PATTERNS AND CONTROLS OF NITROGEN IN TALLGRASS PRAIRIE STREAMS

In prairie streams in Kansas, nitrate concentrations varied depending on the year, season, time of day, stream flow conditions, source of water, and location. Mean nitrate concentrations during the dormant season decreased from 1982-1984, corresponding to above-normal precipitation. Nitrate concentrations decreased from 3rd order (grass/shrub riparian vegetation) to 4th order channels (gallery forests). Nitrate, organic N, and total N were higher in a 3rd order intermittent stream than in a 3rd order perennial stream. Water from seeps and tributaries had higher nitrate concentrations than stream water; but streams and tributaries had higher organic N than seeps. Maximum nitrate concentrations during storm flows were directly related to the magnitude of storms and inversely related to the frequency of storm events. The activity of terrestrial vegetation influenced nitrate concentrations within streams, seeps, and tributaries; nitrate concentrations were always higher during periods of vegetation dormancy. Aquatic biota influenced both spatial patterns (downstream decrease in nitrate concentrations and increase in organic N) and diel patterns of nitrate concentration (night > day). Uptake rates of nitrate by biota were greater during the day than during the night. Algal biomass was N and P limited, but individual taxa responded to specific N and/or P concentrations or atomic N:P ratio. -from Author