Dr. Sarah Ledford and I just got a paper accepted in Hydrological Processes on our nutrient monitoring in Sandy Run (tributary of the Wissahickon). We used hysteresis plots to distinguish nutrient cycles caused by uptake versus variable source term. A site immediately downstream of a WWTP showed little uptake while 5 km downstream, a similar diurnal signal was associated with uptake.
Read the Ledford&Toran-2019-Hydrological_Processes for more details!