The Hogsmill in June 2017
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The Hogsmill in June 2017 May has faded and June is slipping away, but still plenty of time to enjoy the Hogsmill this summer. Why not visit Tolworth Court Farm Moated Manor for Kingston Wildlife Day on 1st July; or help the environment by pulling out Himalayan balsam along the River before it flowers and spreads seeds? The old “moat” at Tolworth Court Farm Himalayan balsam in Elmbridge Meadows This newsletter summarises the results of River Monitoring Initiative (RMI) sampling on the Hogsmill in June, together with other pollution monitoring and River-related activities and events. The RMI is a national scheme for monitoring the health of rivers. Volunteers undertake regular surveys using a standard net sampling technique to count the number of certain “water quality sensitive” invertebrates. An overall “score” is then calculated. A sharp fall or a drop below a “trigger” level could indicate pollution. This can then be reported to the Environment Agency (EA) to enable further investigation. Misconnected wastewater pipes and cross-connected sewers that feed into outfalls are a major source of pollution in the Hogsmill. Under a Pollution Patrol scheme organised by the South East Rivers Trust (SERT) volunteers undertake regular assessments of the outfalls thought most susceptible to pollution, the results being reported to EA and Thames Water (TW) to help steer remedial work. The Hogsmill in June Another month of extreme weather. In the 4 weeks up to mid-June there was about 50mm of rain in the area, close to average, but this was concentrated in a couple of very wet days in the midst of a hot, dry spell. As a result both the level and flow of the Hogsmill fluctuated widely. The level at EA’s Worcester Park Monitoring Station jumped by about 40cm after the downpours with a dramatic impact on the appearance of the River downstream. But the rain flushed through rapidly; and later in the month the level was even lower than in the dry spells in April and early May. 1 Daily River Level - Worcester Park Monitoring Station 1.500 1.400 1.300 1.200 1.100 Metres 1.000 0.900 0.800 2/5/17 4/5/17 6/5/17 8/5/17 1/6/17 3/6/17 5/6/17 7/6/17 9/6/17 14/4/17 18/5/17 16/4/17 18/4/17 20/4/17 22/4/17 24/4/17 26/4/17 28/4/17 30/4/17 10/5/17 12/5/17 14/5/17 16/5/17 20/5/17 22/5/17 24/5/17 26/5/17 28/5/17 30/5/17 11/6/17 13/6/17 15/6/17 17/6/17 19/6/17 Date Average Minimum Maximum Hogsmill at Old Malden after the downpour and a few days later As usual, the impact on water levels varied by site. At Berrylands it was the lowest in the year or so we have been measuring depth at the time of sampling; and over 10cm lower than in May. The monthly change at the other sites was less marked, but apart from Middle Mill the levels were all very low. At both the Bonesgate and Ewell Storm Tanks sites, gravel banks now cover more than half the river width. Bonesgate site Ewell Storm Tanks site We are not aware of any major pollution incidents being reported this month. But we were told that oil had been seen around the Bonesgate confluence a few days before sampling; and the Ewell Storm Tanks 2 overflowed yet again: two weeks after the heavy rain there was still rag and a smell around the outfall. With the rain, the signs of pollution have generally been less marked this month, but there are still plenty of outfalls where pollution can clearly be seen, including Portland Road near Knights Campus in Kingston, which perhaps warrants the prize for “horrid outfall of the month” for June, unless you know of a better candidate? Ewell Storm Tanks outfall Portland Road outfall Hogsmill RMI in June The Hogsmill RMI programme currently covers 7 locations from Green Lanes Ewell to Middle Mill in Kingston. As an urban river with many outfalls, the monitored species we find are mainly olives, gammarus and caddis. 