- 1Trent University, School of the Environment, Canada.
- 2National Institute of Water and Atmospheric Research, Christchurch, New Zealand.
- 3School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Canada.
- 4North China University of Water Resources and Electric Power, Zhengzhou, China.
- 5School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.
Transpiration significantly depletes terrestrial subsurface water stores and plays a crucial role in
the hydrological cycle. While extensive research has been conducted in the Maimai M8 catchment
(New Zealand) and across many catchments on streamflow generation processes and streamflow
sources, we still know little about the sources of transpiration and when transpiration and
streamflow sources are hydrologically connected. Here we leverage M8, a long-term studied
catchment with well-described streamflow generation mechanisms, to investigate the transpiration
source water of Pinus radiata and its connectivity to streamflow sources. We combined monthly
observations of isotopic signatures (δ18O and δ2H) of xylem, bulk soil water, mobile water,
subsurface flow, and stream water with continuous monitoring of tree water stress across a
hillslope to answer: (1) What is the seasonal source of transpiration at Maimai? And (2) how does
transpiration source water interact with streamflow sources? Our data showed that transpiration
sources across the hillslope were not distinct but changed seasonally. During summer, when trees
showed greater periods of water stress, trees relied on shallow soil water. In contrast, during the
winter, trees’ isotopic signatures plotted along the local meteoric water line (LMWL), overlapping
with mobile soil and stream water. Xylem isotopic signatures were not statistically distinct from
stream signatures in the winter, contrasting with distinct isotopic signatures during the summer.
Our results showed that transpiration source water in the Maimai M8 catchment changes
seasonally, influenced by tree water stress and wetness conditions. Overall, our findings suggest
an ecohydrological connectivity between transpiration and streamflow sources during winter
months in this wet temperate climate.
How to cite: Simmons, C., Dudley, B., McDonnell, J., and Nehemy, M.: Seasonal transpiration source water and ecohydrological connectivity with streamflow sources in the Maimai M8 Catchment , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14282, https://doi.org/10.5194/egusphere-egu25-14282, 2025.
