Impact of water-level fluctuations on cyanobacterial blooms: options for management

Abstract

Climate change can promote harmful cyanobacteria blooms in eutrophic waters through increased droughts or flooding. In this paper, we explore how water-level fluctuations affect the occurrence of cyanobacterial blooms, and based on the observations from case studies, we discuss the options and pitfalls to use water-level fluctuations for lake and reservoir management. A drawdown in summer causes an increase in retention time and increased water column nutrient concentrations and temperature of shallow water layers, which may lead to severe cyanobacterial blooms. This effect can potentially be counteracted by the positive response of submerged macrophytes, which compete for nutrients with cyanobacteria, with a higher chance of cyanobacterial blooms under eutrophic conditions. The balance between dominance by submerged macrophytes or cyanobacteria is temperature sensitive with stronger positive effects of drawdown as inhibition of cyanobacterial blooms expected in colder climates. Complete drying out reduces the amount of cyanobacteria in the water column after refilling, with lower water nutrient concentrations, lower fish biomass, lower abundance of cyanobacteria, higher transparency, and higher cover of submerged plants compared to lakes and reservoirs that did not dry out. Water-level rise as response to flooding has contrasting effects on the abundance of cyanobacteria depending on water quality. We conclude that waterlevel fluctuation management has potential to mitigate cyanobacterial blooms. However, the success will depend strongly on ecosystem properties, including morphometry, sediment type, water retention time, quality of inlet water, presence of submerged vegetation or propagules, abundance of fish, and climate.

Toxic cyanobacteria and cyanotoxins in European waters – recent progress achieved through the CYANOCOST Action and challenges for further research

“…Biomanipulation can be successful in lakes where the external and internal loading have been reduced as it can promote the development of submerged macrophytes and help to move from a turbid state to a clear water state (Noordhuis et al, 2016;Triest et al, 2016). This holds true for water-level management (Bakker and Hilt, 2016). Cyanocides can also be used to reduce the cyanobacterial biomass regardless of the cyanobacterial species.…”

Evaluation of several end-of-pipe measures proposed to control cyanobacteria

“…Plant extracts are often used as synonyms for allelochemicals, despite no proof on their exudation from living plants to the surrounding water exists. The effects of living plants on mitigation of cyanobacterial nuisance are reviewed elsewhere in this issue (Bakker and Hilt 2016). Here we add a few words on allelochemicals, as they might contribute to stabilization of clear water states in shallow lakes (Hilt and Gross 2008).…”

“…Several of these curative measures, such as the application of cyanocides and algicides (Jancula et al 2016), and manipulations of the food web through macrophytes (Bakker and Hilt 2016) and artificial mixers (Visser et al 2016) have been dealt with elsewhere in this special issue. Nonetheless, many products remain of which quite a number often have been proposed to water authorities as end-all solutions in controlling cyanobacteria, especially following upon the typical heat waves of 2003 and 2006 with numerous cyanobacterial bloom events in northwestern and central Europe.…”

Potential effects of mechanically removing macrophytes on the phytoplankton community of a subtropical reservoir

“…This process has significant implications in subtropical water bodies, such as the Piraquara II reservoir, as phosphorus is the main factor promoting phytoplankton growth at these latitudes (Aubriot et al 2000;Downing et al 2001;Perkins & Underwood 2001;Horn 2003;Figueredo et al 2016). Phosphorus concentrations in sediments can reach up to 100 times that in the water column (Sondergaard et al 2003), and harmful cyanobacteria usually constitute the most favored group (Bakker & Hilt 2015), posing a serious threat to aquatic organisms and human beings, either by producing secondary metabolites, such as toxins and allelopathic compounds (Leflaive & Ten-Hage 2007;Pearl & Huisman 2009) or by drastically changing the physical and chemical parameters, including the sediment-water interface (Zhu et al 2013). Algal accumulations also interfere with water treatment, making the elimination of organic matter and toxins more time consuming and expensive (Hitzfeld et al 2000;Villacorte et al 2015).…”