Dams have the potential to block individuals as they attempt to shift to more suitable habitats under future climate conditions. Credit: Wayne McLean
Keeping waterways connected depends on maintaining an often large network of streams, rivers, and floodplains. This connectivity may be interrupted by dams, which provide energy and predictable water levels but also prevent fish and other aquatic species from moving freely. High levels of freshwater fragmentation due to dams in the United States, Europe, South Africa, India, and China currently impact thousands of species. Future planned dams are likely to add to that impact, particularly in biodiverse tropical basins such as the Amazon, Mekong and Congo.
Changes in freshwater connectivity from fragmentation are likely to be magnified by climate change. How will freshwater species adapt to the changing climate given that the networks they inhabit are – or may become – blocked by dams? Several recent studies have aimed to find out.
The Ebro River in northeast Spain, which flows from the Cantabrian and Pyrenean Mountains to the Mediterranean Sea, is heavily fragmented and supports numerous threatened endemic species. A recent study compared the combined effects of dams and climate change on the distribution of native and alien species in the Ebro River to get a picture of future connectivity.
Models revealed that climate change will likely species differently, with alien species generally gaining more habitat than native species and also more likely to dominate down‐ and midstream reaches of tributaries. The role of dams overall will be unfavorable, by restricting native species as they attempt to shift habitats upstream. However, restoring connectivity for natives could potentially allow alien species to flourish as well.
Wetlands and floodplains are susceptible to connectivity loss if changes in temperatures or flooding cycle alter river flows. Credit: Rudhrah Gourav
Like rivers, wetlands are also susceptible to the combined effects of dams and climate change. A study across four catchments in the wet–dry tropics of northern Australia revealed that the combination of a drier climate and dam construction could significantly reduce riverine flows, leading to a smaller floodplain and a loss of wetland connectivity.
Analysis predicted that those wetlands closer to the main river channel were more likely to maintain connectivity, while those further away could potentially transition to more terrestrial habitats. If climate change leads to more flooding, dams will likely have a big impact on how and whether connectivity can be maintained for the wetlands and all the species that inhabit them.
Finally, the Andean Amazon region provides a unique place to look at riverine connectivity, climate change, and dams due to its high biodiversity and strong elevational gradient. An analysis of the region showed that most fish species will experience a range contraction under climate change, particularly in the mid- and high-elevations.
While dams were not expected to severely impede these future range shifts, they may reduce the likelihood of persistence for many species by splitting their ranges into smaller, more isolated fragments. Future conservation efforts in the region could help by focusing on species occupying highlands, which are expected to be most impacted by climate change, and species in mid‐elevations, which will be the most threatened by planned dams in the region.
Resources
Barbarossa, V., Schmitt, R.J., Huijbregts, M.A., Zarfl, C., King, H. and Schipper, A.M. 2020. Impacts of current and future large dams on the geographic range connectivity of freshwater fish worldwide. Proceedings of the National Academy of Sciences 117: 3648-3655.
Radinger, J. and García‐Berthou, E. 2020. The role of connectivity in the interplay between climate change and the spread of alien fish in a large Mediterranean river. Global Change Biology 26(11): 6383-6398.
Karim, F., Marvanek, S., Merrin, L.E., Nielsen, D., Hughes, J., Stratford, D. and Pollino, C. 2020. Modelling flood-induced wetland connectivity and impacts of climate change and dam. Water 12(5): 1278.
Nielsen, D.L., Merrin, L.E., Pollino, C.A., Karim, F., Stratford, D. and O’Sullivan, J. 2020. Climate change and dam development: Effects on wetland connectivity and ecological habitat in tropical wetlands. Ecohydrology 13(6): e2228.
Herrera‐R, G.A., Oberdorff, T., Anderson, E.P., Brosse, S., Carvajal‐Vallejos, F.M., Frederico, R.G., Hidalgo, M., Jézéquel, C., Maldonado, M., Maldonado‐Ocampo, J.A. and Ortega, H. 2020. The combined effects of climate change and river fragmentation on the distribution of Andean Amazon fishes. Global Change Biology 26(10): 5509-5523.
