Longitudinal heterogeneity of two prereservoirs in the Harz mountains (Germany)

Sammanfattning: The understanding of longitudinal heterogeneity in pre-reservoirs is crucial for the development of a sophisticated monitoring program which shall be able to represent the water bodies in a resource efficient way. The present study was conducted at two prereservoirs in the Harz mountains (Germany), the Rappbode and Hassel pre-reservoirs which are connected to the largest drinking water reservoir in Germany (Rappbode reservoir). Analyzed were the routine monitoring data from the bi-weekly sampling of the inflow and the outflow of the water bodies. Additionally, in summer 2012, two sampling campaigns of the transects were conducted (6 sampling points per pre-reservoir). Focus was laid on the heterogeneity of major ions, nutrients and dissolved metals, algae (chlorophyll concentration) and CO2 and CH4 concentrations. A further field of investigation was the emission of these GHG from the pre-reservoirs, using a floating chamber during the transect sampling campaigns. It was found out that the current monitoring program represents the pre-reservoir considerably well. However, a heterogeneous distribution of the algae was discovered, making it not suitable for the representation of the reservoirs if only a few spots are sampled. Ebullition fluxes were recognized in the transition zone of the pre-reservoirs, contributing to an emission of the GHG to the atmosphere. The findings of this study confirm the use of the inflow and outflow of the reservoirs as routine spots but to for an extensive and more precise conclusion a more sustainable way in the monitoring should be found.