November 2020 notes

When sampling the waterweed with a grab on the 20th I brought up a recently dead coot with fishing line tangled around its tongue and blocking its throat. Although our anglers follow best practice, illicit anglers may not, and I often bring in discarded line.

Leaf fall was in full swing and blowing them off paths was a major maintenance activity in November. As in previous years, however, they were blown across the part of Ashen Grove Wood beside the large children's play area into a heap beside the golf course fence. Quite unnecessary, because fallen leaves are part of the autumn experinece of woodland. Once fallen, there isn't enough wind in the woodland to move the leaves onto the adjacent path. The natural disposal of woodland leaf litter is done by deep burrowing earthworms which take these leaves underground over the winter months and blackbirds toss the leaves to one side to take the worms.

 

Only a few plants flower in November, but there was a great display of Mahonia beside the Revelstoke Road entrance. 

 

On my monthly bird count on the 18th, I noticed that I failed yet again to find any Dunnocks. This year, I've found only one, back in May. Since around 1990 Dunnocks have declined greatly. The first graph below shows the local trend. This species has declined nationally as well, attributed to changing farming practices, as with many other species. This is shown in the second graph below. At first sight it might seem we are just following this national trend. However, The national statistics cover a longer period, and that great national decline was essentially over by 1986, the year my study began. Since 1986, Dunnock national counts have increased slightly, quite the opposite to our local trend. The same is true for London in the national figures. I cannot account for this great difference, but it seems to be something peculiar to our locality.

Still wondering about the effect of the goose trapping on the golf course, I looked at the numbers. Neither the 30 Egyptian geese nor the 95 Canada geese were fewer than expected, so any depletion is small, but the absence of any Greylags in my count suggests that this native species may be suffering. Others who observe the area have seen a decline. The golf club haven't told us the numbers culled. As with all wild birds, Greylag geese are protected. Whilst control of wild birds can be undertaken by licence, Natural England tell us that a successful applicant must clearly demonstrate – with supporting evidence – that:

• actual damage or a problem is occurring;
• the species is actually causing the damage or problem;
• other reasonable and practical non-lethal alternatives have been considered and tried (such as scaring, trapping or proofing);
• the action is proportionate;
• and the conservation status of the species will not be negatively affected.

Nuisance is not a reason for licenced control so, typically, applicants put forward risk to human health. Such arguments may be facile where other species that present the same theoretical health risks are not subject to control. In my view, any control of Greylags on the golf course does not meet the evidence test of Natural England. Although the Greylag is native, some have argued in the past that the English populations have resulted from escaped or released birds and so are not natural, but the official advice suggests that this distinction, if it was ever real, has broken down: June 2013: Advice produced by Natural England’s Landscape & Biodiversity Team.

At leaf-fall in previous years, dense smoke has drifted across the lake when the golf club burnt damp leaves in Owl Copse. This year, they have finally stopped this unhealthy nuisance, a most welcome change.

The Mahonia by Revelstoke Road

Water quality October 2020

The long-beaked Bosminid

  

The results are out for the Thames Waterblitz 2020. 

(https://freshwaterwatch.thewaterhub.org/thames-waterblitz?utm_source=fww&utm_medium=email&utm_campaign=Thames%20WaterBlitz%20Report%202020%20Email).

We have now contributed October results to this citizen-science survey for four years. As with other lakes, our results have varied greatly from year to year. They continue to show that our lake is limited by the low levels of nitrates, which have always been within the "low" range in October. This accounts for the quality of the lake water in autumn, supporting good populations of fish and other water life when things are not messed about by attempts to remove waterweed. Phosphate levels were high in 2017 and medium in the successive three years, but the lake water did not deteriorate, because blue green bacterial and algal growth was limited by the low nitrate levels. Water clarity is another good measure of lake water quality. The graph above shows that this differed between the four years, being good in the summer and autumn of 2017 and 2019, but poor in 2018 and this year, these being the two years when waterweed growth was removed from the lake, so disturbing the sediment and releasing nutrients into the water. Clearance of waterweed also denies fish fry good shelter from predators, including the cormorants that are visiting the lake in good numbers. It's surely possible to remove waterweed carefully from the parts of the lake used by watersports and for angling, whilst leaving it elsewhere to provide good natural cover for waterlife.

