Recently I attended a talk, courtesy of a dedicated London Wildlife Trust volunteer Derek Coleman, which discussed the varied wildlife and ecosystem of the River Wandle in South London.
The river has often been referred to as a chalk stream, which is in fact very rare, however part of it is heavily influenced and utilised by Beddington Sewage Works as a main effluent carrier and therefore its appearance and habitat varies significantly along its length, particularly in terms of water flow.
There are a wide variety of species to be found in the River Wandle, some of which have very interesting histories:
- Grey wagtail – in 1979 the National History Society did a survey along the Wandle and discovered several sites. By 2012 there were 19 breeding sites (particularly in shopping centre roofs)
- Moorhen – from 1983-2007 BTO surveys water ways for breeding birds and in 1983 they found 15 pairs, but then 62 pairs in 2007 showing a huge incline.It is believed this is a result of better bankside management in the 80s. Post 2007 they are in decline again, probably due to budget cuts reducing the maintenance of river banks.
- Kingfisher – in 1983 there were no breeding pairs.In 1987 the great storm brought down a lot of trees leaving huge exposed root plates that kingfishers loved to nest in, so as a result the population boomed. However, with encroaching ivy and weathering these roots plates have become less accessible and in response kingfisher numbers have dropped again. LWT and London Borough of Sutton have together built kingfisher banks out of excess silt from the river. These have both had uptake by kingfishers, but with some sites being open to the public they have been exposed to disturbance. The Wildlife Crime Unit within the Met Police have tried to patrol more frequently and persecute those that deliberately disturb nesting sites, but it is very difficult to enforce with limited resources.
- Heronries – Beddington Farmland has a huge congregation of heron, where highest number recorded was 90.Nowadays you only see approx. 40, with just 15 breeding pairs last year. It is unknown why their numbers are so rapidly declining.
- Little egret – winter visitor only (non-native species)
- Egyptian goose – numbers are increasingly rapidly and their coverage is spreading significantly (non-native)
- Toads (2 species – common and Nattajack) – they don’t mind where they lay their eggs as fish soon learn they are toxic and let them be.Nattajacks also hibernate on land – the males in the mud and the females much further away (~2miles), which is why the males call so loudly during mating season in order to draw the females back.
- Frogs (1 species – common) – frogspawn can be seen everywhere and they will begin to pop out in the spring.Adult males have incredibly strong forearms which they use to hold on to the females for up to 3 days! This makes sure that they don’t miss out on the opportunity to fertilise the female’s eggs when she drops them (as fertilisation is external). Males even have a hormone releasing gland in their thumbs which stimulate females to drop their eggs. All frogs are so varied in their appearance, with some females even appearing to be red. In Victorian times scientists would use this as a test for human pregnancy testing – if a woman’s urine stimulated an African clawed frog to drop its eggs you would know the pregnancy hormone was present and therefore the patient is pregnant.
- Watervole – these died out in the 80s as a result of tidying up the embankments and predation from invasive mink species as well as rats.London Wildlife Trust have long term plans to reintroduce this species.
- Flora – there are a lot of invasive species along the Wandle including pennyworth, Himalayan balsam
- Fish – Trout stocks have been introduced several times as a result of the Wandle Trusts “Trout in a classroom” project that allows kids to rear trout eggs to populations that can be released into the river.This has been very successful. The World Framework directive has aimed to make rivers more “fish friendly” and as some fish travel up stream in order to spawn, and the construction of many weirs in 1900’s, the fish are unable to continue their journey. As a result some fish paths have been built. These are metal slopes that allow the fish to swim diagonally upwards to the next section of the river, however this has very much been a trial and error experiment, with some having to be lowered significantly. There is little evidence as of yet that these are actually being used. But a similar invention for eels, has been very successful, and has even allowed the Wandle Trust to monitor eel populations in the river at the same time (Abbey Mills watermill).
- Damselfly – the commons and the rare Beautiful Damoiselle have been spotted along the Wandle.The Riverfly Partnership and the Wandle Trust do kick sampling of the river every month to survey the biodiversity of the river, looking for cadis fly, freshwater shrimp and other good indicator species. If there are any big problems this can be reported to the Environment Agency who will investigate for any possible pollution incidents.
There is a serious litter problem which inhibits the growth of many essential plants, and despite regular clear ups, the rubbish builds up as quickly as it is being removed. In 1996 there was a serious pollution incident as a result of Thames Water and most species, particularly fish, were killed. As a result Thames Water provided half a million to restore the habitat.
Clearly the river Wandle is a vital habitat for so many native and non-native species. It is important that volunteer groups such as those associated with London Wildlife trust and Wandle Trust work together to maintain this key ecosystem. Hopefully with more funding and continued dedication from its local community the River Wandle will flourish with life.
Photo credit logos and nattajack – Arkive.