Hydrogeochemistry of shallow groundwater in an upland Scottish catchment

Abstract

Abstract:The hydrogeochemistry of shallow groundwater has been characterized in the Allt a' Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the in¯uence of groundwater on the quality and quantity of stream¯ow. Shallow groundwater in super®cial drift deposits is circumneutral (pH $ 7 . 1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (4900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of base¯ow in the catchment and also buers the chemistry of stream water at high¯ows: groundwater may account for as much as 50±60% of annual runo in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. #

Regionalization of transit time estimates in montane catchments by integrating landscape controls

“… Feng et al , 2004]. The varying levels of damping in the individual catchments are generally consistent with the conceptualizations inferred from the flow duration curves (Figure 2) and those reported by other studies [e.g., Neal and Rosier , 1990; Soulsby et al , 2006a]: little damping at the site in the Strontian region with a suspected predominance of overland and preferential flow pathways, becoming slightly more attenuated at sites at Loch Ard and then increasingly attenuated at Balquhidder, and almost complete loss of the seasonal signal at the Allt a'Mharcaidh site, indicating the dominance of well‐mixed water routed through slower pathways [ Soulsby et al , 1998].…”

Lessons from the 2018 drought for management of local water supplies in upland areas: A tracer‐based assessment

“…This was encouraging in terms of maintaining ecosystem services and industrial abstractions (Folegot et al, 2018; Freire‐González et al, 2017). End‐member mixing showed that this groundwater contribution was 65–100% of streamflow throughout the drought, consistent with other Scottish studies, albeit not in such extreme droughts (Blumstock et al, 2015; Scheliga et al, 2018; Soulsby et al, 1998). This highlights: (a) the resilience of the streamflow quantity and quality (temperature) to the drought, (b) the importance of groundwater recharge to maintain this flow (Cuthbert et al, 2019; Haslinger et al, 2014; Segura et al, 2019), and (c) the fact that shallow sources with high YWFs are less resilient as they dried up (von Freyberg et al, 2018; Zimmer et al, 2013).…”

Experimental evidence of fast groundwater responses in a hillslope/floodplain area in the Black Forest Mountains, Germany

“…The major proportion of total runoff is dominated by pre-event water, which is in agreement with previous studies in mountainous catchments (e.g. McDonnell, 1990;Buttle, 1994;Yasuhara and Marui, 1994;Peters et al, 1995;Soulsby et al, 1998).…”