My monthly water sampling was completed on 23rd October. This showed that the blue-green bacterial bloom was almost gone, there being just the odd declining clump of Dolichospermum in the open water. The recovery of water clarity since the murk in summer reflected this decline. There were few of the bigger water fleas in the cooling water but it was good to see the return of the long-spined waterflea, not seen since April. There were many of a very small species, the long-beaked bosminid, much smaller than a grain of sand. There was a long list of other small animals and small amount of the waterweed, rigid hornwort and of blanket weed. A new discovery was a good number of a tiny green flatworm Dalyellia viridis. As usual, the fish supported many fish leeches.

October 2020

Untidy and ineffective

In mid month scarecrows arrived on the canoe pontoons and the angling jetty. These are doubtless intended to deter cormorants, which have arrived in numbers in recent weeks, as they do in October in years when there's plenty of young fish to be had (see the bar chart of average monthly numbers). The scarecrows are not only ugly but are normally ineffective. Such measures only work where a species is flighty or has equally abundant food nearby. Neither seems to be the case for our cormorants and they can be seen sitting drying their wings beside the scarecrows! Much though I sympathise with fishermen faced with depletion of their fish, I suggest that these unneighbourly and ineffective features be removed.

Common wasp on ivy flowers

 I did my monthly bird count in mid month. The headline was 20 pochard ducks, a record high number for October and continuing the large numbers from last winter. This increase in recent years is a welcome exception to the national decline. The 8 great-crested grebes and one grey heron add to the cormorant story in suggesting that there's a good number of small fish to be had. Wondering about the effect of the cull of geese on the golf course, I compared the numbers with previous Octobers. The 40 Canada geese was a little lower than average. The 9 Egyptian geese suggested a halving of numbers, so perhaps this species is being reduced? The 2 greylag geese was a remarkably low number even for October when numbers tend to be low. Previous counts of all three species are quite variable because they move around a lot, so counts from more months will be needed before any firm conclusions are possible. The waterweed no longer attracts large numbers of non-breeding mute swans. We have only the resident pair and their surviving 7 large cygnets, but coot numbers remain high, suggesting that this species is able to sustain itself on a leaner supply of waterweed (there's still quite a lot of rigid hornwort in the lake despite the efforts of the watersports people to rid the lake of waterweed).

Most wildflowers are now over, but there were some late flowers on horehound and ivy is in full flower. Many common wasps were taking advantage of this in the hedge near the Wimbledon Park Road entrance.

In the tree works early in the year, the honey locust tree amongst the shrubs near the lower brook was felled, but many suckers have emerged from its roots. The opportunity to recover a honey locust appears to be rejected because all the suckers had been cut back. As always, the hart's-tongue ferns on the Revelstoke road railway bridge brickwork have recovered from the most recent attempt to remove them. Following the premature removal of bedding plants near the cafe, others were being planted to replace them.

August & September 20

I did my August standard bird walk in mid-month. I was interested to see if there was any ill effect of the blue-green bacteria, first noted in the lake at the very beginning of August. The bacteria were still very much in evidence, with the lake water quite murky. Well, there was no sign. The 70 coots were a record number for August and the 140 Canada geese the second-highest August count. The greylags were as high as in any previous August. Only the 45 Egyptian geese might suggest an easing back of numbers. Perhaps the trapping and killing of these on the golf course is having an effect? The pair of mute swans and their surviving seven cygnets were healthy. The long-term increase in moorhen numbers seems to be continuing, as the count of 20 birds was twice the previous highest August count. Long-tailed tits don't breed in the public park and even the winter flocks are only occasional there, so it was good to see an unseasonably large flock of 5 in Ashen Grove Wood. Gypsywort is often seen growing in the crevices of the sheet piling on the lakeside, but there was also some water mint seen there for the first time.

