Quantifying aggregation and change in runoff source in accordance with catchment area increase in a forested headwater catchment

Abstract

There has been a great deal of research interest regarding changes in flow path/runoff source with increases in catchment area. However, there have been very few quantitative studies taking subscale variability and convergence of flow path/runoff source into account, especially in relation to headwater catchments. This study was performed to elucidate how the contributions and discharge rates of subsurface water (water in the soil layer) and groundwater (water in fractured bedrock) aggregate and change with catchment area increase, and to elucidate whether the spatial variability of the discharge rate of groundwater determines the spatial variability of stream discharge or groundwater contribution. The study area was a 5‐km2 forested headwater catchment in Japan. We measured stream discharge at 113 points and water chemistry at 159 points under base flow conditions. End‐member mixing analysis was used to separate stream water into subsurface water and groundwater. The contributions of both subsurface water and groundwater had large variability below 1 km2. The contribution of subsurface water decreased markedly, while that of groundwater increased markedly, with increases in catchment area. The specific discharge of subsurface water showed a large degree of variability and decreased with catchment area below 0.1 km2, becoming almost constant above 0.1 km2. The specific discharge of groundwater showed large variability below 1 km2 and increased with catchment area. These results indicated that the variabilities of stream discharge and groundwater contribution corresponded well with the variability of the discharge rate of groundwater. However, below 0.1 km2, it was necessary to consider variations in the discharge rates of both subsurface water and groundwater. Copyright © 2016 John Wiley & Sons, Ltd.

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

“…Also, at Krycklan, Peralta‐Tapia et al () reported increasing contributions from deeper groundwater sources with increasing catchment area during winter baseflow. Similar increases in groundwater contributions with increasing catchment area during baseflow were observed in a forested catchment in Japan by Egusa, Ohte, Oda, and Suzuki () and in the southern Rocky Mountains by Frisbee, Phillips, Campbell, Liu, and Sanchez (). Nevertheless, the spatial variation in groundwater contributions and the specific physical properties that control the variability in water storage and drainage in headwater catchments during dry periods are still not well understood (e.g., Bishop et al, ; McClymont, Hayashi, Bentley, & Liard, ; Pfister et al, ; Smakhtin, ; Tague & Grant, ).…”

“…They observed high variability in streamwater chemistry that was driven by geology, soils and vegetation at small scales (<2-km distance from the measurements), and less variable streamwater chemistry on larger scales. Exfiltration of deeper groundwater can also affect streamwater chemistry, even at larger scales (e.g., Egusa et al, 2016;Frisbee et al, 2011;Katsuyama, Tani, & Nishimoto, 2010;Peralta-Tapia et al, 2015). Thus, it is important to study the spatial variability in streamflow and stream chemistry across a range of scales to gain insight into the landscape characteristics of the dominant streamflow-generating areas (Blöschl, 2001;McDonnell et al, 2007).…”

An Increase in Specific Discharge With Catchment Area Implies That Bedrock Infiltration Feeds Large Rather Than Small Mountain Headwater Streams

“…Water Resources Research specific discharge with area. Furthermore, the increase in specific discharge with increasing catchment size in a steep catchment is likely caused by a commensurate increase in the contribution of deep groundwater (e.g., Egusa et al, 2016;Shaman et al, 2004), but other causes are possible. Spatial variation in precipitation affects stream flow (e.g., Singh, 1997), although these effects have not been tested for the relationship between area and specific discharge in mesoscale catchments.…”

“…In this study, we focused on the pattern of increasing specific discharge with catchment area (Figure 1b). Previous studies using geochemical tracers have shown that an increase in specific discharge is associated with increased deep groundwater/bedrock groundwater exfiltration (Egusa et al, 2016; Fujimoto et al, 2016; Shaman et al, 2004), which is less significant or absent in smaller catchments. Groundwater in weathered or fractured bedrock can contribute substantially to the response of runoff to rainfall in small catchments in steep headwaters (e.g., Anderson et al, 1997; Komatsu & Onda, 1996; Onda et al, 2001, 2006; Uchida et al, 2003).…”

Discovery of zero‐order basins as an important link for progress in hydrogeomorphology

“…Later, Uchida, Asano, Onda, and Miyata () argued that spatial variability of hydrologic response was largely due to flow paths and contributions of bedrock flow in hillslopes and zero‐order basins; variability was dampened in larger catchments, while the bedrock contributions and preferential flow paths occurred at discreet locations along channels. Based on distributed investigations in channel networks (including zero‐order basins and headwater channels), patterns of spatial variability were also assessed by combinations of flow volume and geochemical signatures (Asano, Uchida, Mimasu, & Ohte, ; Egusa, Ohte, Oda, & Suzuki, ). As such, examining the extension from zero‐order basins to larger catchments highlights the unique response and importance of zero‐order basins in the larger catchment context.…”