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Freshwaters provide essential services to humans but are one of the World’s most degraded and threatened ecosystems. Climate change and its impacts are likely to become the dominant driver of biodiversity loss and changes in ecosystem functioning by the end of this century, but how the drivers of climate change will interact with the multiple stressors that already impact ecosystems remains one of the largest uncertainties in projections of future biodiversity change. By understanding the underlying mechanisms driving these interactions and connecting science and policy we will be in a better position to be able to manage, conserve, or even restore, damaged ecosystems in the face of global change.

Description: ext Box:  Fig. 1. The ExStream System and collaborating institutions. See Piggott et al. (2015, Global Change Biology 21: 206-222) for more details.









ExStream research

My past research has focused on: (i) understanding how climate and/or land-use related stressors interact to affect biodiversity and ecosystem function in freshwaters, (ii) prioritizing managementinterventionsfor multiple stressors in freshwaters, and (iii) advancing multiple-stressor theory. I have combined multi-scale survey and experimental approaches to disentangle the individual and combined effects of multiple stressors in running waters. The latter includes the development of the experimental stream mesocosm system (ExStream System; Fig. 1), a powerful field research facility comprising 128 circular stream mesocosms offering the rare combination of strict control of experimental variables, excellent statistical power and a high degree of realism.
Using the ExStream System, I have pioneered the first empirical investigations into how climate warming and multiple agricultural stressors interact to determine the structure (Piggott et al. 2015a, Global Change Biology), function (Piggott et al. 2015, Journal of Applied Ecology) and behavioural/assembly dynamics (Piggott et al. 2015b, Global Change Biology) of stream communities. Collectively, my research demonstrates how the magnitude and complexity of interactions between climate and/or agricultural stressors are magnified or suppressed among trophic levels (algal producers, invertebrate consumers and microbial decomposers) and levels of biological organization (populations, communities and ecosystem), with important implications for our understanding and management of freshwaters in the face of global change.
My work has also made novel conceptual advances in the determination of synergism (amplified effects) and antagonism (reduced effects) among multiple stressors (Piggott et al. 2015, Ecology and Evolution), and more recently, to describe and understand behavioural responses to multiple stressors (Hale et al. 2016). Furthermore, the ExStream System has attracted considerable attention among international aquatic ecologists who then sought research collaborations, leading to an NZ registered spin-off company (ExStream Systems Ltd) and the construction of ExStream Systems in Germany in 2013 (Elbrecht et al. 2016 Freshwater Biology) and Ireland in 2016, with funding secured to establish ExStream Systems in China and Japan to facilitate distributed experiments on a global scale (Fig. 1).

Other research

Previous and ongoing research includes several national and international projects as a Principal investigator on four grants, Associate Investigator/Project Partner on five grants and the recipient of three fellowships. Examples include, in New Zealand I am investigating the relationship between environmental flows and multiple-stressor impacts (MBIE/NIWA Cumulative Effects Programme), in addition to collaborating on the first detailed evaluation of the impact of the agricultural nitrification inhibitor dicyandiamide (DCD) on aquatic ecosystems (MPI funded SLMACC project). In Germany, I am a partner on the GeneStream Project (, studying the biodiversity of freshwaters from genes to ecosystems (funded by the Kurt-Eberhard Bode Foundation). In Japan at Kyoto University, I am investigating the genetic connectivity of freshwater invertebrate species in response to multiple stressors (JSPS Invitation Fellowship). In the UK at Imperial College London, I am developing multiple-stressor ecological network models (Trimble Fellowship), and in China, I have recently established a multiple stressor freshwater research alliance for cooperative research between Peking University, Xi'an Jiaotong-Liverpool University and the Nanjing Chinese Academy of Sciences [NIGLAS] (Peking University Fellowship & UoO Priming Partnerships Grant). Moreover, I am an International Advisor to the EU funded MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress; Management Committee member of the EU COST Action DNAqua-NET (Developing new genetic tools for bioassessment of aquatic ecosystems in Europe; and Project Partner of the Imperial College London led ‘Ring of Fire’ project (£3.7m NERC Grant to G. Woodward) investigating global warming in the Arctic.