My September bird walk was on he 11th. Coot numbers remained high, with 125 the second highest count over the last 35 years. As all too often these days, I found no greenfinches. The graph shows the huge decline of this species. The national monitoring dates the onset of trichomonosis disease to 2006, but my counts suggest that the population declined around 2001 and rallied at 2006 only to decline again around 2014. There's no sign of any recovery as yet. The blue-green bacteria were still evident and the water murky.

In a reply to a query from the Friends of Wimbledon Park, the golf club claims that there are record numbers of Canada and Egyptian geese in the park this year. My monitoring statistics show that this is not the case. The average count of Egyptians rose to a peak in 2018 and has come down somewhat since. Peak counts might give concern, but in every year between 2014 and 2018 these have been higher than in this and last year. Canada goose numbers have increased in recent years, but the long view shows that they did not achieve the peak numbers that occurred in 1989, 1990, 2008 & 2009. The club assert that the cull of these two species is justified further by the nutrients and pathogens that they transport to the lake when they return from feeding on grassland to rest up on the water. Here the agument may have some weight, although it's true that the greylag geese, coots, moorhens and gulls do precisely the same but are not covered by the same general licence to cull and, apparently are not being culled. The statement by the club is odd in citing the carbon content of faeces as a nutrient, wheras the science tells us that the nutrients of concern are nitrogen and phosporous (very likely nitrogen in our lake). The movement of geese from terrestrial feeding places to the lake will import nutrients, but the consequent link to water quality is overstated for two reasons. First, is that Janet Kear established in 1963 that the throughput of food is such that much of what is consumed terrestrially is also deposited terrestrially. Second, is that Robert Unkless in 2006 showed that imported nutrients are sequestered rapidly in the sediment of a lake and so do not pollute the water. The faeces of all birds can contain pathogens and there's no doubt that these two species of goose will contribute to the pathogen load in the water, as will greylags, mute swans, ducks, coots, grebes and gulls. So, a pathogenic risk will remain even if the numbers of these two goose species are controlled effectively. The golf club alludes to the risk to their ground maintenance staff from pathogens in faeces deposited terrestrially that are disturbed as the course is managed. There is certainly a theoretical risk of this, and it's unpleasant, but it's strange that there is no such concern expressed for the public park where large numbers of geese feed on the great field every morning. Why does the London Borough of Merton not control the geese to prevent a pathogenic risk on the great field I wonder? I'm sympathetic to the golf course users and managers when faced with a nuisance and unknown risk, but I observe that goose numbers are still high despite the ongoing cull and that the public might expect that killing wild birds is not undertaken lightly.

Under the veteran oak

During lockdown, I've been studying the vegetation in our various tree initiatives in the public park. There is an interesting story in what's appeared in the fenced area under the veteran oak in the two years since it was fenced off. So far, I have identified 97 species there, quite an impressive total for such a small plot. This richness is because the ground conditions vary from shade and competition for water close to the tree trunk, to ex-amenity grassland across much of the plot and distubed stony ground on the boundaries near to the paths. The area looks a bit untidy at this time of year because many species have finished flowering and are dying back in the drought conditions. The yellow flowers of Hawkweed and Bristly oxtongues, however, add colour.

The most abundant species are those of amenity grassland: Perennial ryegrass, Common bent, Red fescue and a little White clover. The weeds of amenity grassland are less abundant: Ribwort plantain and Daisy,  Other grassland plants have appeared in much smaller numbers: Yarrow, Sweet vernal grass, Creeping thistle, Spear thistle, Cock's-foot grass, Rough and Smooth meadow grasses and Broad-leaved dock. This sward is likely to last for some years before perennial woody species and sedges take over.

