Upland Controls on the Hydrological Functioning of Riparian Zones in Glacial Till Valleys of the Midwest¹

Abstract

Identifying relationships between landscape hydrogeological setting, riparian hydrological functioning and riparian zone sensitivity to climate and water quality changes is critical in order to best use riparian zones as best management practices in the future. In this study, we investigate water table dynamics, water flow path and the relative importance of precipitation, deep ground water (DG) and seep water as sources of water to a riparian zone in a deeply incised glacial till valley of the Midwest. Data indicate that water table fluctuations are strongly influenced by soil texture and to a lesser extent by upland sediment stratigraphy producing seeps near the slope bottom. The occurrence of till in the upland and at 1.7‐2 m in the riparian zone contributes to maintaining flow parallel to the ground surface at this site. Lateral ground‐water fluxes at this site with a steep topography in the upland (16%) and loam soil near the slope bottom are small (<10 l/d/m stream length) and intermittent. A shift in flow path from a lateral direction to a down valley direction is observed in the summer despite the steep concave topography and the occurrence of seeps at the slope bottom. Principal component and discriminant analysis indicate that riparian water is most similar to seep water throughout the year and that DG originating from imbedded sand and gravel layers in the lower till unit is not a major source of water to riparian zones in this setting. Water quality data and the dependence of the riparian zone for recharge on seep water suggest that sites in this setting may be highly sensitive to changes in precipitation and water quality in the upland in the future. A conceptual framework describing the hydrological functioning of riparian zones on this setting is presented to generalize the finding of this study.

Groundwater dynamics in a till hillslope: flow directions, gradients and delay

“…For the gentle sloping sites, groundwater flow directions usually shifted from pointing towards the stream during wet conditions to pointing down the valley parallel to the stream during drier conditions. Vidon and Smith (2007) observed similar variations in groundwater flow directions in the riparian zone of a catchment in Indiana, USA. During periods with higher water tables in winter and spring, the flow direction was towards the stream, whereas it was almost parallel to the stream during the summer months with generally lower groundwater levels.…”

Riparian zone hydrology and soil water total organic carbon (TOC): implications for spatial variability and upscaling of lateral riparian TOC exports

“…In contrast to the transmissivity feedback mechanism (Bishop, 1991;Laudon et al, 2004b;Nyberg et al, 2001;Kendall et al, 1999;Rodhe, 1989), the two additional assumptions (constant hydraulic gradients and homogeneous specific discharge) that underlie the derivation of lateral flow profiles have been less intensively studied in the past. Heterogeneous land cover and topography, for instance, might influence the timing, magnitude and direction of hydraulic gradients in the RZ (Bishop, 1994;Vidon and Smith, 2007;Rodhe and Seibert, 2011), as well as the spatial variability of specific discharge rates Lyon et al, 2012).…”

“…These hydromorphic features have normally evolved over long periods of time ranging from several years to millennia. Understanding RZ functioning is important for understanding long-term and short-term effects of upslope hydrological controls (Vidon and Smith, 2007) on riparian vegetation and soils, which in turn can chemically modulate hydrological fluxes from upslope areas.…”

Implications of hydrologic connectivity between hillslopes and riparian zones on streamflow composition

“…However, many studies found the riparian zone to significantly buffer the nutrient input from the hillslopes before the groundwater discharges into the stream (e.g., McGlynn and Seibert, 2003;Vidon and Smith, 2007). The buffering capacity of the riparian zones is linked to the dominant flow and transport processes as well as to the subsurface properties and biogeochemical conditions that determine the residence time of the groundwater and hence, sorption and degradation rates.…”