Salinization Increase due to Climate Change Will Have Substantial Negative Effects on Inland Waters: A Call for Multifaceted Research at the Local and Global Scale

Abstract

Globally, temperature and precipitation patterns are predicted to change markedly as a result of climate change. Particularly, the regions with a cold or hot semi-arid climate and the Mediterranean climate zone are expected to be strongly affected.1IPCCParry M.L. Canzian O.F. Palutikof J.P. van der Linden P.J. Hanson C.E. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2007Google Scholar,2IPCCSummary for policymakers.in: Field C.B. Barros V.R. Dokken D.J. Mach K.J. Mastrandrea M.D. Bilir T.E. Chatterjee M. Ebi K.L. Estrada Y.O. Genova R.C. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2014: 1-32Google Scholar A 25%–30% decrease in precipitation and increased evaporation are expected by the end of the 21st century in the Mediterranean region, to be accompanied by an even stronger reduction in runoff of up to 30%–40%,1IPCCParry M.L. Canzian O.F. Palutikof J.P. van der Linden P.J. Hanson C.E. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2007Google Scholar,2IPCCSummary for policymakers.in: Field C.B. Barros V.R. Dokken D.J. Mach K.J. Mastrandrea M.D. Bilir T.E. Chatterjee M. Ebi K.L. Estrada Y.O. Genova R.C. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2014: 1-32Google Scholar and this will lead to increasing salinization of lakes in these areas.1IPCCParry M.L. Canzian O.F. Palutikof J.P. van der Linden P.J. Hanson C.E. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2007Google Scholar,2IPCCSummary for policymakers.in: Field C.B. Barros V.R. Dokken D.J. Mach K.J. Mastrandrea M.D. Bilir T.E. Chatterjee M. Ebi K.L. Estrada Y.O. Genova R.C. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2014: 1-32Google Scholar Moreover, land in drought is expected to double from 2000 to 2100 to about 50% of the land worldwide.1IPCCParry M.L. Canzian O.F. Palutikof J.P. van der Linden P.J. Hanson C.E. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2007Google Scholar,2IPCCSummary for policymakers.in: Field C.B. Barros V.R. Dokken D.J. Mach K.J. Mastrandrea M.D. Bilir T.E. Chatterjee M. Ebi K.L. Estrada Y.O. Genova R.C. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2014: 1-32Google Scholar These projections do not consider the concurrent increases in water abstraction, particularly for irrigation purposes, that will increase markedly3Yano T. Aydin M. Haraguchi T. Impact of climate change on irrigation demand and crop growth in a Mediterranean environment of Turkey.Sensors. 2007; 7: 2297-2315Crossref PubMed Scopus (79) Google Scholar,4Rodriguez Diaz J.A. Weatherhead E.K. Knox J.W. Camacho E. Climate change impacts on irrigation water requirements in the Guadalquivir river basin in Spain.Reg. Environ. Change. 2007; 7: 149-159Crossref Scopus (212) Google Scholar in the years to come due to (1) a global increase in demand for food in a growing population, (2) a shift from animal farming to crop farming in semi-arid and arid areas, and (3) a decrease in net precipitation. Thus, increasing irrigation will further accelerate salinization of lakes in the dry climate zones. The magnitude of the future changes poses a major threat to the functioning and biodiversity of inland aquatic ecosystems (IAEs) (Box 1). As salinity increases, many IAEs may even dry out temporarily or permanently.5Jeppesen E. Brucet S. Naselli-Flores L. Papastergiadou E. Stefanidis K. Nõges T. Nõges p. Attayde J.L. Zohary T. Coppens J. et al.Ecological impacts of global warming and water abstraction on lakes and reservoirs due to changes in water level and salinity.Hydrobiologia. 2015; 570: 201-227Crossref Scopus (287) Google Scholar,6Cañedo-Argüells M. Kefford B. Schäfer R. Salt in freshwaters: causes, effects and prospects – introduction to the theme issue.Philos. Trans. R. Soc. Lond. B Biol. Sci. 2019; 374: 20180002Crossref Scopus (68) Google Scholar Studies performed in lakes in north-west China show drastic reductions in biodiversity, food chain length, and average trophic position in the food chain of the lakes, indicating loss of functioning7Vidal N. Yu J. Gutierrez M.F. Teixeira de Mello F. Tavsanoglu Ü.N. Çakiroglu A.I. He H. Meerhoff M. Brucet S. Liu Z. et al.Salinity shapes food webs in lakes: implications for increasing aridity with climate change.Inland Waters. 2021; Google Scholar with increasing salinity. Another study on lakes in Tibet has shown non-linear changes for certain salinity thresholds and suggests that even small changes in salinity after surpassing the critical salinity levels may have drastic effects on the structure and functions of lake ecosystems (Figure 1). How such thresholds change with climate is, however, largely unknown. In addition to the temperature- and evaporation-driven changes, the rise in sea level will also increase the input of saline water to coastal brackish lagoons (CBLs), and some freshwaters may become saline, with similar negative effects on structure and function and their biodiversity.8Schallenberg M. Hall C.J. Burns C.W. Consequences of climate-induced salinity increases on zooplankton abundance and diversity in coastal lakes.Mar. Ecol. Prog. Ser. 2003; 251: 181-189Crossref Scopus (133) Google Scholar, 9Flöder S. Burns C.W. Phytoplankton diversity of shallow tidal lakes: influence of periodic salinity changes on diversity and species number of a natural assemblage.J. Phycol. 