Clark Alexander (r) with team member Mike Robinson examining the light meters beneath one of the mock docks.

New dock designs intended to reduce damage to salt marshes are not much better than traditional docks, according to a recently completed study by Clark Alexander of Skidaway Institute of Oceanography. Alexander also concluded the compass orientation and height of a dock has more impact on the health of the salt marsh than the dock design or materials.

The problem is the shadow docks cast on the salt marsh vegetation beneath them. The marsh grass (Spartina alterniflora) does not flourish in reduced sunlight.  In recent years, alternative materials and designs have appeared on the dock-building market to try to mitigate this problem. Alexander tested three types of alternative material and designs – ThruFlow fiberglass-impregnated plastic grating; Gator Dock Fibergrate grating; and the DockRider Sundock, which uses a set of wooden rails and an electric trolley in place of traditional wood planking. 

“These all sounded good,” said Alexander. “But what we didn’t know was if they actually worked effectively.”

To answer that question, Alexander conducted a three-year, two-part research project funded by a $195,488 grant from the Georgia Coastal Zone Management Program.

The first part of the study was to conduct field-based “before-and-after” studies of salt marshes where some of the new designs were being built. Alexander’s team collected samples and recorded conditions in the marsh before the docks were built and continued to monitor the salt marshes after they were completed.

In the second part of the study, Alexander and his team constructed four dock models, “mock docks”, using alternative materials on high ground at the Skidaway campus. The docks were placed in a field with unobstructed sunlight and were fitted with light meters that measured the amount of sunlight being received above and below each dock. The researchers measured the shadow footprint of the various dock designs over the course of two years.

“Because orientation is an important parameter in light transmission through these materials, we made the mock docks mobile, so we could re-oriented them during the four seasons to see the effects of orientation and seasonal sun angle” said Alexander.

They also adjusted the dock heights to assess the impact of height on light penetration to the ground below. 

In the first part of the study, Alexander and his team examined three separate field sites – Turners Creek (ThruFlow decking), Shell Point Cove (Dockrider) and Betz Creek (traditional plank design) They measured the stem density of the marsh grass before the docks were constructed and then monitored it for two years after construction. Stem density in the dock shadow footprint decreased between 44 and 80 percent compared to nearby, non-dock sites.

The team also observed additional dock-related impacts. Some sections of salt marsh transitioned to denuded mudflats due to the marsh wrack that accumulated around the dock pilings.

The results of the field study were supported by the mock-dock project on the Skidaway campus. Seasonal measurements showed a significant reduction of the light needed to support the health of the marsh plants in the areas affected by the docks’ shadows.  At Skidaway Institute’s latitude, the elevation of the sun is high enough to allow sunlight to penetrate through the grated deck material only during the spring and summer, and even then, provides only about 10% more light than traditional plank decking.

The mock-dock project also documented two additional dock-shading impacts.  The compass orientation of a dock plays a significant role in the effect the dock has on the marsh. Docks that are oriented in a generally north-south direction have a much smaller shading impact than those oriented east-west. The height of the dock also has a significant effect. The duration of the shadow under the dock and the total light loss decreases as the height increases, up to 7 feet above the marsh surface, with smaller, less significant decreases above that height.

“The results of the two studies demonstrate that neither current alternative materials nor construction methods effectively negate the effects of dock shading in our region,” said Alexander. “However, the Dockrider system had one half to one third the shading impact of decked walkways in our study.”

“In addition to shading impacts, marsh wrack accumulation around dock and walkway pilings also negatively impacts the marsh and will be a problem with any piling-supported structure.”

The results of the study have been sent to the Department of Natural Resources, which will use these results to better manage the important coastal saltmarshes of Georgia.

A Georgia Coastal Hazards Portal Training Workshop will introduce a new Web-based tool to study threats to the Georgia coast. It will be held at the Sapelo Island Visitor Center in Meridian, Ga., on Friday, April 13, from 9 a.m. to 4 p.m.

