Temperature distributions as an indicator for groundwater seepage in lowland streams
Hilster, S. de
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Persevering clean water resources is not only important for the aquatic ecology but also for human health. However, many surface water bodies and groundwater resources do not have a good ecological or chemical status. The MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) is improving the knowledge on the effect of multiple stressors, such as climate change and different types of land use, on the aquatic ecosystem. This knowledge is necessary to find what measures are needed to improve the ecological and chemical status of the water resources. Many lowland streams are influenced by groundwater- surface water interaction, which can both have a positive and negative influence on the aquatic ecosystem. In this research the effect of groundwater seepage on the stream temperature of two tributaries of the Dinkel river is examined. Distributed Temperature Sensing (DTS) was used to locate the groundwater seepages zones along the streams, while measurements of the water chemistry, seepage flux and vertical temperature profiles provided more detailed information about the groundwater-surface water interaction. The stream temperature of the Springendalse Beek was found to be highly affected by groundwater which resulted in a reduced temperature variation over time which is an advantage for the aquatic ecology. However, seepage also transported high levels of nutrients to the stream which is an important stressor. For the Elsbeek the effect of groundwater seepage on the stream temperature was found to be minimal, although additional measurements did indicate the presence of groundwater seepage. However, shading was found to have a major effect by significantly reducing both the mean and maximum stream temperature. With global warming in mind, both shading and groundwater seepage were found to be beneficial to aquatic species which are sensitive to high temperature fluctuations as stable temperature habitats are created. However, shading would be an easier measure to reduce the stream temperature. From all measurements and findings it was concluded that the Springendalse Beek and the Elsbeek both have completely different systems and therefore need different measures to assure a healthy aquatic ecosystem.