Groundwater Under
the Pacific Northwest • November 2-3, 2005 •
Keynote Address: Thomas Winter
The
take-home message of Thomas Winter’s keynote talk on the Aquatic Systems Continuum
might well be paraphrased as “The more we know, the better we’ll be able to
predict what will happen to aquatic systems in the event of human manipulation
or climate change.” Winter, a senior
research hydrologist with the U.S. Geological Survey, traced the evolution of
his career during his talk, starting with the numerical models he worked with
early in his professional life and ending with a three-dimensional
representation of the aquatic systems continuum.
Winter started with models designed to look at
how surface water and groundwater interact, especially in lakes and
wetlands. Then he took the obvious next
step and went out into the field to see if the real world and the models
agreed. Along the way, serendipity
happened. On one of the eight target
areas he chose for study, a prairie potholes area in
During all those years, Winter and his colleagues were taking samples: hydrological samples, water chemistry samples, and all kinds of biological samples. Putting all the data together, with the climate from drought to deluge on one axis and the groundwater flow path on another, Winter and his colleagues, led by Chip Euliss, developed the wetland continuum, a two-dimensional matrix showing the plant and animal species that exist for each combination of climate and flow path--in other words, its ecosystem. Without the natural climate experiment, there would be no wetland continuum concept.
The aquatic system continuum is an expansion of the wetland continuum. “When you look at the two-dimensional wetlands, you can see that there are lots of things built into it--water, plants, bugs, amphibians, and the like,” said Winter. “I thought it would be easier to depict if it was pulled apart, so one can look at the individual layers that compose the ecological world.”
Winter also developed the concept of hydrological landscapes, doing so after being asked why wetlands occur in some places but not in others. The question got him to thinking about how a combination of natural factors such as the hydroclimate, aquifer, soils and topography might be expected to affect hydrological transport processes. It also made him realize that the world really consists of fundamental building blocks that show how water moves in the landscape. Using existing data and statistics, colleague David Wolock used these building blocks to create four separate maps depicting potential evapotranspiration, percent sand as a measure of surface permeability, aquifer permeability, and topography. The four were overlaid to produce one map that is a hypothesis of how water moves through the entire country. Winter and Wolock have defined 20 distinct landscapes based on the characteristics used to make the map. For each, the landscape description enables researchers to determine the landscape’s source of water, its major water issues, and how susceptible to climate change or human manipulation the landscape will be.
Winter says that the continuum and the hydrologic landscape offer a framework, a thought process of how to think about how water moves, based on some very simple principles. He suggests if we know about the wetlands continuum as a model, and the hydrologic landscapes as a way of characterizing things, we should then get out there and look at these ecosystems in the same way in all the landscapes. “If we understood all of them as well as we do the potholes wetland, then I think we’ll know what will happen to them with change.”
Summary by Mary Aegerter, Technical Writer,