Sampling the hyporheic zone

The hyporheic zone (sediment subsurface zone) is a central component of fluvial ecosystems, both structurally and functionally. Most protozoan, invertebrate and several fish species inhabit not only the sediment surface layer but also deep subsurface streambed sediments, displaying highly dynamic patch formations among different depth layers1-3. The standpipe-trap method, which constitutes permanently installed wells in specified sediment depths of the streambed, allows a continuous monitoring of algal, protozoan and invertebrate communities. By using this sampling method the spatiotemporal dynamics of any motile organism of the streambed surface and the hyporheic zone can be analysed. The freeze-core technique allows a simultaneous assessment of the streambed surface and the subsurface zone at specified sample sites. This method can be used to assess and analyse physical, sedimentological, chemical and biological parameters in a single streambed sample. The method uses steel-cores that are driven into the streambed and exposed for a defined period. Liquid nitrogen is poured into the freeze-core to allow the freezing of the sediment-water complex around the corer tube. The extracted frozen sediment core is then subdivided for further analyses1-7.