Bio-optical characterization of two Brazilian hydroelectric reservoirs as support to understand the carbon budget in hydroelectric reservoirs

This study aims at carrying out a bio-optical characterization of two Brazilian hydroelectric reservoirs as a support to current investigation regarding their net carbon budget. This characterization is a key step for both (1) developing bio-optical models to retrieve water constituents by remote sensing and (2) describing the availability of light for photosynthesis, whose information is essential to understand biogeochemical processes related to emissions of methane and carbon dioxide in aquatic systems. Twenty-two sampling stations were profiled at each reservoir, using an attenuation-absorption meter (ACS-WET Labs) and a set of six Ramses radiometers (TriOS). Water samples were acquired at each sampling station for determining concentrations of optically active constituents. The results showed spatial heterogeneity in the concentration of constituents which ranged from 1.17-40.45μgL¹ for chlorophyll-a, 0.26-20.41 mgL¹ for total suspended sediments, 0.93-9.48 mgL¹ for dissolved total carbon and 0.93-3.87 m¹ for CDOM absorption. The diffuse attenuation coefficient (K_d(PAR)), ranged from 0.35 to 4.03 m¹ while euphotic depth (Z_eu(1%)) ranged from 1.14 to 13.06 m.