Sources and transit times of water in headwater temperate rainforest streams

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dc.contributor.authorCartwright, Ien_AU
dc.contributor.authorAtkinson, APen_AU
dc.contributor.authorGilfedder, BSen_AU
dc.contributor.authorHofmann, Hen_AU
dc.contributor.authorCendón, DIen_AU
dc.contributor.authorMorgenstern, Uen_AU
dc.date.accessioned2022-01-24T03:52:28Zen_AU
dc.date.available2022-01-24T03:52:28Zen_AU
dc.date.issued2019-04-07en_AU
dc.date.statistics2021-12-24en_AU
dc.description.abstractHeadwater catchments are important sources of water for many river systems. Unlike lower reaches of rivers that are frequently connected to alluvial aquifers, headwater catchments are commonly developed on indurated rocks that lack extensive groundwater systems. The observation, however, that many headwater streams are perennial implies that streamflow is sustained by water contained in fractures, soils, and/or the regolith. Understanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning and predicting the response of catchments to changing climate or land use. This study determines water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream indicates that water from soil pipes is the major contributor to streamflow. By contrast, riparian zone groundwater and water from elsewhere within the soils contributes little to streamflow. The streams are gaining and the lack of riparian zone groundwater inputs may be due to the presence of low hydraulic-conductivity organic-rich streambed sediments or compartmentalisation of shallow groundwater by clays in the weathered rocks. Similarly, pockets of isolated water within the soils that are not connected to the soil pipes also exist. The stream water has tritium (3H) activities of 1.80 to 2.06 TU, with slightly higher activities recorded during the higher winter flows. The water from the soil pipes has 3H activities of 1.80 to 2.25 TU, the riparian zone groundwater has 3H activities of 1.35 to 2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. The 3H activities of all these catchment waters are significantly lower than those of modern rainfall (2.6 to 3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These mean transit times are consistent with the waters being resident in the catchment for sufficient time for weathering reactions and evapotranspiration to occur. While the discharge from the soil pipes increases following periods of high rainfall, this water is stored for several years within the catchment before discharge (probably within the weathered regolith). Thus, the increase in discharge is not the simple transmission of recent rainfall through the macropores but mobilisation of younger stores of water as the catchment wets up. The long mean transit times of the stream water imply that it is derived from a relatively large store (>108 m3) and is buffered against year-on-year variations in rainfall. However, longer-term variations in rainfall or land use will likely impact streamflow. © Author(s) 2018. CC Attribution 4.0 license.en_AU
dc.identifier.articlenumberEGU2019-2341en_AU
dc.identifier.booktitleGeophysical Research Abstractsen_AU
dc.identifier.citationCartwright, I., Atkinson, A., Gilfedder, B., Hofmann, H., Cendon, D.I. Morgenstern, U. (2019). Sources and transit times of water in headwater temperate rainforest streams. Paper presented to the EGU General Assembly 2019, Vienna, Austria, 7-12 April 2019. In Geophysical Research Abstracts, Vol. 21, EGU2019-2341. Retrieved from: https://meetingorganizer.copernicus.org/EGU2019/EGU2019-2341.pdfen_AU
dc.identifier.conferenceenddate12 April 2019en_AU
dc.identifier.conferencenameEGU General Assembly 2019en_AU
dc.identifier.conferenceplaceVienna, Austriaen_AU
dc.identifier.conferencestartdate7 April 2019en_AU
dc.identifier.otherEGU2019-2341en_AU
dc.identifier.otherHS2.2.1en_AU
dc.identifier.urihttps://meetingorganizer.copernicus.org/EGU2019/EGU2019-2341.pdfen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/12713en_AU
dc.identifier.volume21en_AU
dc.language.isoenen_AU
dc.publisherCopernicus Publicationsen_AU
dc.subjectWateren_AU
dc.subjectAquifersen_AU
dc.subjectForestsen_AU
dc.subjectStreamsen_AU
dc.subjectRiversen_AU
dc.subjectWatershedsen_AU
dc.subjectGround wateren_AU
dc.subjectGeochemistryen_AU
dc.titleSources and transit times of water in headwater temperate rainforest streamsen_AU
dc.typeConference Abstracten_AU
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