Microalgal biomass and composition of surface waterbodies in a semi-arid region earmarked for shale gas exploration (Eastern Cape Karoo, South Africa)

Abstract

Proposed hydraulic fracturing in the semi-arid Eastern Cape Karoo region has been a topic of debate over the past few years. Here, we present observations aimed at understanding the dynamics of lower trophic levels, that is the microalgal biomass and species composition in surface waterbodies of this water-scarce region. Thirty-three waterbodies were sampled (13 natural depressions, 9 dams, 11 rivers) during November 2014 (austral spring) and April 2015 (austral autumn). PERMANOVA results indicate that no significant difference was observed for microalgal biomass between waterbody types and sampling events. However, microalgal assemblage data showed a dominance of different algal classes between waterbody types (with depression wetlands and dams dominated by chlorophytes and rivers dominated by diatoms) during both sampling periods and in both biotopes. Some mixing of assemblages (wind- or flow-induced) or exchange between biotopes was found to take place. Several environmental predictors were significantly associated with microalgal assemblage composition according to distance-based Redundancy Analysis (dbRDA) ordinations, most notably, turbidity and light attenuation. Ongoing monitoring initiatives in face of the impending hydraulic fracturing activities should include a comprehensive species-level diversity census, which could further inform management of any impacts associated with this potential disturbance.