Healthy streams are slippery streams …

I couldn’t resist repeating this phrase after reading it in a press release and then to dig a little deeper into the research that it was reporting.   The phrase is a succinct summary of what I want to convey through this blog: that the microscopic life which coats submerged surfaces in lakes and rivers is an essential component of aquatic ecosystems.  Anyone interested in long-term sustainability of freshwaters cannot afford to ignore the composition and functioning of these “biofilms”.  Yet it is, undoubtedly, slippery and slimy and, consequently, sometimes unsightly and often a nuisance.

But “nuisance” is, itself, a loaded term with no more definitive quality than something in the wrong place at the wrong time.   Perhaps the angler who slips on these films in search of recreation is, himself, the nuisance, as he assets himself as an unnatural top predator in the river food chain?   Except that the angler is, in modern parlance, a “stakeholder” and the fishing that he enjoys is an “ecosystem service”, thereby converting the often abstract business of conservation and environmental protection into a tangible benefit for society.

The press release led me to a paper by two US ecologists, Emma Rosi-Marshall and Todd Royer, on the effect of pharmaceuticals on aquatic systems.    The story goes something like this: your doctor prescribes antibiotics to fight a bacterial infection which you dutifully take.   Most of the antibiotics are absorbed by your body and you recover from your infection.  However, a portion of the antibiotic passes through you, into the sewerage system, then through a sewage works and into a river where it continues to exert its antibacterial activity but now on the natural microbial communities which play an essential role in nutrient cycling.

This is not a completely novel idea: there have been reports of antibiotic resistance in natural communities of bacteria for some time now, and the effects of constituents of birth control pills have been widely reported.   Most of these papers have adopted a traditional toxicological approach, looking at effects on a single organism. Rosi-Marshall and Royer go one step further by pulling together the few fragments of evidence of effects at the ecosystem level. For example, antibiotics can influence the decomposition of leaves, leading to fewer bacteria and more fungi which in turn, made the leaves more palatable to some types of invertebrates. The result is a series of small, but potentially consequential, shifts in how energy moves through ecosystems.  Stir in the whole cocktail of healthcare products – antihistamines (inhibit neurotransmitters in invertebrates), birth control pills (inhibit reproduction of fish), even antidepressants (induce spawning in bivalves) – and a picture emerges of aquatic ecosystems subject to a multitude of individually small but cumulatively significant changes.

Where does this leave us?  Two undeniable points are that pharmaceuticals and other health care products bring major benefits to society, and that the cost of removing all traces from wastewaters would be very high.  Balanced against these, the costs to ecosystems might seem a fair price to pay.  Maybe.   Trade-offs such as this happen all the time.  But the trade-off is only valid IF you understand the costs and accept that there may be situations where the consequences are unacceptable.  Nonetheless, simply recognising that these compounds might be a problem is a step in the right direction.  That said, it is yet another stressor to include in the “causal thickets” that we have to untangle when trying to understand river ecology.   “Causal thickets”?  That’s a subject for another post.


Rosi-Marshall, E.J. & Royer, T.V. (2012) Pharmaceutical compounds and ecosystem function: an emerging research challenge for aquatic ecologists.   Ecosystems 15: 867-880.

3 thoughts on “Healthy streams are slippery streams …

  1. Pingback: The River Ehen in January | microscopesandmonsters

  2. Pingback: So what? | microscopesandmonsters

  3. Pingback: Wide Sargassum Sea … | microscopesandmonsters

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