Hydrogen peroxide measurements in subtropical aquatic systems and their implications for cyanobacterial blooms

Hydrogen peroxide is widely recognized as the most stable of the reactive oxygen species ( ROS) produced by both biotic and abiotic pathways in natural waters. Its high reactivity in mediating redox transformations may, directly or indirectly, affect aquatic ecosystem functions, including primary productivity. However, environmental interactions between photoautotrophs, particularly cyanobacteria, and hydrogen peroxide are poorly understood. To gain a better understanding of hydrogen peroxide and cyanobacterial interactions, we determined the hydrogen peroxide concentrations in the presence and absence of cyanobacterial blooms in southwest Florida. Hydrogen peroxide concentrations were determined using a fast response amperometric hydrogen peroxide microelectrode. Our measurements ranged from 0 to 5.3 mu M in freshwater bodies (ponds, lakes and the Caloosahatchee River) and 0 to 92.9 mu M in rainwater. In general, hydrogen peroxide levels were highly associated with cyanobacterial bloom conditions, indicating the potential role of cyanobacteria in hydrogen peroxide production in freshwater. To determine the potential biodegradation of hydrogen peroxide during sample transportation in the dark condition, water samples were passed through 0.2 mu m pore size filters immediately after sampling and compared with unfiltered water samples in the laboratory. We found that filtered water samples retained higher concentrations of hydrogen peroxide than unfiltered samples with a mean biodegradation rate of 44 +/- 10.6 nmol/h. Out of a total of 26 samples, only one unfiltered sample showed a higher hydrogen peroxide concentration than the filtered samples. Overall, our study found the microelectrode technique could accurately measure hydrogen peroxide concentrations in the samples from various freshwater bodies. This measurement method revealed that hydrogen peroxide concentrations vary with temporal and spatial dynamics of cyanobacterial blooms.