GRIL and Centre Eau Terre Environnement, Institut national de la recherche scientifique, Québec, QC, Canada; Department of Environmental Sciences, University of Basel, Basel, Switzerland.
Department of Environmental Sciences, University of Basel, Basel, Switzerland; Université Laval, Quebec, QC, Canada.
Sci Total Environ. 2019 Nov 25;693:133414. doi: 10.1016/j.scitotenv.2019.07.220. Epub 2019 Jul 16.
Mixing regime and CO availability may control cyanobacterial blooms in polymictic lakes, but the underlying mechanisms still remain unclear. We integrated detailed results from a natural experiment comprising an average-wet year (2011) and one with heat waves (2012), a long-term meteorological dataset (1960-2010), historical phosphorus concentrations and sedimentary pigment records, to determine the mechanistic controls of cyanobacterial blooms in a eutrophic polymictic lake. Intense warming in 2012 was associated with: 1) increased stability of the water column with buoyancy frequencies exceeding 40 cph at the surface, 2) high phytoplankton biomass in spring (up to 125 mg WW L), 3) reduced downward transport of heat and 4) depleted epilimnetic CO concentrations. CO depletion was maintained by intense uptake by phytoplankton (influx up to 30 mmol m d) in combination with reduced, internal and external, carbon inputs during dry, stratified periods. These synergistic effects triggered bloom of buoyant cyanobacteria (up to 300 mg WW L) in the hot year. Complementary evidence from polynomial regression modelling using historical data and pigment record revealed that warming explains 78% of the observed trends in cyanobacterial biomass, whereas historical phosphorus concentration only 10% thereof. Together the results from the natural experiment and the long-term record indicate that effects of hotter and drier climate are likely to increase water column stratification and decrease CO availability in eutrophic polymictic lakes. This combination will catalyze blooms of buoyant cyanobacteria.
混合状态和 CO 供应可能控制多型湖泊中的蓝藻水华，但潜在机制仍不清楚。我们整合了一项自然实验的详细结果，该实验包括一个平均湿润年（2011 年）和一个热浪年（2012 年）、一个长期气象数据集（1960-2010 年）、历史磷浓度和沉积物色素记录，以确定富营养化多型湖泊中蓝藻水华的机制控制。2012 年的强烈变暖与以下因素有关：1）表面的浮力频率超过 40 cph，水柱稳定性增加；2）春季浮游植物生物量高（高达 125 mg WW L）；3）向下传输的热量减少；4）表水层 CO 浓度耗尽。CO 耗尽是由于浮游植物强烈吸收（通量高达 30 mmol m d）与在干燥分层期间减少的内部和外部碳输入相结合而得以维持。这些协同作用在炎热的年份引发了浮性蓝藻的爆发（高达 300 mg WW L）。使用历史数据和色素记录进行多项式回归模型的补充证据表明，变暖解释了蓝藻生物量观察到的趋势的 78%，而历史磷浓度仅解释了 10%。自然实验和长期记录的结果表明，更热和更干燥的气候的影响可能会增加水柱分层并减少富营养化多型湖泊中的 CO 供应。这种组合将促进浮性蓝藻的爆发。
