Hydrology and Earth System Sciences
Hydrology and Earth System Sciences
HESS
Articles | Volume 20, issue 11
Articles | Volume 20, issue 11
https://doi.org/10.5194/hess-20-4439-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/hess-20-4439-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Articles | Volume 20, issue 11
Research article
 | 
03 Nov 2016
Research article |  | 03 Nov 2016

Solar-forced diurnal regulation of cave drip rates via phreatophyte evapotranspiration

Katie Coleborn, Gabriel C. Rau, Mark O. Cuthbert, Andy Baker, and Owen Navarre

Abstract. We present results of a detailed study of drip rate variations at 12 drip discharge sites in Glory Hole Cave, New South Wales, Australia. Our novel time series analysis, using the wavelet synchrosqueezed transform, reveals pronounced oscillations at daily and sub-daily frequencies occurring in 8 out of the 12 monitored sites. These oscillations were not spatially or temporally homogenous, with different drip sites exhibiting such behaviour at different times of year in different parts of the cave. We test several hypotheses for the cause of the oscillations, including variations in pressure gradients between karst and cave due to cave breathing effects or atmospheric and earth tides, variations in hydraulic conductivity due to changes in viscosity of water with daily temperature oscillations, and solar-driven daily cycles of vegetative (phreatophytic) transpiration. We conclude that the only hypothesis consistent with the data and hydrologic theory is that daily oscillations are caused by solar-driven pumping by phreatophytic trees which are abundant at the site. The daily oscillations are not continuous and occur sporadically in short bursts (2–14 days) throughout the year due to non-linear modification of the solar signal via complex karst architecture. This is the first indirect observation leading to the hypothesis of tree water use in cave drip water. It has important implications for karst hydrology in regards to developing a new protocol to determine the relative importance of trends in drip rate, such as diurnal oscillations, and how these trends change over timescales of weeks to years. This information can also be used to infer karst architecture. This study demonstrates the importance of vegetation on recharge dynamics, information that will inform both process-based karst models and empirical estimation approaches. Our findings support a growing body of research exploring the impact of trees on speleothem paleoclimate proxies.

How to cite. Coleborn, K., Rau, G. C., Cuthbert, M. O., Baker, A., and Navarre, O.: Solar-forced diurnal regulation of cave drip rates via phreatophyte evapotranspiration, Hydrol. Earth Syst. Sci., 20, 4439–4455, https://doi.org/10.5194/hess-20-4439-2016, 2016.
Received: 09 Jan 2016 – Discussion started: 15 Feb 2016 – Revised: 04 Oct 2016 – Accepted: 11 Oct 2016 – Published: 03 Nov 2016
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Short summary
This is the first observation of tree water use in cave drip water. Our novel time series analysis using the synchrosqueeze transform identified daily and sub-daily oscillations in drip rate. The only hypothesis consistent with hydrologic theory and the data was that the oscillations were caused by solar driven pumping by trees above the cave. We propose a new protocol for inferring karst architecture and our findings support research on the impact trees on speleothem paleoclimate proxies.
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