Walland Marsh drought

21st September 2009, Monday

Many of the ditches to the south east of Rye are dry at the moment, a symptom of the run of dry weather we have had in recent months. Although water could be fed into them from the Royal Military Canal it would need to be pumped uphill, and the sandy/shingly ground means that it would be lost to the ground quite quickly. So is it better to pump water, generate carbon dioxide, and save wetland wildlife, or let nature take it’s course?

The answer rather depends on the ecology of the species concerned. Some are suffering. This is soft hornwort Ceratophyllum submersum, a fairly local water weed of slightly brackish coastal grazing marshes with a whorl of leaves around a central stem that divide up to three times, to provide a plant with the appearance of a bottle brush with an often reddish-green appearance. It’s commoner relative, rigid hornwort C. demersum, is a darker green colour, has leaves that divide only twice, and is more typically found in freshwater.

Both species require sections of ditch that retain water all year. If they get this they will dominate the open water next year.

Conversely the dry mud on the baked ditches is providing good germinating conditions for a different group of species. In the photo below the plant with red stems is red goosefoot Chenopodium rubrum. In brackish areas it is joined by it’s rarer relative saltmarsh goosefoot C. chenopodioides, which confusingly is also a bright red colour! Both species germinate on damp mud, along with water crowfoot seedlings, whose finely divided leaves are also visible in this photo. The goosefoots will grow, flower and seed on the damp mud in late summer/autumn, whilst the crowfoots are waiting for the drought to break and will cover the surface of the ditches with pretty white flowers next year.

These are just a couple of examples of the shifting balance of fortunes on the Marshes. There are others. Water vole do better in ditches that hold water all year, and in ditches that dry up they tend to invade during wetter years, and retreat to permanent water during droughts. Another protected speces, the great crested newt tends to fare better in ditches that dry out as its larvae are very vulnerable to fish predation, and they retreat from ditches that are colonised by sticklebacks during a run of wet years.

It’s easy to look at a dry ditch and think biodiversity disaster, however as long as a ditch system has enough wet and dry ditches across it’s entire area conditions will be provided for a wider variety of wildlife. I’m sure the farmers are longing for wet weather when they can stop checking the ditches for trapped sheep however.