MARSH CREATION: EFFECTS OF PESTICIDES ON THE FLORA 



John L. Gallagher 



College of Marine Studies 



University of Delaware 



Lewes, Delaware 19958 



Marsh managers must contend with 

 two kinds of situations at the ecosystem 

 level with respect to pesticides. In 

 the first situation, the marsh is the 

 target for pesticide application. In the 

 second situation, the wetland ecosystem, 

 whether it be a marsh or a mangrove 

 swamp, is not the target, but the recip- 

 ient of an accidental spill. These sit- 

 uations can be separated into direct ef- 

 fects, e.g., when a herbicide defoliates 

 mangrove trees; or indirect effects, 

 e.g., when pesticide washes out of a 

 wetland to the estuary where it has an 

 effect which feeds back to alter the 

 wetland. We thus have at the ecosystem 

 level a two by two matrix of situations 

 to consider: target or nontarget expo- 

 sure, direct or indirect effects (Ta- 

 ble 1). 



Table 1. Types of interactions between 

 wetland and pesticides. 



In the past, the acreage of natural 

 marshes along our coast has decreased as 

 the result of development. Although 

 slowed by recent laws and public aware- 

 ness, this decline will probably con- 

 tinue. To maintain coastal productivity, 

 new marshes are being planted on dredged 

 material, and suggestions to enhance the 

 productivity of those already in exis- 

 tence are being made. Since numerous 

 workers have shown that marshes will 

 respond to added nitrogen (Sullivan and 

 Daiber 1974; Valiela and Teal 1974; 

 Gallagher 1975), various fertilization 

 schemes have been proposed. 



It appears that there is a trend 

 toward an agricultural type of manage- 

 ment of marshes and other coastal eco- 

 systems. Such intensive management may 

 be a prelude to the kinds of insect and 

 disease situations experienced in agri- 

 culture. Vast areas of single-species 

 stands which are selected for specific 

 purposes, e.g., vigorous forage growth, 

 big roots, or little roots, are often 

 subject to damaging outbreaks of disease 

 and insect attacks. Unless we are ex- 

 tremely careful, we could be creating 

 problem conditions in coastal ecosystems 

 similar to those already existing in 

 agriculture. 



Consider the scenario where there 

 might be a problem with tar spot disease 

 on Spartina alterniflora . Under these 

 circumstances, the marsh flora community 

 might be the target for an application 

 of fungicide. This application would 

 control fungus "X" and protect the 

 plants, a target direct effect (TD) at 

 the species and process level. At the 

 same time, it might "protect" the detri- 

 tus from fungus "Y" which may be impor- 

 tant in mineralizing dead marsh plants, 

 a nontarget indirect effect (NTI) at the 

 species and process level. In addition 

 to influencing plant growth rate in two 

 ways, the management plan might influ- 

 ence the decomposition rate and the re- 

 mainder of the food web. Management 

 programs need to be carefully assessed 

 to avoid doing more harm than good. 

 Once we have determined that a particu- 

 lar pesticide would control the problem 

 with a target organism, extensive test- 

 ing must be done to evaluate the effects 

 on nontarget organisms or processes. 



I do not know of any cases where 

 wetland ecosystems have been the target 

 of fungicide applications to date, but 

 they have been the focus for herbicide 

 and insecticide applications. In a New 

 Jersey study, the mosquito larvicide 

 (No. 2 fuel oil plus Tritan X as a wet- 

 ting agent) decreased the standing crop 



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