Ecology
The river environment is one dominated by flow, erosion and deposition. These three factors are closely linked to one another, but also determine the wildlife communities found within. River’s change significantly along their course and as a result so does the habitat and wildlife found in any one section. The changes are the result of the different geology, and geography of the river’s catchment, which determine the three dominant factors, and their outcome. However for wildlife to thrive there are three more factors required, Water, light and Air. The quality of each also determines the river communities found.
Light stimulates the growth of plants and Algae that are the basis of the community. Invertebrates feed on the plants and Algae, who then also become food for other invertebrates, birds, fish and mammals. Water largely determines which invertebrates will be found, and by looking at what invertebrates are present we can determine the health of the river and communities within.
The more abundant and diverse the populations of invertebrates, the more other animals can be supported. To create these populations we must make sure the water quality is good, containing no; sheep dip, sewage, or chemical effluent. We must also make sure it isn’t too silty, so that the water is clear allowing enough light to penetrate the water to allow plants and algae to grow. The banks should not over shade the water, but must shade it enough, like all of nature a careful balance is needed. The quality of the habitat must be high, there should be good vegetation both in the water and on the banks. On the banks diverse plants allow for adult invertebrates to emerge from the water and provide some cover from predation. It is also a good source of food. Within the water the vegetation provides food and cover, but also somewhere for eggs to be laid. This can be further enhanced by a selection of woody debris.
If these conditions are achieved there should be an abundance of invertebrates on which other birds can feed. In the summer evenings, martins and swallows can be seen doing incredible acrobatics above water ways as they hunt and capture their prey often dimpling the water’s surface as they take an emerging mayfly. Throughout the year a quiet walk on the river bank will also treat you to the activities of the Dipper, as it hops from stone to stone before plunging into the water, where it walks along the bottom gathering invertebrates to feed. Wagtails can be seen bobbing and dipping the water edge feeding on spent mayfly and other invertebrates that have come out from their shelter.
And then there are the fish. From serious anglers to children with dip nets fish have always fascinated humans. All fish at some point in there life cycle are reliant on invertebrates, even the predatory pike. The brown trout can be seen carefully supping invertebrates from the water’s surface, and the mighty salmon can be seem jumping weirs and water falls. Eels can be found tucked into holes or under rocks. Small bullheads and stoneloach can be found in the shallows hunting for food.
It doesn’t stop there, then there are those that feed on the fish, from the colourful king fisher flashing along the river with a minnow or fry in it’s mouth to the grey stalker – the heron, and don’t forget the elusive otter. The otters love eels but will chase and eat anything that they can including crayfish.
The river banks that have the diverse mixture of wildflowers and grasses, protected from livestock, also support other mammals such as; mice, voles, shrew, and water voles. All of which provide food for the Barn owl, kestrel, fox, weasel and stoats. And let’s not forget the bats, who roost in our bridges and waterside trees, emerging in the evening to hunt, some away from the river but some specifically hunt over water.
It is incredible what our rivers can support, and if these are all present, then you can assume the river is in good health, and if the river is in good health you can assume the land within the catchment is also in good health – as it is through the land the water must drain to join the rivers and streams.
Unfortunately the chain is all too often broken. Silt clogs the river beds, banks are grazed by livestock until they are bare, and pollution gets into the water.
It is the trust’s mission to restore and protect the river to make certain that future generations will be able to enjoy the beauty of the river catchment, and an abundance of wildlife and flora.
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