Is the future blue-green? A review of the current model predictions of how climate change could affect pelagic freshwater cyanobacteria

Abstract

There is increasing evidence that recent changes in climate have had an effect on lake 10 phytoplankton communities and it has been suggested that it is likely that Cyanobacteria will 11 increase in relative abundance under the predicted future climate. However, testing such a 12 qualitative prediction is challenging and usually requires some form of numerical computer 13 model. Therefore, the lake modelling literature was reviewed for studies that examined the 14 impact of climate change upon Cyanobacteria. These studies, taken collectively, generally 15show an increase in relative Cyanobacteria abundance with increasing water temperature, 16 decreased flushing rate and increased nutrient loads. Furthermore, they suggest that whilst 17 the direct effects of climate change on the lakes can change the timing of bloom events and 18Cyanobacteria abundance, the amount of phytoplankton biomass produced over a year is not 19 enhanced directly by these changes. Also, warmer waters in the spring increased nutrient 20 consumption by the phytoplankton community which in some lakes caused nitrogen 21 limitation later in the year to the advantage of some nitrogen-fixing Cyanobacteria. Finally, it 22 is also possible that an increase in Cyanobacteria dominance of the phytoplankton biomass 23 will lead to poorer energy flow to higher trophic levels due to their relatively poor edibility 24 for zooplankton. 25 26 KEYWORDS: 27 lake modelling, nitrogen limitation, phenology, water quality, eutrophication 28 3 29

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

“…Furthermore, increasing nutrient loading, warming climate and growing CO2 emissions are likely to favour cyanobacterial expansion in a broad range of aquatic ecosystems (Paerl and Huisman, 2009). However, the effect of environmental change on phytoplankton blooms and its consequences on water quality has only been addressed recently for lakes (Elliott, 2012;Thackeray et al, 2008), and not yet tackled for river systems, except through some qualitative description of potential impacts by Arnell et al (2015), Johnson et al (2009) and Whitehead et al (2009). These studies agree that phytoplankton are likely to increase their concentration above current levels in the future (Johnson et al, 2009), due to lower flows, reduced velocities and higher water residence (Whitehead et al, 2009), also reducing oxygen levels in rivers (Whitehead et al, 2009).…”

The past and future of phytoplankton in the UK's largest lake, Lough Neagh

“…Cyanobacteria may also pose problems in water treatment works with some toxins difficult to remove, especially during bloom periods (Hitzfeld et al, 2000). Furthermore, in a future with a warmer climate, cyanobacteria are predicted to become more prevalent (Carey, et al, 2012;Elliott, 2012). As Lough Neagh is the most important drinking water reservoir in Northern Ireland, supplying daily drinking water to approximately 1 million people, it is useful to understand and predict the behaviour of these cyanobacteria.…”

Advancing projections of phytoplankton responses to climate change through ensemble modelling

“…However, most studies that simulate future impacts on lake phytoplankton have utilised only a single mechanistic model (Mooij et al, 2007;Trolle et al, 2011;Elliott, 2012). Whilst such studies have merit, the advantage of applying multiple, independently developed models -i.e., an ensemble modelling approach -to a given lake system is that some of the inherent uncertainties in the individual model projections can be reduced by conveying the mean and range of the projections.…”