Bacterioplankton abundance and its relationship with biotic and abiotic factors in nine shallow lakes of Carreiros Campus – FURG, Rio Grande – RS (Brazil)

Abstract

In this study we aimed to determine which factors control the abundance of free (FB) and attached bacteria (AB) in nine lakes at the Campus Carreiros of the Federal University of Rio Grande – FURG. Dissolved oxygen, seston weight, dissolved inorganic nutrients (ammonia, nitrite, nitrate and phosphate), chlorophyll a and the abundance of bacteria, flagellates and ciliates were investigated in a sample carried out in all lakes on September 10th 2007. There was no direct relationship between chlorophyll a and bacterial abundance, indicating that the main dissolved organic carbon source for bacteria comes from the decomposition of macrophytes and plants present in the lakes, or in their surroundings. However, it was observed a negative relationship between AB and oxygen, and a direct correlation between this kind of bacteria and seston loads. Similarly, there was a direct relationship between AB and flagellates and ciliates, suggesting a possible “Top-Down” control of attached bacteria in the lakes. On the other hand, FB were positively related to the phosphate concentration, indicating a possible “Bottom-Up” control.