Ch. 3— Wetland Values and the Importance of Wetlands to Man • 51 



Estuarine Systems. — Input-output studies are 

 more difficult to conduct in estuarine or marine en- 

 vironments owing to tidal fluctuations. Nine estua- 

 rine studies were screened using the same criteria 

 used for the freshwater studies. Findings from a 

 single acceptable study (91) are reported in table 

 4. These results suggest that nitrogen was exported 

 from a Massachusetts salt marsh. 



Evaluating Wetlands for Water Quality. — 



To evaluate the value of a wetland for improving 

 water quality, a number of factors must be con- 

 sidered. First is the condition of water in the water 

 body adjacent to the wetlands. In many lakes, 

 estuaries, and rivers, excessive nutrient concentra- 

 tions cause undesirable algal blooms. In other 

 bodies of water, however, desirable levels of 

 primary productivity may be limited by a lack of 

 these nutrients. If these waters have phytoplankton- 

 based food chains, low nutrient concentrations can 

 result in low productivity at all levels of the food 

 chain. In this case, nutrients would be considered 

 beneficial and not pollutants. 



The reduction of excess nutrients necessary to 

 bring about an improvement in water quality is 

 another consideration. For instance, an evaluation 

 of a proposal to reconstruct wedands along the Kis- 

 simmee River in Florida and thereby reduce nutri- 



ent loadings to Lake Okeechobee, concluded that 

 a 50-percent reduction in phosphorous loadings 

 would improve water quality, but a 10-percent re- 

 duction would have little effect (41). In another 

 study, lake-edge wetlands in Wisconsin did retain 

 nitrogen and phosphorus; however, the levels of nu- 

 trients flowing out of the wetland still were high 

 enough to cause excessive algal growth (47). 



The timing of nutrient inputs and outputs also 

 is important. A study of phosphorus inputs and out- 

 puts from a forested riverine wetland in Illinois 

 found that while the swamp took in 1 1 times more 

 phosphorus than was discharged, nearly all of it was 

 retained during flood periods (52). 



Disease-Causing Micro-Organisms 



Viruses and bacteria from sewage effluent or run- 

 off from pastureland may contaminate drinking wa- 

 ter, recreational water, and commercial fisheries. 

 Because these micro-organisms are adsorbed onto 

 particles suspended in the water column, they may 

 be trapped along with the suspended material by 

 wetlands. Pathogens can remain for many months 

 in the soil matrix where they may be exposed to 

 ultraviolet radiation or attacked by chemicals and 

 other organisms, or they may naturally die off. 



Table 4.— Summary of Input-Output Studies 



Artificial/ 

 Reference Wetland type Location natural 



Crisp (1966) Peat bog Britain N 



tvlitsch, et al. (1977) Flood plain Illinois N 



swamp 



Boyt, et al. (1977) Riverine Florida A 



swannp 



Dierberg and Brezonik (1978) . . Cypress Florida A 



swamp 



Novitzki (1978) Fresh marsfi Wisconsin N 



Yonika and Lowry (1979) Fresh marsh Massa- A 



shrub swamp chusetts 

 Zoltek and Bayley (1979) Fresh marsh Florida A/N 



Valiela, et al. (1975) Salt marsh Massa- N 



chusetts 



Including ground water dilution calculated by chloride budget. 



SOURCE: References cited in column 1. 



Sampling frequency/duration Pollutant 



Input Output 

 (kg/ha/yr) 



Percent 

 change 



Weekly/1 year 



745 

 38-57 



4,864 

 71 



+ 552 

 ■^ 25 - - 87 



Monthly and bimonthly 



8,127 



7,694 



Monthly/1 year 



90.0 



11.5 



-87 



Monthly/2 years 



144 

 113 



12 



-91 

 -96 



Monthly (stream, wells); N 233 183 -21 



periodically (runoff)/3 years P 5.0 4.6 -8 



Sediment 3,909 735 -81 



Monthly and bimonthly/ 

 1 year 



4,782 

 859 



1,817 

 205 



-62 

 -76 



Monthly/2 years 



3,565 



2,284^ 



-36 



Monthly/1 year 



N(nat.) 26,252 31,604 



+ 20 



