Aquatic Ecosystems

Courtesy J.G. Wiener, NBS

by
Science Editor
Michael J. Mac
National Biological Service
1849 C St. NW
Washington, DC 20240

Aquatic Ecosystems
*Overview*
Aquatic ecosystems have been especially subjected to the environmental degradation that has occurred over the last century in this country. Nearly every activity that occurs on land ultimately 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 deposition, 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 agricultural and municipal needs, dammed for energy, borrowed as an industrial coolant, and straightened 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 communities trying to deal with finite water supplies.
The traits that make aquatic ecosystems particularly 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 single 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 alterations 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 biodiversity in many groups of aquatic species ranging from freshwater mussels to waterfowl.

Habitat loss on a stretch of the Mississippi River modified for navigation (shown here) contrasts with a diverse complex of habitats on less developed areas of the Upper Mississippi River (see plate previous page). Courtesy J.G. Wiener, NBS

Some encouraging trends are emerging. Persistent organic contaminants in the Great Lakes have declined (see Hesselberg and Gannon), and marginal water-quality improvement 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 conserve aquatic resources. As is evident from the reports on diatoms (see Charles and Kociolek), algae (see Moe), and protozoa (see Lipscomb), little is known of the national trends in their populations, diversity, or biomass. Our knowledge of these groups is poor even though they provide basic functions of photosynthesis, production, and decomposition critical to the normal functioning of aquatic ecosystems.

Without increased monitoring, some very basic attributes of aquatic systems may be unknowingly lost or severely degraded. Groups of species that seem insignificant actually are critical parts of a food web that supports valuable commercial and sport species. Subtle changes such as losses of island habitat and constant water depth or level may lead to drastic declines in productivity or diversity (see Wlosinski et al.; Wilcox and Meeker). The loss of some of these integral pieces of ecosystems may be impossible to restore. The unsuccessful attempt to restore self-sustaining lake trout populations in the Great Lakes, despite massive efforts, exemplifies this (see Hansen and Peck).