Jute carpet bombing to halt killer life-sucking green aliens

By Dick Warner

Monday, January 10, 2011

TEAMS have been out recently laying jute carpets on the bed of several stretches of canal close to where I live.

This apparently eccentric activity is an experiment in controlling water weeds.

Water weeds are not easy to control. In the old days they weren’t much of a problem: canals had continuous commercial traffic and the barges did the job of keeping the channels clear. Then boat traffic declined, the level of agricultural nutrients leaching into the water increased and exotic weeds from other countries got into the canals and started to spread explosively.

In the summer months the weeds grew so thickly they made the canals almost impossible for boaters and anglers. What was perhaps even more serious was that biodiversity declined. The exotic plants, which had originally been imported to oxygenate fish tanks and ornamental ponds, began to crowd out native species and in some cases the weeds grew so thickly that even the fish found it hard to cope.

The initial reaction of the authorities was chemical warfare. There are specialist weedkillers designed for use in water. I’ve some experience of using them myself and they’re not a practical solution. They are difficult to apply correctly in a natural environment because they require complex calculations of water volume and precise application and they have considerable ecological repercussions, particularly on small creatures.

So the next solution was mechanical weed cutting. Waterways Ireland invested heavily in specialist craft fitted with mowing bars and modified buck rakes to lift out the cut weed and deposit it on the bank. This wasn’t an ideal answer either. The weedcutting fuel-thirsty boats needed a lot of manpower and always seemed to be lagging behind the growth rate of the weeds. Neither were they without blame ecologically — many invertebrates and even some fish were lifted out in the cut weed and deposited on the bank.

Cue the entry of a new knight in shining armour called CAISIE. This is an acronym for Control of Aquatic Invasive Species in Ireland. Founded in 2009 it has managed to attract substantial EU funding. It’s a sort of Special Services unit designed to combat invasion, mainly by plants, but it also takes on things like zebra mussels, bloody red shrimps and even some fish. Part of its remit is to invent new weapons of mass destruction to use in the war against these aliens.

This is where jute carpets come in. Jute is a rather wonderful plant — actually several closely-related species of plant. It’s grown as a food plant over much of Africa but also for fibre, mainly in the Ganges delta, which is a bit of India and most of Bangladesh. It’s also known as hessian, burlap, sackcloth and various other names. CAISIE are experimenting with weaving it into a carpet that is carbon-neutral (apart from the carbon footprint involved in bringing it from Bangladesh to Ireland), biodegradable and sinks in water. They are then spreading it on the bed of the canal in areas where invasive weeds have become a serious problem in the hope it will act rather like those mulch mats gardeners and landscapers use to suppress terrestrial weeds.

Nobody knows yet if this will work. It could have bad side-effects, tangling around boat propellers and snagging angler’s hooks. But it does seem like an imaginative and sensitive solution to a growing environmental problem. In fact I can see it being modified for use on land where plants like Japanese knotweed, gunnera and giant hogweed are a problem.

* dick.warner@examiner.ie

This appeared in the printed version of the Irish Examiner Monday, January 10, 2011