Lake-river interactions: Implications for nutrient dynamics in reservoirs

Abstract

Unlike small drainage lakes which receive nutrient inputs from relatively diffuse sources, reservoirs and other river-fed lakes receive a majority of their nutrient income from a single large source located distant from the lake’s outlet. Interactions between lake and river, which are governed by hydrology, the thermal structure of the lake, and lake morphology, will, therefore, play an important role in determining the impact and ultimate fate of influent nutrients. These interactions may also affect the manner in which nutrients are recycled and/or distributed within the reservoir or river-fed lake and lead to the establishment of longitudinal gradients in concentration. Studies conducted at DeGray Lake, Ark., and West Point Lake, Ga., both large Corps of Engineers hydropower reservoirs, provide instructive examples of some of the effects of these interactions. Both lakes exhibit longitudinal gradients in nutrient and chlorophyll concentrations which are influenced by the hydrologic characteristics of the major tributary. Exchanges of water and material between hypolimnion and epilimnion are also affected by flow regime. These exchanges play an important role in the seasonal dynamics of nutrients and metals. © 1984 Taylor & Francis Group, LLC.