The hyporheic zone is an essential component of river ecosystems, yet it is often overlooked in environmental studies. A comprehensive understanding of the interactions between surface water (SW) and groundwater (GW), as well as the role of Groundwater Dependent Ecosystems (GDEs) in providing essential ecosystem services, is crucial for informed and effective land and water management (Yang and 2017).

GDEs are influenced by local hydrogeology and climate, necessitating detailed spatial and temporal monitoring of the physical and chemical interactions occurring within these systems. Traditional monitoring methods, which typically rely on individual sensors to collect point data, can overlook important variations across different sections of a stream. By integrating continuous high-resolution longitudinal stream temperature monitoring with Electrical Conductivity (EC) and discharge measurements, more comprehensive data can be collected. This approach provides both high spatial and temporal resolution, capturing small-scale interactions and patterns that are crucial for understanding the SW-GW interface. Such methods are particularly valuable for localising SW-GW interactions and assessing their seasonal impact on GDEs' baseflow.

To investigate these interactions, we employed a multidisciplinary approach combined with continuous high-resolution longitudinal stream temperature monitoring in the headwater stream of the Wüstebach Catchment, located within the TERENO Observatory in Eifel National Park, Germany. In October 2022, a Fibre Optic Distributed Temperature Sensing (FO-DTS) system (Silixa XT) was installed along a 500-meter-long stream section to monitor temperature changes over a hydrological year. Stream temperature measurements were recorded every 15 minutes at a resolution of 25 cm. Sampling was conducted at 18 sites distributed along the stream, tributaries, and existing groundwater wells, in conjunction with weekly sampling coordinated by site managers. Additionally, two intensive field campaigns were carried out during the wet and dry seasons, incorporating high-frequency EC measurements and tracer tests to capture specific hydrological events such as snowmelt and intense rainfall. These efforts aimed to deepen the understanding of groundwater recharge and discharge processes. Additional discharge and precipitation data were obtained from the TERENO Eifel database.

Despite the limited groundwater network at the study site, this approach significantly enhanced our understanding of SW-GW interactions and their role in driving the seasonal flow variations of GDEs. It also led to the quantification of SW-GW interactions and the development of standardised methods that can be applied and scaled to larger areas, complementing and strengthening existing monitoring efforts.