Drivers of phytoplankton blooms in the Vrutci reservoir during 2014-2015 and implications for water supply and management

Abstract

In December 2013 a dense bloom of the cyanobacteria Planktothrix rubescens occurred in the Vrutci Reservoir (Western Serbia) which has been excluded from the water supply system of the City of Uzice to date. As the Vrutci reservoir has been monitored only occasionally with a low spatial resolution, the water quality data are sparse and cannot support a reliable scientic explanation on the pre-conditions that have led to the bloom through a posteriori analysis. During 2014-2015 water and sediment samples from the reservoir and its major tributaries were taken for: physico-chemical, microbiological and phytoplankton investigations. Concurrently, data on external diuse sources as well as point sources of nutrients within the watershed were collected. During the entire study period P. rubescens dominated the phytoplankton community through prolonged, consecutive blooms. The aim of this study is to search for and discover the drivers of phytoplankton blooms in the Vrutci reservoir and to dene the implications for drinking water supply and management, assuming the long term presence of P. rubescens. The study found that: a low diversity of the phytoplankton community, a low TN/TP ratio, signicant internal/external nutrient loads, a stable water column and favorable light conditions are the main drivers of cyanobacterial blooms in the Vrutci reservoir. Since the existing WTP technology is not capable of handling high cyanobacterial concentrations, an upgrade of the treatment process is recommended in terms of more ecient removal of cyanobacteria and their byproducts.