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How will forested watersheds store, mix and release water in a Greenhouse World? Effects of elevated CO2 on tree water source apportionment


Project Description

This NERC CENTA PhD studentship proposal is an ambitious research program to advance the understanding of how forested headwater catchments store, mix and release water. Forested headwaters supply drinking water to billions of people worldwide (McDonnell et al., 2018). Beyond supplying drinking water, understanding how forested headwater catchments store, mix and release water underpins our ability to predict the water resource outcomes of climate change in the UK. A significant finding in the field of catchment hydrology in the past 10 years is the importance and recognition of watershed ‘storage’ in the generation of streamflow and its associated transit times during and between rainfall and snowmelt events (McNamara et al., 2011). There is often a large contrast in the age of stored water and that of streamflow water (Berghuijs and Kirchner, 2017). For instance, Jasechko et al. (2017) showed that most groundwater below 250 m is older than 10,000 years. New work on the age of water in plants (Zhang et al., 2017 has shown transpired water can be multi-decadal in age (when we would have otherwise predicted water ages of days to weeks).

These studies hint at a terrestrial water cycle that is much more compartmentalized and poorly mixed than previously thought; and at timescales well beyond the now-standard annual catchment water balance calculation.

Water transit time (the time water spends travelling through a catchment to the stream network) is key for understanding the links between streamwater hydrology and water quality (Hrachowitz et al., 2016). By examining isotope signatures in trees, soils, streams and groundwater, several studies have now shown (e.g. Evaristo et al., 2015; Good et al., 2015; Sprenger et al., 2018) have shown that water transit times in relation to compartmentalized water storage—a research frontier beneath our feet (Grant and Dietrich, 2017)—and its mixing and release (to streams) is the crucial research barrier for progress in predicting change in the headwaters. And to date, no studies have yet examined (a) trees compartmentalization of water storage in the context of climate warming and (b) the effects of elevated CO2 on tree water source apportionment.

The goal of this research work is to understand how vegetation controls storage, mixing and release of water now and in a Greenhouse World.

PhD project benefits from supervision by some of the world’s leading research groups.
The UoB research team has been leading research into ecohydrological and biogeochemical processing in hyporheic and riparian zones, with a strong focus on the development of novel experimental technologies and modelling techniques to quantify the interplay of physical, biogeochemical and ecological processes under the impact of global environmental change.
Beside the standard NERC PhD funding, the project is supported by the HiFreq H2020 RISE project, providing unique training and international exchange opportunities.

Funding Notes

CENTA studentships are for 3.5 years and are funded by NERC. In addition to the full payment of their tuition fees, successful candidates will receive the following financial support:

Annual stipend, set at £14,777 for 2018/19
Research training support grant (RTSG) of £8,000

References

Berghuijs, W.R. and Kirchner, J.W. (2017). The relationship between contrasting ages of groundwater and streamflow. Geophysical Research Letters, 44(17), 8925-8935.
Berry, Z.C., J. Evaristo, G. Moore, M. Poca, K. Steppe, L. Verrot, H. Asbjornsen, L.S. Borma, M. Bretfeld, P. Hervé‐Fernández and J.J. McDonnell, 2017. The two water worlds hypothesis: Addressing multiple working hypotheses and proposing a way forward. Ecohydrology, DOI: 10.1002/eco.1843
Brantley, S. L., Eissenstat, D. M., Marshall, J. A., Godsey, S. E., Balogh-Brunstad, Z., Karwan, D. L., Papuga, S. A., Roering, J., Dawson, T. E., Evaristo, J., Chadwick, O., McDonnell, J. J., and Weathers, K. C., Reviews and syntheses: on the roles trees play in building and plumbing the critical zone. Biogeosciences, 14, 5115-5142, DOI: 10.5194/bg-14-5115-2017.
Evaristo, J. and J.J. McDonnell, 2017. Prevalence and magnitude of groundwater use by vegetation: A global stable isotope meta-analysis. Scientific Reports, 7, 44110. DOI:10.1038/srep44110.
Evaristo, J., S. Jasechko, and J.J. McDonnell. 2015. Global separation of plant transpiration from groundwater and streamflow, Nature doi: 10.1038/nature14983.
Good S.P., Noone D., Bowen G.. (2015). Hydrologic connectivity constrains partitioning of global terrestrial water fluxes. Science 349, 175–7.
Grant, G.E. and Dietrich, W.E. (2017). The frontier beneath our feet. Water Resources Research, 53(4), 2605-2609.
Hrachowitz, M. et al. (2016), Transit times—The link between hydrology and water quality at the catchment scale, Wires Water, 3, 629–657.
Jasechko, S., D. Perrone, K.M. Befus, M.B. Cardenas, G. Ferguson, T. Gleeson, E. Luijendijk, J.J. McDonnell, R.G. Taylor and Y. Wada, 2017. Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination, Nature (Geoscience), 10(6), 425-429. DOI: 10.1038/NGEO2943.
McDonnell, J.J., 2017. Beyond the water balance. Nature (Geoscience), 10, 396, doi:10.1038/ngeo2964.
McDonnell, J.J., J. Evaristo, K. Bladon, J. Buttle, I. Creed, S. Dymond, G. Grant, A. Iroume, C.R. Jackson, J. Jones, T. Maness, K. McGuire, D. Scott, C. Segura, R. Sidle and C. Tague. 2018. water sustainability and watershed storage. Nature-Sustainability, 1, 378–379. DOI: 10.1038/s41893-018-0099-8.
McNamara, J. and 10 others (2011). Storage as a metric of catchment comparison. Hydrological Processes, https://doi.org/10.1002/hyp.8113.
Orlowski, N, D. Pratt and J. J. McDonnell, 2016. Intercomparison of soil pore water extraction methods for stable isotope analysis. Hydrological Processes, 10.1002/hyp.10870.
Parnell, A. C., Phillips, D. L., Bearhop, S., Semmens, B. X., Ward, E. J., Moore, J. W., Jackson, A. L., Grey, J., Kelly, D. J., and Inger, R. (2013). Bayesian stable isotope mixing models. Environmetrics, 24(6), 387-399

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