Determining the soil water balance at a large-scale lysimetric facility with 60 years of uninterrupted data comprising a grassland basin, oak/beech and a pine basin

The research facility St. Arnold presented here consists of three individual lysimeters with an area of 400m² and 3.5m depth each. They are similar in soil types but differ in vegetation cover. This unique setup allows the direct comparison of the water balance of grassland, oak/beech forest and pine forest under the same climatic and topographic boundary conditions. The later site were cut after a significant storm occurred in 2007. Since a pioneer forest developed.  The data collection of precipitation, groundwater recharge, temperature, humidity and sunshine duration started in 1964. In addition, stem diameter at certain trees has been determined once a year.  All data until 1997 were collected manually. After that automated collection of hydro climatic data were established and transmitted directly into the database of LANUV. From the data, evaporation rates were calculated with Penman-Montheith. More recently in October 2023 undisturbed soil cores where collected and analyses for their saturated and unsaturated hydraulic conductivity. In addition, the investigation of the water balance has been done with HYDRUS 3D. The data shows significant trends. Further, it can be observed how storm damage and/ or clear-cut of forested areas impact the soil water balance.  The long-term average of the period 1965 to 2007 showed, the grassland basin turns more than half of its annual incoming precipitation into leachate and only 36% into evaporation while the deciduous forest exhibits a ratio of 36% leachate and 56% for evapotranspiration. The evergreen coniferous forest shows the highest evaporation rate 65% and the lowest leachate rate with 26%. (Harsch et al., 2009) An upgrade of the entire facility with state of the art measurements devices is in progress. This will initiated with a geophysical survey in the beginning of 2024 along with the installation of soil moisture and tensiometer sensors. Depending on funding permanent and long term geophysical measurements and stable isotope analysis will be conducted all data will be available open source. We welcome collaborators for joint research at the facility.  Harsch, N., Brandenburg, M., & Klemm, O. (2009). Large-scale lysimeter site St. Arnold, Germany: analysis of 40 years of precipitation, leachate and evapotranspiration. Hydrology and earth system sciences, 13(3), 305-317.