Bridging the gap in freshwater global warming research

An example of sediment sampling from streams
used to characterise and quantify microbial
taxonomic and functional diversity
Image: H. Prentice

Dr Kate Randall, Research Associate and Molecular Microbial Ecologist at the University of Essex, UK is part of a multidisciplinary research team investigating the impacts of temperature on freshwater ecosystems as part of a ‘Ring of Fire’ NERC-funded research project led by Professor Guy Woodward from Imperial College London, UK.

Like soil, marine and freshwater sediment are places where organic and inorganic material is deposited, stored, or used as nutrients and energy to support the main hub of biodiversity within these environments. Due to the isolated locality, influx of water and contents, freshwater ecosystems are particularly vulnerable to changes in land use, biotic and abiotic conditions. The effects of which are manifesting in biodiversity loss at faster rates compared to terrestrial ecosystems (Dudgeon et al. 2006).

The majority of us are aware of the unprecedented rates of warming our planet is experiencing, but the effects on freshwater systems, in particular sediment biodiversity and functioning are not clear. Most research to date focuses on the responses of a small range of larger-bodied organisms to warming. In reality an understanding of foodwebs, combined with measurements of multiple process rates (i.e. denitrification, methanogenesis) is required. In addition, the microbiota are largely underrepresented in the multitrophic climate change studies that do exist (Sarmento et al. 2010), especially within freshwater environments. Given their ubiquity and diversity is considered to be the greatest on the planet, with key roles in biogeochemical nutrient cycles (Krumins et al. 2013), this needed to be addressed.

Through the collection of field samples, mesocosm and microcosm experiments the ‘Ring of Fire’ project has embarked upon bridging the gaps in global warming-freshwater research. It aims to do this by adopting a multidisciplinary, genes to ecosystems approach and spans spatial scales (see below).

Two Icelandic streams – one is 5 ºC and the other
is 20 °C and are only meters apart
Image: M. Jackson

Large spatial scale field based sampling of freshwater streams along natural geothermal gradients

Geothermal activity provides an opportunity to study long-term warming effects on natural freshwater streams as the activity generates a temperature gradient along which streams are located. Our large scale field research targets geothermal activity in multiple high latitude regions, within which, temperature does not correlate with other physicochemical stream variables. This component of the project will provide knowledge of how freshwater streams in an area experiencing some of the fastest rates of warming are responding, and importantly, act as indicators for freshwaters elsewhere in the future (O’Gorman et al. 2014). A core team of us were tasked with venturing to 5 sites during summer 2016 and 2017 (Iceland, Alaska, Greenland, Svalbard and Russia), where stream temperatures ranged from 2-35 oC. Divided into molecular microbial ecologists, freshwater ecologists and biogeochemists we successfully collected samples from stream sediment, the water column and biofilm. Careful planning developed a sampling protocol that was consistent across all streams, protected the integrity of samples for each research group, and will allow complementary downstream data collation.

Global mesocosm warming experiments (Mediterranean to the Arctic)

A number of large mesocosm ponds have/are being established across the globe such as the UK (, Iberia ( and Denmark to investigate warming effects within different climatic zones. Here ponds can be heated at different temperatures and combined with additional stressors associated with climate change, such as spiked warming events, drought regimes and variations in nutrient availabilities. This will allow regulation of treatments and detection of causal relationships between these variables that would not be possible in the field.

Initial 96 mesocosm pond set-up at
Imperial College London – Silwood campus

Hamilton StarLet - Automated robotic liquid handling
to prepare mock microbial communities and to assist
sample preparation for molecular microbial work

Lab based microbial microcosm experiments – Ecological and evolutionary responses to warming

Environmental samples collected from the geothermal streams and global mesocosm sampling will be used to isolate and seed into various combinations. These mock communities will then be subjected to changes in temperature and nutrient availability to disentangle the effects on complex networks of interacting microbial groups for which mechanistic drivers could not be determined within the natural environment.

Collectively, these components of the ‘Ring of Fire’ project will generate high resolution ecological data across spatial and temporal scales at a level previously unexplored. Computational approaches such as machine-learning and species-distribution models can then be applied to characterise and refine predictions of species and community responses to warming within these vulnerable and highly valuable ecosystems.


Further Reading

Dudgeon, D., Arthington, A.H., Gessber, M.O., Kawabata, Z., Knowler, D.J., Leveque, C., Naiman, R.J., Prieur-Richard, A., Soto, D., Stiassny, M.L.J., Sullivan, C.A., 2006. Freshwater biodiversity: importance, threats, status and conservation challenges. Biol. Rev. 81, 163-182. doi:10.1017/S1464793105006950

Krumins, J.A., van Oevelen, D., Bezemer, T.M., De Deyn, G.B., Gera Hol, W.H., van Donk, E., De Boer, W., De Ruiter, P.C., Middelburg, J.J., Monroy, F., Soetaert, K., Thebault, E., van de Koppel, J.A, Viketoft, M., van der Putten, W.H., 2013. Soil and Freshwater and Marine Sediment Food Webs: Their Structure and Function. 63, 35-42. doi:10.1525/bio.2013.63.1.8

O’Gorman, E.J., Benstead, J., Cross, W.F., Friberg, N., Hood, J.M., Johnson, P.W., Sigurdsson, B., Woodward, G., Climate change and geothermal ecosystems: natural laboratories, sentinel systems, and future refugia. Glob Change Biol. 20, 3291-3299. doi:10.1111/gcb.12602