Evaluating topography‐based predictions of shallow lateral groundwater discharge zones for a boreal lake‐stream system

Abstract

Groundwater discharge along streams exerts an important influence on biogeochemistry and thermal regimes of aquatic ecosystems. A common approach for predicting locations of shallow lateral groundwater discharge is to use digital elevation models (DEMs) combined with upslope contributing area algorithms. We evaluated a topography‐based prediction of subsurface discharge zones along a 1500 m headwater stream reach using temperature and water isotope tracers. We deployed fiber‐optic distributed temperature sensing instrumentation to monitor stream temperature at 0.25 m intervals along the reach. We also collected samples of stream water for the analysis of its water isotope composition at 50 m intervals on five occasions representing distinct streamflow conditions before, during, and after a major rain event. The combined tracer evaluation showed that topography‐predicted locations of groundwater discharge were generally accurate; however, predicted magnitude of groundwater inflows estimated from upslope contributing area did not always agree with tracer estimates. At the catchment scale, lateral inflows were an important source of streamflow at base flow and peak flow during a major rain event; however, water from a headwater lake was the dominant water source during the event hydrograph recession. Overall, this study highlights potential utility and limitations of predicting locations and contributions of lateral groundwater discharge zones using topography‐based approaches in humid boreal regions.

Headwater lakes and their influence on downstream discharge

“…Despite this uncertainty, there are three key conclusions that are supported by the analysis: (1) the lake contributions estimated using the isotope mixing model are clearly less than the hydrometric estimates, which helps constrain the estimated contributions and also suggest a strong hyporheic influence in this system (Payn et al ), (2) the lake contribution estimates decrease with distance downstream, and (3) for the 1.4 and 3.4 km downstream sites, the lake contributions appear to peak at moderate lake outlet discharge. The validity of the last point is the most questionable given the uncertainty in the lake water contribution estimates; however, this finding is consistent with the detailed hydrograph separation analysis mentioned above that was conducted at the 1.4 km downstream location (Leach et al ).…”

“…Therefore, we constrained these maximum estimates by using δ 18 O water isotope measurements. Grab water samples have been routinely collected weekly to biweekly at the hydrometric stations for the 2008–2016 period following the water isotope collection and water sample analysis methods outlined in Leach et al (). For every occasion when water isotope samples were made at C5 and one of C6 ( n = 187), C9 ( n = 154), and C13 ( n = 149), the fraction of streamflow comprised of water sourced from the lake ( F lake ) was estimated as: where C stream is the isotope composition at C6, C9, or C13; C lake is the isotope composition at C5 lake outlet; and C hillslope is the isotope composition of hillslope runoff water from combined groundwater, forest soil water, and mire water sources.…”

Empirical Stream Thermal Sensitivities May Underestimate Stream Temperature Response to Climate Warming

“…The throughflow advective flux is often poorly represented in stream temperature models (Leach & Moore, ). However, the importance of throughflow advection for headwater thermal regimes is beginning to be more broadly recognized (Gallice et al, ; Leach et al, ).…”

Saturated areas through the lens: 1. Spatio‐temporal variability of surface saturation documented through thermal infrared imagery

“…Varying riparian morphological traits and upland topographic characteristics have been associated to the variability in hydrological and biogeochemical functions of riparian zones. Several studies have accounted for the spatial variability of riparian zones when exploring riparian functions such as water table fluctuation (Grabs, Bishop, Laudon, Lyon, & Seibert, 2012), vertical and lateral connectivity (Leach et al, 2017;Ploum, Leach, Kuglerová, & Laudon, 2018), or water travel distance and retention of chemicals (Grabs et al, 2012;Ledesma et al, 2018;Vidon & Hill, 2004). On the other hand, riparian surface saturation dynamics have been mainly investigated by taking into account single riparian sections (Zillgens, Merz, Kirnbauer, & Tilch, 2007) or the dynamics of the riparian system as a whole (Ocampo, Oldham, Sivapalan, & Turner, 2006).…”