Comparison of environmental tracers including organic micropollutants as groundwater exfiltration indicators into a small river of a karstic catchment

Abstract

Understanding groundwater–surface water (GW–SW) interactions is vital for water management in karstic catchments due to its impact on water quality. The objective of this study was to evaluate and compare the applicability of seven environmental tracers to quantify and localize groundwater exfiltration into a small, human‐impacted karstic river system. Tracers were selected based on their emission source to the surface water either as (a) dissolved, predominantly geogenic compounds (radon‐222, sulphate and electrical conductivity) or (b) anthropogenic compounds (predominantly) originating from wastewater treatment plant (WWTP) effluents (carbamazepine, tramadol, sodium, chloride). Two contrasting sampling approaches were compared (a) assuming steady‐state flow conditions and (b) considering the travel time of the water parcels (Lagrangian sampling) through the catchment to account for diurnal changes in inflow from the WWTP. Spatial variability of the concentrations of all tracers indicated sections of preferential groundwater inflow. Lagrangian sampling techniques seem highly relevant for capturing dynamic concentration patterns of WWTP‐derived compounds. Quantification of GW inflow with the finite element model FINIFLUX, based on observed in‐stream Rn activities led to plausible fluxes along the investigated river reaches (0.265 m3 s−1), while observations of other natural or anthropogenic environmental tracers produced less plausible water fluxes. Important point sources of groundwater exfiltration can be ascribed to locations where the river crosses geological fault lines. This indicates that commonly applied concepts describing groundwater–surface water interactions assuming diffuse flow in porous media are difficult to transfer to karstic river systems whereas concepts from fractured aquifers may be more applicable. In general, this study helps selecting the best suited hydrological tracer for GW exfiltration and leads to a better understanding of processes controlling groundwater inflow into karstic river systems.

Interactive effects of catchment mean water residence time and agricultural area on water physico-chemical variables and GHG saturations in headwater streams

“…The higher seasonal dampening of δ 18 O and δ 2 H isotopic signals of stream water in the Neckar and Schwingbach catchments relative to the Loisach catchment suggests that most streams within these catchments are mainly groundwater-fed (Figure 3). Our findings agree with previous studies, which found significant groundwater contributions to stream discharge within the two catchments (Orlowski et al, 2016;Glaser et al, 2020). In contrast to streams in the Neckar and Schwingbach catchments, δ 18 O and δ 2 H isotopic signals in the Loisach were more seasonally variable, with summer and autumn peaks coinciding with rainfall events.…”

Anthropogenic activities significantly increase annual greenhouse gas (GHG) fluxes from temperate headwater streams in Germany

“…It has moderate slopes with an elevation ranging from 319-610 m a.s.l. The Ammer stream is a gaining stream fed by an extensive groundwater karst system and has significant discharge levels even during the driest periods of the year (Glaser et al, 2020 Across the five catchments, a total of 28 sites at headwater streams (N=23, orders 1-6, defined after Strahler, 1952), drainage ditches (N=3) and waste water outflows (N=2, Text A1) were sampled every 2-3 weeks for an entire year (Table 1, Fig. 1).…”

Groundwater‐surface water exchange as key control for instream and groundwater nitrate concentrations along a first‐order agricultural stream

“…The radioactive noble gas radon ( 222 Rn) constitutes a good qualitative indicator for GW contributions to the stream because 222 Rn is mainly produced in the aquifer's sediment matrix by the decay of radium‐226 contained therein (Glaser et al, 2020). Stream water was sampled for the analysis of dissolved 222 Rn on 9 February 2018 and 13 August 2018 at the seven stream locations (see Figure 1a).…”

“…GW inflow into the stream was simulated based on the 222 Rn data from stream and GW applying the finite element model FIN-IFLUX (Frei & Gilfedder, 2015;Glaser et al, 2020). The model application did not yield reliable results (see Supporting Information S1).…”