Linking Subsurface Lateral Flowpath Activity with Streamflow Characteristics in a Semiarid Headwater Catchment

Abstract

Streamflow generation in semiarid Mediterranean environments is governed by the timing and amount of precipitation. Although topography is widely considered a dominant factor controlling the delivery of water to streams, we hypothesized that antecedent soil moisture and soil stratigraphy regulates the vertical dimension of hydrologie flowpaths and streamflow generation in a headwater catchment of the Sierra Foothill Region in California. We monitored soil moisture, subsurface lateral flow, streamflow, and meteorological conditions in a 33-ha catchment to study the linkage between hydrologie flowpaths in soil and streamflow characteristics. A total of 100 soil profiles were instrumented with soil moisture sensors at four depths in A, AB, Btl, and 2Btss horizons. A hillslope perched-water collection system was used to measure subsurface lateral flow from these same horizons using tipping buckets. Streamflow was monitored using a V-notch weir for low flows and Parshall flume for high flows. Integrated hydrologie measurements show a close synchrony between streamflow and subsurface lateral flow in AB and Bt horizons overlying a hydraulically restrictive claypan (2Btss horizon). The thickness of the perched water table controlled the magnitude of subsurface lateral flow, which was greatest when AB horizons became saturated. Stream recession characteristics were controlled by lateral flow in less permeable horizons (Bt) directly overlying the claypan. Through the course of the water year, subsurface lateral flow from near surface horizons (A and AB) increased as antecedent soil moisture and thickness of the perched water table increased catchment-wide. The dynamic nature of hydrologie flowpaths in this system has implications for water quality as water is short-circuited to tbe stream through upper soil horizons. This study highlights the need for a detailed understanding of soil stratigraphie relationships to fully understand and model streamflow and water quality dynamies in semiarid soils with strongly contrasting physieal properties.

The Genesis and Exodus of Vascular Plant DOM from an Oak Woodland Landscape

“…Our most complete set of trench samples was collected in conjunction with the January 2008 storm, and it is clear that in terms of lignin compositions, the 10-30 cm depth was the most volatile, with large changes in every lignin parameter during the storm, while the 0-10 and 30-60 cm depths were more stable (Figure 6). The 10-30 cm depth during this storm event accounted for over half of the total flow measured in the trench (Swarowsky et al, 2012). Based on DOC (and to some extent lignin concentrations) in HS stream water that was higher than the trench samples, it is clear that there must be additional sources of DOM to the stream.…”

“…In California oak woodlands, most DOM export from catchments is driven by storm events that rapidly mobilize DOM from the adjacent landscape which in turn flows to streams via several dynamic hydrologic flowpaths (Swarowsky et al, 2012). Scaling our litter/duff leachate yields (mass DOC released per mass of litter/duff) to a total annual amount of litter and duff on the landscape of HS (field observations of litter and duff horizon depths multiplied times density and area) indicates a net production of approximately 450 kg ha −1 DOC (Chow et al, 2009).…”

“…Hysteresis effects, in which DOC concentrations at a given discharge are significantly different between the rising and falling limbs of a storm, are well-known for streams and rivers (McGlynn and McDonnell, 2003), and similar variability extended to DOM composition as represented by lignin parameters (Figure 5). Short time-series sampling during the storm events revealed little in the way of consistent trends in how lignin parameters respond to DOM mobilization in HS (Figure 5 A portion of compositional variability is likely due to firstflush phenomena, which can be delayed by the necessity of wetting up in Mediterranean climates (O'Geen et al, 2010), however, changing contributions from different hydrologic flowpaths also must play a role (Swarowsky et al, 2012). The soil trench samples that isolate water transport through different soil horizons can be potentially helpful in parsing out these differences.…”

“…Leaching experiments generate a posteriori sources of DOM that can be traced through the study region and evaluated for processing effects (Aufdenkampe et al, 2001;Hernes et al, 2007;Spencer et al, 2008). And of course, demarcating and sampling representative hydrologic flowpaths can be instrumental in determining how the bulk of DOM enters headwater streams, which in turn helps to understand which processes and depths within the soil column are most influential in transforming the initial leachate compositions (Sanderman et al, 2009;Swarowsky et al, 2012).…”

Multi–Model Ensemble Approaches to Assessment of Effects of Local Climate Change on Water Resources of the Hotan River Basin in Xinjiang, China

“…The peak flow mainly occurs in summer when there is a large amount of snow and ice melt. Therefore, the differences in ice-snow melting process and snow cover distributions affect the formation of peak flow in both models.Primarily, most of the ice-snow melt water infiltrates into the soil and contributes to stream runoff as subsurface runoff [89,90] in the SWAT model. In the MIKE SHE model, however, the soil lateral flow is ignored [88].…”