19 



Fig. 17. Aerial view of Tinicum Marsh near Philadelphia, Pennsylvania. This marsh is particularly valuable for improving water quality in 

 an urban environment. 



(Lee, et al. 1976). Wetlands have also been proven to be 

 good filters of nutrients and heavy metal loads in dredged 

 material disposal effluents (Windom 1977). 



Aquatic Productivity 



Wetlands are among the most productive ecosystems in 

 the world and they may be the highest, rivaling our best 

 cornfields (Figure 18). Wetland plants are particularly 

 efficient converters of solar energy. Through photosyn- 

 thesis, plants convert sunlight into plant material or bio- 

 mass and produce oxygen as a by-product. This biomass 

 serves as food for a multitude of animals, both aquatic 

 and terrestrial. For example, many waterfowl depend 

 neavily on seeds of marsh plants, while muskrat eat cat- 

 tail tubers and young shoots. Moose, caribou, black bears 

 and brown bears graze on marsh plants in Alaska (Crow 

 and Macdonald 1979). 



Although direct grazing of wetland plants is generally 

 limited, their major food value is reached upon death 

 when plants fragment to form detritus. This detritus 

 fonns the base of an aquatic food web which supports 

 higher consumers, like commercial fishes (Figure 19). 

 This relationship is especially well-documented for coast- 



al areas. Animals, like shrimp, snails, clams, worms, 

 killifish and mullet, eat detritus or graze upon the bacte- 

 ria, fungi, diatoms and protozoa growing on its surfaces 

 (Crow and Macdonald 1979; de la Cruz 1979). Many of 

 these animals are the primary food for commercial and 

 recreational fishes. Salmon are linked with wetlands and 

 detritus. Juvenile salmon in Puget Sound, Washington, 

 feed mainly on salt marsh midge larvae, which subsist on 

 detritus (Crow and Macdonald 1979). Detritus from wet- 

 land vegetation along western rivers feeds aquatic insects 

 important to the diet of resident fishes. Thus, wetlands 

 can be regarded as the farmlands of the aquatic environ- 

 ment where great volumes of food are produced annually. 

 The majority of non-marine aquatic animals depend, ei- 

 ther directly or indirectly, on this food source. 



Socio-Economic Values 



The more tangible benefits of wetlands to mankind 

 may be considered socio-economic values and they in- 

 clude flood and storm damage protection, erosion con- 

 trol, water supply and groundwater recharge, harvest of 

 natural products, livestock grazing and recreation. Since 

 these values provide either dollar savings or financial 

 profit, they are more easily understood by most people. 



