SALT MARSH CREATION: IMPACT OF HEAVY METALS 



Wayne S. Gardner 



Skidaway Institute of Oceanography 



Post Office Box 13687 



Savannah, Georgia 31406 



INTRODUCTION 



The impact of heavy metals on 

 marshes depends on the composition, dis- 

 tribution, availability, and biological 

 effects of the metals in the sediments 

 and water at the site. This report dis- 

 cusses factors affecting the fluxes and 

 biological activities of heavy metals in 

 salt marsh environments. 



Heavy metals differ from synthetic 

 organic contaminants because they occur 

 naturally and are therefore almost al- 

 ways present at low concentrations in 

 estuarine environments. Concentrations 

 in polluted systems include those occur- 

 ring naturally in addition to those add- 

 ed directly or indirectly as a result of 

 human activity. In contrast to organic 

 materials which can generally be degrad- 

 ed, at least to some extent, heavy 

 metals are chemically stable and are not 

 removed from contaminated ecosystems by 

 degradation. However, the mobility and 

 toxicity of certain metals may be af- 

 fected by their chemical form and bio- 

 chemical associations. 



When considering the toxicity of 

 heavy metals, a distinction should be 

 made between those essential to living 

 organisms and toxic metals which have no 

 known beneficial biochemical function. 

 Examples of the former are V, Cr, Mn, 

 Fe, Co, Cu, Zn, Mb, and Sn. These metals 

 are often incorporated into proteins and 

 can exist as metalloenzymes which serve 

 as biochemical catalysts. Organisms usu- 

 ally have some control over the intake 

 of essential metals, and unless they are 

 exposed to overwhelming concentrations, 

 toxicity is not a problem. In some 

 cases increased levels of these metals 

 may actually stimulate growth of marsh 



Present address: Great Lakes Environ- 

 mental Research Laboratory, U.S. Dept. 

 of Commerce, NOAA, 2300 Washtenaw Ave., 

 Ann Arbor, Michigan 48104. 



plants. Organisms are not as well 

 equipped to control their exposure to 

 the toxic metals (Hg, Cd, Pb, and As) 

 which have not been shown to be essen- 

 tial. Natural exposure to these metals 

 is very low and homeostatic control of 

 concentrations has not been developed by 

 most organisms (Buhler 1973). 



SOURCES OF HEAVY METALS IN 



ESTUARINE-SALT MARSH SYSTEMS 



Heavy metals occurring in estuarine 

 ecosystems can be derived from the con- 

 tinental interior or may come from local 

 sources. Weathering processes are re- 

 sponsible for the natural breakdown of 

 minerals. However, these processes can 

 be greatly accelerated by activities 

 such as mining, industrial production, 

 and burning of fossil fuels. 



Estuaries can often be considered 

 as funnels for the transport of pol- 

 lutants to the sea, but some parts of 

 the estuarine system (e.g., salt 

 marshes) may also act as filters for 

 pollutants. Windom (1975) calculated 

 annual net input of several metals into 

 estuaries of the southeastern United 

 States based on metal concentrations and 

 river flow. Annual losses to marsh 

 sediments were estimated by measuring 

 metal concentrations in the sediments 

 and assuming a sedimentation rate of 1 

 mm/yr (0.04 inch/yr). It was estimated 

 that 80% to 90% of Cu, Cd, and Hg were 

 transferred through the estuaries where- 

 as the other 10% to 20% were lost to the 

 sediments. The quantity lost to the 

 sediments was roughly equivalent to the 

 amount found in the particulate matter 

 of the rivers. In contrast, all of the 

 Fe and 60% of the Mn were transferred to 

 the sediments. 



In addition to continental input 

 through rivers, metals can be introduced 

 into coastal regions by local sources of 



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