| 1. |
- Ayala, Ana I., et al.
(författare)
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Analysis of summer heat budget of lakes under a changing climate across a geographic gradient
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Warming surface water temperature is the most direct consequence of climate change in lakes and therefore, predicting the heat exchange at the air-water interface is important to understand how atmospheric forcing will affect lake temperature and thermal structure. Here, we forced a one-dimensional hydrodynamic lake model with outputs from four different climate models under three future greenhouse gas emission scenarios from 1976 to 2099. To investigate the changes in summer (June to August or December to February in the northern or southern hemisphere, respectively) net surface heat flux and the individual flux components for 47 lakes with varying in size and geographic location were analysed. The results show that in the most extreme case (RCP 8.5) summer lake surface temperature is projected to increase by 4.72±0.70 °C by the end of the 21st century, due to increasing absorption of solar radiation (17.40±8.81 W m-2) and of long-wave radiation (33.01±5.44 W m-2). The increased lake surface temperature, also lead to higher heat losses to the atmosphere by outgoing long-wave radiation (27.54±4.07 W m-2) and by latent heat flux (25.10±7.37 W m-2), while a lower heat loss by sensible heat flux is projected (-3.20±1.94 W m-2). Altogether, the net heat balance and thus the accumulation of heat in the lakes over summer remains almost unchanged. However, a shift in the contributions of the individuals heat fluxes is projected, with the latent heat flux gaining relative importance.
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| 2. |
- Ayala, Ana I., et al.
(författare)
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Climate Change Impacts on Surface Heat Fluxes in a Deep Monomictic Lake
- 2023
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 128:11
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent and radiative energy exchanges between lakes and the atmosphere play an importantrole in determining the process of lake-mixing and stratification, including how lakes respond to climate andto climate change. Here we used a one-dimensional hydrodynamic lake model to assess seasonal impacts ofclimate change on individual surface heat flux components in Lough Feeagh, Ireland, a deep, monomictic lake.We drove the lake model with an ensemble of outputs from four climate models under three future greenhousegas scenarios from 1976 to 2099. In these experiments, the results showed significant increases in the radiativebudget that were largely counteracted by significant increases in the turbulent fluxes. The combined change inthe individual surface heat fluxes led to a change in the total surface heat flux that was small, but sufficient tolead to significant changes in the volume-weighted average lake temperature. The largest projected changes intotal surface heat fluxes were in spring and autumn. Both spring heating and autumnal cooling significantlydecreased under future climate conditions, while changes to total surface heat fluxes in winter and summerwere an order of magnitude lower. This led to counter-intuitive results that, in a warming world, there wouldbe less heat not more entering Lough Feeagh during the springtime, and little change in net heating over thesummer or winter compared to natural climate conditions, projected increases in the volume-weighted averagelake temperature were found to be largely due to reduced heat loss during autumn.
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| 3. |
- Ayala, Ana I., et al.
(författare)
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GLOBAL WARMING WILL CHANGE THE THERMAL STRUCTURE OF LOUGH FEEAGH, A SENTINEL LAKE IN THE IRISH LANDSCAPE, BY THE END OF THE TWENTY-FIRST CENTURY
- 2023
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Ingår i: Biology and Environment (Dublin). - : Project MUSE/Royal irish academy. - 0791-7945 .- 2009-003X. ; 123B:3, s. 147-165
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in impact modelling of global warming on lakes have resulted in a greater understanding of how these vital ecosystems are likely to respond. However, there has been little quantitative analysis of this in an Irish context, despite the importance of lakes in the island's landscape. Here, we explore the impact of global warming on the hydrodynamics and thermal structure of a sentinel Irish lake under future climate scenarios. A 1D lake model, Simstrat, was calibrated and validated using water temperature data collected from Lough Feeagh, a site of long-term ecological research in the west of Ireland. Once validated, the model was then driven by daily climate model projections to generate informative thermal metrics for the time period of 2006-2099. Despite the moderating influence of the Atlantic, projections indicate that global warming will have a marked effect on the thermal structure of Feeagh, with surface water temperatures set to warm by 0.75 degrees C under a more stringent mitigation pathway (RCP 2.6) and 2.42 degrees C under a non-mitigation pathway (RCP 8.5).While warming was projected to be greatest in summer in the epilimnion, winter warming was greater than in other seasons in the hypolimnion. Stratification is projected to become more stable and earlier, and the growing season to be longer by 11 to 47 days, depending on mitigation pathways. Future studies could use a similar modelling workflow to investigate the possible implications of global warming on other Irish lakes, particularly those of specific societal importance or those of conservation interest.
