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Environment Strategy Manager, Southern Water.

The Cockshut Stream, Lewes and Invasive non native species - (INNS) The Cockshut Stream in Lewes, East Sussex rises at the foot of the South Downs near Kingston and runs a short 3km distance to Lewes and out to the River Ouse. It is a historically and ecologically important chalk stream that was once a working waterway which was used to transport stone to construct Lewes Priory in around 1080. Later the stream helped feed fish ponds within the Priory grounds which became known as Stew Ponds. Later still in the 1600’s the streams water helped feed Lewes’s first pumped drinking water supply. The upper reaches of this stream near the Lewes Brooks SSSI underwent a fantastic restoration in 2022/3 removing invasive plants like Parrots Feather and remodelling the route to maximise wetland habitat; a project involving Lewes District Council, The Ouse and Adur Rivers Trust, and the Railway Land Wildlife Trust with support from the South Downs National Park Authority and funding form the Veola environmental trust. However a stones throw down stream from this project, there is a significant problem with Japanese Knotweed. One of the very well known invasive plant species and rightly feared as it is so virulent and quick to spread vegetatively (i.e. it can reproduce from small fragments as well as spreading via rhizome's but sexual reproduction is also probable but less understood with this plant). Japanese knotweed can take over huge areas often along streams or river banks and railway lines where it grows very fast and tall and forms deep rhizomes. It will outcompete any other plant, creating a bland and daunting monoculture. This photo from the Ham Lane Lewes towards the Cockshut confluence with the River Ouse show the extent and challenge of Japanese Knotweed when active management has not been in place for some time. Land owners and managers struggle to get on top of this with is technically difficult and expensive and the biodiversity of this valuable chalk stream is shaded and smothered. The UK Non Native Species secretariat manages various partnerships (including the Aquatic Biosecurity Partnership linked below) aimed at reporting, monitoring and managing INNS species, including Japanese Knotweed and helping improve biodiversity of the fragile habitats that are impacted. https://lnkd.in/gdYz-2e4 https://lnkd.in/gBnCJzWm

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Giles Coe

Director & Ecologist at Co-ecology Ltd

2mo

That looks like a challenging project to get that lot under control right on the watercourse Daniel Ross . Are you getting a plan in place?

Matthew Bird

Climate Literacy Lead - Community Energy South, Cllr - Lewes Town Council, Past Mayor of Lewes 2023-24, Active Travel Lead - OVESCo, Director - Get Bikery, Director-Love Our Ouse

2mo

It's a massive challenge and I know the landowners have some plans in place but not sure on the detail. As you say a really important stream, that stone for the Priory came from Caen by boat all the way to the wharf at the Priory, hard to imagine now. Would like to see it become the saline environment it once was by moving the flood flap gate further from the Ouse. Not sure if the culvert under the A27 is still blocked?

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