A link exists between global warming and the worldwide proliferation of harmful cyanobacterial blooms.

https://science.sciencemag.org/content/sci/320/5872/57.full.pdf

Blooms like it hot

The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change

While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2009.54.6_part_2.2283

Lakes as sentinels of climate change

Climate change: links to global expansion of harmful cyanobacteria.

Cyanobacteria are the Earth's oldest known oxygen-evolving photosynthetic microorganisms, and they have had major impacts on shaping our current atmosphere and biosphere. Their long evolutionary history has enabled cyanobacteria to develop survival strategies and persist as important primary producers during numerous geochemical and climatic changes that have taken place on Earth during the past 3.5 billion years. Today, some cyanobacterial species form massive surface growths or 'blooms' that produce toxins, cause oxygen depletion and alter food webs, posing a major threat to drinking and irrigation water supplies, fishing and recreational use of surface waters worldwide. These harmful cyanobacteria can take advantage of anthropogenically induced nutrient over-enrichment (eutrophication), and hydrologic modifications (water withdrawal, reservoir construction). Here, we review recent studies revealing that regional and global climatic change may benefit various species of harmful cyanobacteria by increasing their growth rates, dominance, persistence, geographic distributions and activity. Future climatic change scenarios predict rising temperatures, enhanced vertical stratification of aquatic ecosystems, and alterations in seasonal and interannual weather patterns (including droughts, storms, floods); these changes all favour harmful cyanobacterial blooms in eutrophic waters. Therefore, current mitigation and water management strategies, which are largely based on nutrient input and hydrologic controls, must also accommodate the environmental effects of global warming.

Climate change: A catalyst for global expansion of harmful cyanobacterial blooms

Dense surface blooms of toxic cyanobacteria in eutrophic lakes may lead to mass mortalities of fish and birds, and provide a serious health threat for cattle, pets, and humans. It has been argued that global warming may increase the incidence of harmful algal blooms. Here, we report on a lake experiment where intermittent artificial mixing failed to control blooms of the harmful cyanobacterium Microcystis during the summer of 2003, one of the hottest summers ever recorded in Europe. To understand this failure, we develop a coupled biological-physical model investigating how competition for light between buoyant cyanobacteria, diatoms and green algae in eutrophic lakes is affected by the meteorological conditions of this extreme summer heatwave. The model consists of a phytoplankton competition model coupled to a one-dimensional hydrodynamic model, driven by meteorological data. The model predicts that high temperatures favour cyanobacteria directly, through increased growth rates. Moreover, high temperatures also increase the stability of the water column, thereby reducing vertical turbulent mixing, which shifts the competitive balance in favour of buoyant cyanobacteria. Through these direct and indirect temperature effects, in combination with reduced wind speed and reduced cloudiness, summer heatwaves boost the development of harmful cyanobacterial blooms. These findings warn that climate change is likely to yield an increased threat of harmful cyanobacteria in eutrophic freshwater ecosystems.

/pdf/summer-heatwaves-promote-blooms-of-harmful-cyanobacteria-4a7gf8ngzr.pdf

Summer heatwaves promote blooms of harmful cyanobacteria

The intriguing impact of physical mixing processes on species interactions has always fascinated ecologists. Here, we exploit recent advances in plankton models to develop competition theory that predicts how changes in turbulent mixing affect competition for light between buoyant and sinking phytoplankton species. We compared the model predictions with a lake experiment, in which the turbulence structure of the entire lake was manipulated using artificial mixing. Vertical eddy diffusivities were calculated from the measured temperature microstructure in the lake. Changes in turbulent mixing of the lake caused a dramatic shift in phytoplankton species composition, consistent with the predictions of the competition model. The buoyant and potentially toxic cyanobacterium Microcystis dominated at low turbulent diffusivity, whereas sinking diatoms and green algae dominated at high turbulent diffusivity. These findings warn that changes in the turbulence structure of natural waters, for instance driven by climate change, may induce major shifts in the species composition of phytoplankton communities.

