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. June diel dissolved organic P (DOP) concentrations steadily increased, while soluble reactive P (SRP) concentrations remained constant. June diel PP concentrations associated with sand‐sized particles (PP sand : >63 μm) exhibited a clockwise hysteresis, indicating possible sediment source depletion on a daily timescale. June diel PP associated with silt‐ and clay‐sized particles (PP SC : >0.45 μm and <63 μm) exhibited counterclockwise hysteresis behavior, suggesting a potential groundwater contribution to PP SC . PP SC comprised the majority of PP concentration, except during high‐discharge events when PP sand concentration was dominant. Areal PP loading, specifically PP sand , appears to originate primarily from the lower eastern branch of Incline 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 such as slope are influencing loading of small‐sized P fractions.