Diel patterns of temperature, conductivity and dissolved oxygen in an Amazon floodplain lake: description of a friagem phenomenon

Abstract

AIM: The aim of this work was to study the diel stratification parameters temperature, dissolved oxygen and conductivity, providing a more detailed description of a friagem event. METHODS: the mixing behavior of the limnetic water column in Lago Catalão, an Amazon floodplain lake flooded by two of the world’s largest rivers (Solimões and Negro), was studied through diel profiling of temperature, conductivity and dissolved oxygen, between 2006 and 2007. Measurements were made every four hours at 1m depth intervals to the lake bottom. RESULTS: The water column remained stratified during most of the year with the exception of one month with low water level, when nocturnal mixing occurred and one friagem event during high water (May 2007) when an isothermal temperature profile and an atypical orthograde oxygen profile were observed. CONCLUSIONS: The friagem event, a large drop in air temperatures due to the intrusion of a polar air mass in the Amazon, constitutes an important force in the dynamics of the water column, which produces a profound redistribution of dissolved gases and solutes in the system. This is the first time that the effects of the friagem on the mixing patterns in a lowland Amazon lake have been documented in detail. The decline in air temperature, observed during the friagem event destabilized the normally stratified water column, which can be associated with an environmental disturb.