The River Mimram is a chalk river, so named because most of the water in the river comes from springs flowing from the underground chalk aquifer – a natural underground water store. This creates the clear and well oxygenated water that you can see flowing today. Chalk rivers are a globally rare habitat as there are only 200 worldwide and England has 85% of them!
The high-quality water provides a habitat for rare species such as brown trout, otters, and water voles. The clear chalk river water allows lots of light through which makes it a good habitat for many rare water plants such as water crowfoot to grow.
The roots of these plants hold the mud and sand together on the bed of the stream to make the water even clearer. The plants also give out oxygen so the water provides a well-oxygenated environment for many invertebrates in the water.
This month you may see some of these invertebrates emerging from their larval stages under the water and taking flight above the water to look for a mate. The aptly named Mayfly tends to be present flying above the water in huge numbers during this time. In adult form, they only live for 24 hours as without a mouth they cannot eat – only mate and die!
Both when beneath the surface and above, these fly larvae and other invertebrates form the basis of a food chain for larger creatures such as kingfishers, trout, and grayling fish to feed on. The fish especially will be coming to the surface at this time to peck off any fallen flies on the water’s surface.
Water voles also live in this river – they create their burrows in the bank and feed on the vegetation there. Water vole are rare but thankfully Panshanger Park is a stronghold for them.
Many different species rely on a clean clear chalk river as their home and the stretch of the River Mimram that flows through Panshanger Park is a prime example of a chalk river.
To help preserve the river habitat and wildlife at Panshanger, fencing has been erected which allows for the river banks to recover from the erosion caused by human activity. This will protect those habitats to ensure that the wildlife relying on it continues to be able to live in a healthy chalk stream environment.
When visiting Panshanger Park please remember to adhere to local government restrictions, keep to the paths and keep dogs on leads where requested to ensure the park remains a great place for human visitors and wildlife alike.
Jo Whitaker is the Panshanger Park People and Wildlife Officer.
She works for Herts and Middlesex Wildlife Trust and her role is funded by Tarmac.
Image credit: Russell Savory.