Unravelling causal thickets …

The workshop I mentioned in a post a few days ” (the “thirty-three percent rule”) had the somewhat cryptic title “Untangling the Causal Thickets in River Health Assessment”. Time to explain: few of the issues which we encounter in rivers can be distilled to a single, straightforward cause. The jargon term in freshwater biology is “multiple stressors” but even this is a simplification because nature, itself, introduces further layers of complexity. A river at the end of a long, dry spell during the summer changes dramatically after a natural event such as a heavy downpour causes a flood which scours away the vegetation and turns the stones. Finally, we have to stir climate change into the mix, as these natural seasonal processes are gradually tweaked by greenhouse gases.

The term “causal thickets” is no more than a synonym for “multiple stressors” except that it also recognises that not all of the complexity that we observe is due to human activity. Also, more importantly, it links ecology, via the work of Wimsatt and other philosophers, to a broader literature on decision-making in the face of complexity. Wimsatt’s argument, in a very condensed form, is that a robust understanding of a complex system requires that we do not become over-reliant on a single strand of evidence. “Things are robust”, he argues, “if they are accessible (detectable, measurable, derivable, producible, or the like) in a variety of independent ways.”

The problem we all recognised was that the current approach to assessing the health of rivers in the UK and Ireland involves putting a lot of effort into a relatively small number of methods. This is inevitable, to some extent, as we have been grappling with the requirements of a new and, in many ways, radical piece of legislation, the Water Framework Directive. The wording of the WFD is such that the focus of methods has been on describing the structure of ecosystems, rather than looking in detail at how it works. I can identify the carburettor of my car by shape, but I need to know that this is where the fuel and air are mixed together if I want to tune the engine to perfection.

This does not mean that effort over the past ten years has been wasted. The big achievement has been to develop a shared ambition for the state of Europe’s waters. We’ve got the broad brush picture; we can compare the state of a stream in the west of Ireland with one in Cyprus. But now we need to start filling in the details and this is where the problems lay. However, the armoury of techniques we’ve developed may be too limited, too focused on structure, rather than on function, to let us do this.

This brings me back to Wimsatt’s definition of robustness as being accessible in multiple ways. Could it be that too much of the limited budget for this assessment is being spent on labour-intensive techniques that focus on structure rather than function? I went into the workshop thinking that this was probably the case but, intriguingly, the message I heard back from agency staff gave only limited support. The loudest message from them was the need for rapid assessment tools, to fill in the gaps in space and time within the broad picture that the current approaches gave them. The current network of sites (constrained by resources required to survey and sample these) is such that there may be 40 or more tiny tributaries, any of which may be contributing to the total pollution detected at the monitoring site. Methods that allowed 15 or 20 of these to be surveyed in a day with limited lab work afterwards was what they needed. Not cutting edge ecology. Sorry.

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One thought on “Unravelling causal thickets …

  1. Pingback: What does it all mean? – microscopesandmonsters

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