Diurnal Changes in Lake Systems

Abstract

Environmental conditions may change markedly within aquatic ecosystems during a 24-h period. Solar radiation varies from high intensity at midday to darkness. Surface temperatures and concentrations of dissolved gases also may fluctuate between extremes of day and night, especially in shallow, littoral areas. Organisms within the lake may move vertically or otherwise relocate themselves in response to these environmental changes. For example, various species of Zooplankton undergo marked vertical migrations during a 24-h cycle [cf., Hutchinson (1967) and Wetzel (1983, 1999)]. These movements are keyed to light, food availability, and predation pressures. In this exercise, we shall examine some of the relationships between these factors and the vertical movements of Zooplankton in a lake.