Use of sensors to improve water quality monitoring and process understanding in agricultural catchments

Sensor technology used for water quality monitoring is relatively novel, and the potential uses are still not fully explored. Sensors provide high-frequency data that can be used as a substitute for traditional monitoring, and can also give improved understanding on the movement of pollutants (both in dissolved and particulate phases) through a catchment. The latter can be used to target mitigation measures against diffuse pollution. In the SENSIMON Project we have examined data from sensors in streams, focusing on turbidity, conductivity, nitrate, and water level. Cost-effectiveness of three monitoring methods were compared, viz. near-continuous sensor recordings; grab samples of varying frequency; and composite sampling. The main purposes of the monitoring were taken into account; these varied from finding annual mean or maximum concentrations, calculating loads and mass balances, and understanding processes. Effectiveness was assessed based on the uncertainty of the data obtained for such various purposes. Analyses of temporal patterns of water flow/water level and the transport of particulate and dissolved matter (derived from sensor data) have been used to assess the sources of different substances (nutrients, sediments). Campaign measurements and investigations of streambank erosion were used to further assess sources. The results are being prepared for scientific and popularized publications.

SENSIMON has a duration of 2.5 years, and is a small-scale project that aims at investigating the use of sensors for improved water quality monitoring and catchment process studies. The project answers to two challenges when implementing the WFD: (1) the uncertainty of water quality monitoring (including support parameters such as nutrients and suspended sediments) in streams due to high concentration fluctuations; and (2) the effect, or often lack of effect, of mitigation measures in agricultural areas with predominantly diffuse nutrient sources. We intend to use a well-instrumented and monitored small (4.5 km2) catchment in south-eastern Norway, where we have already installed sensors for nitrate, turbidity, pH, conductivity, temperature and water level. In addition to the on-going monitoring we wish to perform additional sampling during selected events (rainstorms, snow-melt, low flow), in order to obtain a better understanding of pathways of nutrients. We will use a nested catchment approach, using two smaller tributaries in addition to the main stream. We have divided the project into three main tasks: (1) Analysis of sensor potential in monitoring for the WFD; (2) Use of sensor data to improve process understanding; and (3) Synthesis and dissemination. Our approach has been to focus less on cooperation within the project, but we intend to organise a workshop for fellow researchers from Nordic/Baltic countries where we will discuss these topics. We will also use our existing network of managers and stakeholders (river basin managers, agricultural advisers, agricultural offices in municipalities and counties, etc.) to discuss and disseminate results from the project.