The workshop will focus on the Georgia Coastal Hazards Portal (GCHP) -- a Web-based interactive tool designed to provide a better understanding of coastal resources, coastal hazards and the effects of rapid population growth and development. It was created through a partnership between the Skidaway Institute of Oceanography and the Savannah Area GIS program with funding provided by the Georgia Coastal Zone Management Program.

“This online tool can be utilized in many ways, such as, identifying vulnerability to coastal hazards and identifying connections between hazards and natural resources,” said Skidaway Institute’s Clark Alexander, the lead scientist on the GCHP project.

The workshop is targeted towards community planners, resource managers, research scientists, outreach specialists and elected officials. They will have the opportunity to discuss current coastal hazard research, network with others from the coastal hazards community and learn how to use the new interactive GCHP website as a resource and tool for communicating the facts and risks of coastal hazards.

The workshop is sponsored by the Skidaway Institute of Oceanography, the University of Georgia Marine Extension Service, the Sapelo Island National Estuarine Research Reserve and the Georgia Department of Natural Resources Coastal Resources Division. 

  Registration is available on-line at http://www.surveymonkey.com/s/CGHPRegistrationForm.

Workshop participants will receive lunch and a flash drive containing presentations and GCHP reference material.

The American Planning Association has approved the GCHP Training Workshop for six credits.

For additional information, contact Angela Bliss at abliss@uga.edu.

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New clues as to how the Earth’s remote ecosystems have been influenced by the industrial revolution are locked, frozen in the ice of glaciers. That is the finding of a group of scientists, including Aron Stubbins of the Skidaway Institute of Oceanography.

The research is published in the March 2012 issue of Nature Geoscience.

The key to the process is carbon-containing dissolved organic matter (DOM) in the glacial ice. Glaciers provide a great deal of carbon to downstream ecosystems. Many scientists believe the source of this carbon is the ancient forests and peatlands overrun by the glaciers. However, Stubbins and his colleagues believe the carbon comes mainly from contemporary biomass and fossil fuel burning that gets deposited on the glacier surfaces. Once deposited on the glacier surface by snow and rain, the DOM moves with the glacier and is eventually delivered downstream where it provides food for microorganisms at the base of the marine food web.

“In vibrant ecosystems like in the temperate or tropical zones, once this atmospheric organic material makes landfall it is quickly consumed by the plants, animals and microbial populations,” said Stubbins. “However in frigid glacier environments, these carbon signals are preserved and standout.”

 “Remote regions are often perceived as being pristine and devoid of human influence”, Stubbins continued. “Glaciers show us that nowhere goes untouched by industry. Instead, burning fuels has an impact upon the natural functioning of ecosystems far removed from industrial activity.”

Glaciers and ice sheets together represent the second largest reservoir of water on earth, and glacier ecosystems cover ten percent of the Earth, yet the carbon dynamics underpinning those ecosystems remain poorly understood.

“Increased understanding of glacier biogeochemistry is a priority, as glacier environments are among the most sensitive to climate warming and the effects of industrial emissions” said Stubbins.

Globally, glacier ice loss is accelerating, driven in part by the deposition of carbon in the form of soot or “black carbon”, which darkens glacier surfaces and increases their absorption of light and heat. Biomass and fossil fuel burning by people around the globe are the major sources of that black carbon.

Stubbins and his fellow scientists have conducted much of their research at the Mendenhall Glacier near Juneau, Alaska. Mendenhall and other glaciers that end their journey in the Gulf of Alaska receive a high rate of precipitation. High levels of rain and snow acts to strip the atmosphere clean of organics, dumping it on the glacier. Consequently, these glaciers are among the most sensitive to global emissions of soot.

