Water Research Targets Trees

Anecdotal evidence suggests that trees growing along stream channels take large amounts of water from the alluvial aquifers, but little research has been conducted in Kansas to quantify the impact of water use by trees

CONTENTS

Water Research–page 1

From the Director–page 2

New Publications–page 3

Online Water Data–page 3

A Place To Visit–page 4

Upcoming Events–page 4

As ground-water levels in western Kansas continue to decline, ground-water managers need better information about how aquifers work. At a study site along the Arkansas River east of Larned, researchers at the Kansas Geological Survey are looking to trees to help get a more accurate picture of how water moves through the aquifer and connected streams.

Along with others from the University of Kansas and Kansas State University, KGS researchers are monitoring various components of the stream-aquifer system. They want to figure out the overall water budget—that is, how much water is coming in and flowing out of the system.

Anecdotal evidence suggests that trees growing along stream channels take large amounts of water from alluvial aquifer—those aquifers connected to streams. However, little research has been conducted in Kansas to quantify the impact of water use by trees on the water budget in stream-aquifer systems. In 2002, researchers at the Larned site began studying this issue by labeling roughly 860 trees, mostly cottonwoods, mulberries, and willows. Although salt cedars (another tree that is thought to use large amounts of water) have become common in western Kansas, only a few grow at the Larned site.

In the summer of 2002, monitors were installed on selected trees to measure the water flowing up the trunk. Similar monitoring will continue at two-week intervals during the summer of 2003. At the same time, researchers are also attempting to measure leaf transpiration, or the amount of water given off to the atmosphere by leaves.

Although it’s too soon for any definitive results, initial results indicate that the trees use water during the day and very little during the night, as would be expected. These fluctuations in water use appear to correlate well with diurnal (daily) fluctuations in the water table in the aquifer. During the growing season, the water table is highest during the early morning and lowest about 12 hours later, in the early evening. These diurnal water-table fluctuations cease after the first killing frost.

“One objective,” said Survey water scientist Jim Butler,“is to see if we can use the magnitude of the diurnal water-table fluctuations to estimate how much ground water is being used by the trees—in other words, to come up with a simple tool to use in Kansas to estimate the role of trees in the hydrologic budget of stream-aquifer systems.” This research is partially funded by Groundwater Management District #5. However, Butler cautioned, to develop such a tool, they’ll need to understand the system better. This understanding will be based on an extensive period of monitoring the different components of the stream-aquifer system. “Our aim is to develop a practical tool that does not require monitoring or modeling the whole system,” Butler said. “What components can you ignore? What do you need to include? These are the key questions.”

Researchers at the Larned research site are also monitoring other parts of the hydrologic system: how much water is entering the system through precipitation and leaving the system through evaporation. They are also measuring the amount of water flowing through the soil zone above the water table and how much water is flowing in and out of the aquifer.

The Larned site was established to serve as a long-term area for research on the interactions of streams and aquifers in conditions common to the Great Plains region.

Online July 18, 2003

Comments to: lbrosius at kgs.ku.edu

Kansas Geological Survey

URL:http://www.kgs.ku.edu/Publications/GeoRecord/2003/vol9.2/Page1.html