Streams integrate the water, solutes, and sediments from their drainages, and thus they act as mirrors of the surrounding landscape. Patterns of streamflow, chemistry, and sediment flux can therefore shed light on physical, chemical, and biological processes at the scale of whole ecosystems. However, landscapes are complex and heterogeneous on all scales, and thus they store waters over a wide spectrum of time scales, complicating efforts to interpret hydrological and chemical signals in streamwaters.
Here I review current and recent research linking landscapes to the streams that drain them. Groundwater levels and stream flows exhibit diurnal cycles in response to snowmelt in springtime and plant water use during the growing season. These cycles vividly illustrate how aquifers and streams mirror ecological processes in their surrounding landscapes.
Stream flow and water quality vary dynamically across multiple scales. Stream networks extend and retract, both seasonally and in response to individual rainfall events, dynamically mapping out variations in subsurface transport and in the balance between precipitation and transpiration. Water quality time series spanning the periodic table, from H+ to U, exhibit universal fractal scaling on time scales from hours to decades, complicating efforts to identify water quality trends. Isotope tracers such as 18O, 2H, 3H, and 14C can used to quantify water ages over seven orders of magnitude, from hours to thousands of years. These tracers show that streamwaters are often much younger than the groundwater aquifers from which they are derived.
Examples such as these will be presented to illustrate the close coupling between landscapes and the waters that drain them, and to demonstrate how streams can be used as windows into landscape processes.
About the Speaker: James Kirchner (Professor, Physics of Environmental Systems, ETH Zurich)
A physicist by training, James Kirchner has worked in fields ranging from hydrology, aqueous geochemistry, and geomorphology to evolutionary ecology and paleobiology. Much of his current work focuses on the flow, chemistry, and geomorphology of mountain streams. Dr. Kirchner received his bachelor’s and master’s degrees from Dartmouth College, and his Ph.D. from the University of California, Berkeley. He was a member of the Berkeley faculty from 1991 through 2010, most recently as Goldman Distinguished Professor for the Physical Sciences and Director of Berkeley’s Central Sierra Field Research Stations. From 2007 to 2012 he served as Director of the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), where he supervised a scientific staff of 550, and where he remains as a senior scientist. He is currently Professor for the Physics of Environmental Systems at ETH Zurich, the Swiss federal technical university. He became a Fellow of the American Geophysical Union in 2008. He was the European Geosciences Union’s 2013 Ralph Alger Bagnold Medalist and the American Geophysical Union’s 2016 Langbein Lecturer.
Host: Bhavna Arora