Use of sensor data for turbidity, pH and conductivity as an alternative to conventional water quality monitoring in four Norwegian case studies

Abstract

Sensor technology represents a relatively novel opportunity for water quality monitoring, and some of its many potential uses have been explored and assessed in this paper. Four Norwegian case studies with sensor recordings of turbidity, pH, conductivity and water level have been used for this assessment. The cases have included rivers, creeks and storm water overflow systems, with both point- and non-point sources of pollution from different types of land use including agriculture, road construction works, road salt application and acidic bedrocks. The results indicated that: (1) good correlations were found between sensor-based turbidity data and concentrations of both suspended particulate matter and phosphorus in grab samples from a small agricultural stream; (2) sensor recordings of turbidity proved superior to both fortnightly grab sampling and time-integrated composite sampling in terms of detecting high values of suspended sediments from both diffuse and point sources. However, the calculation of average concentrations based on fortnightly grab samples and sensor data gave almost similar results; (3) at a road construction site, the use of equipment with multiple sensors revealed that anticipated cause and effect relationships between fish deaths and high sediment loads could not be detected, but episodes of low pH of 5–5.5 did occur during rainstorms, probably as a result of weathering of acidic bedrock; and (4) in an urban road system subject to salt application in the wintertime, sensor technology revealed short-term peaks of salinity, on occasions as high as for sea water. Overall, these findings have demonstrated the usefulness of sensor data compared to traditional methods, in particular due to the possibility of high-frequency recordings of several parameters in systems with rapid changes in water quality.