ConservationBytes.com

Even the most obtuse, right-wing, head-in-the-sand, consumption-driven, anti-environment yob would at least admit that they’ve heard of forest conservation, the plight of whales (more on that little waste of conservation resources later) and climate change. Whether or not they believe these issues are important (or even occurring) is beside the point – the fact that this particular auto-sodomist I’ve described is aware of the issues is at least testament to growing concern among the general populace.

But so many issues in conservation science go unnoticed even by the most environmentally aware. Today’s post covers just one topic (I’ve covered others, such as mangroves and kelp forests) – freshwater biodiversity.

The issue is brought to light by a paper recently published online in Conservation Letters by Thieme and colleagues entitled Exposure of Africa’s freshwater biodiversity to a changing climate.

Sure, many people are starting to get very worried about freshwater availability for human consumption (and this couldn’t be more of an issue in Australia at the moment) – and I fully agree that we should be worried. However, let’s not forget that so many species other than humans depend on healthy freshwater ecosystems to persist, which feed back in turn to human benefits through freshwater filtering, fisheries production and arable soil accumulation.

Just like for the provision of human uses (irrigation, direct water consumption, etc.), a freshwater system’s flow regime is paramount for maintaining its biodiversity. If you stuff up the flow regime too much, then regardless of the amount of total water available, biodiversity will suffer accordingly.

Image by James Marvin Phelps (mandj98) via Flickr

Thieme and colleagues focus specifically on African freshwater systems, but the same problems are being seen worldwide (e.g., Australia’s Murray-Darling system, North America’s Colorado River system). And this is only going to get worse as climate change robs certain areas of historical rainfall. To address the gap in knowledge, the authors used modelled changes in mean annual runoff and discharge to determine fish species affected by 2050.

The discharge/runoff results were:

• decreased discharges expected along Mediterranean coast, parts of West Africa, southern Madagascar, in many areas of southern Africa
• increases expected in Nile Basin, Lake Chad, Guinean-Congolian forest, coastal Angola, Horn of Africa, several East African freshwater lakes, swamps, and coastal rivers
• runoff had similar pattern except in Nile Delta
• > 80 % of African land surface shows change in long-term average discharge/runoff
• ~ 35 % of region shows changes of > 40 %
• 73 of 87 ecoregions expected to experience absolute change in discharge/runoff of > 10 %

And for the freshwater species:

• of > 3000 described freshwater fishes, ~ 95 % occur in ecoregions with a change in discharge/runoff of > 10 %
• ~ 92 % of endemic species could be affected
• 10 ecoregions expected to experience > 10 % change in discharge/runoff
• ~ 33 % of fish species & 20 % of all endemics occur in ecoregions experiencing extreme of 40% change in discharge/runoff

Of course, just because a flow regime shift takes place doesn’t mean these species will necessarily go extinct; however, we do know that range-restricted/endemic species are more likely to experience range reductions with climate change, and these are some of the first species we know have already gone extinct from climate shifts worldwide. Therefore, we can reasonably expect that in areas with the greatest flow regime changes and highest endemism, extinctions will be highest.

What can we do? The take-home message is relatively simple – make sure historical flow regimes are maintained as best as possible, taking into consideration climate projections for each region. Catchment-level predictions of water availability change and flexibility to adjust water allocation/use management accordingly are paramount.

We also need more studies like this for other parts of the world where flow regime changes are already causing havoc. Murray-Darling Basin Authority – are you listening?

CJA Bradshaw

M.L. Thieme, B. Lehner, R. Abell, & J. Matthews (2010). Exposure of Africa’s freshwater biodiversity to a changing climate Conservation Letters DOI: 10.1111/j.1755-263X.2010.00120.x