GCE-II Question 1: Environmental Forcing

Description Background Components Projects Publications Data Sets Personnel Show All  

Research Question

Q1: What are the long-term patterns of environmental forcing to the coastal zone?

Overview

Coastal 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

  • Atmospheric forcing
    • Weather stations
    • Atmospheric deposition
    • Additional studies
  • Oceanographic forcing
    • Sea level
    • Oceanographic conditions
    • Additional studies
  • Upstream forcing
    • River discharge
    • Altamaha river water chemistry
    • Watershed properties
    • Coastal subwatersheds

Research Question Background

The 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.

Atmospheric forcing

Weather stations

We 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 (more information). 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 deposition

Atmospheric 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 forcing

Sea level

Sea 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 conditions

We 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 forcing

River discharge

The 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.

Altamaha Discharge
Altamaha Discharge

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 chemistry

We 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 properties

The 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.

Atmospheric forcing

Weather stations

Eddy covariance flux tower for measuring gas exchange between salt marshes and the atmosphere
description: GCE web page, plain web page
date range: ongoing (since 2012)
principal investigator(s): Daniela Di Iorio

Georgia Coastal Ecosystems LTER Climate monitoring program
description: GCE web page, plain web page
date range: ongoing (since 2002)
principal investigator(s): Daniela Di Iorio, Dorset Hurley, Wade M. Sheldon Jr.

Additional studies

Effects of large-scale climate drivers on precipitation and river discharge in the GCE study area and the Altamaha River watershed
description: GCE web page, plain web page
date range: 2007 to 2012
principal investigator(s): Adrian B. Burd

Oceanographic forcing

Sea level

Seawater Addition Long Term Experiment (SALTEx), a long-term field manipulation experiment in a Zizaniopsis marsh in the Altamaha River
description: GCE web page, plain web page
date range: ongoing (since 2011)
principal investigator(s): Christopher B. Craft

Additional studies

Effects of climate on coastal ecosystems
description: GCE web page, plain web page
date range: 2007 to 2012
principal investigator(s): Merryl Alber

Upstream forcing

Altamaha River water chemistry

Altamaha river water chemistry monitoring
description: GCE web page, plain web page
date range: ongoing (since 2000)
principal investigator(s): Samantha B. Joye

Coastal subwatersheds

Water use patterns in hydrologic units of the 5 major coastal river watersheds in Georgia
description: GCE web page, plain web page
date range: 1999 to 2001
principal investigator(s): Merryl Alber

Additional studies

Altamaha watershed nutrient budgets from 1954 to 2002
description: GCE web page, plain web page
date range: 2004 to 2006
principal investigator(s): Merryl Alber

Altamaha watershed water quality
description: GCE web page, plain web page
date range: 2003 to 2005
principal investigator(s): James T. Hollibaugh, Samantha B. Joye

Maps and Locals (MALS)
description: GCE web page, plain web page
date range: 2009 to 2012
principal investigator(s): Merryl Alber

Watershed nitrogen input and export of N to coastal systems along the east coast of the U.S.
description: GCE web page, plain web page
date range: 2004 to 2006
principal investigator(s): Merryl Alber

Watershed nitrogen input and export of N to coastal systems along the west coast of the U.S.
description: GCE web page, plain web page
date range: 2007 to 2009
principal investigator(s): Merryl Alber

Journal Articles

Craft, C.B., Herbert, E., Li, F., Smith, D., Schubauer-Berigan, J.P., Widney, S., Angelini, C., Pennings, S.C., Medeiros, P.M., Byers, J. and Alber, M. 2016. Climate change and the fate of coastal wetlands. Wetland Science and Practice. 33(3):70-73.

O'Connell, J. 2016. A smart classifier for extracting environmental data from digital image time-series: Applications for PhenoCam data in a tidal salt marsh. Environmental Modelling & Software. 84:134-139. (DOI: 10.1016/j.envsoft.2016.06.025)

Herbert, E., Boon, P., Burgin, A.J., Neubauer, S.C., Franklin, R.B., Ardon, M., Hopfensperger, K.N., Lamers, L. and Gell, P. 2015. A global perspective on wetland salinization: Ecological consequences of a growing threat to freshwater wetlands. Ecosphere. 6(10)(206):1-43. (DOI: 10.1890/ES14-00534.1)

Sheldon, J.E. and Burd, A.B. 2014. Alternating Effects of Climate Drivers on Altamaha River Discharge to Coastal Georgia, USA. Estuaries and Coasts. 37:772788. (DOI: 10.1007/s12237-013-9715-z)

Schaefer, S.C., Hollibaugh, J.T. and Alber, M. 2009. Watershed nitrogen input and riverine export on the west coast of the U.S. Biogeochemistry. 93(3):219-233. (DOI: 10.1007/s10533-009-9299-7)

