Catchment properties shape seasonal variation in groundwater- surface
water interaction - geogenic silicate as a proxy for hydrological
turnover induced mixing
Abstract
The cumulative and bidirectional groundwater-surface water (GW-SW)
interaction along a stream is defined as hydrological turnover (HT)
influencing solute transport and source water composition. However, HT
proves to be highly variable, producing spatial exchange patterns
influenced by local surface- and groundwater levels, geology and
topography. Hence, identifying factors controlling HT in streams poses a
challenge. We studied the spatiotemporal variability of HT processes at
a third order tributary of the river Mosel, Germany at two different
stream reaches over a period of two years. Additionally, we sampled for
silicate concentrations in the stream as well as in the near-stream
groundwater. Thus, creating snapshots of the boundary layer between
ground- and surface water where turnover induced mixing occurs. We
characterize reach specific drainage behavior by utilizing a
delayed/base flow separation analysis for both reaches. The results show
a site-specific negative correlation of HT with discharge, while
hydraulic gradients and reach scale absolute discharge changes
correlating with HT only at the upstream site which is characterized by
steeper hillslopes compared to the downstream section. Analyzing the
variation of silicate concentrations between stream and wells shows that
in-reach silicate variation increases significantly with the decrease of
HT under groundwater dominated flow conditions.. In Summary, our results
show that discharge shapes the influence of HT on solute transport as
visualized by silicate variations. Yet, reach specific drainage behavior
shapes seasonal states of groundwater storages and thus, can be an
additional control of HT magnitudes, influencing physical stream water
composition throughout the year.