Fish Bulletin 141. Artificial Destratification of El Capitan Reservoir By Aeration. Part I: Effects on Chemical and Physical Parameters

Most lower elevation California lakes experience one yearly cycle of stratification. Thermal stratification generally starts about March and extends through November, greatly influencing chemical and biological stratification. The metalimnion and hypolimnion of eutrophic lakes often are devoid of oxygen. Concomitant with the oxygen deficit is the build-up of anaerobic decomposition products and the exclusion of biota from the oxygen deficient zones.Artificial destratification by aeration reduces or eliminates thermal stratification. Oxygen is distributed to all depths and products of anaerobic decomposition are oxidized. Barriers to biotic distribution are minimal.The diffuse aeration system is probably the most effective for destratifying large lakes. Other methods are discussed.Artificial lake destratification increases the lakes's heat budget. The winter temperature regime is not affected by destratification. Summer surface temperatures during stratified and destratified periods are about equal. Bottom temperatures are greatly increased by destratification and may equal the surface temperatures. The coldest water temperature in a destratified lake may approach those found at the lake's surface during stratified periods. This increased heat content should benefit the fishery by increasing invertebrate forage production and decomposition of organic sediments. However, increased bottom temperatures may eliminate or preclude the establishment of a coldwater fishery.Two hypolimnion aeration systems are discussed. These systems aerate the bottom waters without causing thermal destratification and enhance coldwater fisheries.Lake aeration is economically feasible. Evaporation and chemical treatment savings alone may more than pay for the aeration system. Improved drinking water quality and fishery habitats results from aeration.This report is the first of a series describing our El Capitan Reservoir destratification study. Subsequent reports will describe the effects of artificial destratification on the zoobenthos, phytoplankton and fishes