Weston, N.B., Hollibaugh, J.T. and Joye, S.B. 2009. Population growth away from the coastal zone: Thirty years of land use change and nutrient export from the Altamaha River, GA. Science of the Total Environment. 407:3347-3356. (DOI: 10.1016/j.scitotenv.2008.12.066)

Hopkinson, C.S., Lugo, A., Alber, M., Covich, A. and Van Bloem, S.J. 2008. Understanding and forecasting the effects of sea level rise and intense windstorms on coastal and upland ecosystems: the need for a continental-scale network of observatories. Frontiers in Ecology. 6(5):255-263. (DOI: 10.1890/070153)

Schaefer, S.C. and Alber, M. 2007. Temperature controls a latitudinal gradient in the proportion of watershed nitrogen exported to coastal ecosystems. Biogeochemistry. 85(3):333-346. (DOI: 10.1007/s10533-007-9144-9)

Schaefer, S.C. and Alber, M.A. 2007. Temporal and spatial trends in nitrogen and phosphorus inputs to the watershed of the Altamaha River, Georgia, USA. Biogeochemistry. 86(3):231-249. (DOI: 10.1007/s10533-007-9155-6)

Theses and Dissertations

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.

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)

Schaefer, S.C. and Alber, M. 2005. Trends in agricultural sources of nitrogen in the Altamaha River watershed. In: Hatcher, K.J. Proceedings of the 2005 Georgia Waters Resources Conference, Institute of Ecology, University of Georgia, Athens, Georgia.

Weston, N.B., Hollibaugh, J.T., Sandow, J. and Joye, S.B. 2003. Nutrients and dissolved organic matter in the Altamaha river and loading to the coastal zone. Hatcher, K.J. (editor). Proceedings of the 2003 Georgia Water Reseurces Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Alber, M. and Smith, C. 2001. Water use patterns in the watersheds of the Georgia riverine estuaries. Pages 752-755 in: Hatcher, K.J. (editor). Proceedings of the 2001 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Conference Posters and Presentations

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.

Sheldon, J.E. and Burd, A.B. 2008. Poster: Seasonal effects of the Southern Oscillation and Bermuda High on freshwater delivery to the central Georgia coast. GCE-LTER 2008 Annual Meeting, March 14-15, 2008, Athens, Georgia.

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. Poster: Detecting climate signals in river discharge and precipitation data for the central Georgia coast. 2007 AERS/SEERS Meeting, March 15-17, 2007, Pine Knoll Shores, NC.

Sheldon, J.E. and Burd, A.B. 2007. Poster: Detecting climate signals in river discharge and precipitation data for the central Georgia coast. 2007 AERS/SEERS Meeting, March 15-17, 2007, Pine Knoll Shores, NC.

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

Sheldon, W.M. 2006. Mining and Integrating Data from ClimDB and USGS using the GCE Data Toolbox. DataBits: An electronic newsletter for Information Managers, Spring 2006 issue. Long Term Ecological Research Network, Albuquerque, NM.

Data Sets by LTER Core Area and Site Research Topic

Core LTER Data Sets

Chemistry

Surface water DIC, total alkalinity, and pH for the September 2002 through December 2004 Georgia Coastal Ecosystems LTER oceanographic surveys

General Nutrient Chemistry

Porewater chemistry measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx)

Baseline soil chemistry data measurements from the GCE-LTER Seawater Addition Long-Term Experiment (SALTEx)

Long-term water quality monitoring on the Altamaha River and major tributaries from September 2000 through April 2009

Meteorology

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2016 to 31-Dec-2016

Long-term Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 03-Jan-2003 to 31-Dec-2016

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2015 to 31-Dec-2015

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2014 to 31-Dec-2014

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2013 to 31-Dec-2013

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2012 to 31-Dec-2012

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2011 to 31-Dec-2011

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2010 to 31-Dec-2010

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2009 to 31-Dec-2009

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2008 to 31-Dec-2008

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2007 to 31-Dec-2007

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2006 to 31-Dec-2006

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2005 to 31-Dec-2005

Annual summaries of daily climatological observations from the National Weather Service weather station at the UGA Marine Institute on Sapelo Island, Georgia for 1958 to 2004

Annual summaries of daily climatological observations from the National Weather Service weather station at Brunswick, Georgia for 1915 to 2004

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2004 to 31-Dec-2004

Climate data from the SINERR/GCE/UGAMI weather station at Marsh Landing on Sapelo Island, Georgia, from 01-Jan-2003 to 31-Dec-2003

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 Ecology

Pot experiment on fresh and brackish marsh plants responses to salinity pulses in summer 2013

Ancillary Data Sets

GCE Data Portal - NWS Brunswick climate data

GCE Data Portal - Marsh Landing data

GCE Data Portal - UGA Marine Institute climate data

GCE Data Portal - Hudson Creek/Meridian Landing data

Research Project Principal Investigators

Merryl 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 Personnel

Merryl 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, Virginia Institute of Marine Science

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 O'Connell, University of Georgia

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

 
LTER
NSF

This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959 and OCE-1237140. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.