Metabolism temporal dynamics in tropical lakes

We studied the metabolic rates temporal dynamics in two tropical lakes located in a rain forest catchment at southeast, Brazil, during 2011 and 2012. For that we used high frequency sensors deployed on the central deep region of the lakes. Gross primary production (GPP) and ecosystem respiration (R) were estimated using an inverse modeling approach based on variations of dissolved oxygen (DO) at the upper mixed layer. Our general hypotheses are: (1) Overall high availability of light during the whole year in the tropics allows the epilimnion to be light saturated in a substantially amount of days and even have days with some degree of photoinhibition. (2) Once the light is not a limiting factor in the surface mixed layer, the nutrients are quickly consumed, making the metalimnion and hypolimnion important sources of this resource during the deepening of the mixed layer. Thus, throughout the year, primary production in the upper mixed layer is strongly influenced by variations in mixed layer depth influencing inputs of nutrients and light available in the upper mixed layer. (3) Provided that the euphotic zone deeper than the mixed layer, a significant proportion of the phytoplankton is expected to be located in the metalimnion where more nutrients are available.