marshes of S5().0(K) per acre. This assumes that the replacement of this function, 

 following v\etland destruction, would require construction of a tertiary treatment 

 facility. The potential for managing freshwater wetlands for removal of excess 

 nutrients has been studied in various parts oi the world.''' in the United States such 

 diverse communities as cypress domes"' and northern peat marshes'^ have been 

 intensively studied for their potential to treat waste water. In addition to nutrient 

 removal, wetlands may at times remove significant amounts of metals and reduce the 

 sediment load transported in streams.'** Figure 4 illustrates some of the forces that 

 govern these activities in a lakeshore wetland. 



Techniques for assessing the role of individual wetlands for this role in water 

 quality control are crude. It may be that estimates of primary productivity of a site 

 may be useful."* In Virginia'- guidelines for regulating wetland alteration rank plant 

 communities in their ability to act as sediment traps. If the current estimates of 

 tertiary treatment value are at all reasonable, and if there is high potential for using 

 some wetlands to treat effluent, then there is a critical need to translate knowledge 

 developed in the past decade into evaluation procedures that can be used in practical 

 wetland regulation. 



Fish Nursery 



The bulk of the United States' commercial fish catch, by weight and value, and the 

 saltwater sport fish catch, by weight, are dependent upon coastal estuaries and their 

 wetlands for food sources, spawning grounds, nurseries for the young, or for all o\ 

 these purposes.'** The importance of the fin and shellfish industry and the general 

 acceptance of these roles of coastal wetlands have persuaded most coastal states and 

 communities that wetlands are "fish nurseries." Protection of these functions was the 

 purpose of the earliest wetland legislation. These functions have been so well 

 accepted by the public that no techniques have been developed to rank or rate specific 

 wetlands for this value. Some state regulations single out certain wetland plant 

 communities for protection of these functions but this is usually based on the rate of 

 primary productivity. 



Freshwater wetlands have not received as much attention as coastal wetlands for 

 their role as "fish nursery" areas. Studies in Michigan during the past decade have 



Wet And 

 Dry Fal 



jlf internal %\\i 

 ^ Plani 



Consumer 

 Migration 



Groundwater 



nt \\f ' Through Flow 

 Cycle jL 



7~Jljilr~ Flood ^ 



. I Transport I 



i ^ ► '-C. 



Groundwater 



Permanent 

 Burial 



Figure 4. A conceptual input-output model for a lakeshore wetland. ^^ 



112 



