The Hogsmill in September 2020
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The Hogsmill in September 2020 It’s been calm and felt more like a renewed summer than autumn this month along the Hogsmill river corridor. But some of our critters seem to think this could be before storms this winter – even floods – as they’ve been practising lining up “two-by-two” and trying out perches high above the water! This newsletter reports on volunteer activities to monitor and restore habitat along the Hogsmill; this month including scrub clearance by the indomitable Moles as well as regular invertebrate monitoring. It also looks at mammals along the Hogsmill, including the Citizen Zoo project to return water voles to the Hogsmill. This is at a critical stage: it needs your money to enable “Ratty” once again to enjoy picnics on the river! If you’d like to know more go to: https://www.citizenzoo.org/water-voles/ or to donate to the crowd-funding appeal go to: : https://www.avivacommunityfund.co.uk/bringing-back-water-voles/backers#start Elmbridge Meadows (photo thanks to LMP) Thanks to the ‘Wind in the Willows’ 1 The Hogsmill in September It’s been a period of contrasts since our last sampling: substantial rain with torrential storms in August followed by another long dry spell. The rain led to spectacular but short “spikes” in the river level but it then settled back to values that looked on the low side, but do not appear noticeably below those in recent years. Maximum Daily River Level at Ewell Max Dly River Level at King Charles Rd 0.8 1.2 1.0 0.6 0.8 0.4 0.6 Metres Metres 0.4 0.2 0.2 0.0 0.0 The spikes showed the effect of “urban run-off” and its “nasties”: after one storm the level rose over a metre from the usual shallow trickle at the end of Tolworth Brook’s “concreted backstreet” section. The spikes also dislodged balsam from main river banks, spreading seeds and exposing bare areas that will be more at risk of erosion. But on the plus side they flushed away weed and algae that had clogged the river, especially through Kingston, and the rain gave the meadows a welcome tinge of green after the long summer brown. Bank by Elmbridge Meadows Long Meadow There do not appear to have been any new pollution incidents this month, though fresh booms have been placed around more outfalls so some could have been missed. With the dry spell, there have been signs of pollution at several of the “usual suspect” outfalls. Most have appeared fairly minor but Rose Walk has looked particularly “horrid” with, unusually, a “stream” of pollution being visible stretching downriver. 2 Southwood Drive Rose Walk If you see pollution along the river or indications of possible pollution, such as dying fish, please call the Environment Agency Hotline: 0800 80 70 60, and ideally take a photo. Hogsmill RMI in September The River Monitoring Initiative (RMI) is a national scheme that uses counts of “water quality sensitive” invertebrates to calculate “scores” used to assess river health. Scores below a “trigger” level or that drop sharply can indicate problems that require further investigation Surveys were undertaken at 6 sites between 16th and 21st September. For once all were after a period of stable, albeit low, water levels and flows, though there are still puzzles and contrasts in the results. Scores were mostly better than last month’s lows and overall near the average for September. But there was one big exception to the recovery and “quirks” in the scoring system hid some large drops in counts: Hogsmill RMI Scores September 2020 10.0 8.0 6.0 4.0 RMI Score 2.0 0.0 Sep 19 Sep Sep 19 Sep 20 Sep 19 Sep 20 Sep 19 Sep 20 Sep 20 Sep 19 Sep 20 Sep 19 Sep 20 Sep Aug 20 Aug 20 Aug 20 Aug 20 Aug 20 Aug 20 Average Average Average Average Average Average GL Upstm GL Dwnstm Storm Tanks Bonesgate Berrylands Middle Mill Olives Caseless caddis Cased caddis Gammarus • The best scores – “8s” – were at the downstream sites, Berrylands and Middle Mill, both up on August and with all 4 main indicator species found. One late August storm had its biggest impact here and its “flushing” of weed, algae and “nasties” might have contributed, though it seems quick for a 3 positive effect. There were also unusually high scores here in drier conditions at the same time in 2019, so perhaps there is a “special” seasonal effect at these sites, though it is not obvious why; • By contrast there was a sharp drop to “4” at the upstream site at Ewell, though again the reasons are unclear. There were no signs of pollution upstream. The water – and trays – were full of detritus, probably from last month’s rain, though as the August sample was taken after the “big” Ewell storm, this doesn’t seem to explain the