Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations

Abstract

Abstract:To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995-96) had abnormally low snow precipitation, which gave a deep frost down to 40-80 cm, whereas the two following winters had frost depths of 5-20 cm. During winter 1995-96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5-7 vol.% in the mineral soil and 10-15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage.

Evaluating digital terrain indices for soil wetness mapping – a Swedish case study

“…In terms of the undulating terrain covered by compacted glacial till about 5-10 m deep in Areas 1 and 2 , saturated hydraulic conductivities would decrease rapidly with depth (Nyberg et al, 2001), as is mostly the case on till deposits across Scandinavia and elsewhere (Nyberg, 1995;Beven and Germann, 2013). As a result, (i) 90 % of lateral water movements on compacted tills would occur within the top 50 cm (Bishop et al, 2011), and (ii) the soil portions of these till deposits would saturate quickly during wet weather and wet seasons.…”

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

“…That 1991 study also examined lateral versus vertical hydraulic gradients during stream events and concluded that on two till hillslopes in the vicinity of the ROK, upwelling groundwater is not a major factor as lateral subsurface flow is the dominant flow component. 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).…”

Riparian Zone Influence on Stream Water Dissolved Organic Carbon Concentrations at the Swedish Integrated Monitoring Sites

“…The flow function, q rip (z), can be derived by differentiating the relationship between stream discharge and groundwater table (GWT) depth (Moldan and Wright 1998;Fölster 2001;Nyberg et al 2001;Seibert et al 2003):…”