THE END

I had thought when I set out that this blog would focus on the specific effects that climate change would have upon freshwater ecosystems, which I now realize stemmed from two prior assumptions: that climate change would have a huge negative effect on biodiversity and that science had a pretty good idea of what that would be. Although I don't think these are entirely incorrect, I have encountered far more ambiguity than expected (and hoped to be honest - after all it would be nice if science could provide answers to environmental problems!). While predictive studies expect huge biodiversity losses in the future, examples of a warmer planet from paleoecology don't always agree with this widely accepted idea. While many specialized or isolated freshwater species are likely to become extinct, others will be able to expand their ranges or will flourish in their native environment as temperatures rise toward their physiological optima. There are certain areas where understanding is seriously lacking; how will climate change affect ecosystem functioning, particularly food web dynamics? How many species will go extinct, and what will be the most important factor behind this? 

I currently think that in combination with a range of other anthropogenic threats, climate change will affect every ecosystem on Earth to some degree. I expect there to be both positive and negative changes in biodiversity on a local scale, as the impact of climate change plays out, but I think it's probable that global biodiversity will decrease unless habitat fragmentation is improved. These opinions are pretty tentative - there are still huge knowledge gaps in this branch of science. Perhaps, despite my ranting at Le Page's New Scientist article, the question "How serious a threat is global warming to life?" is an 'unknown' after all...

Take a look!

Check out this blog post listing the authors 'recommended' blogs on biodiversity for some insights into the general subject. My favorite is this one on invasive species, which has loads of posts relevant to freshwaters, though none relating to freshwaters and climate change. 

How will climate change affect arctic aquatic ecosystems?

In this post I will pick out and summarize the most important and likely effects that climate change will have upon arctic freshwater ecosystems from a fascinating paper by Wrona et al. (2006). This paper is unusual in that it delves deeper into the impacts of climate change than most, and focuses on ecosystem structure and function at a community level rather than a broader scale.

There is a lot of evidence that climate change will result in accelerated species extinctions in the arctic. How many will go in any one community will be controlled by the functional diversity (number and type of taxa present) of the ecosystem. Highly specialised species with low population numbers that are restricted to small areas of suitable habitat are most at risk of extinction or marginalisation as conditions change beyond their tolerance. Many valued fish species fit this description. Many arctic species are pre-adapted to adapt and evolve quickly to meet challenging new conditions. Sub-species genetic diversity is often very high and organisms have enzymes with a range of thermal ranges. Some species are likely to benefit from warmer conditions; many filamentous algae at high latitudes will flourish as they exist in waters colder than their temperature optima, and certain fish species will benefit from better egg development and a faster life cycle. These 'positive' changes for some species may not result in high local biodiversity however.

The northward expansion of the range of many sub-arctic or temperate freshwater fauna has already been observed, and will continue as climatic boundaries shift north and optimal habitat for native arctic species is reduced, leaving underused resources. There is potential for invasives to cause further biodiversity loss among natives as they introduce disease, parasites and competition for resources. A strong possibility is hybridisation between native and invader species; this could help increase the adaptability of some fauna. Emergent macrophyte species will also expand northward, increasing primary productivity and food supply in many parts of the arctic where this is currently very low.

It is still relatively unknown how climate change will affect the structure and dynamics of aquatic food webs. Melting permafrost will free up sediment, nutrients and organic carbon to enter the aquatic system and climate change is projected to increase the inputs of dissolved organic carbon (DOC, particulate organic carbon (POC) and dissolved inorganic carbon (DIC). These chemical changes are expected to combine with increasing water temperatures to affect the microbial food web, probably increasing rates of nutrient recycling and changing phytoplankton community assemblages. Changes at these levels are expected to 'cascade' up the trophic systems. The few studies that have been done show that temperature increases can destabilise predator-prey dynamics and cause younger fish to require a greater calorific intake to stay healthy.

It's probable that climate change will alter the distribution, migratory routes and phenology of aquatic birds and mammals, as arctic conditions change. Alterations in snow and ice extent will directly affect species ranges, and changes such as coldest winter temperatures and peaks in pond and lake productivity will affect the timings of migration and seasonal behaviours.

References:
Wrona, F.J., T.D. Prowse, J.D. Reist, J.E. Hobbie, L.M.J. Lévesque and W.F. Vincent (2006) 'Climate change effects on aquatic biota, ecosystem structure and function', AMBIO: A Journal of the Human Environment, 35, 7, 359-69.