Heat-Wave Effects on Oxygen, Nutrients, and Phytoplankton Can Alter Global Warming Potential of Gases Emitted from a Small Shallow Lake

Abstract

Increasing air temperatures may result in stronger lake stratification, potentially altering nutrient and biogenic gas cycling. We assessed the impact of climate forcing by comparing the influence of stratification on oxygen, nutrients, and global-warming potential (GWP) of greenhouse gases (the sum of CH4, CO2, and N2O in CO2 equivalents) emitted from a shallow productive lake during an average versus a heat-wave year. Strong stratification during the heat wave was accompanied by an algal bloom and chemically enhanced carbon uptake. Solar energy trapped at the surface created a colder, isolated hypolimnion, resulting in lower ebullition and overall lower GWP during the hotter-than-average year. Furthermore, the dominant CH4 emission pathway shifted from ebullition to diffusion, with CH4 being produced at surprisingly high rates from sediments (1.2-4.1 mmol m(-2) d(-1)). Accumulated gases trapped in the hypolimnion during the heat wave resulted in a peak efflux to the atmosphere during fall overturn when 70% of total emissions were released, with littoral zones acting as a hot spot. The impact of climate warming on the GWP of shallow lakes is a more complex interplay of phytoplankton dynamics, emission pathways, thermal structure, and chemical conditions, as well as seasonal and spatial variability, than previously reported.

Assessment of methane and carbon dioxide emissions in two sub‐basins of a small acidic bog lake artificially divided 30 years ago

“…High temperatures amplified CH 4 emissions (Sepulveda‐Jauregui et al., ), which led to markedly higher amounts of CH 4 stored and emitted from the basins in the hotter summer of 2014 with a clear correlation between CH 4 emissions and temperature. Similar responses to regional temperature have been shown in ponds, in small shallow, and medium‐sized lakes (Bartosiewicz, Laurion, & Macintyre, ; Bartosiewicz et al., ; Encinas Fernández et al., ; Liikanen, Huttunen, Valli, & Martikainen, ; Miettinen et al., ; Natchimuthu et al., ; Room et al., ) and in enclosure experiments (Audet et al., ; Yvon‐Durocher et al., ), suggesting that in predicted warming scenarios, an increase in carbon greenhouse gas emissions can be expected in lake ecosystems regardless of DOC inputs and their biogeochemical effects in the water column (e.g., in stratification, temperature regimes, pH, microbial metabolism and CO 2 dynamics).…”

Heat‐wave effects on greenhouse gas emissions from shallow lake mesocosms

“…Furthermore, HWs might alter CH 4 emission pathways as was observed in a Canadian shallow lake where the dominant pathway of CH 4 emission shifted from ebullition to diffusion during a summer HW (Bartosiewicz et al, 2016). HWs can promote water stratification in lakes (Jankowski et al, 2006;Jeppesen, Sondergaard, Lauridsen, Liboriussen, et al, 2012) and a study of a Canadian shallow lake found that GHGs produced in the sediment were trapped in the colder water of the hypolimnion (Bartosiewicz et al, 2016). N 2 O and CH 4 fluxes might be affected by diel dynamics in light, pH (related to changes in primary production) and temperature (K€ aki, Ojala, & Kankaala, 2001).…”

“…"0" means that the HW 1 treatment did not differ significantly from the HW 2 treatment, that is, the effect of the HW did not differ from the effect of the ambient summer temperature (see "Materials and methods" and , 2014;Michaletz, Cheng, Kerkhoff, & Enquist, 2014) and for GHG processes in shallow lakes (Bartosiewicz et al, 2016;Davidson et al, 2015). It might be at least partially explained by the effect of changes in biotic interactions related to warming overriding the direct metabolism-related temperature effect on GHGs, at least for a moderate increase in temperature.…”

“…Plant-mediated fluxes across the water-air interface did not occur in our study as only submerged plants were present in the mesocosms. Consequently, when shallow lakes stratify, GHG might be released only when the water column becomes fully mixed again (Bartosiewicz et al, 2016). Although diel variation in gas fluxes is probably of significance, we assumed that this would bear no impact on our conclusions since we aimed at comparing fluxes across the different treatments and did not have focus on absolute fluxes.…”

“…HWs can severely affect the thermal regime of lakes; by way of example, the 2003 summer HW in Europe resulted in strong oxygen depletion of the hypolimnion of two deep lakes in Switzerland (Jankowski, Livingstone, B€ uhrer, Forster, & Niederhauser, 2006). Despite these adverse trends, the effect of such potentially stressful climatic events on GHG emissions is largely unknown (Bartosiewicz, Laurion, Clayer, & Maranger, 2016). Despite these adverse trends, the effect of such potentially stressful climatic events on GHG emissions is largely unknown (Bartosiewicz, Laurion, Clayer, & Maranger, 2016).…”