Diatoms of North AmericaI’ve written my series of posts about why riverbeds are often smothered with filamentous algae against a backdrop of heightened political concern in the UK about the state of the rivers but also, with the triathalons at the Paris Olympics postponed due to the bacterial load in the Seine, an awareness that the problems currently debated in the media are not exclusive to these islands. And it is possible that the dull, damp early summer we have experienced has not created the conditions needed for algae to flourish, and therefore for media to report these and, instead, the high rainfall has led to more storm sewer overflows which has focussed attention on the dangers of infection. That’s just speculation but go read Flat Earth News by Nick Davies if you don’t believe me.
My objective, in these posts, was to point out that there are many more reasons why filamentous algae flourish in rivers than simply elevated nutrients and that it is bad science – and bad policy, and ultimately bad use of public money – to assume this causal link without good evidence. It’s important to stress that many British rivers do have high nutrient concentrations and that these high concentrations do help support dense filamentous algal growths but, equally, they are not the only reason. For this reason, I wrote a post in 2018 entitled “eutrophic or euphytic?”, which argued that casual use of the term “eutrophic” for any river with lush algal growths was inappropriate, and the term “euphytic”, that directly referred to the algae without imputing the reason, might be more appropriate.
The term “eutrophic” was first applied to deep lakes where a tight relationship between nutrients and algal concentrations with, ultimately, detrimental effects on other parts of the ecosystem, could be demonstrated. An extensive literature demonstrating the benefits of reducing nutrient concentrations in lakes has grown up as a result of this. Even so, exceptions occur: Zebra mussels, for example, can filter phytoplankton cells out of water creating situations where there are high nutrient concentrations but low algal abundances. With this in mind, I wrote another post, “An embarassment of riches …” in which I tried to disentangle the hazard caused by high nutrients from the risks presented by high algal biomass.
With this in mind, let’s look at the World Health Organisation’s guidelines for naming human illnesses and apply these criteria to excessive filamentous algae in rivers. These state that “..a disease name should consist of generic descriptive terms, based on the symptoms that the disease causes (e.g. respiratory disease, neurologic syndrome, watery diarrhoea) and more specific descriptive terms when robust information is available on how the disease manifests, who it affects, its severity or seasonality (e.g. progressive, juvenile, severe, winter). If the pathogen that causes the disease is known, it should be part of the disease name (e.g. coronavirus, influenza virus, salmonella)”.
“Eutrophic” does not fulfil the criterion for being “… a generic desciptive term based on the symptoms ..” whereas “euphytic” does fit this criterion, at least for rivers. The second part of the definiton, a “more descriptive term … on how the disease manifests” could help us to differentiate the many cases where blanket weed is prolific in the summer from the situations I encounter in the Lake District where algae are most abundant in the winter. Finally, the WHO guidelines suggest that “if the pathogen … is known … it should be part of the disease name”. Following these rules (and treating the term “pathogen” very librally), the many lowland rivers that have high algal abundance and elevated nutrient concentrations are suffering from “nutrient-induced summer euphytic condition” which, I admit, does not trip off the tongue as easily as “eutrophic” but does differentiate these cases from situations such as that posed by the River Nent (“metal-induced perennial euphytic conditon”? See “Understanding verdant rivers (II))”). This type of approach would also emphasise the differences in diagnosis and treatment required in each case. We would, I am sure, find that “nutrient-induced summer euphytic condition” was very common in the UK, but would be taking an important first step towards recognising the complexity of the challenge that this presents.
