Sorry to bang the same drum repeatedly, but I want to return to the theme I explored on 17 November, when I suggested that not all situations where man interacts with water will necessary benefit from “good ecological status”. Last time, I used the example of angling, suggesting that, as fish yields were a consequence of productivity, there would be situations where anglers, an important stakeholder community, would prefer enriched ecosystem to the pristine ecosystems that us Fundamentalist Ecologists yearn for.
I also mentioned in my post on 9 November that other recreational users of water, rowers, for example, might not appreciate the removal of weirs, even if some conservationists regarded this as desirable. Having written these words, I started to wonder if there were any situations where conservationists themselves might not regard good status to be a desirable outcome?
I think we can take as a general rule-of-thumb that protecting natural habitats and restoring degraded habitats to their “pristine” state is a general goal for conservation. But maybe there are exceptions that go against this general dogma? Perhaps, too, conservationists sometimes overstate the link between high quality habitat and naturalness? One example that springs to mind is the recent spread of the otter. For a long time, we regarded the spread of the otter as a sign of the gradually increasing health of our freshwaters. Yet it is now so widely distributed, often in rivers that are not pristine, that we need to re-examine this assumption. Evidence for the ink between otters and toxic pollutants that biomagnify along the food chain is quite good. However, some other types of pollution, such as a moderate amount of enrichment by organic and inorganic nutrients might not be problematic and, indeed, by boosting overall productivity, might raise the carrying capacity of the habitat. I have never seen this idea explored in detail but it would be worth a look.
Another example of an organism that might actually thrive from enrichment is an unprepossessing but rather rare aquatic plant called Najas marina which is found in only six locations in the UK. One of these is Upton Great Broad, a habitat that is far from pristine. Yet it appears that Najas marina is a relatively recent arrival to this lake, only being recorded after the onset of enrichment. This, of course, creates a conundrum as restoring Upton Great Broad back to more “natural” conditions might bring other conservation benefits, but what would happen to the population of Najas marina if we did this?
I recall a situation that arose in the early 1990s when Northumbrian Water were required, by EU law, to build a sewage works at the mouth of the Tees, rather than discharge raw sewage as they had been doing. The problem was that the sewage provided an excellent food supply for worms on the tidal mudflats which, in turn, sustained an internationally-important wading bird sanctuary. This location was, indeed, protected by a different piece of EU legislation, the Birds Directive. Work on the wading birds of the Tees Estuary was led by Professor Peter Evans of Durham University whilst I was still working there. I have, however, not seen any of this published in a peer-reviewed journal, which is a shame as it would provide a thought-provoking case study of the trade-offs that many involved in applied ecology have to face. Here, as in the other examples I’ve mentioned, it might well be the case that an ecosystem at less than good status is actually of greater conservation value than one that has been restored back to good status.
At this point I had better duck my head below the parapet and wait to see what kind of responses this generates.
A diagram illustrating the relationship between conservation and ecological status. The EU’s Water Framework Directive expresses the quality of an ecosystem in terms of five classes, from “high” to “bad”, with good status being the theoretical target that all water bodies should achieve.
Ayres, K.R., Sayer, C.D., Skeate, E.R. & Perrow, M.R. (2008). Palaeolimnology as a tool to inform shallow lake management: an example from Upton Great Broad, Norfolk, UK. Biodiversity and Conservation 17: 2153-2168
Mason, C.F. & MacDonald, S.M. (1990). Impact of organochlorine pesticide residues and PCBs on otters (Lutra lutra) in eastern England. Science of the Total Environment 138: 147-160.