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River ecosystem resilience to hydrologic drought in a changing world


Project Description

Water scarcity and drought are among the most pressing environmental issues of the century. River ecosystems, already degraded by excessive water use associated with growing populations, will be further affected by widespread shifts in rainfall patterns where climate change alters natural flow regimes. Across Europe, droughts have increased dramatically in frequency and intensity over the past 30 years, and where water availability declines the timing, frequency and intensity of low flow periods will occur. In some regions, river flows may shift from perennial to intermittent, with profound consequences for the ecological connectivity and functioning of these systems. Where low river flows persist, connections to riparian ecosystems are likely to be enhanced as terrestrial flora and fauna colonise the riverscape, with unknown consequences for ecosystem functioning and food webs. Despite its growing prevalence, research on the ecology of low flow regime change in streams and rivers lags far behind that of other stressors (e.g. acid pulses or pesticides) and has focused on in-stream responses at the community level. Far less is known about impacts on functioning, or how aquatic-terrestrial linkages may change in response to altered hydrological connectivity.

The successful candidate will undertake research to address these research gaps, and conduct flow manipulation experiments in a new state of the art mesocosm facility at the University of Birmingham: https://www.birmingham.ac.uk/research/activity/ecolaboratory/index.aspx. These will be combined with sampling and analysis of long-term records of flow and biodiversity in streams monitored by our industry partner Wessex Water. Specifically, the project will test the effect of modification of low flow regimes on ecosystem functioning and food webs, including aquatic-terrestrial links. The doctoral researcher will: (1) Use artificial streams in the Birmingham ECOLAB facility (see Fig. 1 below) to replicate elements of natural flow regimes and simulate natural and modified flow regimes; (2) Determine the mechanistic basis of flow change effects, via factorial manipulation of habitat connectivity, habitat/sediment area, temperature and water quality; and (3) Monitor effects on water quality and ecosystem processes using state of the art sensor networks. The results of the research will reveal how key ecosystem processes are affected by flow modification, identify tipping points and non-linear responses along gradients of low flow stress as well as key environmental stressors that modify ecosystem processes when flows are modified, to form the basis of mitigation strategies.

Funding Notes

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.
• Annual stipend, set at £15,009 for 2019/20
• Research training support grant (RTSG) of £8,000

References

Leigh, C, Aspin, TWH, Matthews, TJ, Rolls, RJ & Ledger, ME 2019, 'Drought alters the functional stability of stream invertebrate communities through time', Journal of Biogeography. https://doi.org/10.1111/jbi.13638
Aspin, TWH, Hart, K, Khamis, K, Milner, AM, O'Callaghan, MJ, Trimmer, M, Wang, Z, Williams, GMD, Woodward, G & Ledger, ME 2019, 'Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment', Freshwater Biology. https://doi.org/10.1111/fwb.13259
Aspin, T, Khamis, K, Matthews, T, Milner, A, O'Callaghan, M, Trimmer, M, Woodward, G & Ledger, M 2019, 'Extreme drought pushes stream invertebrate communities over functional thresholds', Global Change Biology, vol. 25, no. 1, pp. 230-244. https://doi.org/10.1111/gcb.14495
Aspin, T.W.H., Matthews, T.J., Khamis, K., Milner, A.M., Wang, Z., O’Callaghan, M. & Ledger, M.E. (2018) Drought intensification drives turnover of structure and function in stream invertebrate communities. Ecography. DOI: 10.1111/ecog.03711.
Lu, X., Gray, C., Brown, L.E., Ledger, M.E., Milner, A.M., Mondragon, R., Woodward, G., Ma, A. (2016) Drought rewires the cores of food webs. Nature Climate Change, 6, 875–878.
Woodward, G., Bonada, N., Brown, L.E., Death, R.G., Durance, I., Hladyz, S., Ledger, M.E., Milner, A.M., Ormerod, S.J., Thompson, R.M. (2016) Extreme climatic events and their consequences for biodiversity, food webs and ecosystem properties in running waters. Philosophical Transactions of the Royal Society B: Biological Sciences, 371, doi: 10.1098/rstb.2015.0274.
Ledger, M.E. & Milner, A.M. (2015) Extreme events in running waters. Freshwater Biology, 60, 2455-2460.Ledger, M.E. & Milner, A.M. (2015) Extreme events in running waters. Freshwater Biology. doi:10.1111/fwb.12673.
Ledger, M.E., Brown, L.E., Edwards, F.K., Hudson, L.N., Milner, A.M., Woodward, G. (2013). Extreme climatic events alter complex food webs: evidence from a mesocosm drought experiment. Advances in Ecological Research, 48, 343-395.
Ledger M.E., Brown L.E., Edwards F., Woodward G., Milner A.M. (2013) Drought impacts on the structure and functioning of complex food webs. Nature Climate Change, 3, 223-227.
Ledger M.E., Harris R.M.L., Armitage P.D. & Milner, A.M. (2012). Climate change impacts on community resilience: experimental evidence from a drought disturbance experiment. Advances in Ecological Research, 46, 211-258.

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