Text by Lauri Laanisto
Ülo and his colleagues – this time mainly from Estonia – have published two subsequent papers in journal Regional Environmental Change. Both deal with more or less similar topic, and both are actually review papers.
The first paper emphasizes that we have so far quite limited knowledge regarding the effects and co-effects of abiotic stress and climate change in aquatic systems. We have some ideas by now, how these interactions change the productivity, diversity and other crucial characteristics of terrestrial ecosystems, but it is rather difficult or even impossible to extrapolate these ideas on aquatic communities.
The second paper takes the next step and tries to give an overview of potential mechanisms, feedbacks and feedback loops that one has to keep in mind, when starting to study the interactions mentioned in the paragraph above.
Both reviews have considerable length and they contain numerous schemes that provide fundamental framework how to approach research in this area.
Citation 1: Niinemets, Ü., Kahru, A., Mander, Ü., Nõges, P., Nõges, T., Tuvikene, A., & Vasemägi, A. (2017). Interacting environmental and chemical stresses under global change in temperate aquatic ecosystems: stress responses, adaptation, and scaling. Regional Environmental Change, 17(7), 2061–2077. (link to full paper)
Unfavorable environmental conditions—abiotic stress—constitute one of the key drivers of evolution leading to environmental adaptation. Since the start of industrial revolution, natural populations are also facing a new stress—global warming—that, in turn, leads to alteration of the severity of most of the existing stress factors and emergence of novel stress combinations. Biological adaptation to environmental perturbations occurs at all levels of biological organization, but the current knowledge on the role of adaptation in responses of ecosystems to global change is limited, especially concerning the interplay of climatic and chemical/pollutant stressors. Particularly limited is the understanding of how biological adaptation alters the performance of aquatic ecosystems that integrate the pollution and nutrient loads from large catchment areas. This review describes the responses, tolerance, acclimation, and adaptation of species at different levels of aquatic food chain to globally changing environmental drivers with emphasis on arctic to temperate ecosystems. The analysis highlights major variations in tolerance and in extent and speed of acclimation and adaptation to various environmental drivers within and among species and among species groups at different trophic levels. The variety of responses to novel stressors causes modifications in species composition and diversity and can lead to asynchronous peak activities of organisms at different trophic levels. All these effects are expected to profoundly alter the aquatic ecosystem productivity, resilience, and adaptation capacity and can ultimately modify the global feedbacks between ecosystem-level processes and environmental drivers. We argue that joint efforts of researchers working at different levels of biological organization are needed to understand and predict global change effects on various functional types of organisms and scale up from physiological responses to large-scale integrated ecosystem responses in future climates.
Citation 2: Niinemets, Ü., Kahru, A., Nõges, P., Tuvikene, A., Vasemägi, A., Mander, Ü., & Nõges, T. (2017). Environmental feedbacks in temperate aquatic ecosystems under global change: why do we need to consider chemical stressors?. Regional Environmental Change, 17(7), 2079–2096. (link to full paper)
Globally increasing temperature and modifications in precipitation patterns induce major environmental alterations in aquatic ecosystems. Particularly profound changes are predicted for arctic to temperate shallow lakes where modifications in temperature affect the distribution of ice and ice-free periods, thereby altering the timing of peak productivity, while changes in precipitation strongly alter water table depth with concomitant modifications in light distribution, temperature, and water chemistry, collectively altering the balance between primary production, organic matter consumption, and decomposition. Due to direct effects of temperature on primary productivity and microbial decomposition, raising temperatures alter the capacity of aquatic ecosystems for carbon sequestration and greenhouse gas release, and this affects atmospheric greenhouse gas concentrations and temperature, implying a feedback loop between environmental effects on ecosystems and climate change. Moreover, elevated temperature can modify the bioavailability of pollutants deposited in the past, and increase the probability for their uptake by aquatic organisms. The latter processes in turn reduce primary productivity and alter microbial decomposition, creating thus another key feedback loop between productivity, climate change, and environmental pollutants. However, warming can also enhance eutrophication and deposition of pollutants in organic sediments, further speeding up productivity and eutrophication, with the overall net effects depending on the quantitative significance of different processes. Therefore, the feedbacks arising from pollution stress must be incorporated in models intending to predict the carbon balance of aquatic ecosystems under globally changing environmental conditions. Further work on carbon balance and greenhouse gas release of aquatic ecosystems should focus on quantitative characterization of the feedback loops operative, and on how global change affects these feedback loops.