The Serial Discontinuity Concept and other Factors affecting the Diversity and Abundance of Ephemeroptera (Mayflies) in the Green River

Tristan Leong

Modern society is vitally linked to its water resources for direct consumption as well as transportation, agriculture, recreation, and power generation. As a result, most major rivers in the United States have been impounded by human-made dams, which alter a river’s dynamic natural processes, also called “natural flow regime.” Changes to a river’s natural flow regime may dramatically affect its geologic integrity, biotic community, and ecosystem function.

Consequently, many have proposed guidelines to assist river conservation and restoration efforts to reproduce a river’s natural dynamic character. (Poff et. al1997) Still others such as Stanford and Ward (2001) suggest that riverine processes and function will eventually recover downstream from a point of disturbance with the natural addition of tributary inputs, as described by their Serial Discontinuity Concept. A major contention to this argument however is that, rivers are characteristically dynamic entities, influenced by many factors, and rarely exist entirely within the framework of either the SDC or other ecological theories we describe. Consequently, ecologists and geomorphologists such as Stanford and Ward, are constantly updating their theories in order to “better describe” the functioning of these dynamic river ecosystems.

While the Serial Discontinuity Concept has been discredited in some cases (Powell et. al 2005), it may help provide the framework for accurately describing some riverrine phenomena, such as the assessment of lower level invertebrate communities. For example, when examining aquatic communities such as those found in the Green River of Utah and Colorado, Stanford and Ward described downstream trending improvements found by Mark Vinson (2001), which showed an increased aquatic invertebrate diversity downstream from a major impoundment. This dataset appears to show a strong association with the SDC theory because aquatic invertebrate communities replenish diversity downstream. It is the purpose of this paper to closely analyze this dataset in order to examine the original SDC as it pertains to predictions concerning the effects on aquatic invertebrate communities. In doing so, this paper focuses on how aquatic invertebrates can be used as measures of biotic change, with specific emphasis on Green River mayflies.