Ponds, Rivers and Canals

Ponds may be naturally occurring or man-made although most with any permanence are probably not natural. Whatever their origins though, they are of great value for wildlife. This value varies significantly as parameters such as nutrient level, shading, disturbance, acidity and altitude are altered. As with many situations, structural variety will give rise to the greatest diversity of species, although not necessarily the greatest productivity. A combination of marginal vegetation, submerged aquatic plants, open water and marshy margins will ensure that many of the commoner taxa are allowed to proper. Some important species associated with ponds include the great crested newt, water vole, shining ram’s-horn snail and the lesser silver diving beetle. A common problem in ponds is eutrophication, when an excess of nutrients causes a rapid expansion in algae or bacteria populations which place huge demands on dissolved oxygen which in turn can lead to the suffocation of fish or anything relying on gills to breathe. Eutrophication can be caused by sewage spills, fertiliser run-off or leachate from agricultural land.

Canals and rivers vary most obviously in that canals are man made and have very limited water flow, whereas of course rivers occur naturally and flow freely. Rivers may be canalised in urban environments to fit into development schemes. Between them they provide some of our richest habitats as well as acting as linkages between other existing biodiverse areas. Linear waterbodies are susceptible to the same threats from pollution as ponds, but in addition their nature may facilitate the spread of invasive species such as Japanese knotweed, Himalayan balsam and the American mink. All of these spread rapidly and displace native wildlife in so doing.

There is, however, more to these habitats than the aquatic elements. Ponds often have boggy margins or areas of wet grassland associated with them which offer opportunities for wildlife in their own right. Rivers and canals provide corridors of significant importance in the landscape, with often herb-rich banks or strips of linear woodland that provide feeding, breeding and migration opportunities for insects, birds and mammals.