The quality of water from native landscapes in the baseline against which the impact of pollutants on surface water resources must be evaluated. The King's Creek watershed has been a U.S. Geological Survey benchmark watershed since 1979. It represents the landscape type tyat gave rise to much of the agricultural midwestern United States. Hydrologic, chemical, and biological measurements have been made by ecologists performing long-term ecological research (LTER) in tallgrass prairie. Streamwater chemistry varies seasonally with the amount and movement of groundwater and soil water, with changes in prairie vegetation, and in response to changes in surface water discharge. Concentrations of organic carbon, organ and inorganic nitrogen, and phosphorus increase during storm flows. The particulate fractions in transport and in storage in the stream bed and on the flood plain vary seasonally with recent hydrologic history and changes in vegetation