Nitrogen transport from tallgrass prairie watersheds

Discharge and N content of surface water flowing from four Karst watersheds on Konza Prairie Research Natural Area, Kansas, managed with different burn frequencies, were monitored from 1986 to 1992. The goal was to establish the influence of natural processes (climate, fire, and bison grazing) on N transport and concentration in streams. Streams were characterized by variable flow, under conditions that included an extreme flood and a drought during which all channels were dry for over a year. The estimated groundwater/stream water discharge ratio varied between 0.15 to 6.41. Annual N transport by streams, averaged across all watersheds and years, was 0.16 kg N ha(-1) yr(-1). Annual N transport per unit area also increased as the watershed area increased and as precipitation increased. Total annual transport of N from the prairie via streams ranged from 0.01 to 6.0% of the N input from precipitation. Nitrate and total N concentrations in surface water decreased (P < 0.001, r values ranged from 0.14-0.26) as length of time since last fire increased. Increased watershed area was correlated negatively (P < 0.0001) to stream water concentrations of NO3--N and total N (r values = -0.43 and -0.20, respectively). Low N concentration is typical of these streams, with NH4+-N concentrations below 1.0 mu g L(-1), NO3--N ranging from below 1.4 to 392 mu g L(-1), and total N from 3.0 to 714 mu g L(-1). These data provide an important baseline for evaluating N transport and stream water quality from unfertilized grasslands.