ALBERT

Description: To assess the influence of storage dynamics and non-linearities in hydrological connectivity on time-variant stream water ages, we used a new long-term record of daily isotope measurements in precipitation and stream flow to calibrate and test a parsimonious tracer-aided runoff model. This can track tracers and the ages of water fluxes through and between conceptual stores in steeper hillslopes, dynamically saturated riparian peatlands and deeper groundwater; these represent the main landscape units involved in runoff generation. Storage volumes are largest in groundwater and on the hillslopes, though most dynamic mixing occurs in the smaller stores in riparian peat. Both stream flow and isotope variations are generally well-captured by the model, and the simulated storage and tracer dynamics in the main landscape units are consistent with independent measurements. The model predicts that the average age of stream water is ∼1.8 years. On a daily basis, this varies between ∼1 month in storm events, when younger waters draining the hillslope and riparian peatland dominates, to around 4 years in dry periods when groundwater sustains flow. This variability reflects the integration of differently aged water fluxes from the main landscape units and their mixing in riparian wetlands. The connectivity between these spatial units varies in a non-linear way with storage that depends upon precipitation characteristics and antecedent conditions. This, in turn, determines the spatial distribution of flow paths and the integration of their contrasting non-stationary ages. This approach is well-suited for constraining process-based modelling in a range of northern temperate and boreal environments. This article is protected by copyright. All rights reserved.

Description: Hydrogeophysical surveys were carried out in a 3.2 km 2 Scottish catchment where previous isotope studies inferred significant groundwater storage that makes important contributions to streamflow. We used electrical resistivity tomography (ERT) to characterise the architecture of glacial drifts and make an approximation of catchment-scale storage. Four ERT lines (360-535 m in length) revealed extensive 5-10 m deep drift cover on steeper slopes, which extends up to 20-40 m in valley bottom areas. Assuming low clay fractions, we interpret variable resistivity as correlating with variations in porosity and water content. Using Archie's Law as a first approximation, we compute likely bounds for storage along the ERT transects. Areas of highest groundwater storage occur in valley bottom peat soils (up to 4 m deep) and underlying drift where up to 10,000 mm of precipitation equivalent may be stored. This is consistent with groundwater levels which indicate saturation to within 0.2 m of the surface. However, significant slow groundwater flow paths occur in the shallower drifts on steeper hillslopes, where point storage varies between ~1,000 mm–5,000 mm. These fluxes maintain saturated conditions in the valley bottom and are recharged from drift-free areas on the catchment interfluves. The surveys indicate that catchment scale storage is 〉2,000 mm which is consistent with tracer-based estimates. This article is protected by copyright. All rights reserved.

Description: Hydrogeophysical surveys were carried out in a 3.2 km2 Scottish catchment where previous isotope studies inferred significant groundwater storage that makes important contributions to streamflow. We used electrical resistivity tomography (ERT) to characterize the architecture of glacial drifts and make an approximation of catchment-scale storage. Four ERT lines (360–535 m in length) revealed extensive 5–10 m deep drift cover on steeper slopes, which extends up to 20–40 m in valley bottom areas. Assuming low clay fractions, we interpret variable resistivity as correlating with variations in porosity and water content. Using Archie's Law as a first approximation, we compute likely bounds for storage along the ERT transects. Areas of highest groundwater storage occur in valley bottom peat soils (up to 4 m deep) and underlying drift where up to 10 000 mm of precipitation equivalent may be stored. This is consistent with groundwater levels which indicate saturation to within 0.2 m of the surface. However, significant slow groundwater flow paths occur in the shallower drifts on steeper hillslopes, where point storage varies between ~1000 mm–5000 mm. These fluxes maintain saturated conditions in the valley bottom and are recharged from drift-free areas on the catchment interfluves. The surveys indicate that catchment scale storage is 〉2000 mm which is consistent with tracer-based estimates. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Description: We calibrated an integrated flow-tracer model to simulate spatially distributed isotope time series in stream water in a 7.9-km2 catchment with an urban area of 13%. The model used flux tracking to estimate the time-varying age of stream water at the outlet and both urbanized (1.7km2) and non-urban (4.5km2) sub-catchments over a 2.5-year period. This included extended wet and dry spells where precipitation equated to 〉10-year return periods. Modelling indicated that stream water draining the most urbanized tributary was youngest with a mean transit time (MTT) of 171days compared with 456days in the non-urban tributary. For the larger catchment, the MTT was 280days. Here, the response of urban contributing areas dominated smaller and more moderate runoff events, but rural contributions dominated during the wettest periods, giving a bi-modal distribution of water ages. Whilst the approach needs refining for sub-daily time steps, it provides a basis for projecting the effects of urbanization on stream water transit times and their spatial aggregation. This offers a novel approach for understanding the cumulative impacts of urbanization on stream water quantity and quality, which can contribute to more sustainable management. © 2015 John Wiley & Sons, Ltd.

Description: Climate change increases the occurrence and severity of droughts due to increasing temperatures, altered circulation patterns, and reduced snow occurrence. While Europe has suffered from drought events in the last decade unlike ever seen since the beginning of weather recordings, harmonized long-term datasets across the continent are needed to monitor change and support predictions. Here we present soil moisture data from 66 cosmic-ray neutron sensors (CRNSs) in Europe (COSMOS-Europe for short) covering recent drought events. The CRNS sites are distributed across Europe and cover all major land use types and climate zones in Europe. The raw neutron count data from the CRNS stations were provided by 24 research institutions and processed using state-of-the-art methods. The harmonized processing included correction of the raw neutron counts and a harmonized methodology for the conversion into soil moisture based on available in situ information. In addition,the uncertainty estimate is provided with the dataset, information that is particularly useful for remote sensing and modeling applications. This paper presents the current spatiotemporal coverage of CRNS stations in Europe and describes the protocols for data processing from raw measurements to consistent soil moisture products. The data of the presented COSMOS-Europe network open up a manifold of potential applications for environmental research, such as remote sensing data validation, trend analysis, or model assimilation. The dataset could be of particular importance for the analysis of extreme climatic events at the continental scale. Due its timely relevance in the scope of climate change in the recent years, we demonstrate this potential application with a brief analysis on the spatiotemporal soil moisture variability. The dataset, entitled “Dataset of COSMOS-Europe:A European network of Cosmic-Ray Neutron Soil Moisture Sensors”, is shared via Forschungszentrum Jülich: https://doi.org/10.34731/x9s3-kr48 (Bogena and Ney, 2021).