Assessment of possible hydrologic connection between kettle holes and the Quillow river across the northeast of Brandenburg state, Germany

Characterizing the hydrologic connection between the small water bodies, like so-called kettle holes, and river network at a watershed scale is of paramount importance for water management. This is due to the fact that if a hydrologic connection between kettle holes and river network is established, kettle holes, which are distributed across farming lands and are therefore vulnerable to agricultural practices including fertilizing, can be a source of contamination, thereby impacting the water quality of the river network. As a consequence, the ecohydrological conditions of the river network and thereafter downstream waters would be adversely influenced. In the current study, we have attempted to evaluate if a hydrologic connection between kettle holes, distributed over the Quillow watershed in the northeast of Brandenburg, Germany, and the Quillow river can be ascertained. To that end, the geochemistry of 8 chemical elements (Ca, Mg, K, Na, Br, Cl, NO3, and SO4), 4 in situ parameters (temperature, pH, EC, and redox), and two stable water isotopes (oxygen (18O) and deuterium (2H)) collected and analyzed on a monthly basis during 17 months for 36 kettle holes and 7 river sites distributed from the upstream to the downstream of the Quillow watershed have been appraised. We have established cross-correlation functions between stable water isotopes of the Quillow river and kettle holes at different time lags. In addition, an advanced yet well documented clustering algorithm, namely applied Gaussian finite mixture modelling has been employed to identify similarity and dissimilarity of geochemical facies of the 12 (8 + 4) parameters of the Quillow river and kettle holes. Assuming a hydrologic connection between these two, the proposed approach can be considered as a promising yet straightforward technique to discern the hydrologic connectivity between small water bodies and a river system, thus supporting an effective management of water resources in terms of quantity and quality at a watershed scale.