April 2023

The floating scum of silt near the weir

Cuckoo flower

A holiday meant that I made no observations in Wimbledon Park in February and March.

I sampled the lake water on 12th April and did the bird count on the 16th. Lake water clarity showed the normal Spring recovery from a low value in March to good clarity in April. As usual, this corresponded to an abundance of the Long-spined waterflea, with lesser numbers of the Big waterflea. In the past, up until Summer of 2021, Rigid hornwort and Fennel pondweed were found, but neither was found on the 16th. The hornwort was previously found in each month of the year, so it's absence is concerning. The pondweed is more of a summer plant and may yet come. I fear that nutrient pollution may have increased some time after summer 2021, but monitoring of nutrients is dependent on citizen science projects (the Environment Agency doesn't do it) and we await the next! Meanwhile, I fear that there could be problems with Blue-green bacterial blooms again this summer, and that these could compromise all public use of the lake. In my absence earlier in Spring, people were concerned over scummy floating material. I investigated this on the 24th, when I saw a migrant Common sandpiper walking on an accumulation of surface scum near to the outflow weir. The scum proved to be sediment from the bottom of the lake, made buoyant by microscopic algae photosynthesising and releasing bubbles of oxygen. I have not noticed this before and it is a worrysome sign of further deterioration in lake water quality. I also noted a considerable accumulation of chopped up leaf material, probably Common reed, in the normally clear bottom near to the stadium entrance. It seems that someone has been strimming the reedbeds in the lake, the decay of which just might account for the presumed excess nutrients. It really is time for the Environment Agency to take the water quality of the lake seriously and to get the owners of the surrounding properties to adopt better policies.

In the absence of waterweed, the resident pair of Mute swans are pretty much dependent on food provided by the public, as is the other waterweed feeder, the Coot. Both species have declined to the lower numbers that prevailed before the waterweed recovery in 2014. On the 12th, the Cob was seeing off an interloping pair of Mute Swans, apparently successfully. The Pen is incubating her eggs in a nest within the reedbed near to the stadium, just where AELTC propose to construct their silly boardwalk out over the lake. Another place slated to be destroyed is the trees and shrubs of the island, where there is a small heronry. In April, up to three Grey herons were on nests there and on the 24th, these were joined by a Little egret. The two highlights, though, were species new to my list for the park. I spotted a Perigrine falcon flying over the Great field to disappear into Horse Close Wood. This species is widespread in London, but everywhere scarce. Two Shelducks flew up from the southern arm of the lake to disappear flying north-west, possibly to the Wetland Centre.

As is usual in April, the Black-headed gulls have made off to breed in places not so disturbed by watersports use. No Common terns have been spotted yet, but they too are prevented from breeding by disturbance. There was little song from small birds, as breeding is in full swing and they are focussed on finding food to feed their young. Exceptions were Wrens, which maintain their singing right through summer. Others still noisy were later-breeding species, such as the Great spotted woodpecker, which was drumming in both woods. Blackcaps, too, were still singing, in both Horse Close Wood and at the eastern extremity of the park. A Nuthatch was calling near the Home Park Road entrance. These, and other species, will have suffered from the felling of trees on the adjacent railway embankment. This area is included in a Borough Grade II Site of Importance for nature conservation, but London Underground Limited routinely ignores such designations.

The early spring flowers, Snowdrop, Blackthorn, Sweet violet and Lesser celandine were largely over, being superceded by Hawthorn, Bluebell, Green alkanet, Cow parsley, Dandelion, Ivy-leaved speedwell, White deadnettle and Red dead-nettle. There were around 15 plants of Cuckoo flower blooming in the long grass between the tennis courts and the steps up towards Home Park Road. These have flowered every April, following an agreement 10 years-ago that mowing should wait the end of the flowering. If only similar sensitivity could be shown elsewhere. 

Norway maple trees were in full flower, making them a conspicuous bright yellow-green colour. The most obvious one is beside the perimeter path near to the Horse Close Wood car park. The Wild cherry on the edge of Horse Close Wood east, and another beside the main path in the middle of the wood were in flower. Ash and Oak leaves broke bud in the middle of the month, but were still not fully out at the end. An excellent bit of good news is that the Dog's mercury that was harmed by having a pile of logs heaped over it has survived. Depleted to about 10% of its previous extent, it was nevertheless flowering. This area could benefit from some sensitive gardening to promote the spread of this ancient woodland indicator.

The park was opened at 06:45, giving runners and dog walkers use before work. Work at the base of the stadium fence led to extensive clearance under the Leylandii hedge by the eastern edge of the stadium, removing almost all of the Ti (Cordyline australis) that was filling a gap and obscuring the ugly lower branches of the conifer. The Ti did not threaten the integrity of the fence, and I cannot think of a good reason for this. The Ti, being self-established, were a bonus. AELTC have cleared much of the dumped rubbish in the bit of Ashen Grove Wood between the golf clubhouse and the public park boundary. This is welcome, but the work seems to have cut back the young growth of trees and shrubs also. We might hope that there is a management plan for this little bit of ancient woodland. It is likely that some important woodland species will regenerate there. The fence that had collapsed into the western end of Horse Close Wood has finally been repaired.

Work was under way maintaining the crazy golf facility, including the construction of another bridge across the sinuous course of Wimbledon Park Brook. One might hope for a better design of bridge this time! A forlorn Egyptian goose stands guard, doubtless with a mate sitting on eggs in one of the large trees there. The new course of Wimbledon Park Brook remains compromised by poor design, despite recent works to restore and strengthen it where it enters the park. The old underground pipe has been restored to use, so that much of the normal flow from the stilling pond now flows underground to issue from the pipe near to the toilet block. Despite this effort to lessen the erosion of the new brook, some coir rolls have been carried downstream in flood flows as before. The grille on the new pipe under the path near the cafe is still badly blocked by debris, leading to silt accumulating in the brook just upstream of there. This design fault remains to be fixed, putting the public park and crazy golf at risk of flooding in a rainstorm. In an apparent effort to ease this problem, half of the flow has been diverted into the old, inadequate pipes that bypass the cafe. LB Merton and the Environment Agency who funded these works do not seem to have been well-served by the design of the brook.