Lake and Reservoir Food Webs

Food webs are graphic representations of the flow of energy and carbon through organisms in ecological systems. In simple ecosystems, energy may flow along a simple food chain consisting of a primary producer (plants), a primary consumer, a secondary consumer, ... and a top predator.  In most ecosystems, however, the linkages among organisms are more complex and form a food web.

Primary productivity of southern Appalachian reservoirs is usually dominated by phytoplankton, which are harvested by primary consumers such as zooplankton, benthic invertebrates, and filter-feeding fish like threadfin shad (Dorosoma petenense). Another energy pathway comes from organic detritus, which is consumed by detritivores such as bottom-feeding or filter-feeding invertebrates and fishes.

At a higher trophic level, secondary consumers like predatory invertebrates and fishes feed on zooplankton and benthic invertebrates. At the top of the aquatic food web are the large piscivores(fish that eat other fish) such as the basses.

Lake and Reservoir Food Web

A generalized food-web diagram for Watts Bar Reservoir, a main-stem storage impoundment on the Tennessee River, in eastern Tennessee, illustrates the multiple trophic levels and flow of energy from producers to the top predators (Soballe and others 1992). See figure at right:

In reservoirs, productivity is usually high after initial basin inundation, but stabilizes at lower levels after 5-10 years (Ostrofsky and Duthie 1980, Kimmel and Groeger 1986).

However, microbial food webs may be more important than previously believed in the carbon cycle of lakes and reservoirs and in the flow of energy from producers to the top predators.