea level has risen about 0.3 cm/yr over the last 50 years along the Georgia coast. Variation about this trend reveals an annual fluctuation of about 20-30 cm caused by the annual increase in specific volume of the North Atlantic Ocean from solar heating. Less obvious are fluctuations over a time scale of several years due to interannual variations in atmospheric pressure and the wind field associated with it. Sea level is measured at 6 minute intervals by NOAA/NOS CO-OPs at Fort. Pulaski in the Savannah River, and daily and monthly sea level data sets are obtained from NOAA for analysis. USGS and SINERR have also begun referencing water level measurements to newly installed USGS elevation benchmarks, allowing us to report data at Meridian Landing referenced to NADV88 datum. Oceanographic conditionsWe access data on oceanographic conditions from two platforms: the National Data Buoy Center’s Station at Gray’s reef and the South Atlantic Bight Synoptic Offshore Observational Network (SABSOON). Data from these stations serve as an oceanic end-member for various estuary studies and can be used to characterize oceanic forcing in physical models. Upstream forcingRiver dischargeThe Altamaha River is the largest source of freshwater to the GCE domain and provides a natural gradient of freshwater inflow to the sites. Over the last several decades, Altamaha River discharge varied seasonally but did not show clear long-term directional patterns.   Figure. Freshwater input into the GCE domain. Top: 50 year daily mean and median Altamaha River discharge at Doctortown, with extreme dry and wet periods superimposed. Bottom: Annual discharge at Doctortown. Note low discharge in 1999-2002, and earlier but shorter droughts in the 1980s Data from USGS. The USGS gage at Doctortown (Station 02226000) provides near real-time data on discharge into the Altamaha estuary. There are also several other USGS gages located throughout the watershed. We use harvesting technology developed at the GCE (based on the GCE Data Toolbox for MATLAB) to automatically download and process data from USGS so that it is documented documented and standardized to compatible units and date formats for comparison with other GCE monitoring data, providing GCE investigators with high quality standardized data in various file formats to support synthetic research projects. Altamaha river water chemistryWe collect water samples at the head of tide in the Altamaha River as well as in the main tributaries of the river to assess nutrient concentrations in the water entering the GCE domain. Additional water quality information is available from USGS. Watershed propertiesThe largest source of freshwater is the Altamaha River, which is formed by the confluence of the Oconee and Ocmulgee Rivers. The Altamaha River watershed encompasses an area of 36,718 sq. km and drains 24% of the state of Georgia, including parts of metro Atlanta. While some of our studies to understand the influence of upstream changes are at the scale of the Altamaha watershed, the actual GCE domain covers three adjacent sounds (Altamaha, Doboy, and Sapelo) as well as the Duplin River on Sapelo Island, each of which have their own drainage areas. We are therefore also interested in the more local effects of runoff and other influences from the coastal areas that are directly adjacent to our study site. |
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Atmospheric forcingWeather stationsEddy covariance flux tower for measuring gas exchange between salt marshes and the atmosphere Georgia Coastal Ecosystems LTER Climate monitoring program Additional studiesEffects of large-scale climate drivers on precipitation and river discharge in the GCE study area and the Altamaha River watershed Oceanographic forcingSea levelSeawater Addition Long Term Experiment (SALTEx), a long-term field manipulation experiment in a Zizaniopsis marsh in the Altamaha River Additional studiesEffects of climate on coastal ecosystems Upstream forcingAltamaha River water chemistryAltamaha river water chemistry monitoring Coastal subwatershedsWater use patterns in hydrologic units of the 5 major coastal river watersheds in Georgia Additional studiesAltamaha watershed nutrient budgets from 1954 to 2002 Altamaha watershed water quality Maps and Locals (MALS) Watershed nitrogen input and export of N to coastal systems along the east coast of the U.S. Watershed nitrogen input and export of N to coastal systems along the west coast of the U.S. |
