Installation Matters: Implications for In Situ Water Quality Monitoring

Novel in situ sensor technologies can measure water chemistry at high temporal frequencies, yet few studies have evaluated how installation affects measurements. In this study, we assessed the effects of commonly used protective housings on in situ sensor readings. Working in two mountain streams, we colocated specific conductance sensors in four different housing types that varied in openings for water exchange (mesh, screen, holes, and open). We compared measured conductance values through time and performed repeated salt tracer additions to evaluate the influence of housing type on calculated discharge. Sensors readings in mesh and, to a lesser extent, screen housings frequently diverged from housings with larger openings (i.e., holes and open), indicating reduced water exchange between stream water and housed sensors. Further, mesh and screen housings recorded more damped and delayed response to salt tracer additions compared to the other two housings, resulting in markedly different discharge values. From these findings, we recommend that water chemistry sensors should be deployed in a protective housing with large openings for sufficient water exchange. Plain Language Summary Many sensors are now available to measure water quality parameters in streams and rivers. Sensors are commonly installed in a housing to secure them in stream locations and for protection from floating debris. Yet, it is not well understood if different housing options influence measurements. In this study, we placed sensors that measured the electrical conductivity of water in four different housing types. Housings with smaller openings, including metal meshes and polyvinyl chloride pipes with narrow slots, caused sensor readings to differ from sensors placed in housings with larger openings. From these findings, we recommend that water quality sensors should be deployed in a protective housing with large openings for sufficient water exchange. Key Points Study was conducted to evaluate effects of common sensor housings on specific conductance measurements Housings with smaller openings appeared to reduce rate of water exchange, causing measurement artifacts and errors We recommend water quality sensors be installed in housings with large holes or openings for sufficient water exchange