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| 4. |
- Ayala, Ana I.
(författare)
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Modelling impact climate-related change on the thermal responses of lakes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In response to climate-related changes, lakes worldwide have experienced warmer surface water temperatures, shorter ice cover periods and changes in lake stratification. As these aspects of lake dynamics exert substantial control over nutrient availability, oxygenation and biogeochemical cycling, predicting changes in lake water temperature and stratification dynamics can improve our understanding of the consequences of warming on lake ecosystems. This thesis investigates the long-term and short-term (extreme event) effects of climate change on lake thermal dynamics using 1D hydrodynamic lake models.Long-term lake water temperature simulations showed that water temperatures and thermal stratification metrics were projected to clearly shift toward lake thermal conditions that are consistent with a warmer climate at the end of the 21st century, i.e. warmer surface and bottom temperatures and a stronger and longer duration of summer thermal stratification as a result of an earlier onset of stratification and later fall overturn. The simulated lake thermal structure was controlled by energy exchange between the lake surface and the atmosphere (surface heat fluxes) and wind stress. The individual surface heat flux components were projected to change substantially under future climate scenarios. However, the combined changes showed compensating effects, leading to a small overall change in total surface heat flux, that was still sufficient to lead to important changes in whole-lake temperature. On a seasonal scale, spring heating and autumnal cooling were projected to decrease, while only small changes were projected in winter and summer. An extended analysis during summer using 47 lakes showed that while all lakes gained heat during summer under all scenarios, differences in the amount of heat gained during historical and future conditions were small. Additionally, hydrodynamic lake models performed well in reproducing the magnitude and direction of changes in lake temperature and stratification metrics during storms and heatwaves. However, the lake model performance decreased in accuracy compared to non-extreme condition, which should be taken into account. 1D hydrodynamic lake models have been shown to be powerful tools to predict long-term and short-term climate-related changes in lake thermal dynamics, making an in-depth analysis of the surface heat fluxes possible.
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| 5. |
- Mesman, Jorrit P., 1993-
(författare)
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Assessing future effects on lake ecosystem resilience using data analysis and dynamic modelling : Modelling the effects of extreme weather events and climate warming on lakes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Extreme weather events can have short-term and long-term effects on lake thermal structure, nutrient dynamics, and community composition. Moreover, changes in lake variables induced by global climate change may influence the response and recovery of lake ecosystems to extreme weather events. The linkage between extreme weather and lakes includes interactions between physics and biology, and long-term and short-term dynamics, which are not yet well understood. Process-based modelling is used in this thesis to further explore this topic, and to assess how lake responses to extreme weather events may change under the influence of climate warming.Lake-internal feedback mechanisms were shown to potentially cause sudden shifts in climate-induced transitions in lake mixing regimes, with a role for extreme weather events to induce such shifts. Additionally, one-dimensional physical lake models performed well in reproducing trends in lake variables during storms and heatwaves in a study covering multiple locations and models. However, extreme weather events still presented periods of increased model uncertainty, which should be taken into account. A software package was developed to promote the use of ensemble lake modelling, which is one way to include uncertainty in model forecasting efforts. This could be particularly helpful in periods of extreme weather. With tools and theory now in place, a coupled physical-biogeochemical model was then used to assess what are the most important drivers of how lake phytoplankton responds to storms, and how this response might change with climate warming. Storm intensity, thermal structure, nutrients, and light all affected the phytoplankton concentration after storms. Moderate wind speeds had increasing effects compared to high wind speeds, but a sufficiently deep mixed layer reduced the response to wind strongly. Higher nutrients and light promoted increasing effects of wind, and higher temperatures promoted decreasing effects. The response of phytoplankton to storms did not change markedly between present-day and future-climate scenarios.This thesis furthers our understanding of the processes involved in extreme events acting on lakes. A more complete understanding is necessary to develop more reliable models and anticipate future conditions. Furthermore, modelling was shown to be a viable approach to study these events and validation data and tools were provided to increase the reliability of this method. In these times of increasing environmental pressures and changing extreme weather patterns, more insight into future effects of extreme events is much needed.
