Ecosystem capacity for sustaining long-term water supplies – Overview of symposium

Background/Question/Methods

Headwaters are key areas for sustaining water supplies to downstream agriculture, industry, aquatic ecosystems, and cities.  However, the vast majority of streamflow records are affected by water regulation or land use change, complicating efforts to discriminate signals of land and water management from climate variability.  Long-term ecological research sites in headwaters are key repositories of long-term data on climate and water that are critical for understanding trends in ecosystem capacity to sustain long-term water supply.  The most complete long-term records in headwaters are maintained by the LTER Network, US Forest Service Experimental Forests, USDA Agricultural Research Service, and USGS Water, Energy, and Biogeochemical Budgets program.  This symposium brings together analyses of long-term trends in climate and streamflow of headwater sites, combined with records of long-term population growth and trends in streamflow in downstream sites, throughout the United States and parts of Canada. 

Results/Conclusions

The talks in this symposium examine climate and streamflow trends, and the associated challenges of managing water resources for ecological and social benefits, in major river basins of the United States, including the Columbia, Sacramento, upper Colorado, Salt/Verde, North Platte, upper Mississippi, Ohio, Connecticut, Merrimac, and Ipswich rivers.  Although climate change effects on streamflow are apparent in undisturbed headwater basins, particularly in areas with seasonal snowpack or permanent snow and ice, these trends have been obscured or counteracted by land management in headwaters, and by land use and water regulation signals in downstream portions of river basins over the past 50 to 60 years.  Thus, from an ecological standpoint, many river basins appear to be experiencing contrasting and diverging temporal trends in flow, temperature, and nutrients in headwaters compared to downstream areas.  These trends raise challenges both for ecologists in understanding the causes and consequences of change in aquatic ecosystems, and for water managers interested in meeting multiple objectives.