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Journal ArticlesLi, F., Angelini, C., Byers, J., Craft, C.B. and Pennings, S.C. 2022. Responses of a tidal freshwater marsh plant community to chronic and pulsed saline intrusion. Journal of Ecology. 110:1508-1524. (DOI: 10.1111/1365-2745.13885) Nahrawi, H.B., Leclerc, M.Y., Pennings, S.C., Zhang, G., Singh, N. and Pahari, R. 2020. Impact of tidal inundation on the net ecosystem exchange in daytime conditions in a salt marsh. Agricultural and Forest Meteorology. 294:108133. (DOI: https://doi.org/10.1016/j.agrformet.2020.108133) Li, F. and Pennings, S.C. 2019. Response and Recovery of Low-Salinity Marsh Plant Communities to Presses and Pulses of Elevated Salinity. Estuaries and Coasts. 42:708-718. (DOI: 10.1007/s12237-018-00490-1) Li, F. and Pennings, S.C. 2018. Responses of tidal freshwater and brackish marsh macrophytes to pulses of saline water simulating sea level rise and reduced discharge. Wetlands. 38:885-891. (DOI: 10.1007/s13157-018-1037-2) Theses and DissertationsSchaefer, S.C. 2006 Nutrient budgets for watersheds on the southeastern Atlantic coast of the United States: temporal and spatial variation. M.S. Thesis, University of Georgia, Athens, Georgia, 105 pp. Schaefer, S.C. 2006 Nutrient budgets for watersheds on the southeastern Atlantic coast of the United States: temporal and spatial variation. M.S. Thesis, University of Georgia, Athens, Georgia, 105 pp. Conference Papers (Peer Reviewed)Conference Posters and PresentationsWidney, S., Smith, D., Schubauer-Berigan, J.P., Herbert, E., Desha, J. and Craft, C.B. 2017. Poster: Changes in sediment porewater chemistry in response to simulated seawater intrusion in tidal freshwater marshes, Altamaha River, GA. Society of Wetland Scientists Annual Meeting, June 5-8, San Juan, Puerto Rico. Smith, D., Herbert, E., Li, F., Widney, S., Desha, J., Schubauer-Berigan, J.P., Pennings, S.C., Angelini, C., Medeiros, P.M., Byers, J., Alber, M. and Craft, C.B. 2016. Poster: Seawater Addition Long Term Experiment (SALTEx). Georgia Department of Natural Resources Coastal Resources Division 2016 Climate Conference, November 2-3, 2016, Jekyll Island, GA. Sheldon, J.E. and Burd, A.B. 2009. Presentation: An In-depth Look at Alternating Effects of Climate Signals on Freshwater Delivery to Coastal Georgia, U.S.A. Hydrologic Prediction in Estuaries and Coastal Ecosystems. CERF 2009: Estuaries and Coasts in a Changing World, November 1-5, 2009, Portland, OR. Alber, M., Schaefer, S.C., Pomeroy, L.R., Sheldon, J.E. and Joye, S.B. 2008. Presentation: Nitrogen inputs to the Altamaha River estuary (Georgia, USA): a historic analysis. American Society of Limnology and Oceanography, 3/08, Orlando, FL. Alber, M., Schaefer, S.C., Pomeroy, L.R., Sheldon, J.E. and Joye, S.B. 2008. Presentation: Nitrogen inputs to the Altamaha River estuary (Georgia, USA): a historic analysis. American Society of Limnology and Oceanography, 3/08, Orlando, FL. Schaefer, S.C. and Alber, M. 2007. Presentation: Temperature as a Control on Proportional Nitrogen Export to Coastal Ecosystems: An application of the SCOPE nitrogen budgeting method. Estuarine Research Federations 2007 Annual Meeting, 4-8 November 2007, Providence, Rhode Island. Sheldon, J.E. and Burd, A.B. 2007. Presentation: Seasonal Effects of the Southern Oscillation and Bermuda High on Freshwater Delivery to Coastal Georgia, U.S.A. Estuarine Research Federation 2007 Annual Meeting, 4-8 November 2007, Providence, Rhode Island. Schaefer, S.C. and Alber, M. 2006. Nutrient inputs to the Altamaha River Watershed, 1954-2002. Southeastern Estuarine Research Society, Savannah, Georgia. Schaefer, S.C. and Alber, M. 2006. Poster: Temperature response of denitrification drives a latitudinal gradient in coastal export. LTER All Scientists Meeting, September 20-24, 2006, Estes Park, Colorado. Schaefer, S.C. and Alber, M. 2006. Presentation: A latitudinal gradient in the percentage of net anthropogenic nitrogen input exported to Atlantic coast rivers. Estuaries session. Semi-annual meeting of the Southeastern Estuarine Research Societ, March 31-April 1, 2006, St. Augustine, Florida. Alber, M., Pomeroy, L.R., Sheldon, J.E. and Schaefer, S.C. 2005. Presentation: Forty years of watershed nitrogen inputs and estuarine response in the Altamaha River estuary (Georgia, USA). Symposium on "Examining nutrient enrichment effects on coastal ecosystems through comparative ecological approaches and perspectives". 