Contribution of rain events to surface water loading in 3 watersheds in Canada's Alberta Oil Sands region

Study region: In the oil sands region of Canada, hydrology of rivers is strongly influenced by snowmelt and a shifting climate resulting in shortening of snow cover duration and increases in the frequency of rain events.Study focus: To evaluate the importance of rain events to these rivers, discharge and water quality sampling was conducted at river sites in this region. Two approaches were used to collect water quality samples: (1) event-based automated samplers that triggered repeated sampling in response to 10% increases in surface flow, and (2) an intensive program of routine sampling at daily, weekly or biweekly intervals from April 2013 to January 2014.New hydrological insights for the region: The importance of rain events as contributors to loading of nutrients and priority pollutants differed temporally. During fall, when baseflow conditions prevailed, average daily loads differed when calculated using routine only versus routine + rain-event data. However, on an annual basis, the inclusion of rain-event sampling did not change pollutant loads. Thus, when assessing loads on an annual basis, rain event sampling may not provide enough benefit to warrant the additional logistical considerations for this remote region. However, when monitoring focuses on capturing fall conditions, efforts should be expanded to include rain event sampling in order to capture spikes in chemical concentration during this ecologically important time period. Predictions of a shorter snow season with more precipitation falling as rain rather than snow reinforce the need to adapt monitoring schemes to ensure that the timing and frequency of water chemistry sampling reflects changing climate and hydrological patterns.

Automated summary

The hydrology of rivers in the oil sands region of Canada is influenced by snowmelt and shifting climate. The study evaluated the importance of rain events in these rivers by collecting discharge and water quality samples. It was found that the significance of rain events in contributing to nutrient and pollutant loads varied temporally. While rain event sampling may not be beneficial for annual assessments, it is necessary when monitoring fall conditions.