2004; 40: 54-61Crossref Scopus (29) Google Scholar, 10Jeppesen E. Søndergaard M. Pedersen A.R. Jürgens K. Strzelczak A. Lauridsen T.L. Johansson L.S. Salinity induced regime shift in shallow brackish lagoons.Ecosystems. 2007; 10: 47-57Crossref Scopus (97) Google ScholarBox 1Effects of Global ChangeGlobal change including warming will:•increase the proportion of inland aquatic ecosystems (IAEs) that are saline and then markedly reduce the available freshwater resources;•result in the disappearance of many lakes, some of which are old and host many endemic species;•enhance the variability in salinity, which, in turn, increases the probability that critical salinity thresholds in IAEs and coastal brackish lagoons (CBLs) are passed;•make IAEs and CBLs more sensitive to other stressors such as excess nutrients and species invasions•cause a substantial decrease in species richness and functional diversity of the various biotic communities along with an increasing salinity;•lead to major reduction in ecosystem functions and services of IAEs and CBLs. Global change including warming will:•increase the proportion of inland aquatic ecosystems (IAEs) that are saline and then markedly reduce the available freshwater resources;•result in the disappearance of many lakes, some of which are old and host many endemic species;•enhance the variability in salinity, which, in turn, increases the probability that critical salinity thresholds in IAEs and coastal brackish lagoons (CBLs) are passed;•make IAEs and CBLs more sensitive to other stressors such as excess nutrients and species invasions•cause a substantial decrease in species richness and functional diversity of the various biotic communities along with an increasing salinity;•lead to major reduction in ecosystem functions and services of IAEs and CBLs. Global warming will further increase the frequency and duration of extreme weather events such as droughts, heatwaves, and seawater intrusions, which will further increase the variations in salinity and risk of passing vital thresholds in the IAEs and CBLs. While the understanding of the dynamics of freshwater ecosystems and their response to stressors, including climate change, is well advanced, comparatively little is known about saline IAEs and CBLs. This is unfortunate given the ongoing drastic changes in many lakes, including a shift from freshwater to saline conditions and increased salinity of already saline systems.5Jeppesen E. Brucet S. Naselli-Flores L. Papastergiadou E. Stefanidis K. Nõges T. Nõges p. Attayde J.L. Zohary T. Coppens J. et al.Ecological impacts of global warming and water abstraction on lakes and reservoirs due to changes in water level and salinity.Hydrobiologia. 2015; 570: 201-227Crossref Scopus (287) Google Scholar Moreover, the mutual effects of salinity with other stressors (temperature, nutrient loading, and type of salt composition) are virtually unknown. We call for (1) multifaceted and multidisciplinary approaches to fill the major research gaps outlined (Box 2)—an important area for a new generation of scientists; (2) coordinated research worldwide following common protocols for sampling, experiments, and modeling, allowing strong syntheses across climate and biogeographical gradients with virtual scientific networking and collaboration that would not need direct physical contact (regarding the current pandemic) and with much reduced carbon footprints.Box 2Research Approaches SuggestedTo study the effects of global change on IAEs and CBLs, we need multifaceted and multidisciplinary approaches, including:•space-for-time substitute approaches using common well-defined protocols across the dry climate zones of the globe for studying nutrient cycling, biodiversity, food webs and functions;•analyses of existing time series data;•high frequency data collection to reveal the effects of extreme events;•remote sensing studies across larger spatial scales;•controlled parallel running mesocosm experiments on a global scale;•hydrological and ecosystem modeling on a catchment scale;•socio-ecological and economic evaluations and research. To study the effects of global change on IAEs and CBLs, we need multifaceted and multidisciplinary approaches, including:•space-for-time substitute approaches using common well-defined protocols across the dry climate zones of the globe for studying nutrient cycling, biodiversity, food webs and functions;•analyses of existing time series data;•high frequency data collection to reveal the effects of extreme events;•remote sensing studies across larger spatial scales;•controlled parallel running mesocosm experiments on a global scale;•hydrological and ecosystem modeling on a catchment scale;•socio-ecological and economic evaluations and research. To provide effective mitigation solutions, collaborations between hydrologists, ecologists, modelers, economists, engineers, social scientists are needed, both locally and globally, as well as strong engagement of politicians, NGOs, and local citizens (citizen science). The authors were supported by the TÜBITAK program, BIDEB 2232 (ID:118C250), Turkey and Erik Jeppesen also by Åge V. Jensen Nature Foundation, project “Østlige Vejler”, Denmark.