fall. Again there is a precedent: a similar large drop in September 2018. The likely cause then was thought to be low flow combined with oxygen-depleting weed and this may be a factor this time, though water conditions did not look as bad as two years ago; • At the 3 mid-stream sites, scores were at or slightly above those for August. Repeats of last month’s breaches of the “trigger” score at the Storm Tanks and Bonesgate were avoided, but the increases in numbers were small and counts remained low so these sites remain of concern. They are the ones with the lowest “normal” water depth and with often-uncovered gravel beds so are probably particularly susceptible to low water levels; • again a stand-out feature this month was the large changes in individual species’ counts. Olive numbers recovered substantially to levels close to normal for this time of year. But the gammarus count fell sharply to its lowest overall level for 3 years and that for cased – only 6 across all sites – was the lowest for 4 years. Mammals along the Hogsmill The most visible wildlife along the Hogsmill are insects and birds. But while less conspicuous, the greenspace also provides home and safe passage for a wide range of mammals, creatures “great and small”. At the “great” end, rural scenes of cattle grazing the river banks have long gone, but there are plans to re- introduce them at Tolworth Court Farm Moated Manor to improve grassland management for other wildlife. Old Malden c.1900 Moated Manor 2022? (photo thanks to Elliot) 4 Some shy creatures hard to find even in rural areas have made their home along the Hogsmill. Deer – mainly roe but the occasional muntjac – have for some time lived in the Ewell Nature Reserve and by the Bonesgate in Tolworth Court Farm and Chessington. They’re now moving downstream. In the last couple of years, roe deer have become common sights around Six Acre Meadow and the Hollows in Old Malden, and this year they have been seen “resting” by the river close to the A3. There are also badger families living close to the Hogsmill and the upstream sections of the Bonesgate and Tolworth Brook that can occasionally be glimpsed. Six Acre Meadow Bonesgate (photo thnaks to Paul) (photo thanks to Robb) Foxes and squirrels can also be seen close to the river, though paradoxically these “wild” creatures now seem more attuned to the comforts of urban living and are more likely to be found in streets and gardens. The Hogsmill corridor provides some good habitat for bats; enabling them to move about, roost in riverside trees and forage for insect above the water. Light pollution is a problem with increasing development close to the river, but surveys and “bat walks” in darker spots, such as Six Acre Meadow, Berrylands Nature Reserve and Tolworth Court Farm, have identified several species by the river: not only common ones like soprano pipistrelles but also rarities, such as noctules, Leisler’s and Daubenton’s. The one “real water” mammal sometimes seen along the Hogsmill is the American mink. These “predatory invaders” probably access the river from the Thames and have most often been spotted in central Kingston, but in recent years there have also been sightings in Old Malden and even along the Bonesgate. Leisler’s bat at Tolworth Moated Manor Mink by Viliers Road (photo thanks to Alison) (photo thanks to Kingston Univ) 5 At the “small” end, a range of rodents and other tiny critters make their home along the Hogsmill. Brown rats seem to have a penchant for polluted outfalls, while voles, shrews and mice can occasionally be seen close to the banks. For these the concrete/brick banked sections can be a menace – very hard for a pygmy shrew to climb out if it falls in! – or a comfort – a safe refuge for a wood mouse. Short-tailed vole Pygmy shrew Wood mouse (Thanks to Alison for photos and material in her ‘Mammals of Kingston upon Thames 1998-2020’ Report) One rodent you won’t find now is a water vole. As recently as the 1980s the Hogsmill was said to be teeming with them, but numbers then fell dramatically and there have been only a handful of sightings in the last 20 years. But this is hopefully set to change soon thanks to Citizen Zoo’s GetInvoled project that is spearheading a local community effort to bring back these charismatic critters. Already the river has been surveyed and stretches with suitable habitat identified and mammal footprint rafts have been deployed to identify other creatures currently in the river that could be a threat, notably mink: none found so far so fingers crossed! The next step is to obtain sufficient water voles from a specialist breeder to produce a viable population and to recruit a vole “ranger” to manage their release and progress.