Forecasting the magnitude and composition of phytoplankton blooms in a eutrophic lowland river (Rivière Yamaska, Que., Canada)

Abstract

The mechanisms controlling phytoplankton biomass and composition in the lower reach of the eutrophic (total phosphorus > 100 μg P·L−1) Rivière Yamaska were studied over six consecutive summers characterized by high (2008–2009) and low (2012–2013) discharge conditions. In the lower river reach, periods of low river discharge favoured planktonic blooms (>20 μg Chl-a·L−1) dominated by centric diatoms, in sharp contrast with numerous public reports of simultaneous occurrence of cyanobacterial proliferation in the upstream lakes and reservoirs. Daily cycles of hourly dissolved oxygen production were disrupted by floods but resumed in the days following flow abatement and persisted under low discharge conditions, suggesting that booms in the lower river reach resulted from local production rather than advection from upstream reservoirs. Motile, flagellate chlorophytes and cryptophytes were more important under extreme high and low discharge conditions, whereas cyanobacteria co-occurred with centric diatoms under intermediate discharge and highly illuminated conditions. Although the Rivière Yamaska’s flow remained sufficient to avoid cyanobacterial proliferation even under lowest discharge conditions, our results suggest that increasing water residence time, either through severe drought or river damming, will amplify the risk of toxic algal blooms in the free-flowing reaches of the lower Rivière Yamaska.

Environmental factors controlling phytoplankton dynamics in a large floodplain river with emphasis on cyanobacteria

“…Annual variation in discharge and water level further complicates understanding in large river ecosystems. Shifting water levels, seasonally and annually, change residence times, connectivity, and riparian/littoral interactions (K. K. Baker & Baker, 1981;Remmal, Hudon, Hamilton, Rondeau, & Gagnon, 2017). Light and temperature also change seasonally, and timing of water level shifts is highly correlated with seasonal changes in discharge relating to thaw and overland runoff.…”

“…Differential sinking rates of taxa depend on buoyancy (Baker & Baker, 1981) and the shape of cells (Reynolds & Irish, 1997). Different sinking rates interact with water velocity and turbulence (Bouma-Gregson, Power, & Bormans, 2017;Reynolds, 1994) to drive highly variable taxa-specific light environments for species living in riverine environments (Remmal et al, 2017;Reynolds & Descy, 1996). Seasonal shifts in overland runoff change sediment load and directly impact light availability for benthic and water column primary producers.…”

Hydrological management strategies for the control of algal blooms in regulated lowland rivers

“…During the dry season, the hydrodynamic conditions of the estuary backwater area of eutrophic lowland rivers are weakened (Ha et al, 2002), and the water is prone to stratification and nutrient backflow replenishment, which provides suitable conditions for the growth and accumulation of planktonic algae (Johnson et al, 2016;Pilkaityte & Baziukas, 2020). The special hydrodynamic conditions formed in the estuary backwater area of eutrophic lowland rivers have become an important driving factor for the outbreak of algal blooms in rivers (Remmal et al, 2017). However, our understanding of this physical-chemical-biological nonlinear coupling mechanism is insufficient (Pedersen, Göthe, Larsen, et al, 2016;.…”

Zoning the risk of transporting phytoplankton blooms from multiple reservoirs to the primary drinking water intake in Uruguay

“…Arti cial reservoirs can accumulate substantial amounts of cyanobacterial biomass, posing the constant risk of downstream transport of these organisms (Grill et al, 2019;Remmal et al, 2017). Furthermore, these reservoirs may experience over ow during heavy rainfall, leading to the transport of large quantities of biomass (Aubriot et al, 2020;Grabowska & Mazur-Marzec, 2011).…”