Wednesday, 29 October 2008

Duckweed Rescue!

In the 19th Century the Manchester region seems to have been well served by botanists. There were three local floras (annotated lists of plants) published during that century: ‘Flora Mancuniensis’ by John Bland Wood (1840), ‘A Botanical Guide’ by Richard Buxton (1849) and ‘The Manchester Flora’ by Leo Grindon (1859). These three books contain many records from Chorlton. One group of plants which were well represented were those which grew in water: Five Pondweeds (Potamageton sp.), eight Sedges (Carex sp.), two Water Milfoils (Myriophyllum sp.) and three Duckweeds (Lemna and Spirodela sp.) were listed, as well as plants such as Floating Club-rush (Eleogiton fluitans), Bog Myrtle (Myrica gale) and White Water Lily (Nymphaea alba) – which are all now locally extinct.

In those days Chorlton was well provided with brooks, ponds, pits and ditches, where all of these choice plants could grow. There were Chorlton and Longford Brooks and several large ponds, such as Sally’s Pond, adjacent to Hawthorn Lane, which was filled in within living memory. The Meadows were also dissected by numerous drainage ditches which were probably associated with directing the water (with its burden of rich silt) from the river and on to the Meadows during winter floods, and off again during the spring.

One area which seems to have contained many flooded pits was that known as ‘The Isles’. This roughly corresponds to the district now centred on the long roads of Nicolas, Newport and Longford and bounded on the south by Edge Lane and Wilbraham Road, on the west by Longford Park, on the North by the Manchester/Trafford Boundary and on the east by Manchester Road. This area seems to have been quite damp – probably because of an underlying layer of clay. It’s highly likely that the numerous pits, marked on the old maps of the area, were created by digging for ‘marl’ (calcareous clay used for liming fields). Later the clay was used for brick making and there were once brick pits and a brickworks in the vicinity of St. John’s Primary School and Ryebank Fields.

Recently, it was announced that a new branch of the Metro Link Tram System would be built along the old railway line which runs from Wilbraham Road (near Morrison’s Supermarket) to Old Trafford (this old track, of course, skirts the eastern edge of the ‘Isles’ district). This line has had forty years in which to develop into a sort of linear nature reserve and wildlife corridor. Mindful of this, GMPTE and their contractors have put mitigation plans in place to ensure that as much of the line’s biodiversity as possible is conserved. Alison Hunt, of West Didsbury Resident’s Association, and I have shared our thoughts on this mitigation, with GMPTE and the contractors, and have been listened to sympathetically.

On Sunday 19th October I thought that, as clearing of the track bed was to start the next day, I would take one last look. It was very hard going – a dense, secondary woodland, mainly of Ash, Sycamore, Willow and Birch had developed along with numerous bramble patches. In addition long sections of track bed were flooded and industrial quantities of fly-tipping had accumulated (especially near bridges). It occurred to me that if this had been an ‘official’ nature reserve it would be long overdue for some management!

In one of the flooded areas I spotted something that I had not seen before. It turned out to be Ivy-leaved Duckweed (Lemna trisulca), which had been listed in all three 19th Century floras. It was a member of Chorlton’s ‘missing’ suite of water plants!
It is not particularly rare nationally but it is a bit unusual and atypical for a Duckweed. Unlike Common Duckweed (Lemna minor), which floats on the water’s surface and can form a dense blanket, L. trisulca floats just below the surface film. I like to imagine that this plant was once common in the flooded pits of the Isles and had somehow managed to cling on to life on the old railway line (well, I suppose it’s possible …).

With some trepidation I rang Katie White (GMPTE Environmental Manager). I knew that the project timings were now getting very tight, and that they were unlikely to be very happy with my request, but asked if I could rescue some of the Duckweed? Katie said that she would get back to me.

Next day I got a phone call from Peter Jones, Project Manager with Laing O’Rourke (part of the MPT consortium building Metro Link), inviting me to the MPT offices in Old Trafford. The day after that I found myself, dressed in hard hat, fluorescent jacket and steel toe-capped boots and armed with a plastic vessel and my trusty ‘Duckweed scoop’ (a suitable kitchen utensil), trudging along the track with Katie, her colleague Vivien Lees and MPT Engineer, Peter Statham. They were all very helpful and remarkably good humoured about it!

We rescued some of the Duckweed and it is now in a plastic washing up bowl in my back garden. I spoke to Alex Krause (MVCWS) about it and she suggested that we quarantine it, for a few months, just to ensure that it doesn’t contain any invasive ‘nasties’ like Azolla (Water Fern) or Crassula (Australian Swamp Stonecrop) – then we can probably introduce it into some of the (newish) ponds in the Mersey Valley.

This has been a very interesting and heartening experience for me. Just a few years ago the old track would just have been bulldozed and my Duckweed, and everything else, would have disappeared. Now there appears to be a genuine willingness to do the right thing and to conserve and enhance local biodiversity as much as possible. GMPTE and the MPT contractors are to be congratulated.
Just think, we’ll soon have an enhanced, ‘state-of-the-art’ public transport system, a functioning wildlife corridor and Chorlton will still have Ivy-leaved Duckweed in its flora.
Dave Bishop, 29th October, 2008

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