Revealing the spatial variability of water fluxes at the groundwater‐surface water interface

Abstract

[1] There is widespread recognition that the groundwater-surface water interface can have significant influence on the pattern and form of the transfer of nutrient-rich groundwater to rivers. Characterizing and quantifying this influence is critical for successful management of water resources in many catchments, particularly those threatened by rising nitrate levels in groundwater. Building on previous experimental investigations in one such catchment: the River Leith, UK, we report on a multimeasurement, multiscale program aimed at developing a conceptualization of groundwater-surface water flow pathways along a 200 m reach. Key to this conceptualization is the quantification of vertical and horizontal water fluxes, which is achieved through a series of Darcian flow estimates coupled with in-stream piezometer tracer dilution tests. These data, enhanced by multilevel measurements of chloride concentration in riverbed pore water and water-borne geophysical surveying, reveal a contrast in the contribution of flow components along the reach. In the upper section of the reach, a localized connectivity to regional groundwater, that appears to suppress the hyporheic zone, is identified. Further downstream, horizontal (lateral and longitudinal) flows appear to contribute more to the total subsurface flow at the groundwater-surface water interface. Although variation in hydraulic conductivity of the riverbed is observed, localized variation that can account for the spatial variability in flow pathways is not evident. The study provides a hydrological conceptualization for the site, which is essential for future studies which address biogeochemical processes, in relation to nitrogen retention/release. Such a conceptualization would not have been possible without a multiexperimental program.Citation: Binley, A., S. Ullah, A. L. Heathwaite, C. Heppell, P. Byrne, K. Lansdown, M. Trimmer, and H. Zhang (2013), Revealing the spatial variability of water fluxes at the groundwater-surface water interface, Water Resour. Res., 49,[3978][3979][3980][3981][3982][3983][3984][3985][3986][3987][3988][3989][3990][3991][3992]

Influence of emergent vegetation on nitrate cycling in sediments of a groundwater-fed river

“…Particle size sieving of a sediment core collected from the thalweg of the river in the UVS revealed that about 50 % of the overlying sediments mainly consisted of gravels ([2 and \63 mm) in the upper 40 cm Binley et al 2013), which is consistent with Krause et al (2009). DET probes fabricated into 30 cm long plastic plates and protected in stainless steel holders were deployed into the river bed for four occasions between July and September 2010 coinciding with the main plant growth season.…”

“…Dissimilatory nitrate reduction to ammonium (DNRA) could be an additional sink for pore water nitrate loss beneath VS (Kelso et al 1997); however, the potential for NO 3 -loss through DNRA was of minimal importance compared to denitrification in the un-vegetated sediments of River Leith . That said, dilution of pore water NO 3 -by down-welling surface water (with lower NO 3 -levels than the upwelling groundwater) may have been another possibility for the observed low NO 3 -under VS; however, the likelihood of significant dilution effect particularly in sediments deeper than 10 cm appear minor given the fact that the river is predominantly groundwater-fed under base flow conditions (Kaeser et al 2009;Binley et al 2013). ?…”

“…1). The study site for the research described in this paper lies within a 200 m reach of the River Leith used for the larger project: the detailed lithology and hydrology are given in Binley et al (2013). For reference, Site C in Binley et al (2013) corresponds to the UVS.…”

“…All deployments were undertaken under base flow conditions with discharges of 0.11, 0.27, 0.08 and 0.11 m 3 s -1 on the day of DET probes retrieval in July to September. Typical base flow discharge in this river is around 0.1 m 3 s -1 (Kaeser et al 2009;Binley et al 2013). …”

“…1). A petrol driven Cobra TT drill was used to drill the river bed using a 50 mm corer equipped with a plastic liner as in Binley et al (2013). The collected cores were sectioned into 5 cm interval at the field site, placed in zip-lock bags, transferred to the laboratory on ice and frozen until further analysis.…”