The picture above shows a rather unprepossessing view of a river bed, photographed earlier this month. The stones, to give a sense of scale, are all less than ten centimetres across. What is your immediate reaction? My guess is that it is probably negative: that mass of green filaments cannot indicate a healthy ecosystem. However, the next picture is a view of the same river bed photographed a month earlier and that shows a very different scene. There are just a few tufts of filamentous algae, if you look closely but, overall, the stones are clean. First impressions, at least, are not negative.
That phrase “first impressions” is important. If you were to take a closer look at the composition of the plants and animals at this site, you will see little to cause concern. There is a good diversity of algae and invertebrates, and these include several that thrive only in high quality rivers. The larger plants, too, are those that we associate with rivers with low nutrient concentrations and there are also salmon and trout present. There are issues with the river but these are not my primary concern today. What is of interest to me today is the reason behind the negative reaction.
The same river bed as the upper photograph, but photographed in August 2016, rather than September 2016. Both photographs taken on an Olympus TG2 camera.
There is a trend for pictures such as the one above to be included in reports. The reason is, I think, quite straightforward: waterproof digital cameras of a reasonable quality are now sufficiently affordable that many of us carry them about as standard parts of our field kit. They are useful for documenting many different aspects of the aquatic world but I worry that the audiences for these pictures have few opportunities to calibrate their experiences.
The contrast between the two pictures illustrates the danger of relying on a single photograph to infer the condition of a stream or lake. Many types of aquatic survey may take place annually; a picture in a report can, therefore, never be wholly representative of the state of algae at a site, as quantities can change rapidly. Inferring the condition of a water body from a short-lived fast-responding group of organisms is never straightforward and depends upon those interpreting the data (and, in this instance, visual evidence) being able to place this into context. I worry when I see pictures such as those above included in reports of surveys of aquatic plants, in particular, because surveyors are used to studying organisms with longer life-cycles and more stable assemblages. A photograph of mass algal growths offers a “snapshot” with few guarantees that this is typical for the the lake or stream under consideration. The reality is that the beds of even healthy streams turn green for brief periods during the year; the problem for the surveyor unversed in algal lore, is how to separate “signal” from “noise”.
Some of my earlier posts have demonstrated the advantages that a close-up view of the underwater world that these cameras offer to freshwater biologists (see “Bollihope Burn in close-up”). We are in a better place through having the ability to record the underwater world directly, rather than simply naming, counting and measuring; photography gives us a higher level cognitive experience and a more holistic overview of systems. But these rewards are accompanied by new challenges. In the same way that Wikipedia is an asset, only if used with safeguards to ensure that information that is presented can be verified; therefore we need to treat photographs of the underwater world with respect. As for most of our technological advances, they complement, rather than replace, existing knowledge and wisdom.