SALT MARSH CREATION: IMPACT OF SEWAGE 



Evelyn Haines 



University of Georgia 



Marine Institute 



Sapelo Island, Georgia 31327 



Under the auspices of a project 

 funded by the Office of Water Research 

 and Technology entitled The. Capacity of 

 the Spartina Salt Marsh to Assimilate 

 Nitrogen from Sewage Sludge, two gradu- 

 ate students, Barry Sherr and Alice 

 Chalmers, and I have been studying the 

 nitrogen cycle in coastal marine ecosys- 

 tems. Our focus has been on the basic 

 nitrogen cycle in the marsh as well as 

 the impact of applying sewage sludge on- 

 to the marsh; specifically, what happens 

 to the nitrogen in the sludge? I will 

 compare our study to a similar, although 

 longer and more comprehensive, study 

 which has been carried out by Valiela 

 et al. (1974) in a Massachusetts salt 

 marsh. 



Increasing amounts of sewage are 

 being deposited in coastal wetlands be- 

 cause this is an inexpensive and conve- 

 nient way for urban areas on the coast 

 to dispose of sewage. Unfortunately, a 

 lot of the sewage has not even had pri- 

 mary treatment, and the increasing bio- 

 logical oxygen demand (BOD) in coastal 

 wetlands has already resulted in marked 

 deterioration of water quality in some 

 northern estuaries. We cannot treat 

 estuaries like giant flush toilets be- 

 cause they do not flush. Estuaries are 

 naturally productive because physical 

 processes in the estuaries, e.g., sedi- 

 mentation in the marshes and estuarine 

 water circulation, tend to keep mate- 

 rials that come into estuaries within 

 the estuary. Thus, when sewage is intro- 

 duced into an estuary, the materials 

 tend to remain there. 



One of the major components of sew- 

 age that we should be concerned about 

 are the plant nutrients, e.g., in sec- 

 ondarily treated sewage there will be 

 phosphate, ammonia, and nitrate in large 

 quantities which will stimulate phyto- 

 plankton growth in the estuary, and 

 vascular plant and benthic algal produc- 

 tion in the marshes. Impacts from other 



sewage materials may be a bit more 

 subtle. Heavy metals and chemicals, 

 such as pesticides and petroleum hydro- 

 carbons, are abundant in sewage. Also, 

 very little is known about the fate of 

 the pathogenic microorganisms in sewage 

 in estuaries. 



Sewage impact on salt marshes can 

 be experimentally evaluated by analyz- 

 ing: (1) accumulation of substances such 

 as inorganic nitrates, heavy metals, and 

 pesticides in plants, fauna, and soils; 



(2) the stimulation of certain biologi- 

 cal processes in the marsh, e.g., plant 

 production and microbial activity; and 



(3) the inhibition of microbial process- 

 es. There are also subtle, indirect ef- 

 fects that cannot be predicted. By ob- 

 serving a whole range of processes in 

 the marsh, one may detect indirect chain 

 reaction effects resulting from the im- 

 pact of sewage on salt marshes. 



Gosselink et al. (1974) assigned a 

 high monetary value to the ability of 

 salt marshes to act as tertiary sewage 

 treatment systems. Salt marshes are not 

 very effective for secondary sewage 

 treatment because salt marshes and estu- 

 aries are such highly productive systems 

 to begin with, and already contain plen- 

 ty of organic material. If more organic 

 matter in primary or untreated sewage is 

 added, the estuaries will be overloaded, 

 and the water will show decreased oxygen 

 tensions and other signs of deteriora- 

 tion. However, estuaries may be effi- 

 cient at tertiary treatment for removal 

 of inorganic nutrients in secondarily 

 treated sewage. Pomeroy et al. (1972) 

 reported the ability of marsh clay sedi- 

 ments to extract phosphorus from water 

 via chemical reaction. Apparently nitro- 

 gen is the nutrient which is more inter- 

 esting to study because addition of ni- 

 trogen can increase plant productivity 

 in salt marshes. Gosselink et al. 

 (1974) assigned a per year value of 

 $34,580 per ha ($14,000 per acre) to 



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