Posts Tagged ‘saltmarsh’

UGA Skidaway Institute researchers complete ‘26 Hours on the Marsh’

July 30, 2014

Pitching a tent in the woods and fighting off mosquitos may not sound like logistics of a typical oceanography experiment, but that is how researchers at the University of Georgia Skidaway Institute of Oceanography completed an intensive, round-the-clock sampling regimen this month. The project, dubbed “26 Hours on the Marsh” was designed to investigate how salt marshes function and interact with their surrounding environment—specifically how bacteria consume and process carbon in the marsh.

The team set up a sampling station and an outdoor laboratory on a bluff overlooking the Groves Creek salt marsh on the UGA Skidaway Institute campus. The scientists collected and processed water samples from the salt marsh every two hours, beginning at 11 a.m. on July 16 and running through 1 p.m. July 17. By conducting the tests for a continuous 26 hours, the team can compare the samples collected during the day with those collected at night, as well as through two full tidal cycles.

The UGA Skidaway Institute team processes water samples at their outdoor laboratory. (l-r) Megan Thompson, John DeRosa (UGA Intern), Zachary Tait and Dylan Munn (UGA Intern.)

The UGA Skidaway Institute team processes water samples at their outdoor laboratory. (l-r) Megan Thompson, John DeRosa (UGA Intern), Zachary Tait and Dylan Munn (UGA Intern.)

“We wanted to be able to compare not only what is happening to the carbon throughout the tidal cycle, but also what the microbes are doing at high and low tides and also during the day and night,” said Zachary Tait, a UGA Skidaway Institute research technician. “So we had to have two high tides and two low tides and a day and night for each. That works out to about 26 hours.”

The research team ran more than 30 different tests on each sample. The samples will provide data to several ongoing research projects. A research team from the University of Tennessee also participated in the sampling program. Their primary focus was to identify the bacterial population using DNA and RNA analysis.

This sampling project is one of many the researchers conduct during the year. They use an automatic sampling system for most of the other activities. The automatic system collects a liter of water every two hours, and holds it to be collected and processed at the end of the 26-hour cycle. The team could not use the auto sampler this time for several reasons; the scientists needed to collect much more water in each sample than the auto sampler could handle and the auto sampler tends to produce bubbles in the water, so it is not effective for measuring dissolved gasses.

Megan Thompson supervises Dan Barrett (l) and John DeRosa, both UGA interns, as they process samples in a UGA Skidaway Institute laboratory.

Megan Thompson supervises Dan Barrett (l) and John DeRosa, both UGA interns, as they process samples in a UGA Skidaway Institute laboratory.

“The UT scientists wanted to conduct enzyme analysis as well as RNA and DNA tests on the samples, and for those, the samples must be very fresh,” said Megan Thompson, a UGA Skidaway Institute research technician. “You can’t just go out and pick them up the next day.”

About a dozen scientists and students were involved in the project, including Thompson, Tait, a group of undergraduate students completing summer internships at UGA’s Skidaway Institute and a similar group from UT. They split their time between the tent and outdoor laboratory on a bluff overlooking Groves Creek, and the UGA Skidaway Institute laboratories a mile away.

“It was an interesting experience, and I think it went very well,” said Thompson. “However, when we wrapped it up, we were all ready to just go home and sleep.”

“26 Hours on the Marsh” is supported by two grants from the National Science Foundation, totaling $1.7 million that represent larger, three-year, multi-institutional and multi-disciplinary research projects into salt marsh activity. These projects bring together faculty, students and staff from UGA’s Skidaway Institute, UT and Woods Hole Research Center. UGA Skidaway Institute scientists include principal investigator Jay Brandes; chemical oceanographers Aron Stubbins and Bill Savidge; physical oceanographers Dana Savidge, Catherine Edwards and Jack Blanton; and geologist Clark Alexander. Additional investigators include microbial ecologist Alison Buchan and chemical oceanographer Drew Steen, both from UT; as well as geochemist Robert Spencer from WHRC.

Little help for marsh from eco-friendly dock designs

April 25, 2012

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.

Clark Alexander (r) and research team member Mike Robinson examine the light meter equipment beneath on of the mock docks.

“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.

Skidaway Institute scientists study Intracoastal Waterway erosion

November 17, 2011

The banks of the Atlantic Intracoastal Waterway (AIWW), an artificial channel running through Georgia’s marshes behind the barrier islands, are steadily eroding, and there are several possible causes, including wakes from recreational boats. That is the conclusion of a year-long study by scientists at the Skidaway Institute of Oceanography.

 “Our goal was to quantify the impact that waves are having on the Georgia segment of the AIWW,” said Skidaway Institute professor Clark Alexander. “We also wanted to see if the salt marshes that line much of the waterway were expanding or retreating.”

Georgia contains more than one third of the salt marsh on the eastern coast of the United States and more than 90 percent of its AIWW shoreline is salt marsh. These marshes are essential habitat for fish and crustaceans because they play an important role in the life cycle of most local commercial and recreational species. The AIWW was designed to support both recreational and commercial vessel traffic.

“The major environmental impact of boats on the estuarine environment is the erosion of the channel margins from wakes,” said Alexander. “In Georgia, this diminishes the extent of the salt marsh habitat and causes the channels to widen – in some cases, at rates of up to half meter a year, which is pretty significant.”

Wakes undercut the marsh, causing to them to fail and collapse, particularly at low and mid-tides. Frequently, intertidal oyster bars are buried by eroded sediment, and oyster larvae are hindered from settling because shell material is not available upon which to settle.

Erosion is a natural process in salt marshes. However, in a natural setting, when one side of a tidal creek erodes, the other side usually accretes. Along the AIWW this was typically not the case. Alexander found extensive stretches where the shoreline was eroding on both sides of the channel.

Alexander and his team used historic and recent charts and aerial photography to track the erosion and accretion along the entire 91 mile length of the waterway between South Carolina to Florida. They also used a combination of high-definition video camera connected to a Global Positioning System (GPS) receiver to document both sides of the waterway along its length.

The research team examined shoreline change over two time periods, the first from 1933 to 1976 and the second from 1976 to 2004. The team limited their study to the eight relatively narrow main sections and six alternative sections of the waterway, avoiding the sounds where wind and storm waves might have a significant impact on shoreline change.

“Erosion has become increasingly significant and widespread in the 1976  -2002 time period,” Alexander said. “That isn’t to say that every section is eroding, but most of them are.”

Comparing the earlier time period to the later, the study found a strong trend towards more erosion in the more recent time period. Boat traffic and their wakes provide a mechanism for bank erosion.

“We don’t see commercial boating as being significant because the number of ships and tonnage in the AIWW has gone down by about 80 per cent in the past 18 years,” said Alexander. “But recreational boat registrations in coastal counties (currently about 29,000) have continued to increase.”

Alexander also has another explanation that cannot be ruled out with current information. Except for two short segments, the Corps of Engineers is no longer dredging the AIWW to maintain its target depth and sea level is rising at about 1 foot per century.  The channel could be widening because it is becoming shallower but must still transport and contain the same amount of water.  “Boating is most likely the immediate primary erosion force, but rearrangement of the channel cross section may contribute as well,” he said. “We just don’t know absolutely at this time.”