The River Path
Habitats and Wild Life
Diverse Habitats
Rivers create a rich range of broad as well as small habitats for wild life. Young rivers, high in the hills, work hard to incise their path by wending their way along the line of least resistance, the steep sided valleys and spurs offer alternate exposure and protection from wind and sun.
Meanders provide different conditions on the inside and the outside of their bends where erosion and accretion constantly reinvent habitats (top left: meanders on the Stour in the Blackmore Vale, Dorset). Sandy cliffs, often found on the outside of a bend, are vital for sand martins for their tunnel nests. Kingfishers burrow in steep banks making tunnels 90 -180 cms above water. Water voles, in addition to plenty of waterside vegetation like banks over a metre high for their excavations.
Floodplains are those flat areas created by rivers as they have moved their course over millennia and on which they naturally overflow in times of plenty. Where the river's gradient is small, meanders migrate slowly across the extending floodplains and help accommodate silt laden, languid water not yet anxious to meet the sea.
Many floodplains have either been partly drained, or have been encroached on by development. As a result, rivers and streams have been separated from their floodplains: if they cannot flood, the accumulating water becomes a bigger problem downstream.
Washlands receive periodic sediments and nutrients from inundation, because of this and their high water tables, they are very important feeding and breeding places for waders and waterfowl. The plants living in them are adapted to fluctuating water levels, fish and amphibians benefit from the periodic replenishment of backwaters where they can take refuge from the swift currents in the main river.
Estuaries present new challenges - salt laden water and diurnal changes in levels. The Severn has the second highest tides in the world which, with the funnel shape of the estuary, causes the Severn Bore and extreme scouring: difficult conditions for plants and wild life to deal with as well as providing a natural spectacle and a challenge for surfers.
According to English Nature, about 600 species of plants (one third of the indigenous plants in England) are found in or by rivers - the interface between water and land offering the richest range of habitats of all.
When not abused rivers act as purifying agents, diluting and dispersing as they flow. Natural floodplains with higher water tables are also able to remove amounts of nitrate leached from agricultural land so preventing them from polluting water courses. Research by the Wetlands Ecosystems Research Group and Westcountry Rivers Trust has shown that "special bacteria in wetland soils can perform a process called denitrification", they transform nitrates for their own use and give off nitrogen safely as a gas. Wetlands also release water slowly into rivers, so modifying floods.
Islands provide important refuges for plants and animals, especially if inaccessible to humans and predators. They increase the flow of water around them offering different aquatic habitats.
The vegetation fringing river banks is crucially important for wild life, providing safe staging places for birds and otters moving along river valleys. Reed beds have declined drastically in the last 100 years and are vital for birds such as the reed warbler, bittern, bearded tit and marsh harrier (top right: Lapwings at Marnhull in Dorset). Wonderful as a field of swans looks, the grass offers a poor diet in comparison with what they can find amongst water reeds.
Farmers are encouraged to leave wide riparian buffer strips to minimise the risk of fertilisers and pollutants reaching watercourses. Banks which are fenced off will survive erosion better, but small areas with mild poaching by cattle can help to provide contrasting micro habitats.
Field names which imply wetness are a good place to start restoration planning: Drunken Field (waterlogged land), Feggy leasow (marshy land), Flaggy Doles (land on which marsh plants grow), Mizzey (muddy land), Plashets (marshy place), The Orles (land on which alders grow). In the Somerset Levels the dampness of the fields is increasingly being exploited for biomass and for withies - willows and other woody species cut frequently at ground level for energy production and for weaving respectively.
Trees
Certain trees enjoy the riparian life. Willows and alders in particular thrive with their roots partly in water. Some small streams are characterised by alders which cling to their serpentine banks such as the Petterill which runs into the Eden at Carlisle. Less common are whole woods of alder alder carr - with their mangrove-like root systems, which can withstand substantial periods of inundation. Phytophthora, a fungus which invades the stems and roots of alder is spreading, and threatening to change those river scenes already much diminished by our actions.
