The symposium entitled “Regional Assessment of Freshwater Ecosystems and Climate Change in North America,” held October 24-26, 1994 in Leesburg, Virginia and jointly sponsored by the American Society of Limnology and Oceanography (ASLO) and the North American Benthological Society (NABS), has resulted in two compendia of publications. The ®rst was published as a special issue of the journal Limnology & Oceanography (Vol. 41, No. 4, 1996) and contained the contributed papers presented at the symposium. The second publication is this special issue of Hydrological Processes.

The symposium was structured around a regional approach, and to this end, eight regional panels were assembled to address the central question, “What would be the impact to and response of freshwater ecosystems in your region as a result of a hypothetical doubling of CO2 in the atmosphere?” The panels were composed of experts in several ®elds: geochemistry, climatology, hydrology, and aquatic ecology. Each was provided with the input from the Canadian General Circulation Models (GCM) which used a doubling of atmospheric CO2. The panels considered model predictions and various scenarios prior to the symposium and then met again as a group during the symposium to develop and come to some conclusions as to the impact on and response of freshwater ecosystems in their respective regions. A preliminary report was presented orally on the ®nal day of the symposium and published in a symposium report. Following the symposium, the panels prepared a full report on their evaluations; these are published in this special issue of Hydrological Processes. Also included is an introductory chapter explaining the approach for identifying regions by Dr. George Leavesley and a concluding chapter by Dr. David Schindler which presents a synthesis of the concepts and ®ndings of the regional chapters.

The preface to the special issue of Limnology and Oceanography presents a thorough explanation of what might be called the “history” leading to this symposium. This includes previous symposia jointly or individually sponsored by ASLO and NABS, development of governmental working groups addressing projected global climate change scenarios, etc. Suce it to say here, that the present symposium was held at an auspicious time and has focused much needed attention to freshwater ecosystems.

Basically, the organizers of the present symposium had three goals:

  • evaluate current evidence for directional change in inland waters;
  • examine potential important responses to climatic changes resulting from a hypothetical doubling of atmospheric carbon dioxide (or its radiative equivalent); and
  • develop recommendations for experimental studies or augmentation of monitoring programs.

The eight regional groups represented the following geographical areas for the purposes of this symposium: Laurentian Great Lakes and Precambrian Shield of U.S.A. and Canada; Arctic and Sub-Arctic Regions of U.S.A. and Canada; Rocky Mountains in U.S.A. and Canada; Mid-Atlantic and New England Areas of U.S.A.; Southeastern U.S.A. and Coastal Mexico; Paci®c Coast Mountains and Western Great Basin; Great Plains of U.S.A. and Canada; and Basin and Range Regions and Adjacent Arid and Semi-arid Regions of U.S.A. and Mexico.

The papers prepared by these panelists and presented herein represent their interpretation of what a doubling of atmospheric CO2 would do to the freshwater ecosystems in their respective regions. Consensus was not always reached among all panel members for every aspect considered, and both agreements and disagreements are presented. As I wrote in the Conclusions to the Symposium Report, despite the expected challenges associated with the scenarios considered, some general patterns were identi®ed. These included potential ecosystem responses linked to changes in transpiration and evapotranspiration rates which, in turn, were further linked to interactions with stream-¯ow and water temperature changes. For some regions, catchment-wide interactions had overriding in¯uences on changes at the stream- and lake-ecosystem level. Direction of climatic change varied from straightforward predictions of warmer and drier condition in the Mid-Atlantic and New England region to one of complete unpredictability in the Basin and Range, Arid Southwest and Mexico region. Historical and annual variations in climate, hydrology, and ecosystem characteristics needed to be considered in the context of the models used. Further postulated responses varied widely, ranging from predictable detrimental impacts on species existing in warm waters already near lethal thermal conditions to dramatic increases in primary productivity and dependent food-webs in regions where increasing temperatures may extend ice-free conditions. Efects to endemic organisms appear to be mainly indirect through links to changes in other ecosystem components, such as changing nutrient regimes resulting from increased or altered runoff patterns.

It is hoped that the regional papers and synthesis published herein will provide a solid foundation upon which scientists can proceed and build in their efforts to provide other scientists, regulators, and decisionmakers with meaningful information concerning the important phenomena associated with climate change.


The work of many individuals contributed to the success of the symposium and deliberations which produced this series of papers. Trevor Platt, ASLO president, suggested the theme and Sue Weiler helped in the initial planning and preparation of the symposium report. Diane McKnight and Alan Covich were the co-chairs of the symposium, and the steering committee was composed of Colbert Cushing, John Eaton, William Eichbaum, Nancy Grimm, George Leavesley, Harry Lins, John Melack, David Schindler, and Steven Schneider. Diane McKnight also acted as a facilitator in the handling of manuscripts. Debra Litwin made logistical arrangements for the symposium.

The chairs of the regional panels, who are the lead authors of the following eight regional reports, were especially instrumentive in leading, cajoling, and seeing that the panel members participated in the evaluations, discussions, and writing of the final reports. Thanks go to them and their panel members, as well as others who freely participated in the panel discussions during the symposium and the reviewers who critically commented on the manuscripts.

Primary support for the symposium, the initial symposium report, and the symposium issues of Limnology and Oceanography and Hyrological Processes has been provided by the U.S. Environmental Protection Agency, Environmental Research Laboratory-Duluth, and the U.S. Geological Survey, Water Resources Division, through an Interagency agreement DW 14936586 with the U.S. Geological Survey.