Climate change and geothermal ecosystems: natural laboratories, sentinel systems, and future refugia

Abstract

Understanding and predicting how global warming affects the structure and functioning of natural ecosystems is a key challenge of the 21st century. Isolated laboratory and field experiments testing global change hypotheses have been criticized for being too small-scale and overly simplistic, whereas surveys are inferential and often confound temperature with other drivers. Research that utilizes natural thermal gradients offers a more promising approach and geothermal ecosystems in particular, which span a range of temperatures within a single biogeographic area, allow us to take the laboratory into nature rather than vice versa. By isolating temperature from other drivers, its ecological effects can be quantified without any loss of realism, and transient and equilibrial responses can be measured in the same system across scales that are not feasible using other empirical methods. Embedding manipulative experiments within geothermal gradients is an especially powerful approach, informing us to what extent small-scale experiments can predict the future behaviour of real ecosystems. Geothermal areas also act as sentinel systems by tracking responses of ecological networks to warming and helping to maintain ecosystem functioning in a changing landscape by providing sources of organisms that are preadapted to different climatic conditions. Here, we highlight the emerging use of geothermal systems in climate change research, identify novel research avenues, and assess their roles for catalysing our understanding of ecological and evolutionary responses to global warming.

Interbasin flow of geothermally modified ground water stabilizes stream exports of biologically important solutes against variation in precipitation

“…Previous investigators focused on the role of some geothermal systems in buffering streams against effects of temperature shifts subsequent to climate change (O'Gorman et al 2014), but our work demonstrates the importance of geothermal systems in buffering against changes in stream flow and nutrient export. Inflows from groundwater sources can stabilize fluxes against seasonal and interannual variability in local precipitation (e.g., Tague et al 2008), and this effect is amplified by the magnitude of interbasin flow of GMG at our study site in Costa Rica.…”

Temperature Effects on Biomass and Regeneration of Vegetation in a Geothermal Area

“…These approaches obviously have their place and contribute to our understanding, but each of these methods come with their own set of limitations (Shaver et al, 2000). Geothermally-heated ecosystems have recently been identified as complementary natural warming experiments, where one can investigate long term adaptation of real-world communities across natural temperature gradients (O’Gorman et al, 2014). Typically, geothermal hotspots have been heated above ambient conditions for a very long time (Bibby et al, 1995).…”

Substratum‐dependent responses of ciliate assemblages to temperature: a natural experiment in Icelandic streams

“…Yet, contrary to the observational studies, experiments have revealed contrasting and contingent community-level effects for grasses (Post & Pedersen 2008;Yang et al 2011;Lamb et al 2011;Sherry et al 2012;Wahren et al 2013;Post 2013), fungi and bacteria (Lamb et al 2011), and larger eukaryotes (Villalpando et al, 2009;Bakonyi et al, 2007;Strecker et al, 2004;Meerhoff et al, 2012). Given the criticisms that can be leveled at either approach -confounding variables in surveys, and a lack of realism in experiments -research that incorporates both the realism of observational studies and the lack of confounding variables in experimental studies is needed to reconcile these apparently contrasting findings at the community level (O'Gorman et al 2014).…”

“…This system allows us to evaluate longterm effects of temperature on community composition and organism abundance in a "natural experiment", without the confounding effects of biogeography associated with altitudinal or latitudinal gradients (O'Gorman et al 2014). Previous studies carried out in the same system have found some clear effects of temperature: e.g.…”