Baseflow dynamics

multi-tracer surveys to assess variable groundwater contributions to montane streams under low flows

M. Blumstock, D. Tetzlaff, I. A. Malcolm, G. Neutzmann, C. Soulsby

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Abstract

We monitored changing groundwater-surface water interactions during a drought with a 10 year return period in a 3.2 km2 catchment in the Scottish Highlands. The montane catchment is underlain by granite and metasediments and has extensive cover of diverse drift deposits (70%), which are up to 40 m deep. Flat valley bottom areas fringing the stream channel are characterised by deep peat soil (0.5–4 m deep) which covers about 20% of the catchment and receive drainage from upslope areas. The drought resulted in small declines in soil moisture and groundwater levels in the valley bottom wetlands, but marked, rapid declines on steeper upland slopes. These coincided with gradual decreases in discharge; however, the chemical and isotopic composition of reduced stream flows showed both temporal and spatial variation. Synoptic hydrogeochemical surveys were carried out on four occasions as flows declined. Each survey repeated sampling of 26 sites along the 3 km long stream network. Samples were analysed for major anions, cations and water isotopes. Initial surveys just after the last winter rain showed relatively homogenous stream chemistry, consistent with dominant near-surface drainage from acidic riparian peat soils. Stream chemistry became increasingly enriched with weathering-derived solutes (e.g. alkalinity, Ca2+, Mg2+, etc.) as flows declined and groundwater dominance of flow increased. However, these changes showed marked spatial variability implying geochemical differences in the bedrock geology and the distribution of storage in drift deposits. Temporal dynamics inferred heterogeneous montane groundwater bodies contributed to flows differentially during the recession. Isotope data indicated that in places the stream was also influenced by evaporative losses from the surface of the peat soils. The largest sources of groundwater appear to be located in the drift in the lower catchment where the most marked increase in weathering-derived ions occurred, and depleted, non-fractionated isotope signatures implied deeper inflows.
Original languageEnglish
Pages (from-to)1021-1033
Number of pages13
JournalJournal of Hydrology
Volume527
Early online date1 Jun 2015
DOIs
Publication statusPublished - Aug 2015

Fingerprint

mountain stream
baseflow
low flow
peat soil
tracer
catchment
groundwater
isotope
weathering
drought
drainage
groundwater-surface water interaction
valley
stream channel
metasediment
return period
alkalinity
streamflow
anion
solute

Keywords

  • base flow
  • low flow
  • droughts
  • groundwater
  • tracers
  • isotopes

Cite this

Baseflow dynamics : multi-tracer surveys to assess variable groundwater contributions to montane streams under low flows . / Blumstock, M.; Tetzlaff, D.; Malcolm, I. A.; Neutzmann, G.; Soulsby, C.

In: Journal of Hydrology, Vol. 527, 08.2015, p. 1021-1033.

Research output: Contribution to journalArticle

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abstract = "We monitored changing groundwater-surface water interactions during a drought with a 10 year return period in a 3.2 km2 catchment in the Scottish Highlands. The montane catchment is underlain by granite and metasediments and has extensive cover of diverse drift deposits (70{\%}), which are up to 40 m deep. Flat valley bottom areas fringing the stream channel are characterised by deep peat soil (0.5–4 m deep) which covers about 20{\%} of the catchment and receive drainage from upslope areas. The drought resulted in small declines in soil moisture and groundwater levels in the valley bottom wetlands, but marked, rapid declines on steeper upland slopes. These coincided with gradual decreases in discharge; however, the chemical and isotopic composition of reduced stream flows showed both temporal and spatial variation. Synoptic hydrogeochemical surveys were carried out on four occasions as flows declined. Each survey repeated sampling of 26 sites along the 3 km long stream network. Samples were analysed for major anions, cations and water isotopes. Initial surveys just after the last winter rain showed relatively homogenous stream chemistry, consistent with dominant near-surface drainage from acidic riparian peat soils. Stream chemistry became increasingly enriched with weathering-derived solutes (e.g. alkalinity, Ca2+, Mg2+, etc.) as flows declined and groundwater dominance of flow increased. However, these changes showed marked spatial variability implying geochemical differences in the bedrock geology and the distribution of storage in drift deposits. Temporal dynamics inferred heterogeneous montane groundwater bodies contributed to flows differentially during the recession. Isotope data indicated that in places the stream was also influenced by evaporative losses from the surface of the peat soils. The largest sources of groundwater appear to be located in the drift in the lower catchment where the most marked increase in weathering-derived ions occurred, and depleted, non-fractionated isotope signatures implied deeper inflows.",
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AU - Soulsby, C.

