Monitoring flow periods of tile drains in Brittany (France): use of low-cost and tiny temperature loggers

Abstract

Tile drains alter the natural water cycle and are major pathways for pollutants input into rivers. For a project that aims to sensibilize farmers to water quality issues, we analyzed water quality of tile drains located in Brittany, north-western France. In order to interpret and to discuss results, we needed to follow the aquatic and dry periods of these tile drains during the hydrological season. Temperature loggers are common tools used by scientists to detect water presence/absence in semi-aquatic ecosystems, because temperature range is bigger for dry periods than for aquatic periods. In this work, we aimed to know if low-cost and convenient temperature loggers are scientifically relevant to follow dry and aquatic periods of tile drains. To answer this question, we set HOBO water temperature loggers (Onset Company) in five tile drains. These loggers are cheap, tiny and waterproof. We recorded temperature every hour from October 2023 to May 2024, and we checked whether the drains were flowing during 13 field visits to each collector. The processed data focused on daily temperature range in relation to field observations. The results show that drains with flow exhibit significantly lower temperature ranges (less than 5°C) than when they are dry (up to more than 15°C). This difference is statistically significant (p < 0.001). A daily range threshold of 2.9°C was established to reliably identify the presence of flow. In conclusion, we can say that low-cost and tiny temperature loggers are suitable tools to follow dry and aquatic periods of tile drains.