Growing on the stony soil near the path edges of the plot are a range of species that are common on road verges and pavements: Mugwort, False oat-grass, Spear-leaved orache, Buddleia, Soft brome, Shepherd's purse, Sticky mouse-ear, Couch grass, Cleavers, Herb robert, Pineappleweed, Buck's-horn plantain, Broad-leaved plantain, Annual meadow-grass, Bramble, Wild lettuce, Oxford ragwort, Groundsel, Sow thistles, Lesser chickweed, Wheat, Wall barley and Barley. An unusual species is Flax, the seed of which has probably originated in the "Wildflower meadow" plots elsewhere around the great field.  As the plot matures most of these will be displaced by perennial plants of Buddleia and Bramble and management of these may be required to direct the vegetation more appropriately.

Some trees and shrubs have arrived as seeds carried by birds or squirrels: there are many seedling Hawthorns, one horse chestnut, some Stinking iris and a few plums or cherries not yet big enough to identify to species. There are also a two plants typical of woodland edge or hedgerows: Jack-by-the-hedge and Cow parsley. It's these species and the introduced sedges that are likely to form the future vegetation

Across the whole of the plot Pendulous sedge, which was introduced as young plants last winter is surviving quite well and there's just the one clump of Wood sedge and Wild garlic, similarly introduced.

As the plot matures, the annual species will get shaded out by perennials and the number of species will decrease greatly. Eventually, the vegetation will need management so it doesn't compete too much with the veteran oak and it remains a disincentive for people to encroach and so risk harming the oak's trunk.

Blue-green bacteria in the lake

When checking the water clarity on the 30th July I saw a green scum on the surface near the jetties. It looked like blue-green bacteria, so I took a sample for microscopic examination. The scum proved to be mainly a coiled blue-green bacterium (first image). There were smaller amounts of Aphanizomenon flos-aquae (second image) and two or three other species (remaining images below). There are a large number of blue-green bacteria that occur in the UK and it's a specialist matter to identify most species, and beyond my resources. The Environment Agency takes a precautionary approach to blue-green scums, recognising the need to regard all cyanobacterial species and strains as capable of producing toxins, and potentially posing a threat to animal and human health and safety (A DECADE OF MONITORING AND MANAGEMENT OF FRESHWATER ALGAE, IN PARTICULAR CYANOBACTERIA, IN ENGLAND AND WALES. Krokowski, J. & Jamieson, J. 2002). Particular concerns with our lake will be the risk to those undertaking watersports, anglers and, to a lesser extent, the general public on the lakeside path. Some dog walkers encourage their animals into the water, which could put dogs at particular risk.

One can only speculate on the reasons why we have got a bloom this year. Blue-green bacteria thrive in nutrient-rich water in warm summer conditions and it's possible that waterweed clearance has stirred up nutirents normally locked away in the sediments of the lake bed. The lake is already rich in phosphates, but algal growth is probably limited by nitrogen availability. The ability of blue-greens to fix atmospheric nitrogen could be another factor leading to the bloom.

Works in Horse Close Wood

In a meeting with National Grid in early March this year it was agreed that the works area within the wood should have temporary fencing, which would serve to protect surrounding trees from damage.

At subsequent meeting in mid June it was again agreed that the fencing of the works area should be set sufficiently back from the edges of the Glade as to avoid inadvertent damage to the surrounding trees.

When I saw the preparation of the Glade for the works, I was happy that it had been cleared well, but didn't notice that the eastern edge of the glade was not fenced off. [I have edited my account here, as my recollection was that the eastern edge of the glade was fenced off. I was incorrect in that.] The sharp edge of the cleared area, nevertheless showed the edge of the woodland. On the 23rd July, However, work was in progress removing the underground cables at the Glade. I was disturbed to find that the huge amounts of excavated soil had been stockpiled within the part of the woodland behind two Small-leaved Lime trees at the woodland edge. This is entirely contrary to the agreeement reached in the meetings with National Grid and their contractors and cannot but cause harm to the wood.

The photographs below each show a Small-leaved Lime tree at the edge of the Glade which should have been protected by fencing. The high mound of soil is within the woodland behind the Limes.

View E to a Lime with a mound behind

View SE to two Limes and a mound behind

View NE to a Lime and a mound