Changes in CO2 dynamics related to rainfall and water level variations in a subtropical lake

Abstract

We investigated the implications of low rainfall and reduced water level for changes in nutrients and chlorophyll-a in a subtropical lake, and how these changes affected levels and atmospheric fluxes of CO2. Based on nine consecutive years of monthly monitoring of pH, alkalinity, oxygen, and temperature, we calculated the pCO2 and CO2 flux and related these to environmental drivers. Variations in annual rainfall, with extreme low levels along 2012–2014 caused the water level to decrease up to 1 m. Low water levels were associated with higher concentrations of chlorophyll-a and organic carbon as well as reduced water transparency. Under these conditions, pCO2 increased and the lake was predominantly a source of CO2 to the atmosphere. Applying a generalized linear model, we found that water temperature, water column stability, and water level were linked to pCO2. The influences of predicted regional changes in rainfall associated with low water levels will according to our model further deteriorate the water quality and enhance CO2 emissions from the lake to the atmosphere.