6 sites were surveyed between the 13th and 20th June with a wide range of results: A score of “4” at Bonesgate, below the trigger level and the lowest ever recorded at this site. The low river level and flow seem likely explanations. We don’t know the extent of the reported oil pollution so it is hard to assess its impact; Also a “4” at the Ewell Storm Tanks, in line with recent months. Likely causes are the low water level; and pollution from the Tanks: there was rag and a smell at the sampling site; A score of “5” at Berrylands; and one only “saved” from a breach by a single caddis. This may also have been affected by the low river level and flow, though scores of 5 are the norm here; Scores of “6” to “9” at Green Lanes and Middle Mill, comfortably above the trigger level and broadly in line with historical averages. These scores may have been helped by the substantial amount of weed and other vegetation in the river at these sites. This has grown markedly in recent weeks and should be boosting oxygen levels, thereby countering the effects of low river flow. 3 Weed at Middle Mill site Green Lanes (photo thanks to Pamela) The detailed results are below: Total Score Hogsmill June 2017 10.0 9.0 8.0 7.0 6.0 5.0 4.0 RMI Score 3.0 2.0 1.0 0.0 GL Upstm GL Downstm Ewell Storm Tanks Bonesgate Berrylands Middle Mill Olives Caseless caddis Cased caddis Gammarus Counts of the individual species were particularly variable this month. Notable features were: Trays teeming with gammarus at Green Lanes Downstream – over 600 repeating the high count of a year ago – and almost 200 at the next downstream site at the Storm Tanks – the highest for 2 years. But gammarus counts were well down on May at most other sites, and also well below average at what has in the past been one of the best times of year for “catching them; again 100 plus cased caddis of all shapes and sizes at the Green Lanes Upstream site, but a grand total of 3 at all other sites downstream, albeit some fine specimens; 4 Green Lanes: “Move over darling….” “Stone” cased caddis at Berrylands (photo thanks to Bill) 90 per cent falls in olive numbers compared to May at Green Lanes Downstream and Berrylands. Elsewhere numbers were broadly stable relative to last month, but below average and generally well below the numbers at this time last year, which has also tended to be a good time for olives. Notable “catches” of other species this month were about 60 bullheads, mostly “teenagers” 1-2cm long and presumably developed from the small fry we have seen in the past couple of months; and 10 “budding” demoiselles. We also found cranefly larvae at 2 sites. Bullheads at Bonesgate “Fighting Demoiselle?” Improving the River habitat Tackling the threat to Hogsmill habitat from Himalayan balsam has been a priority for the last few weeks. Its large size and rapid spread squeeze out native species and increase the risk of bank erosion. Balsam “bashes” were held in May at Knights Park Campus in Kingston; in Old Malden as part of a Local Community Clean-Up; and at the end of the month in Malden Rushett along the Bonesgate and in Elmbridge Meadows. 5 Rushett Lane (photos thanks to Sivi) “The Elmbridge Meadows Bashers” Good progress was made, but there is still a massive amount by the River. If you’re walking by the Hogsmill and see balsam not yet in flower and easy to access why not pull out a few stems and leave them to decay? Balsam is easy to identify from its leaves and soft hollow stem; and its small roots make it easy to remove. Vigorous plant growth at this time of year is also bringing out the best in recent restoration work. At Knights Park, the bank started in 2014 is a spectacular sea of green; and in Ewell, plants are now beginning to flourish along the river where brash berms where installed and bank restoration was undertaken last year. “Great place to sit between lectures! Hogsmill in Ewell Nature Reserve The regular monitoring of the eel “trap” at Middle Mill in Kingston continues to find one or more eels at least once a week with a range of sizes: some 30cm plus “monsters” and others in the 15-20cm range; while eels are also regularly being found around the eel tiles installed at the Kingston Gauging Station earlier this year. “Come out if you’re hiding in there!” “I’m over 30cm long!” 6 Get active along the River! If you would like to become a RMI volunteer, the next training course will be on 30th September at Kingston University, but potential recruits are welcome to come to our monthly sampling sessions before then. If you don’t know a chub from a dace, places are still available on EA’s Fish ID Training session at the Snuff Mill in Morden Hall Park on Tuesday 11th July. If you’re interested in attending, contact Polly Bryant at SERT for more details: [email protected] If you don’t know a damselfly from a dragonfly, London Wildlife Trust are holding an Identification Workshop at Knights Park Campus, Kingston University on 8th July.