September 2022

A startling update on the blue-green bacterial story:

Subsequent events proved toxicity of the blue-green bloom this year, with at least one dog getting acute poisoning from contact with, possibly swallowing, the bacteria. This was reported extensively on Nextdoor Wimbledon Park and I posted there on 15th September with the following summary:

I have been monitoring water quality of Wimbledon Park Lake for six years and have warned of blooms of Blue-green algae (now known to be bacteria) several times. The Council put up little warning notices in response, but don't monitor water quality themselves. Only in two years of the six has the summer bacterial bloom been missing. It looks as if the lake is declining badly, because the last three summers have had blooms. The problem is excessive nutrients in the lake. No-one is studying where the nutrients come from, but it will not get better if the All England Lawn Tennis Club get permission for their 38 new courts on the golf course, because the intensive management of those courts involves much use of fertiliser and there is no effective proposals to stop these leaching into the nearby lake. It's likely also that misconnections and storm overflows allow sewage and other nutrients to flow down to the lake from the underground brooks that feed it. The Environment Agency does nothing about this. Nutrients are locked away in the sediment on the bottom of the lake and these can be disturbed by fish feeding or the watersports people cutting waterweeds. Dogs are most at risk, but people can also suffer and I have found big effects on the tiny water life that the fish feed upon. Unfortunately, it is difficult to tell toxic blue-greens from their safe relatives. I have identified three species in our lake and this year a bright green one has predominated. It's called Dolichospermum sprioides. I agree that more prominent warning notices are needed, even though we are not able to tell which blue-greens will prove to be toxic. Unfortunately, the blooms make activities like watersports and angling dubiously safe.

I did my monthly bird count on the 23rd. There was no sign that the blue-green bloom was adversely affecting any of the waterbirds, which were seen in similar numbers to recent Septembers. The northern part of the golf course has been closed down and not used except for parking and such during the fortnight. The grass has been allowed to grow much longer than when golf was active, but a group of 25 Canada geese were seen marching up to feed on the new growth of grass folowing the breaking of the drought. With a hundred birds in total, this goose remains in numbers comparible to recent years. A count of 50 Coots was below those of the water-weed rich recent years, back nearer to the numbers in the 2000s. There were just 12 Mallards, but this is consistent with the long-term decline, so propably not an effect of the continuing blue-green bacterial bloom. This is the season to see autumn passage migrants and I had seen some Pied wagtails in recent days, but not on the day of the count. Similarly, there are usually one or two Grey wagtails at the lake outfall, but this is difficult to view from the public park nor does my route give good views of the modified brook, where they can sometimes be seen. There was no sign of the House martins that often visit on passage.

Most flowering was over, but there were a few on Yarrow, Black horehound and Buddleia. Most important, however, are the Ivy flowers. These provide a valuable late nectar source. I found a large beefsteak fungus at the base of the Oak we are trying to protect with new planting on the SE edge of Horse Close wood. This will infect the heartwood and so is not usually a threat. Old Oaks often have heart rot, but thrive for many years. I'm still looking for any definate sign of Ash dieback. An ash beside the eastern end of the Horse Close Wood car park was looking decidedly ill, but that could be an effect of the summer drought.

 

There was a pollution incident on the 27th. At around 14:30, I saw a milky flow issuing from the pipe that carries surface water from Home Park Road and flows into the brook beside the toilet block. The photo was taken 15 mintes later, when the water was becoming somewhat less milky. This colour is unprecedented in my six years' observation of this pipe, so clearly originating from an illicit action upstream. I reported the incident to Thames Water, who tried to convince me at first that this was a matter for the local authority. I expressed surprise, as I thought that pollution into a watercourse was a matter for TWA. After consulting a colleague, the TWA pollution person logged it for investigation. As I suspected, by the time a large incident lorry and two operatives arrived 90 minutes later, the water was running clear! They weren't interested in having my photograph, as their procedure was to take their own photograph on arrival. They then began a long wait for instructions from the boss. It was clear to me that it wouldn't be at all easy to trace the source now that the pipe was running clear, but it seems that such decisions are not delegated to the site crew. I await their report on the upshot.

An Idverde person turned up and told me that samples were taken just before I arrived by people comissioned by LB Merton to investigate the Blue Green bloom. Confusion all round, but he agreed that my photo didn't show blue-green bacteria! I hope that the experts comissioned by Merton weren't confused by this co-incidence and sampled for blue-greens. Rather late I might say, as the accumulation on the water surface is now largely cleared by the recent rains. I hope that they sampled the origin of the blue-greens, the lake. There, water clarity remains low (Secchi disk 400mm only).