Aquatic Ecosystems 



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Overview 



Aquatic ecosystems have 

 been especially subjected 

 to the environmental degradation that has 

 occuned over the last century in this country. 

 Nearly every activity that occurs on land ulti- 

 mately affects the receiving waters in that 

 drainage. Whether it's pesticides and herbicides 

 applied to crops, silt washed away because of 

 vegetation removal, or even atmospheric depo- 

 sition, aquatic ecosystems are a product of all 

 local disturbances regardless of where they 

 occur. In addition, waterways have been used 

 for numerous activities other than providing 

 habitat to aquatic organisms. They have been 

 altered for transportation, diverted for agricul- 

 tural and municipal needs, dammed for energy. 

 boiTOwed as an industrial coolant, and straight- 

 ened for convenience. These abuses have taken 

 their toll as evidenced by worldwide declines in 

 fisheries, monumental floods, an ever-growing 

 list of endangered aquatic species, and commu- 

 nities trying to deal with fmite water supplies. 



The traits that make aquatic ecosystems par- 

 ticularly vulnerable also make them useful for 

 monitoring environmental quality. Water serves 

 to integrate these impacts by distributing them 

 among the elements within aquatic ecosystems. 

 Although dilution is occurring, subtle changes 

 can be detected in habitats or organisms over a 

 much larger area that may be the result of a sin- 



gle point source. A clean aquatic ecosystem 

 with a healthy biological community will be 

 indicative of the condition of the terrestrial 

 habitat in the watershed, whereas the reverse 

 may not necessarily be true. 



This section features accounts of the alter- 

 ations of aquatic habitats and their impacts on 

 the biota. Evidence is presented documenting 

 habitat destroyed by dams or channelization 

 (see this section, Bogan et al.; Wlosinski et al; 

 and Wiener et al.), contaminants affecting 

 organism health {see Hesselberg and Gannon: 

 Lerczak and Sparks), wetlands affected by 

 water-level control {see Wilcox and Meeker), 

 reduced water quality {see Charles and 

 Kociolek), and introductions of exotic species 

 (see Hansen and Peck; Wiener et al.). These 

 kinds of changes have caused declining biodi- 

 versity in many groups of aquatic species rang- 

 ing from freshwater mussels to waterfowl. 



Some encouraging trends are emerging. 

 Persistent organic contaminants in the Great 

 Lakes have declined {see Hesselberg and 

 Gannon), and marginal water-quality improve- 

 ment has been accompanied by increased 

 diversity of the fish community (see Lerczak 

 and Sparks). Despite these achievements, much 

 needs to be done to effectively manage and con- 

 serve aquatic resources. As is evident from the 

 reports on diatoms (see Charles and Kociolek). 



by 



Science Editor 



Michael J. Mac 



National Biological 



Service 



1849 C St. NW 



Washington, DC 20240 



