Source-to-mainstream: Hydrochemical water changes in a channel head in the young glacial area (Pomeranian Lakeland, Poland)

Abstract

A channel head is a zone where hydrological changes occur that shape the chemical features of water, during the final stage of underground flow and the beginning of the surface water cycle. The study aims were as follows: (i) to characterise spatial water chemistry patterns; (ii) to establish the role played by the hyporheic zone in the chemical transformations associated with the groundwater that supplies the first-order stream; and (iii) to identify the factors that control the chemical composition transformations that occur in headwater alcoves. The analysis was performed on three sets of samples taken at the Żarnowo channel head situated in the young glacial landscape of the Parsęta drainage basin (NW Poland).The performed hydrochemical measurements showed that the waters found in the alcoves displayed a mosaic pattern, with spatial variability in the levels of trace metals and nutrients. In turn, geogenic ions featured in the mineralogical-petrographic compositions of deposits found in headwater catchments, such as Ca2+, HCO3−, Mg2+, and Na+, showed low temporal variability and small differences among the various sampled headwater alcoves. These results indicated that the majority of spatial variance associated with the chemical composition of water is driven by the transformation of groundwater discharges in the hyporheic zone. The locations of hydrochemical transformation hotspots can be explained by the influences of critical physical variables, such as the intensity of seepage erosion, sediment texture, bottom microtopography, groundwater discharge characteristics, water temperatures, and the diversity of groundwater-fed vegetation. Hydrochemical studies performed in the ground- and surface-water contact zones within a channel head can identify the underlying causes of changes to water chemistry, which, in turn, can facilitate the protection of water resources against unfavourable changes that may affect the water quality at the headwater catchment.