2005 Estuarine Research Federation Meeting. October 16-20, 2005, Norfolk, Virginia. Schaefer, S.C. and Alber, M. 2005. Presentation: Comparison of net anthropogenic nitrogen inputs and riverine export in estuarine watersheds of the Southeast. 2005 Estuarine Research Federation Meeting. October 16-20, 2005, Norfolk, Virginia. Alber, M., Cronin, T., Giblin, A., Howarth, R., Jay, D., Justic, D., Kimmerer, W., Montagna, P., Knowles, N., Najjar, R., Peterson, B., Scavia, D., Ulanowicz, D. and Walker, H. 2003. Presentation: Effects of climate-induced changes of freshwater inflow on estuaries: Report of the ERF biocomplexity working group. 2003 Estuarine Research Federation meeting. September 2003, Seattle, WA. Alber, M. 2002. Presentation: Freshwater inflow to estuaries. Biocomplexity in estuarine responses to climate change and variability. ERF Workshop. April 2002, Woods Hole, MA. Alber, M. 2002. Presentation: The ERF Biocomplexity Initiative: The implications of climate change for estuaries. Southeastern Estuarine Research Society meeting. October 2002, Conway, SC. Newsletter and Newspaper Articles |
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Data Sets by LTER Core Area and Site Research TopicCore LTER Data SetsAlgal ProductivityBotanyChemistryGeneral Nutrient ChemistryGeologyGroundwater HydrologyMarsh EcologyMeteorologyLong-term Meteorological Data from the GCE-LTER Eddy Covariance Flux Tower on Sapelo Island, Georgia Daily climatological observations from Sapelo Island, Georgia, from May 1957 through July 2001 Daily climatological observations from Sapelo Island, Georgia, from June 1980 through June 2001 Plant EcologyLeaf area index for Spartina alterniflora near the GCE-LTER Flux Tower in 2018 and 2019 Pot experiment on fresh and brackish marsh plants responses to salinity pulses in summer 2013 Ancillary Data SetsGCE Data Portal - NWS Brunswick climate data GCE Data Portal - Marsh Landing data |
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Research Project Principal InvestigatorsMerryl Alber, University of Georgia Adrian B. Burd, University of Georgia Christopher B. Craft, Indiana University at Bloomington Daniela Di Iorio, University of Georgia James T. Hollibaugh, University of Georgia Dorset Hurley, Sapelo Island National Estuarine Research Reserve Samantha B. Joye, University of Georgia Wade M. Sheldon Jr., University of Georgia Other Associated PersonnelMerryl Alber, University of Georgia Wei-Jun Cai, University of Delaware Emily Davenport, University of Georgia Evelyn Gaiser, Florida International University (FCE LTER) Jane Garbisch, University of Georgia Marine Institute Sasha Greenspan, University of Georgia Marine Institute Patrick Hagan, Sapelo Island National Estuarine Research Reserve Ellen Herbert, Ducks Unlimited James T. Hollibaugh, University of Georgia Charles S. Hopkinson, University of Georgia Kimberley S. Hunter, University of Georgia Owen Langman, Indiana University Monique Y. Leclerc, University of Georgia Fan Li, University of Houston Justin P. Manley, University of Georgia Deepak Mishra, University of Georgia Elizabeth Ashby Nix, University of Georgia Marine Institute Jessica L. O'Connell, University of Texas at Austin Steven C. Pennings, University of Houston Colin Polsky, Clark University (PIE LTER) Robert G. Pontius, Clark University (PIE LTER) Dan Runfola, Clark University Jack T. Sandow Jr., Aquatic Research South Sylvia C. Schaefer, University of Georgia Jacob Shalack, University of Georgia Marine Institute Joan E. Sheldon, University of Georgia Wade M. Sheldon Jr., University of Georgia Dontrece Smith, University of Georgia Marine Institute Carrie Beth Smith, University of Georgia Shiyu Wang, University of Georgia Nathaniel B. Weston, University of Georgia Gengsheng Zhang, University of Georgia |
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