Chapter 2 - An Overview of Inland Aquatic Habitats

Abstract

This chapter presents an overview of inland aquatic habitats. While the percentage contribution of inland fresh and saline waters to the planet's total biospheric water is insignificant (<1%), it is vital to the inland aquatic biota, terrestrial life, and our human population. Although pool-lake habitats (lentic) contain 100 times as much water as streams and rivers (lotic), most of the former is held within huge basins. Because most freshwater invertebrates are clustered within shallow photic zones of aquatic ecosystems, the relative importance of wetlands, small ponds, creeks, and rivers as aquatic habitats is much greater than their volume percentages would otherwise indicate. Many taxa of freshwater invertebrates are restricted to headwater streams and rivers by unique environmental characteristics of these ecosystems. Compared to lentic habitats, streams are generally more turbulent than lakes, and, therefore, stratification of the water mass with a thermocline is rare. Subterranean habitats include hyporheic zone within lotic systems and karst topography that are widespread in North America. Although rivers and streams are important biologically, more than 99% of the inland surface waters are in fresh and saline lakes. These standing water, or lentic, ecosystems occur in every continent, but are concentrated in the formerly glaciated regions of the northern hemisphere. Lentic ecosystems can be divided into several abiotic zones, primarily based on distance from shore, light penetration, and temperature change.