Multi-method approach to quantifying nutrient retention in a wastewater irrigated watershed. Friesen, Anthony MAs water is becoming more scarce, the application of wastewater onto land is becoming increasingly common. It is of particular interest in places where the otherwise receiving water body is considered too sensitive to handle the increased load of nutrients, and other wastewater constituents. This study utilized three methods to determine the extent to which phosphorus and nitrogen are being retained within a wastewater irrigated watershed in southern B.C., Canada. The methods include; Mass Balance, an End Member Mixing Analysis (EMMA) to determine real time and seasonal retention, and a soil analysis to determine long term retention within the soil profile. Retention estimates of P and N using the mass balance method were found to be between 53-93% and 48-77% respectively. Using the End Member Mixing Analysis, retention rates of P and N were found to be between 72-91% and 64-81% respectively. Seasonally, summer and winter had the highest retention rates, while the lowest retention was found during spring freshet. The soil analysis results found a 32% increase in phosphorus storage in irrigated soil over non-irrigated soils. This increase translated to a 40% retention rate (11,300 kg) of phosphorus in the irrigated soils during the course of the 35-year irrigation program. This master's thesis provides detailed information relating to areas such as wastewater irrigation, the City of Vernon Wastewater Irrigation program, location in the Okanagan Valley, geology, climate, hydrology and watershed, evaporation and transpiration, surface water hydrology, atmospheric deposition sampling, nutrients, and soil sampling.