N1 - Acknowledgements This work is part of the Aqualink project and has been funded by the Leibniz Association: Joint Initiative for Research and Innovation (PAKT). We would like to thank the NRI staff for their help during field and laboratory work, especially Audrey Innes and Jonathan Dick. The water samples were analysed for major ions at the Marine Scotland Science, Freshwater Fisheries Laboratory, in Pitlochry. We also would like to thank Guillaume Bertrand and two anonymous reviewers for the constructive comments which helped improve this manuscript.

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N2 - We monitored changing groundwater-surface water interactions during a drought with a 10 year return period in a 3.2 km2 catchment in the Scottish Highlands. The montane catchment is underlain by granite and metasediments and has extensive cover of diverse drift deposits (70%), which are up to 40 m deep. Flat valley bottom areas fringing the stream channel are characterised by deep peat soil (0.5–4 m deep) which covers about 20% of the catchment and receive drainage from upslope areas. The drought resulted in small declines in soil moisture and groundwater levels in the valley bottom wetlands, but marked, rapid declines on steeper upland slopes. These coincided with gradual decreases in discharge; however, the chemical and isotopic composition of reduced stream flows showed both temporal and spatial variation. Synoptic hydrogeochemical surveys were carried out on four occasions as flows declined. Each survey repeated sampling of 26 sites along the 3 km long stream network. Samples were analysed for major anions, cations and water isotopes. Initial surveys just after the last winter rain showed relatively homogenous stream chemistry, consistent with dominant near-surface drainage from acidic riparian peat soils. Stream chemistry became increasingly enriched with weathering-derived solutes (e.g. alkalinity, Ca2+, Mg2+, etc.) as flows declined and groundwater dominance of flow increased. However, these changes showed marked spatial variability implying geochemical differences in the bedrock geology and the distribution of storage in drift deposits. Temporal dynamics inferred heterogeneous montane groundwater bodies contributed to flows differentially during the recession. Isotope data indicated that in places the stream was also influenced by evaporative losses from the surface of the peat soils. The largest sources of groundwater appear to be located in the drift in the lower catchment where the most marked increase in weathering-derived ions occurred, and depleted, non-fractionated isotope signatures implied deeper inflows.

AB - We monitored changing groundwater-surface water interactions during a drought with a 10 year return period in a 3.2 km2 catchment in the Scottish Highlands. The montane catchment is underlain by granite and metasediments and has extensive cover of diverse drift deposits (70%), which are up to 40 m deep. Flat valley bottom areas fringing the stream channel are characterised by deep peat soil (0.5–4 m deep) which covers about 20% of the catchment and receive drainage from upslope areas. The drought resulted in small declines in soil moisture and groundwater levels in the valley bottom wetlands, but marked, rapid declines on steeper upland slopes. These coincided with gradual decreases in discharge; however, the chemical and isotopic composition of reduced stream flows showed both temporal and spatial variation. Synoptic hydrogeochemical surveys were carried out on four occasions as flows declined. Each survey repeated sampling of 26 sites along the 3 km long stream network. Samples were analysed for major anions, cations and water isotopes. Initial surveys just after the last winter rain showed relatively homogenous stream chemistry, consistent with dominant near-surface drainage from acidic riparian peat soils. Stream chemistry became increasingly enriched with weathering-derived solutes (e.g. alkalinity, Ca2+, Mg2+, etc.) as flows declined and groundwater dominance of flow increased. However, these changes showed marked spatial variability implying geochemical differences in the bedrock geology and the distribution of storage in drift deposits. Temporal dynamics inferred heterogeneous montane groundwater bodies contributed to flows differentially during the recession. Isotope data indicated that in places the stream was also influenced by evaporative losses from the surface of the peat soils. The largest sources of groundwater appear to be located in the drift in the lower catchment where the most marked increase in weathering-derived ions occurred, and depleted, non-fractionated isotope signatures implied deeper inflows.

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KW - droughts

KW - groundwater

KW - tracers

KW - isotopes

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DO - 10.1016/j.jhydrol.2015.05.019

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JO - Journal of Hydrology

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SN - 0022-1694

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