Pollarding a willow can extend its life and will provide an extraordinary range of habitats as the tree ages - good nesting places for owls, ducks and bats and lying up places for otters, as well as nourishment for moths and flies. In the Somerset Levels, the fields, bounded by slow flowing rhynes crossed by grassy bridges and lonely gates, are often picked out by lines of pollarded willows leaning at angles across the water (top, centre).
In the 1800's blowline fly fishing for trout relied on the wind to carry the line over the water. As a consequence anything which got in the way of the line trees, tall vegetation was removed. Now modern fishing tackle has improved and fishermen realise the importance of overhanging trees (especially oak, alder (above) and sycamore) which provide falling insects for fish as well as shade. Trees, especially those on the south banks can reduce the growth of water plants, but it is recommended that only half of a stretch of river is shaded. Mature oak, ash and sycamore trees can offer root cavities perfect for otter holts and, according to the Environment Agency, waterside trees can reduce river bank erosion by as much as 85-90%.
In reestablishing trees along banks and floodplain forests, the aim should be to encourage those trees, adapted to local conditions, which have a history of intimacy with the local ecosystem.
Weed Cutting
The extent to which we need to control aquatic plants such as water buttercup and water cress is open to debate. On chalk and limestone streams, weed cutting by scything is a traditional management practice used to control flooding and improve game fisheries. This work is now frequently done mechanically from boats, and the scale, frequency and impact are detrimental to the complex cycles of plant growth. If water plants grow in profusion they can slow down the flow of water which may be beneficial for other purposes and creatures. But if they grow too much they may induce the river to flood, allow silt to accumulate and cover the bare gravel areas needed by salmon and trout for spawning.
Fish and invertebrates rely on water-weed and mud for cover and coarse fish use the weed to spawn in. Weed cutting will diminish the ecological diversity of a river and it is important to keep it to a minimum, to retain areas of uncut weed and to time the cuts very carefully. Cut vegetation should be left on the banks for 24 hours to allow creatures to return to the river. Weed cutting needs permission from the Environment Agency.
Fish
Most rivers would have evolved their own varieties of particular fish because the populations were isolated, the same is true of other waterbound creatures. Isaak Walton talks of several kinds of trout "which differ in their bigness, and shape, and spots, and colour". He describes the habits of a little trout called a Samlet in the Thames at Windsor, one named after Fordidge in Kent, an Amerley trout from Sussex, a Bull trout in Northumberland.
The assemblages of fish vary in different parts of a river and between rivers. The Dorset Stour is rich in coarse fish - roach, dace, chub, pike, perch, barbel, bream, grayling, tench, minnow, gudgeon, stone loach, bullhead and eel.
Artist Peter Ursem has made linocuts of some of them (above) which are available as postcards. See www.commonground.org.uk for details on how to buy copies.
The brown trout in the Stour are thought to be natural/wild and hence important, ironically persisting here because the catchment is predominantly clay, and thus has not been idealised for trout fishing unlike its sister the Hampshire Avon, which it meets at Christchurch. The Avon drains a chalk catchment and has been restocked with trout for generations, the coarse fish which predate or compete have been forcibly diminished. Biodiversity Action Plans are increasingly seeking to redress the balance, or safeguard the endangered, the plan for the Wye Valley (Herefordshire) includes aims to improve conditions for two particular fish - the rare allis and twaite shad.
Few rivers have been allowed to remain 'natural'. Straight, featureless drains are deserts for wild life and aren't very attractive to us either. The more complicated the river system the more habitats, but the aim is not merely to have complexity and as many species as possible. Each place has a propensity towards difference because of the particular array of features and evolutionary processes. Recently our tendency has been towards homogenising the things around us including nature, but even in the places which have been severely changed, with a new care, we can work towards variegation and local distinctiveness.
From Rivers Rhynes and Running Brooks -
Local Distinctiveness and the water in our lives
Common Ground, 2000.
You can order a copy from Common Ground.
See our publication pages for details.
