SHORT-TERM WATER-LEVEL FLUCTUATIONS AND LONG-TERM WATER-LEVEL DECLINE AT THE KONZA PRAIRIE: DROUGHT OR VEGETATION?

A long-term decline in the water-level in the Morrill Limestone aquifer at the Konza Prairie, a NSF Long-Term Ecological Research Site in northeastern Kansas, is not coupled with a period of below average precipitation. Water-level fluctuations at the Konza Prairie show a seasonal pattern of high water-levels early in the year followed by a decline that stabilizes in the fall and early winter. Daily water-level oscillations, in the two wells used for high frequency monitoring, have been measured during August, 2003, and June through September, 2005. The range in magnitude of the oscillations was greatest during August, 2003, and the range was smallest during September, 2005. The average amplitude was approximately 3 cm. During periods of daily oscillations, the maximum daily water-level occured between 0 and 5.5 hours after sunrise. The minimum daily water-level occured between 0 and 4 hours after sunset. The Konza Prairie has seen an increase in the area covered by woody vegetation from 222.5 ha in 1969 to 240.9 ha in 1985 (Knight et al., 1994). The daily water-level fluctuations, occuring during times of growth and relatively long periods without meteoric precipitation, suggest that the vegetation uses groundwater when other water sources are not available. The increasing use of groundwater by vegetation may be the cause of the long-term water-level decline.

Knight, C. L., J. M. Briggs, and M. D. Nellis (1994), Expansion of gallery forest on Konza Prairie Research Natural Area, Kansas. Landscape Ecology 9: 117-125.