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Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions.

Tetzlaff D, Birkel C, Dick J, Geris J, Soulsby C - Water Resour Res (2014)

Bottom Line: Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water.Our study is novel in showing that they act as "isostats," not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.Hillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution.

View Article: PubMed Central - PubMed

Affiliation: Northern Rivers Institute, School of Geosciences, University of Aberdeen Aberdeen, UK.

ABSTRACT

: We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. "pre-event" water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as "isostats," not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.

Key points: Hillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution.

No MeSH data available.


Depth to groundwater versus streamflow for two of the wells for the entire study period. Markers were plotted at 15 min intervals: (a) an example for a riparian well and (b) an example for a well at steeper hillslope. Arrows show general direction of hysteresis loops.
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fig05: Depth to groundwater versus streamflow for two of the wells for the entire study period. Markers were plotted at 15 min intervals: (a) an example for a riparian well and (b) an example for a well at steeper hillslope. Arrows show general direction of hysteresis loops.

Mentions: This was also consistent with the lag times between the groundwater and streamflow responses exhibiting spatial variability when all 13 groundwater wells in the catchment were considered (not all data shown). Depending upon antecedent conditions, the riparian wells close to the channel exhibited peak water table levels 1–5 h before peak discharge, while those on the upper hillslopes peaked 1–3 h after the highest flow (Figure 5). This also tended to result in positive clockwise but narrow hysteresis curves in the relationships between water table levels in riparian wells and stream discharge (Figure 5a). This was usually reversed deeper in the podzol, indicating drainage contributions on the stream recession (Figure 5b). The nonlinear response of the steeper hillslopes was also evident, where for the larger events the water table was close to the ground surface, but in moderate events only reached into the B horizon. Consequently, the magnitude of water table variations tends to increase with distance from the channel. This resulted in a positive relationship between altitude and mean water table depth and the degree of water table fluctuations.


Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions.

Tetzlaff D, Birkel C, Dick J, Geris J, Soulsby C - Water Resour Res (2014)

Depth to groundwater versus streamflow for two of the wells for the entire study period. Markers were plotted at 15 min intervals: (a) an example for a riparian well and (b) an example for a well at steeper hillslope. Arrows show general direction of hysteresis loops.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4257581&req=5

fig05: Depth to groundwater versus streamflow for two of the wells for the entire study period. Markers were plotted at 15 min intervals: (a) an example for a riparian well and (b) an example for a well at steeper hillslope. Arrows show general direction of hysteresis loops.
Mentions: This was also consistent with the lag times between the groundwater and streamflow responses exhibiting spatial variability when all 13 groundwater wells in the catchment were considered (not all data shown). Depending upon antecedent conditions, the riparian wells close to the channel exhibited peak water table levels 1–5 h before peak discharge, while those on the upper hillslopes peaked 1–3 h after the highest flow (Figure 5). This also tended to result in positive clockwise but narrow hysteresis curves in the relationships between water table levels in riparian wells and stream discharge (Figure 5a). This was usually reversed deeper in the podzol, indicating drainage contributions on the stream recession (Figure 5b). The nonlinear response of the steeper hillslopes was also evident, where for the larger events the water table was close to the ground surface, but in moderate events only reached into the B horizon. Consequently, the magnitude of water table variations tends to increase with distance from the channel. This resulted in a positive relationship between altitude and mean water table depth and the degree of water table fluctuations.

Bottom Line: Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water.Our study is novel in showing that they act as "isostats," not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.Hillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution.

View Article: PubMed Central - PubMed

Affiliation: Northern Rivers Institute, School of Geosciences, University of Aberdeen Aberdeen, UK.

ABSTRACT

: We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. "pre-event" water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as "isostats," not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.

Key points: Hillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution.

No MeSH data available.