Lateral water flux in the unsaturated zone: A mechanism for the formation of spatial soil heterogeneity in a headwater catchment

Abstract

Measurements of soil water potential and water table fluctuations suggest that morphologically distinct soils in a headwater catchment at the Hubbard Brook Experimental Forest in New Hampshire formed as a result of variations in saturated and unsaturated hydrologic fluxes in the mineral soil. Previous work showed that each group of these soils had distinct water table fluctuations in response to precipitation; however, observed variations in soil morphology also occurred above the maximum height of observed saturation. Variations in unsaturated fluxes have been hypothesized to explain differences in soil horizon thickness and presence/absence of specific horizons but have not been explicitly investigated. We examined tensiometer and shallow groundwater well records to identify differences in unsaturated water fluxes among podzols that show distinct morphological and chemical differences. The lack of vertical hydraulic gradients at the study sites suggests that lateral unsaturated flow occurs in several of the soil units. We propose that the variations in soil horizon thickness and presence/absence observed at the site are due in part to slope‐parallel water flux in the unsaturated portion of the solum. In addition, unsaturated flow may be involved in the translocation of spodic material that primes those areas to contribute water with distinct chemistry to the stream network and represents a potential source/sink of organometallic compounds in the landscape.

Redistribution of soil metals and organic carbon via lateral flowpaths at the catchment scale in a glaciated upland setting

“…Fig. 4b; Bailey et al, 2014;Gannon et al, 2014Gannon et al, , 2017 (1983) and Lundstrom et al (2000). The chemical composition of typical podzols was also consistent with vertical podzolization under unsaturated conditions.…”

“…The HPUs classified at HBEF embodied differing vertical and lateral podzolization processes. The documentation of unsaturated lateral flux provided a hydrologic basis for the observed morphology and lateral podzolization which had previously been assumed (Gannon et al, 2017).…”

“…In near-stream zones or bench areas where Bh-podzols were found, spodic materials were thought to accumulate in the subsurface due to a decrease in slope, which reduced hydraulic gradients and altered downslope drainage conditions (e.g., Crave and Gascuel-Odoux, 1997;Hjerdt et al, 2004). Previous studies had hypothesized that the Bh horizon in WS3 was mostly developed through lateral podzolization (Bailey et al, 2014;Bourgault et al, 2015a;Gannon et al, 2017). This hypothesis was supported by the observation that the top of the Bh horizon extended above the water table and slope-parallel unsaturated water flux was observed in the upper Bh horizon (Gannon et al, 2017).…”

Time variability and uncertainty in the fraction of young water in a small headwater catchment

“…The 2015 European heat wave was among the top 10 heat waves of the past 65 years and was accompanied by the lowest surface water temperatures of the North Atlantic in the period of 1948 to 2015 (Duchez et al, 2016). The North Atlantic influences the European summer climate (Ghosh et al, 2017) and is an important vapor source for precipitation over Europe (Hurrell, 1995;Trigo et al, 2004). The combined effects of low ocean water temperatures and high air temperatures in Europe were visible in the d excess that lost its clear seasonal signal in summer 2015 (Fig.…”

Mineral Weathering and Podzolization Control Acid Neutralization and Streamwater Chemistry Gradients in Upland Glaciated Catchments, Northeastern United States

“…Soils at HBEF are dominantly Spodosols, a common soil type in cool humid forested regions (Sauer et al, 2007) where primary mineral weathering and leaching and precipitation of Al and Fe complexed by organic acids are dominant soil forming processes. A hydropedologic soil classification (Gannon et al, 2014 ; Table 1), based on relationships between soil morphology and groundwater regime observed at the soil profile-and catena-scale distinguishes between soils formed primarily by vertical leaching processes, above the influence of the water table, and laterally formed soils that reflect groundwater influence on soil development and lateral translocations between profiles at the hillslope scale Gannon et al, 2017). Thus soil development patterns may be used to understand processes occurring along hydrologic flowpaths.…”