1. Guiding Research Hypothesis
Matter fluxes in catchments are dominantly controlled by the hydrologic dynamics that result from an interplay between catchment structure and dynamic external forcing, and by specific “functional zones” where mobilization and biogeochemical transformation predominantly occur. Against this scientific background, different research infrastructures and research activities are implemented within the CZO “Selke”.
The main complexes of research are:
Advanced sensing, fingerprinting and monitoring
- Refined techniques (e.g. isotopic & reactive tracers, FTICR-MS)
- Data driven statistical analysis
- Identification of functional zones
Development of bottom-up concepts
- Soil-Landscape modeling
- Quantitative pedology and pedogenetical modelling
- Model-based prediction of parameter fields for modeling
Functional zone processes
- Processes of mobilization and transport
- Biogeochemical transformations
- Linking hydrology and ecology
Development of integrated top-down concepts
- Dynamic residence time distributions
- Data-driven catchment-scale models for water fluxes
The monitoring scheme includes and combines:
Water quality monitoring using multi-parameter probes
- Selke hyporheic monitoring
- Stable isotope monitoring
- N,C dynamics in soils
- DOC mobilization (from soil to streams)
- Hyporheic zone solute and transformation
- Remote sensing of temporal patterns of (surface properties)
- Geophysical monitoring campaigns
2. Site Description
The CZO “Selke” is integral part of the nested catchment monitoring approach within the hydrological observatory “Bode”, the central study site for water-related research at the Helmholtz-Centre for Environmental Research (UFZ). The area of the CZO “Selke” is very well equipped with long-term meteorological and hydrological infrastructure (long-term data on discharge, precipitation, climate). Within the CZO two intensive research sites have been implemented.
2.1 Intensive Research Site "Schaefertal"
Main goal of the research at this site is the development of methods for quantification and prediction of water fluxes at the small catchment scale (including selected aspects of coupled water and solute flux). Knowledge gained by intensive measurements and detailed process studies will in future be used to transfer observation concepts and process understanding to larger or less instrumented catchments.
The Schaefertal catchment is a small headwater catchment with an area of 1.44 km². It is located on a plain in the Lower Harz Mountains (51°39'N, 11°03'E). Hydrological research in the catchment started in 1965, when a river gauge and a meteorological station were installed. Since the early stages the research focus was comparable to one of the TERENO research goals - the long-term investigation of water balance characteristics at the landscape scale including feedbacks and interaction with climatological, pedological, geological, topographical, and ecological factors. Meanwhile, the original hydrological station is maintained and operated by the University of Applied Sciences Magdeburg-Stendal, which continuously extended and modernised the research infrastructure. Today, the research infrastructure includes a highly equipped climate station, a dense groundwater observation network, a river gauge equipped with multi-parameter probe and automated sampler, and several plots to measure soil water content, soil water potential and snow water equivalent. For many parameters data records dating back to the 1960's are available.
In the context of a scientific cooperation between the UFZ and the University of Applied Sciences Magdeburg-Stendal, TERENO extended the already existing research infrastructure by a number of new technologies, operating at different scales, whereby the focus is on the monitoring of soil moisture. These soil moisture (resp. soil moisture proxy) measurements include:
- point measurements at modern lysimeters (e.g. TERENO SoilCan) using single FDR- and TDR-sensors and tensiometers
- integration of point measurements via a wireless soil moisture monitoring network at the hillslope scale
- cosmic ray probes
- field-scale geophysical measurement campaigns (electromagnetic induction, gamma spectrometry)
- airborne remote sensing campaigns (hyperspectrum imagery, passive and active radar)
With this, a unique research infrastructure of sensors, operating at different, but overlapping scales is available, delivering information about soil moisture and/or water stored in the soil as well as about hydrological processes within the catchment for different spatial and temporal scales.
2.2 Intensive Research Site "Selke River"
The test site is an approximately 1 km long reach of the Selke, 3 km downstream of the Meisdorf gauge station. The reach is characterized by a near natural morphology with meanders, pool-riffle sequences and point and mid-channel bars.
Research activities at the Selke test site focus on the pattern and dynamics of water flow and solute transport within in the morphological features (e.g. gravel bars). It is hypothesized that the residence time of stream water in the streambed significantly influences solute turnover and stream metabolism. Reactions in the streambed are essentially control by the redox conditions. For instance: denitrification can only occur at oxygen concentration lower than 1 mg/l. One other key parameter is streambed temperature. Temperature controls microbially mediated reactions and is a crucial parameter for reactive transport modeling.
The key objective at the Selke test site is to understand which hydraulic and morphological factors control the reactivity of the hyporheic zone.
At the Selke test site stream and streambed temperature is continuously monitored with multilevel temperature probes. The temperature data is used for reactive transport models and also as natural tracer to estimate direction and magnitude of water flow. Water level in the stream and pressure in the stream and the shallow aquifer is monitored with pressure transducers to derive the dynamics of hydraulic gradients. Electrical conductivity is continuously monitored in the stream and the streambed and used as natural tracer to derive travel times in the streambed. Oxygen is measured in the streambed applying newly developed vertical optical oxygen profilers. The gauging station Meisdorf is equipped with a multi-parameter probe and automated water samplers for water quality monitoring.
PI: Steffen Zacharias
PI: Ute Wollschläger
CO-PI: Jan Fleckenstein
CO-PI: Hans-Joerg Vogel