n 



£ 

 n 



CO 



* -200 



A 



W 



4> 



I? 



-400 



• Average Eh Control Sites 

 O Average Eh Weired Sites 



— i— 

 8 



10 



2 4 6 



Month 



Figure 3. Seasonal soil Eh in marshes with and without weir data 

 (from Hoar 1972). 



12 



Fixed-crest weirs are relatively innocuous compared to more intensive structural approaches 

 (see Cowan et al. 1988 for a discussion of the various types of structural approaches to water 

 level management). If a little bit of extra flooding has this impact on vegetation, then additional 

 serious flooding, especially during summer, may lead to even higher rates of wetland loss through 

 either increased waterlogging or decreased sedimentation. A management adaptation might be to 

 have the least restrictive hydrologic changes during summer when soil oxidation and reduction 

 potentials are naturally the lowest. 



This particular management approach was implemented coast-wide before appropriate 

 comparative studies were initiated to determine the long-term consequences. Fortunately, the 

 student theses cited herein, although unreviewed in the scientific literature and perhaps largely 

 ignored as a result, are a valuable resource of information on natural marshes and the impacts of 

 water level management. 



ACKNOWLEDGMENT 



This effort was supported by the Louisiana Sea Grant Program and the Department of Marine 

 Sciences, Louisiana State University. Ms. S. Kaswadji greatly helped to track down literature 

 citations and prepare figures. 



LITERATURE CITED 



Burdick, D.M., and I.A Mendelssohn. 1987. Waterlogging responses in dune, swale and marsh 

 populations of Spartina patens under field conditions. Oecologia (Berl.)74:321-329. 



Burleigh, J.G. 1966. The effects of Wakefield weirs on the distribution of fishes in a Louisiana 

 saltwater marsh. M.S. Thesis. School of Forestry and Wildlife Management, Louisiana State 

 University, Baton Rouge. 68 pp. 



161 