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| 6. |
- Mesman, Jorrit P., 1993-, et al.
(författare)
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Drivers of phytoplankton responses to summer wind events in a stratified lake : a modelling study
- 2022
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 67:4, s. 856-873
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Tidskriftsartikel (refereegranskat)abstract
- Extreme wind events affect lake phytoplankton amongst others by deepening the mixed layer and increasing internal nutrient loading. Both increases and decreases of phytoplankton biomass after storms have been observed, but the precise mechanisms driving these responses remain poorly understood or quantified. In this study, we coupled a one-dimensional physical model to a biogeochemical model to investigate the factors regulating short-term phytoplankton responses to summer storms, now and under expected warmer future conditions. We simulated physical, chemical and biological dynamics in Lake Erken, Sweden, and found that wind storms could increase or decrease the phytoplankton concentration one week after the storm, depending on antecedent lake physical and chemical conditions. Storms had little effect on phytoplankton biomass if the mixed layer was deep prior to storm exposure. Higher incoming shortwave radiation and hypolimnetic nutrient concentration boosted growth, whereas higher surface water temperatures decreased phytoplankton concentration after storms. Medium-intensity wind speeds resulted in more phytoplankton biomass after storms than high-intensity wind. Simulations under a future climate scenario did not show marked differences in the way wind affects phytoplankton growth following storms. Our study shows that storm impacts on lake phytoplankton are complex and likely to vary as a function of local environmental conditions.
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| 7. |
- Mesman, Jorrit P., 1993-, et al.
(författare)
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The role of internal feedbacks in shifting deep lake mixing regimes under a warming climate
- 2021
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 66:6, s. 1021-1035
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Forskningsöversikt (refereegranskat)abstract
- Climate warming is causing changes in the physics of deep lakes, such as longer summer stratification, increased water column stability, reduced ice cover, and a shallower depth of winter overturns. An ultimate consequence of warming would be a transition to a different mixing regime. Here we investigate the role of physical, chemical, and biological feedback mechanisms that unfold during a shift in mixing regime, and whether these feedbacks could prompt and stabilise the new regime. Although climate, interannual temperature variation, and lake morphometry are the main determinants of a mixing regime, when climate change causes shifts in mixing regime, internal feedback mechanisms may gain in importance and modify lake ecosystem functioning.We review the role of these feedbacks in three mixing regime shifts: from polymictic to seasonally stratified, from dimictic to monomictic, and from holomictic to oligomictic or meromictic.Polymictic lakes of intermediate depth (c. 3–10 m mean depth) could experience seasonal stratification if a stratification event triggers phytoplankton blooms or dissolved organic matter release, reducing transparency and therefore further heating the surface layer. However, this feedback is only likely to have influence in small and clear lakes, it would be easily disturbed by weather conditions, and the resulting stratified state does not remain stable in the long term, as stratification is lost in winter.The ice-albedo feedback might cause an accelerated shift from ice-covered (dimictic) to ice-free (monomictic) winters in sufficiently deep (mean depth 50 m or more) lakes, where temperature memory is carried over from one winter to the next. Nevertheless, there is an ongoing debate into whether this process can persist during natural weather variations and overcome self-stabilising mechanisms such as thermal insulation by snow. The majority of studies suggest that a gradual transition from dimictic to monomictic is more likely than an abrupt transition.A shift from a holomictic to a meromictic regime can occur if anoxia is triggered by incomplete mixing and an increase in deep-water density—through the accumulation of solutes—exceeds a density decrease by hypolimnetic warming. A shift to meromixis would strongly alter the biology of a lake and might be difficult to reverse. If solutes accumulate only minimally in the hypolimnion, an oligomictic regime is formed, in which years with complete and incomplete mixing alternate.Understanding the importance of feedback mechanisms and the role of biogeochemistry when lakes shift in mixing regime could lead to a better understanding of how climate change affects lake ecosystems.
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