If you went to the doctor with an ailment, your discussions would be based on a shared assumption about the properties of a healthy human body. Understand this and you can put your ailment into perspective and, more importantly, the doctor knows how to treat you. The same type of thinking is now permeating the world of ecology: if we all understand the characteristics of ecosystems in their natural state, then we have a basis for discussing what needs to be done (if anything) to restore those damaged by man’s actions.
One way of finding healthy ecosystems against which we can compare modern lakes and rivers is to look at evidence from the past, and there is a thriving discipline called palaeolimnology which addresses this question. One of the uses of this is to find the dates before which the hand of man has little or no discernible effect on freshwater ecosystems. Putting evidence from a very large number of studies together, colleagues at University College London suggested that the period between 1800 and 1850 could act as a rough “rule of thumb” for this baseline (see abstract). There are a lot of caveats but , very roughly, the types of organisms we find preserved in lake sediments dated to before these dates correspond to the types of organisms we find in the most remote (and, therefore, pristine) lakes in Europe today.
I was thinking about this whilst visiting the Royal Academy’s exhibition on the origins of British landscape painting and, in particular, whilst standing in front of two large canvases by John Constable. Both date from the 1830s, so lie within this period when we would expect rivers and lakes to be closer to their pristine states. The problem is that Constable has depicted landscapes where the hand of man is very evident: there are mills and boatyards as well as artificially managed rivers and thriving agriculture. You can see similar trends in prints based on Turner’s sketches: indeed, I can take you to a point on the River Tees near Barnard Castle where Turner clearly depicts a mill and a weir that have both now disappeared completely. What is going on?
Constable and Turner both depict what are, to modern eyes, rural idylls. They tie in with the 1800-1850 baseline insofar as they reflect a period in Britain before the use of fossil fuels became widespread, before sewage was routinely dumped in rivers and well before artificial fertilisers were widespread in agriculture. So the chances are that the ecology in the rivers at the time was much closer to its natural state than we would find in many modern rivers. But these were no pristine wildernesses: the Romantic painters were portraying landscapes where men were present but as likely to be dominated by nature as to dominate it themselves. Their paintings suggest a tension between the economic and spiritual (for want of a better word) impulses in us and, as such, suggest this era as a pragmatic baseline for assessing the “health” of our lakes and rivers.
It is important to keep this in perspective: Blake wrote about England’s “green and pleasant land” in this period yet the same poem also refers to “dark, satanic mills”. The Romantics were hunting out their own idealised views of the world and did not always depict the views they chose with strict topographic accuracy. Nonetheless, there are lessons here, not least of which is that we, too, are creating a “vision” for what our lakes and rivers should look like. As scientists, we try to do this with hard evidence but an occasional afternoon contemplating Turner and Constable, or any of the other landscape painters of this era can be a useful means of calibrating our ideas. That’s my excuse, anyway.