A hidden world in a salty puddle …

An exchange of emails amongst a group of us preparing an obituary for Hilary Belcher led me to a short paper written by herself and Erica Swale on diatoms from a salty puddle close to a bridge under the M11 motorway in Cambridgeshire.  They had noticed some brown patches that looked like diatoms on the bottom of this puddle in 1979 and took a sample home to examine under the microscope. What they saw was an assemblage of diatoms that was more suggestive of a brackish habitat than freshwaters, leading them to conclude that the road salt that was spread on the M11 in winter was draining off the road and creating these mini salt lakes.  These were not one-off observations: they returned several times to find similar assemblages of diatoms in the same puddles.   Of these, only Surirella brebissonii is common in freshwaters.  Entomoneis and Cylindrotheca are two genera that I have written about before, both from marine or brackish habitats (see “A typical Geordie alga …” and “Back to Druridge Bay”).

Some diatoms associated with a puddle close to the M11 in Cambridgeshire: A: Entomoneis paludosa var. salinarum; B: Surirella brebissonii; C: Tryblionella hungarica; D: Nitzschia sigma; E: Nitzschia vitrea; F: Cylindrotheca closterium; G: C. gracilis.  From Belcher and Swale (1993).

I do occasionally find diatoms from marine habitats in rivers, and often suspect road salt to be the culprit.  One of the most extreme cases I encountered was a sample from the Ingrebourne, a small stream close to my childhood home where Bacillaria paxillifer constituted a third of all the diatoms present.  Bacillaria paxillifer is an intriguing diatom (see “The paradox that is Bacillaria” and links) but one that is very definitely a species that prefers saline rather than fresh water.  The Ingrebourne passes under the M25 motorway within about a kilometre of its source and crosses the busy A12 trunk road just upstream of the sampling location, so periodic pulses of salt are a possibility.

The ephemeral nature of these events, however, make them hard to prove and we are left with scattered notes such as this one in a small natural history journal.   These journals are, in many cases, struggling to survive in the modern age and I guess blogs such as this are taking over from them as records of botanical observations that are not structured in a way that makes publication in a mainstream scientific journal a possibility.  Hilary Belcher and Erica Swale made a number of substantial contributions to algal research over the course of their careers, but they were also consummate observers and recorders of their local environment – the wellspring from which an understanding of the natural world ultimately flows.

I am thankful to Hilary in one other way: she and her partner Erica Swale wrote a small (47 page) booklet with clear line drawings of the most common freshwater algae that was a required purchase for all undergraduates (and demonstrators) attending Brian Whitton’s algae practicals at Durham and it was through this book that I started to learn how to identify algae.  There are, I notice, just 17 genera of diatoms illustrated in this book but there was enough here to start putting names onto the shapes that floated – or flitted – through my field of view as I struggled to learn the rudiments of the craft.

Left: Hilary Belcher on a sampling trip to the Thames in the early 1990s (photo: Alison Love) and, right: the cover of her introductory guide to freshwater algae, co-authored with Erica Swale.

Reference

Belcher, H. & Swale, E. (1993).  Some diatoms of a small saline habitat near Cambridge.  Nature Cambridgeshire 35: 75-77.

A full appreciation of the life and work of Hilary Belcher, compiled by Jenny Bryant, will appear in the next edition of The Phycologist.

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