AGW01 Long-term measurement of groundwater physical and chemical properties from wells on watershed N04D

In 1988 and 1990, the U.S. Geological Survey, Lawrence, KS, drilled 35 wells at 16 sites within the N04D watershed at the Konza Prairie Research Natural Area. The wells range in depth from about 2 to 13 meters, and are nested to include wells completed in alluvium/colluvium near the N04D drainage and in two Permian-aged limestone’s. These sites comprise four transects running approximately east-west across the drainage, and occupy the lower 10% of the surface area of the watershed. The geology of the area is characterized by patchy, near-stream alluvium/colluvium which overlies bedrock, composed of thin (1-2 meter) limestones alternating with thicker (2-4 meter) shales. The limestones are fractured, and records of water levels in the wells show that in some parts of the watershed water levels are nearly constant, while in others they respond noticeably to precipitation events. Beginning in 1991, water samples for inorganic chemical analysis have been collected every four to six weeks by bailing wells to remove 1-2 well volumes. A bailed sample is then filtered through 0.45µ membrane filters by gravity feed. One 50-mL aliquot is reserved for alkalinity determination by titration with 0.02 N H2SO4. One 250-mL LDPE bottle is filled with 250 mL of sample and 5 mL of concentrated HNO3 for cation analysis by atomic absorption spectrophotometry (Na, K, Ca, Mg). One 250-mL LDPE bottle is filled to the brim for anion analysis by ion chromatography (Cl, SO4, NO3). The latter two samples are stored on ice and later in a refrigerator. Anion determination is completed within 1 to 3 days of collection.