Research
Climate Change and Freshwaters
Scientists predict that rising levels of carbon dioxide and other greenhouse gasses will continue to increase mean global temperatures over time. What will these changes mean for our earth’s freshwater systems? Changes in freshwater ecosystems are expected to include increases in water temperature, changes in precipitation patterns, changes in rates of flow for rivers and streams, and changes in species distributions. CAC researchers are investigating many of these changes, with a particular focus on how changes in species distribution will alter ecosystem processes.
Millennium Ecosystem Assessment Scenarios
Changes in temperature and patterns of precipitation are expected to increase river flow in some parts of the world and decrease it in others. Not surprisingly, freshwater biodiversity is expected to decline in rivers with less water. CAC Director David Lodge and collaborators developed scenarios of the future number of fish species in rivers worldwide. As part of the Millennium Ecosystem Assessment, these researchers developed global scenarios of future river discharge due to climate change and water use by humans. They combined these scenarios with known relationships of riverine fish species and river discharge. The results indicate that by 2070 for some large river systems, up to 75% of local fish biodiversity could be moving towards extinction. Many of the rivers predicted to be hardest hit are in poor countries, where many people depend on the river has both a water source and a source of fish for food. While climate change was found to be the larger driver of biodiversity loss, reductions in water consumption by humans could stave off many of the extinctions predicted in these scenarios. These scenarios will help shape policy that might be able to protect the most at-risk river systems and the people who depend on them by re-examining water withdrawal practices.
Effects of Possible Changes in Dissolved Organic Matter
Another possible implication of reduced run-off of precipitation due to climate change is the reduction of dissolved organic matter (DOM) from vegetation and soils entering stream and river systems. Researchers at Notre Dame are exploring how changes in dissolved organic matter may affect the Ontonogan River, part of the Lake Superior watershed in the Upper Peninsula of Michigan. Some forecasts include decreased flow for this region as climate changes. DOM is an important part of the carbon cycle and energy flow in aquatic systems, serving as a food source for some organisms in the aquatic food web, and protecting other organisms from the harmful impact of the sun’s UV radiation. CAC researchers Gary Lamberti, David Lodge and others predict that any loss of dissolved organic matter in streams could lead to an increase in the penetration of UV light and alter ecosystems processes. The goals of the project are threefold: (1) to relate DOM concentration and chemistry to streamflow, wetland and upland landscape characteristics, and stream size; (2) determine interactions among UV radiation intensity and DOM chemistry, photodegradation, photoaggregation, and biodegradation; and (3) determine the response of stream foodwebs to the interactions among UV radiation intensity and DOM concentration and type. Results indicate that many organisms are very sensitive to reductions in DOM. The implications for future management efforts would be to manage upstream and wetland areas to maximize DOM availability, especially in light of future climate change.
Changing Species Distributions
Many scientists predict that on-going temperature increases will alter the distributions of species and even of ecosystems. In general, organisms requiring colder temperatures will migrate poleward towards cooler climates, but few scientists are equipped to understand the details of these likely interactions. CAC’s Jason McLachlan is one of the rare scientists who can speak confidently of the impact of climate on species distributions because he can apply lessons learned from past climate change. McLachlan is investigating the question “Can plants migrate quickly enough to keep pace with climate change?” McLachlan is looking at fossil and molecular records from the last big change in climate--the ice age. He finds that previously undetected remnant populations of trees led the northward expansion of some species. The results of this work suggest that plant populations were not actually able to move as quickly as previously proposed, which is worse than anticipated news for the likely effects of the much more rapid climate changes now underway. Such insights suggest efforts to slow climate change are more important than expected.
CAC researcher Jessica Hellmann and her team are also investigating how species distributions respond to climate, using several species of butterfly as model organisms. Hellmann and her colleagues are using genetic techniques and experiments to test alternative theories about how readily species might adapt to new conditions at the northern range edge or migrate poleward. Her group proposes that if a species is able to adapt locally it may alter the poleward species migration theory. While this research is terrestrial in nature, the questions and methods will inform future work on aquatic species under climate change scenarios.
Links
Related Publications
Frost, PC, Larson, JH, Kinsman, LE, Lamberti, GA, Bridgham, SD. 2005. Attenuation of ultraviolet radiation in streams of northern Michigan. Journal of the North American Benthological Society 24 (2): 246-255.Hellmann, J. J. 2002. The effect of an environmental change on mobile butterfly larvae and the nutritional quality of their hosts. Journal of Animal Ecology 70: 925-936.
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McLachlan, J. S. and Clark, J. S. 2004. Reconstructing historical ranges with fossil data.
Forest Ecology and Management 197: 139-147.
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Clark, J. S., M. Lewis, J. S. McLachlan, and J. Hille Ris Lambers. 2003. Estimating population spread: what can we forecast and how well? Ecology 84: 1979-1988.
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McLachlan, J. S., D. R. Foster and F. Menalled. 2000. Anthropogenic origins of late -successional structure and composition in four New England hemlock stands. Ecology 81: 717-733.
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Xenopoulos, M.A., D.M. Lodge, J. Alcamo, M. Marker, K. Schulze, and D.P. van Vuuren. 2005. Scenarios of freshwater fish extinctions from climate change and water withdrawal. Global Change Biology 11: 1-8, doi:10.1111/j.1365-2486.2005.001008.x.
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