Daily phosphorus variation in a mountain stream

Monthly diel monitoring studies for phosphorus content were conducted (1995 -1996 period) for multiple stations on Incline Creek, a mountain stream in the Lake Tahoe basin (California-Nevada). Large discharge and particulate P (PP) concentration fluctuations occurred during June in the early evening as snowmelt from higher elevations arrived at the lower stream reaches. Jun e diel dissolved organic P (DOP) concentrations steadily increased, while s oluble reactive P (SRP) concentrations remained constant. June diel PP conc entrations associated with sand-sized particles (PPsand: >63 mu m) exhibite d a clockwise hysteresis, indicating possible sediment source depletion on a daily timescale. June diel PP associated with silt- and clay-sized partic les (PPsc: >0.45 mu m and <63 mu m) exhibited counterclockwise hysteresis b ehavior, suggesting a potential groundwater contribution to PPsc. PPsc comp rised the majority of PP concentration, except during high-discharge events when PPsand, concentration was dominant. Areal PP loading, specifically PP sand, appears to originate primarily from the lower eastern branch of Incli ne Creek during the spring snowmelt season. Possible sources include a ski resort/parking lot and a golf course. DOP and SRP areal loads were greatest from the undeveloped upper subwatershed, suggesting that natural factors s uch as slope are influencing loading of small-sized P fractions.