Editors Note: This is the seventh in a series of articles to explain environmental monitoring efforts associated with the Savannah Harbor Expansion Project (SHEP). This series focuses on the various monitoring activities that must take place as construction begins.
SAVANNAH, Ga. – Several large impoundments in South Carolina along the lower Savannah River provide habitats for thousands of birds who migrate to the area seasonally. These sites, also known as dredged material containment areas (DMCAs), attract a variety of migratory birds who feed on area fish, invertebrates and vegetation.
Some dredged material that will be removed during the harbor deepening may contain concentrations of cadmium at levels that can be harmful to birds, according to William G. Bailey, Savannah District Planning chief. Cadmium is a naturally-occurring toxic metal, buried deep within clay material at the bottom of the river.
Cadmium is not present in all the sediments that will be excavated. In areas where it is present, it is not found to be enough to put humans at risk; however, studies show that birds feeding in areas with cadmium concentrations of approximately 30 parts per million may suffer adverse effects to their reproductive systems or experience behavioral changes, said the Savannah District’s avian expert and biologist Ellie Covington.
A team of scientists from the University of Georgia are currently conducting one year of baseline monitoring through blood and tissue samples tested to measure cadmium levels in bird species found at the DMCAs. These tests, conducted before placement of dredged material with associated concentrations of cadmium, will help biologists determine if the dredged material in question is having an impact on birds once the deepening begins. Testing is conducted based on the migratory patterns of the species of birds, said UGA ecologist Larry Bryan.
“Metal analysis from drawn blood is indicative of recent uptake in adult birds,” said Bryan. “It’s a nonlethal technique that has little impact on avian populations but allows for assessments of possible cadmium uptake and avian health.”
The team targets between 10 to 12 bird species with different habitats and diets, including Mockingbirds, Eastern Towhees, Black-necked Stilts, Avocets, Mottled Ducks and Northern Shovelers, said Bryan. The birds include those that use the land portion of the DMCAs and the flooded portion of the sites.
A variety of capture techniques such as mist nets and nest traps are used to capture the birds, he said.
“At present, we have only completed the spring and summer sampling of resident birds,” said Bryan. “We are initiating winter sampling of migrant birds and a few resident birds and will analyze all the blood samples in late winter.”
Collected birds are banded for future sampling that will continue during construction and three years post-construction, said Bryan.
The lowest cadmium concentration for which environmental impacts would be expected is 14 parts per million, according to the Corps’ 2012 Sediment Quality Evaluation report.
DMCAs 14A and 14B, pictured above, are where sediments with higher cadmium levels will be placed, said Bailey.
During SHEP construction, the sediments that are removed from the bottom of the river and placed in DMCAs 14A and 14B will be maintained in a “ponded” or wet state to prevent cadmium from becoming mobile and ecologically available, said Bailey.
After the cadmium-enriched sediments have been placed in the DMCAs, markers will be placed on the sediment surface across the sites in a grid to demarcate the top of that layer. After three to six months, the DMCAs will be covered with two feet of soil containing less than 4 ppm of cadmium, or clean sediment, to prevent exposure to the environment. Covering the cadmium-enriched sediments will make them unavailable to plants and birds feeding within the DMCA, said Bailey.
A layer of crushed limestone or coal will cover the capped area for isolation and future identification purposes, said Bailey. Furthermore, development of the site in the future for a port in Jasper County, S.C., would provide additional covering through the concrete and asphalt used for such a facility.
If immediate concerns arise during the construction, methods of deterrence to clear birds from the DMCA will be coordinated with the United States Fish and Wildlife Service, said Covington.
~ Chelsea Smith, Public Affairs Specialist