My latest trip to Cassop Vale was, by some margin, also the shortest. The very worst of Storm Arwen had blown through overnight but the winds were still considerable, and I had to steer the car around trees that had fallen across the roads. I parked in Cassop village, then darted down the hill to the pond amidst the sleet. All I did when I got to the edge of the pond was dip my hand in to grab some of the flocs of Riccia fluitans, and stuff this into a bottle, before dashing back up the hill to the warmth of the car. Don’t judge me: the thermometer was hovering around zero and the considerable wind chill made it feel much colder. You would have done the same.
These flocs of Riccia fluitans have been present around the edge of the pond all year, typically floating just under the surface. I’ve written about them on several occasions already (most recently in “Microscopic mysteries in Cassop Pond …”). The main difference apparent with the naked eye today was that there was more duckweed on top of them than on previous visits. This, however, could be due to nothing more than wind action on the surface of the pond. Duckweeds float at the water surface rather than just underneath, as Riccia fluitans doe, so are more susceptible to be moved around by the wind.
Under the microscope, the main difference was that the fronds seem to have lost some of their vitality. There are more dead or dying cells, it seems, and these impart a brownish, rather than green, hue to many of the fronds. In addition, the Nostoc that had smothered the Riccia fronds during the summer had disappeared, leaving just a few cells of Epithemia as epiphytes. They are quite hard to see against the brown backdrop of the Riccia fronds, so I have arrowed them in the photograph below. One way or another, nitrogen-fixing organisms have been an ever-present in Cassop Pond over the course of the year, which must be telling us something about the pond’s supply of nutrients.
We recently bought a copy of Gordon Graham’s Flora and Vegetation of County Durham, first published in 1988 when we were too impoverished to afford a copy. I remember Gordon Graham expressing great scepticism of my first report of Riccia fluitans from Cassop, but I must have convinced him to look because he records it in his book as “in abundance” here, along with just two other records from the county. This is about as far north in the country as you will find this species. Quite why it flourishes here but in so few other places, I do not know. Just ahead of Riccia fluitans in the flora is Ricciocarpos natans, the only other aquatic liverwort in the UK. Again, there are just a few records in the county, one from Cassop Pond and the others from ponds nearby. I remember Ricciocarpos natans being quite abundant in the pond in the past but I have not seen it this year. The Atlas of British and Irish Bryophytes mentions that there has been a decline in in R. natans which began in the 1950s and has continued to the present day, with a brief resurgence in the 1980s (when I first found it here). That gives me confidence that its absence from Cassop is not simply due to my overlooking it, but it does not really offer any cogent explanation. A species at the northern limit of its range and said to favour eutrophic water would seem to be encouraged, rather than threatened, by recent changes across the country.
Noticing an absence is harder than recording a presence. It needs a long-term perspective, and we will only ever have the personal memory that is required for a few locations. In other cases, we may have the benefit of other people’s records (see Heather’s parallel account of the poor condition of the terrestrial flora at Cassop, but having that personal link over time adds a personal, poignant element to the experience. There does not seem to be an obvious human-induced cause of its decline nationwide, so I am not led to reflections of the follies of mankind. But it does reinforce in me an awareness of change: that things that were are no longer. Not knowing why only adds further layers of reflection.
Enough for now. I am getting maudlin when there is no real need. Eleven months into my investigations into Cassop Pond have reignited memories that have pulled me 35 years back into the past. One month left and my year of visits will be complete. Then I will need to step back and see if I can put all the pieces of the jigsaw together again.
Wrote this whilst listening to: Christmas in Puebla, 17th century Christmas music from Siglo de Ora.
Cultural highlights: Petit Maman, latest film from Céline Sciamma, best known for Portrait of a Lady on Fire. Wonderful film, well worth seeking out.
Currently reading: The Thursday Murder Club by Richard Osman.
Culinary highlight: A chocolate and almond cake from Claudia Roden’s The Food of Spain.