of Spartina patens by about 37% (Slavin, 

 Good, and Squiers 1975). At the ecosys- 

 tem level, it was a target direct inter- 

 action (TD). At the floral species and 

 process level, it was nontarget direct 

 (NTD). 



Before considering situations where 

 wetland ecosystems are not the target 

 pesticides, let us consider another 

 hypothetical case for the types of prob- 

 lems that must be considered during 

 management planning. Consider a mosquito 

 control ditch that is filled with grass 

 in a marsh in Delaware. One of two 

 things needs to be done if the ditch is 

 going to be maintained (another deci- 

 sion): 1) the ditch will have to be re- 

 dug soon, or 2) a herbicide could be 

 used to kill the plants, maintain the 

 water flow, and minimize siltation. If 

 the herbicide is used in the ditch, the 

 chances are great that it is going to 

 have a dramtic effect on the phytoplank- 

 ton which are present. The diatom com- 

 munity is very sensitive to various her- 

 bicides. It is much easier to show the 

 effect of the herbicide on the phyto- 

 plankton than on the emergent plants. 

 The film on the surface of the water in 

 the marsh is rich in phytoplankton. In 

 Georgia marshes, as much as 40% of the 

 phytoplankton in the marsh water may be 

 concentrated on this surface film (Gal- 

 lagher and Pfeiffer 1977). Some pesti- 

 cides may concentrate in the surface 

 film, thus reducing a large percentage 

 of this productivity. The algal produc- 

 tion on the soil surface in the marsh 

 may amount to as much as 50% or 30% of 

 the total production (Pomeroy 1959; Gal- 

 lagher and Daiber 1974). The standing 

 crops are very small, but the turnover 

 rates are high. The possible impacts on 

 the marsh from chemical treatment may be 

 great even if only the primary producers 

 are considered. However, the alternative 

 of redigging the ditches more frequently 

 may be as, or more, damaging and less 

 cost effective. 



There are other situations where 

 the marsh is not the target ecosystem, 

 but someone makes a mistake. Maybe 

 workers are filling their sprayers at a 

 bridge over a stream when something dis- 

 tracts their attention, and some of the 

 spray runs back into the river. Perhaps 

 a plane spraying cotton fields in Ala- 

 bama passes over a river without turning 



off the sprayer. Even worse, a crop 

 duster's plane may crash in the marsh. 

 There have been some studies on these 

 kinds of problems with herbicides. 



Edwards and Davis (1974) chose the 

 most common herbicide used in cotton 

 fields for experiments conducted in the 

 Georgia marsh. In the first year of 

 their study, they sprayed an arsenate 

 type of herbicide on marsh plots in a 

 series of concentrations and measured 

 the impact on the plants, animals and 

 soils. Edwards and Davis (1974) thought 

 that the heavy, waxy cuticle on Spartina 

 leaves caused the spray to run off and 

 not be absorbed. In the second year of 

 the study, they designed an experiment 

 which could soak the plants more like 

 the exposure they would get under real 

 world conditions. In the new design, 

 they placed galvanized rings in the 

 marsh and during normal high tides they 

 pumped in water with various concen- 

 trations of an arsenate herbicide, mono- 

 sodium-methane-arsenate. The low con- 

 centrations were 10 and 100 ppm, twice 

 the highest recommended rate for any 

 agricultural situation. Their high con- 

 centration was 90,000 ppm which was 20 

 times that recommended to sterilize 

 soil. 



The arsenate herbicide works as a 

 contact killer and only turned parts of 

 the leaves brown. The next spring there 

 was no observable difference between 

 plots where either the high or low con- 

 centration of the arsenate herbicide was 

 applied. Edwards and Davis (1974) also 

 considered the animals that live on and 

 in the marsh. Although the arsenate 

 accumulated in the soil, the impact was 

 small since arsenic is abundant in the 

 crust of the earth. 



In later studies, the Auburn Uni- 

 versity group applied fluorometuron, a 

 systemic herbicide, to Spartina alterni- 

 flora (personal communication from D.E. 

 Davis, Auburn University, Auburn, Ala- 

 bama). Preliminary results indicate 

 this herbicide had a somewhat greater 

 impact on the marsh than did the arse- 

 nate herbicide. The dynamics of the 

 breakdown of the pesticide may be more 

 important than its immediate short-term 

 effect. Accumulation with long-term, 

 low-level application associated with 

 slow degradation could result in damag- 

 ing levels accumulating. 



137 



