Identifying the drivers and distributions of cyanobacteria abundances in a hypereutrophic drinking water reservoir

Abstract

Cyanobacteria are increasingly appearing as nuisance blooms in freshwater bodies worldwide, causing problems for drinking water treatment, recreation and ecology. These blooms are often the result of accelerating eutrophication caused by anthropogenic influences, such as nutrient inputs from agriculture. This study focussed on Argal Reservoir, a eutrophic lake and source of drinking water that suffers from blooms of cyanobacteria, complicating the water treatment process. Through a combination of spatially distributed data collected through fieldwork (from moorings and sampling) and long-term monitoring data from third parties, the spatial distribution and environmental drivers of cyanobacteria were investigated. Results identified vertical variations of chlorophyll and temperature within the reservoir, despite the presence of a de-stratification mixing system. Aphanizomenon Sp. and Microcystis Sp. were identified as the most dominant species of cyanobacteria in the reservoir, driven predominantly by nutrients, and demonstrated seasonal succession. Both species showed variation to their assumed preferences and therefore exhibited evidence of adapting to different environments. Further, Microcystis was identified as the species producing extremely high concentrations of cyanotoxins, including Microcystin-LR. Catchment management to reduce the sources of nutrients entering the reservoir should continue to be implemented to reduce further eutrophication. Additionally, the impact of the de-stratification system should be investigated further as it may have encouraged the transition towards Microcystis blooms due to the shallow depth of the reservoir. The simple and low-cost methods employed in this study have allowed considerable insight into the conditions within the reservoir. The same approach could be applied to other freshwater reservoirs enabling inexpensive bespoke reservoir management.