Controlling blooms of Planktothrix rubescens by optimized metalimnetic water withdrawal: a modelling study on adaptive reservoir operation

Abstract Background Aggregations of cyanobacteria in lakes and reservoirs are commonly associated with surface blooms, but may also occur the metalimnion as subsurface or deep chlorophyll maxima. Metalimnetic blooms great concern when potentially toxic species, such Planktothrix rubescens, involved. P. rubescens have apparently increased frequency severity recent years, so there is a strong need to identify reservoir management options control it. We hypothesized that can be suppressed using selective withdrawal maximize its export from reservoir. expect altering light climate affect dynamics this species. tested our hypothesis Rappbode Reservoir (the largest drinking water Germany) by establishing series scenarios based on calibrated quality model (CE-QUAL-W2). Results The novel strategy, which withdrawn certain depth below within instead at fixed elevation relative dam wall, significantly reduced biomass According simulation results, we defined an optimal volume approximately 10 million m 3 (10% volume) during bloom phase. results illustrated growth most effectively if metalimnetic applied early stage rapid growth, i.e., before occurs. In addition, study showed gradually decreased increasing extinction nearly disappeared coefficient exceeded 0.55 −1 . Conclusions Our indicates rise offset well reducing intensity beneath surface. Considering widespread occurrence stratified worldwide, believe will helpful for scientists managers working other bodies minimize negative impacts harmful cyanobacteria. serve transferable tool explore local standing waters.