Evaluating diffuse and point source phosphorus inputs to streams in a cold climate region using a load apportionment model

Variation in the timing and quantity of diffuse versus point-source inputs of phosphorus (P) to streams can be evaluated by examining P concentration-flow relationships. Diffuse load inputs usually increase with stream flow (due to increased delivery caused by precipitation); whereas, point-source concentrations decrease with rising river flow (due to increased dilution). This study tested the suitability of a load apportionment model (LAM), a power-law function of flow, to estimate contributions of diffuse and point inputs to P loads for eight sub-watersheds in the Red River Valley, a cold-climate rural region of Manitoba, Canada. For all but two sub-watersheds, annual and seasonal (snowmelt and summer) models of P concentration versus flow best fit a strictly diffuse source contribution. The models identified significant point-source inputs (in addition to diffuse sources) in two sub-watersheds, during summer in both watersheds (consistent with the fact that wastewater from sewage lagoons is discharged to upstream reaches between June and September) and during snowmelt for one watershed. Application of a LAM proved to be a simple and rapid method for nutrient source apportionment as well as detection of unknown sources for cold-climate, rural sub-watersheds. Such information is critical for developing the most effective mitigation strategies to reduce P concentrations and eutrophication risk

Hydrological variability affects particulate nitrogen and phosphorus in streams of the Northern Great Plains

Study region: The study area is located in southern Manitoba, in the prairie region of Canada Study focus: This study examined the impact of hydrological variability on the timing and magnitude of nutrient export from seven agriculturally-dominated watersheds in the Red River Valley, Manitoba, Canada. New hydrological insights for the region: In 2013, discharge showed a seasonal pattern typical of streams traversing the Canadian prairies: high discharge during snowmelt followed by cessation of flow in early June due to lack of precipitation. In 2014, discharge still peaked during snowmelt but, compared to 2013, was 49% lower during snowmelt yet 21% higher during summer and fall due to greater rainfall. These hydrologic differences were associated with differences in fractionation of nutrients between years. Thus, higher concentrations and loads of particulate phosphorus (P) and nitrogen (N), and a greater (p < 0.05) share of the total nutrient pool in particulate forms (particularly for P), were observed during the snowmelt- dominated year (2013). Our findings show that the nutrient concentrations, fractionation and export from prairie watersheds differ between years, and amongst hydrological seasons, in relation to hydrological conditions. Additional management actions may be required to address changes in the quantity, timing and fractionation of nutrient export associated with rainier summers forecasted under future climate scenarios. Keywords: Nutrients, Hydroclimatology, Canadian prairies, Lake Winnipeg, Eutrophicatio