Bartosiewicz Maciej, Maranger Roxane, Przytulska Anna, Laurion Isabelle
Department of Environmental Sciences, University of Basel, Basel, Switzerland; Groupe de recherche interuniversitaire en limnologie (GRIL); Centre Eau Terre Environnement, Institut national de la recherche scientifique, 490 de la Couronne, Québec, Canada.
Groupe de recherche interuniversitaire en limnologie (GRIL); Département des Sciences Biologiques, Université de Montréal, C.P. 6128 succ. Centre-ville, Montréal, Canada.
Water Res. 2021 May 15;196:116985. doi: 10.1016/j.watres.2021.116985. Epub 2021 Feb 27.
Lakes are important sources of greenhouse gases (GHGs) to the atmosphere. Factors controlling CO, CH and NO fluxes include eutrophication and warming, but the integrated influence of climate-warming-driven stratification, oxygen loss and resultant changes in bloom characteristics on GHGs are not well understood. Here we assessed the influence of contrasting meteorological conditions on stratification and phytoplankton bloom composition in a eutrophic lake, and tested for associated changes in GHGs inventories in both the shallow and deep waters, over three seasons (2010-2012). Atmospheric heatwaves had one of the most dramatic effects on GHGs. Indeed, cyanobacterial blooms that developed in response to heatwave events in 2012 enhanced both sedimentary CH concentrations (reaching up to 1mM) and emissions to the atmosphere (up to 8 mmol m d). That summer, CH contributed 52% of the integrated warming potential of GHGs produced in the lake (in CO equivalents) as compared to between 34 and 39% in years without cyanobacterial blooms. High CH accumulation and subsequent emission in 2012 were preceded by CO and NO consumption and under-saturation at the lake surface (uptakes at -30 mmol m d and -1.6 µmol m d, respectively). Fall overturn presented a large efflux of NO and CH, particularly from the littoral zone after the cyanobacterial bloom. We provide evidence that, despite cooling observed at depth during hot summers, CH emissions increased via stronger stratification and surface warming, resulting in enhanced cyanobacterial biomass deposition and intensified bottom water anoxia. Our results, supported by recent literature reports, suggests a novel interplay between climate change effects on lake hydrodynamics that impacts both bloom characteristics and GHGs production in shallow eutrophic lakes. Given global trends of warming and enrichment, these interactive effects should be considered to more accurately predict the future global role of lakes in GHG emissions.
湖泊是大气中温室气体（GHGs）的重要来源。控制二氧化碳、甲烷和一氧化二氮通量的因素包括富营养化和气候变暖，但气候变暖驱动的分层、氧气损失以及由此导致的水华特征变化对温室气体的综合影响尚不清楚。在这里，我们评估了不同气象条件对富营养化湖泊分层和浮游植物水华组成的影响，并测试了三个季节（2010 - 2012年）浅水和深水中温室气体存量的相关变化。大气热浪对温室气体有最显著的影响之一。事实上，2012年因热浪事件形成的蓝藻水华增加了沉积物中甲烷的浓度（高达1毫摩尔/升）以及向大气中的排放（高达8微摩尔/平方米·天）。那年夏天，甲烷在湖泊产生的温室气体综合变暖潜势（以二氧化碳当量计）中占52%，而在没有蓝藻水华的年份这一比例为34%至39%。2012年高甲烷积累及随后的排放之前，湖面出现了二氧化碳和一氧化二氮的消耗以及不饱和状态（吸收量分别为 - 30微摩尔/平方米·天和 - 1.6微摩尔/平方米·天）。秋季水体翻转呈现出一氧化二氮和甲烷的大量外流，特别是在蓝藻水华后的沿岸带。我们提供的证据表明，尽管在炎热的夏季深处水温下降，但甲烷排放通过更强的分层和表面变暖而增加，导致蓝藻生物量沉积增加和底层水缺氧加剧。我们的结果得到了近期文献报道的支持，表明气候变化对湖泊水动力的影响之间存在一种新的相互作用，这种相互作用影响了浅水富营养化湖泊中的水华特征和温室气体产生。鉴于全球变暖和富营养化的趋势，应考虑这些相互作用效应，以便更准确地预测湖泊未来在全球温室气体排放中的作用。