/pdf/changes-in-turbulent-mixing-shift-competition-for-light-4u5vjuow31.pdf

Changes in turbulent mixing shift competition for light between phytoplankton species

The problem of Lake Nieuwe Meer (area = 1.3 km 2 , max. depth 30 m, Ptot = 500 mg/m 3 ) was extensive growth of Microcystis with disturbing scum forming. Since 1993 the lake has been artificially mixed in summer by a bubble plume installation. The result is quite successful since the mass of Microcystis is up to 20 times lower than in the years before mixing and no scum is present any more. The study in Lake Nieuwe Meer showed a shift from cyanobacterial dominance (mainly Microcystis) to flagellates, green-algae and diatoms when artificial mixing was applied. Total phosphorus and nitrogen concentrations did not change as a result of mixing and had apparently no effect on the shift in the phytoplankton composition. The chlorophyll- a concentration was much lower in the mixed lake as a result of dilution. The total algae biomass decreased. The transparency did not improve. The total heat energy of the lake is slightly higher than before mixing but still remains in the range of annual fluctuation. The temperature on the surface is approximately 2°C lower. In the whole water-body oxygen was always higher than 5 mg/l. Living space for fish is therefore wider. The installation in Lake Nieuwe Meer consists of flexible pipes near the sediment, built in a way to prevent sediment erosion and transport into the water. There are no constructions in the water-body. All mechanical parts are on land. The layout of the installation is shown in Fig. 1. Installed compressor energy is 85 kW. This is equivalent to an upper middle-class motor-car. The design was made specifically for this problem. It is based on the physical data of the algae and the plant. It would be beneficial to use this 7 years' experience for further applications e.g. elimination of toxic algae in drinking-water reservoirs.

/pdf/artificial-mixing-to-reduce-growth-of-the-blue-green-alga-3l8mjuu0rg.pdf

Artificial mixing to reduce growth of the blue-green alga Microcystis in Lake Nieuwe Meer, Amsterdam: an evaluation of 7 years of experience

Water managers worldwide are facing the serious problem of dense blooms of cyanobacteria in surface waters. In the quest for the optimal method to combat cyanobacterial dominance, many questions and many possible solutions arise. This paper presents a three-phase strategy to fight harmful cyanobacterial proliferation. Water managers who apply this strategy can generate a tailor-made set of measures. The three phases consist of (1) defining the ecological water quality targets of the waterbody in question, (2) assessing its current ecological state, and (3) selecting which measures will yield optimal results. The paper provides assistance in the quantitative diagnosis of the state of both shallow and deep temperate freshwater lakes by means of a lake system analysis, and presents a survey of measures. Measures are divided into two sets. Preventive measures are based on switching to a clear state (shallow lake) or reducing the overall cyanobacterial biomass (deep lake). They are subdivided into nutrient reduction, hydromorphological adjustments, and food web management. Concerning nutrient reduction, in many situations phosphorus management alone should suffice. Nitrogen management can be important to increase the species diversity of macrophytes, or to relieve downstream (marine) consequences. Control measures (including mitigation) have a direct impact on cyanobacterial blooms by biomass removal, flushing, or mixing; however, the number of proven technologies is limited.

/pdf/how-to-combat-cyanobacterial-blooms-strategy-toward-lwrmcxjy87.pdf

How to combat cyanobacterial blooms: strategy toward preventive lake restoration and reactive control measures

Artificial mixing to reduce growth of the blue-green alga Microcystis in Lake Nieuwe Meer, Amsterdam: the design of the aeration system and an overview of 6 years experience

J. Stroom

Papers

Summer heatwaves promote blooms of harmful cyanobacteria

Changes in turbulent mixing shift competition for light between phytoplankton species

Artificial mixing to reduce growth of the blue-green alga Microcystis in Lake Nieuwe Meer, Amsterdam: an evaluation of 7 years of experience

How to combat cyanobacterial blooms: strategy toward preventive lake restoration and reactive control measures

Artificial mixing to reduce growth of the blue-green alga Microcystis in Lake Nieuwe Meer, Amsterdam: the design of the aeration system and an overview of 6 years experience