January 2021

I looked at the lake water on the 10th. Unlike deep lakes, where water temperature lags behind air temperatures and show much little seasonal variation, our shallow lake tracks air temperatures more closely. About half the lake had a thin layer of ice and the water temperature was 0 Celcius accordingly. The summer waterweed had died right back, with just traces of rigid hornwort and blanketweed and there were many oak leaves on the lake bed. With its high tannin content, oak decays much more slowly than other species, such as the crack willow. Water clarity had recovered slowly from the summer minimum and was still lower than is typical in winter. The nutrients in the lake water were the reverse of the usual situation with some nitrate pollution but no evidence of phosphate pollution. Despite the cold water, there was a reasonable number of long-spined waterfleas helping to maintain the water quality. As well as providing food for young fish, the waterfleas helped to feed Panzer's lesser waterboatman and damselfly larvae, both still active in the cold water.

Water clarity was checked on the 28th. The clarity was declining as water temperatures and increasing daylength allowed algal growth. Water clarity generally doesn't improve until the long-spined waterflea multiplies sufficiently to graze down the algae in April.

I did the monthly bird count on the 15th. The park was very damp and almost all users were confined to the narrow perimeter paths, leading to poor distancing. The fencing on the great field was still in place, funneling people at the corner of the stadium perimeter path and stirring up much mud. People don't seem to realise that the much lower risk outdoors is not zero risk. Risk increases with exposure. The worst behaviour was from those dropping off at the nursery - not enough distancing and prolonged chatting. This doesn't measure up to one healthy walk a day with a maximum of one other from outside the household. The Christmas tree plot was bare muddy ground.

The dam had overtopped recently, the brook was flowing fast and there was standing water at the south-west corner of the athletics stadium, in the low parts of Horse Close Wood and all along the bottom edge of the dam.

Following the snow on the 24th there was about 20mm of rainfall overnight 27th-28th. This brought the lake level up the the top of the sheet piling (between the waterfall and the boat compound). Water was flowing across the lakeside path, through the hedge and down to the path beside the crazy golf, which was flooded. There wasn't much wind, but wave overtopping was significant in several other places, with flooding around the watersports building and in the park compound behind the bowls pavilion. All this happens regularly, but people don't realise that a slightly greater rainfall would lead to significant overtopping and extensive flooding of the public park. Worse still, there is a small probability that the overtopping is so much that it erodes the dam and causes it to fail, flooding extensively in the Grid and other places downstream. LB Merton owns and manages the public park and lake and know that their regulation of the lake level causes regular flooding and risks the failure of the dam. Despite being urged to lower the level of the lake to prevent this, they have repaired the outflow weir at a dangerously high level. In these days of covid precautions there's no angling and watersports have closed down for the winter, so holding the lake well above historic levels has no justification. Removing one or two boards from the weir would remove the risk overnight. Why not?

I did the monthly bird count on the 15th. The very wet conditions brought in many black-headed gulls to feed on the great field. The 300 birds being the third highest January count over the 35 year study. Coot numbers Were also at historic highs. A remarkable sight was a flock of Canada geese feeding on the green roof of the athletics clubhouse. Green roofs are often sold as special habitat for wildlife, but I hadn't heard of goose use before. The 35 pochards was another record count, showing the great increase in this species.

Hazel and Italian alder catkins were out. The sweet violets on the south edge of Horse Close Wood were beginning to flower. These keep going right through to March, when the dog violets take over. The earliest flowers on cow parsley were just breaking out.