The hyporheic zone (HZ) describes the interface between ground and surface waters. It plays a significant role in the ecology of streams and their self-cleaning potential. In this project, we investigate the hypothesis that changing climatic drivers significantly endanger the function of the HZ. Increased temperature leads to increased respiration and formation of oxygen-free areas,. Under conditions of stream low flow (and with a high proportion of groundwater) down welling of oxygen rich stream water is limited while reduced substances enter the upper parts of the HZ and surface water. This can lead to loss of habitat for stream invertebrates, reduced spawning areas for fish as well as reduce the self-cleansing capacity of streams and rivers.
We have designed an experiment to map the spatial distribution (vertical and horizontal) of dissolved oxygen in the hyporheic zone on scales of tens of meters. The aim is to identify oxygen rich areas in the HZ and determine how well they correlate with down-welling or upwelling zones as well as other geochemical parameters. We use the oxidation of iron rods (nails) as a cost-efficient tracer for oxygen levels in the riverbed subsurface. This method provides only a bivariate information, i.e. is there oxygen present or not rather than an accurate concentration of DO levels. Initial experements have been conduceted using a tank experiment, we simulate hyporhic exchange and depending on the degree of rust on the nails, we want to quantify the presence of oxygen by comparing it to the measured oxygen concentration profiles in the sediment. This will form the basis for further field experiments in two rivers (Mähringsbach and Wiesent) to make a 3D oxygen map over riffle pool structures.