The researchers’ findings also reveal how the ocean may have changed over past centuries. The microbes that form the very bottom of the food web are particularly sensitive to changes in the quantity and quality of the carbon entering the marine system. Since the study found that the organic matter in glacier outflows stems largely from human activities, it means that the supply of glacier carbon to the coastal waters of the Gulf of Alaska is a modern, post-industrial phenomenon. “When we look at the marine food webs today, we may be seeing a picture that is significantly different from what existed before the late-18th century,” said Stubbins. “It is unknown how this manmade carbon has influenced the coastal food webs of Alaska and the fisheries they support.”

A warming climate will increase the outflow of the glaciers and the accompanying input of dissolved organic material into the coastal ocean. This will be most keenly felt in glacially dominated coastal regions, such as those off of the Gulf of Alaska, Greenland and Patagonia. These are the areas that are experiencing the highest levels of glacier ice loss.

“Although it is not known to what extent organic material deposition has changed and will continue to alter glacially-dominated coastal ecosystems or the open ocean, it is clear that glaciers will continue to provide a valuable and unique window into the role that the deposition of organic material plays in our changing environment,” Stubbins said.

Stubbins collaborators on the project included Eran Hood and Andrew Vermilyea from the University of Alaska Southeast; Peter Raymond and David Butman from Yale University; George Aiken, Robert Striegl and Paul Schuster from the U.S. Geological Survey; Patrick Hatcher, Rachel Sleighter  and Hussain Abdulla from Old Dominion University; Peter Hernes from the University of California-Davis; Durelle Scott from Virginia Polytechnic Institute and State University; and Robert Spencer from Woods Hole Research Center.

The paper can be viewed on-line at http://dx.doi.org/10.1038/NGEO1403

Further details are available at http://www.skio.usg.edu/?p=research/chem/biogeochem/glaciers. This work is being continued with support from the National Science Foundation: http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1146161

The Skidaway Institute of Oceanography is an autonomous research unit of the University System of Georgia located on Skidaway Island in Savannah, Ga. The mission of the Institute is to provide the State of Georgia with a nationally and internationally recognized center of excellence in marine science through research and education.

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Skidaway Institute of Oceanography scientist Clark Alexander has begun a multi-investigator project to assess the vulnerability of the Southeast Atlantic coast to future threats ranging from sea-level rise to shoreline erosion.

The project is funded by a $377,000 grant from the National Oceanographic and Atmospheric Administration. It is part of a larger, $1.06 million project awarded to the Governors’ South Atlantic Alliance (Alliance), to coordinate efforts in Georgia, Florida, South Carolina and North Carolina to develop a consistent method of assessing coastal threats in the four states.

“Our overall goal is to develop a process to evaluate our coast’s physical and economic vulnerability to hazards like sea level rise, flooding, storms, hurricanes and erosion, and do so in a uniform way throughout the region,” said Alexander.

A key component of the project is further development of a computer program called AMBUR. Originally created by Georgia Southern University’s Chester Jackson when he was a graduate student at Skidaway Institute, AMBUR is a powerful tool to evaluate erosion and accretion on a changing coastline. 

“Dr. Jackson will enhance AMBUR’s capabilities so that it can be used to evaluate additional coastal characteristics,” Alexander said. “We want to include additional factors such as habitat, elevation, population density, economic valuation and different shoreline types.”

While Jackson is working on AMBUR, Alexander and his team will be collecting data on coastal physical, biological, demographic and economic parameters, while also meeting with coastal managers from the four states comprising the Alliance to determine which parts of the Southeast coast are most critically in need of assessment. Once identified, these areas will become the first coastal regions targeted for analysis with the new AMBUR tools.  When completed, the scientists will be able to present coastal managers with information and maps describing coastal vulnerability for at least a portion of each state. Future funding will be sought to expand the analysis to the whole southeastern coastal region.

“By its very nature, this project will identify the most vulnerable areas along the coast and will provide an unbiased analysis of the incentives and disincentives for development in those areas,” said Alexander.  

The project is expected to run for 18 months.