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  • Pesticide-Free Cambridge

From gnats to bats, via newts and frogs: seeing biodiversity flourish in real time

Updated: Nov 4, 2022

On the occasion of World Biodiversity Day, Sat 22 May 2021, Ben writes about the Cambridge pond restoration project that he's been working on for the last 12 months. His story which includes consideration of the impact of pesticides on amphibians, illustrates how such micro-localised projects can contribute positively towards tackling global biodiversity breakdown.

Ben @ Pesticide-Free Cambridge

New Chesterton Allotments, off Histon Rd in Cambridge, has had a sizeable pond for over 20 years. It attracted healthy numbers of newts, frogs, dragonflies and many other creatures. Over time, however, the liner disintegrated and it ran dry every summer. The surrounding foliage grew to overshadow the area. A plan was hatched to restore both the pond and the area around it for wildlife. Allotment volunteers cleared some of the scrub and willow to let in more light. The thick mat of vegetation that had formed in the pond base was used to create a new shelf around the edge.

April 2020: full of vegetation but no water

In late 2020 a new liner was put in and the winter rains filled the new pond to the brim. Pond plants like Brooklime, Water Forget-me-not, Yellow Flag Iris, Hornwort and others were introduced. Then it was a question of waiting to see what happened.

November 2020: New liner fitted

December 2020: Topping it up

January 2021: Restored pond full with winter rain

On 23rd February 15 Common Frogs, including three 'couples', six Smooth Newts and a Whirligig beetle were seen.

February 2021: Common Frog

In early April there were about 20 Smooth Newts including several pregnant females, Greater Water Boatman, Greater Diving Beetle, more Whirligig beetles, Pond Skaters, gnat larvae, water fleas and Pond Snails. Mallard ducks also frequented the site.

May 2021: Male Smooth Newt

In mid-May there were still good numbers of newts including pregnant females and the emerging adult gnats attracted Common Pipistrelle bats to forage low over the pond at dusk.

May 2021: Common Pipistrelles over pond

It has been a lesson in recreating a suitable habitat but then letting nature take its course. In doing so, it's possible to see biodiversity flourish in real time over the course of a year as new creatures continuously arrive, from water boatman to bats. Most of the species inhabiting the pond have come of their own accord. Only the plants were deliberately put there.

One of the main motivations for the restoration project was to help the local Smooth Newt and Common Frog populations. Although the allotment site is sizeable, it is increasingly cut off due to development and new roads. So if numbers drop due to drought for instance, they can't be easily 'topped up' by individuals migrating in. The water-filled ditch next to the pond, previously an ideal location for frogspawn and tadpoles, now runs dry due to over-abstraction of the Cambridge water table.

Amphibians globally face the triple threat of habitat loss, climate change and pesticides. It's estimated that they are declining at a rate of 3.7% every year (1) so in 20 years time they will be found in half as many places compared to now. Because amphibians' skin is porous they are especially susceptible to chemicals in the environment. ]

Glyphosate, the active ingredient in the commonly used weedkiller Roundup (still in use all over Cambridge), has been shown to interfere with growth hormones in tadpoles causing them to change shape (2), making them less well-adapted to their environment. Other pesticides seriously affect frogs' ability to reproduce, actually turning males into females, threatening them with extinction altogether (2)(3).

We hear the term 'biodiversity' a lot, but how many of us get to see it blossoming before our very eyes? And to see some of our most precious native species - Common Frogs and Smooth Newts - doing well. Who knows what will turn up next?

[BG @ PFC]

1. Adams MJ, Miller DAW, Muths E, Corn PS, Grant EHC, Bailey LL, et al. (2013) Trends in Amphibian Occupancy in the United States. PLoS ONE 8(5): e64347.

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