Freshwater habitat

Freshwater

The rain-soaked lands of Britain and Northern Ireland are rich in rivers, streams, lakes, ponds, canals and ditches. Whether natural or artificial, they are the life-force behind the wildlife we love.

Development and history

Waterbodies vary greatly according to topography and underlying geology and, of course, the movement (or otherwise) of water. Streams derive from springs, snowmelt or rainwater. This drains from a catchment area, flowing rapidly downhill in the uplands, over time eroding a ‘v’-shaped valley (or following a ‘u’ shaped glacial valley). These streams broaden out in the middle reaches, as multiple streams join together to form a river until, in the lowlands, the river slows and meanders across a broad, flat and fertile floodplain. The floodplain itself is created from sediment carried by the water from further upstream, dropped when floodwaters breach the river bank. As nowhere in the UK is that far from the sea there is not sufficient distance for very large rivers to form.

Most natural lakes are found where glaciers gouged out and deepened existing valleys or deposited a barrier of debris that creates a natural dam. In the southern lowlands, which were less heavily glaciated, natural lakes are quite rare, although some are formed where coastal sediment has trapped freshwater. However, lakes and ponds created by gravel extraction or as reservoirs, fish ponds, mill ponds or for livestock are common. Lakes are temporary features, eventually filling with sediment and developing fen vegetation, but this is generally far too slow a process to be appreciated over human timescales.

Canals and ditches are also artificial waterbodies. Canals have very little flow and have more in common with ponds than rivers. Originally created to extend water transport, they fell into decline with the rise of rail and road transport, but many have been restored and are now used for recreation. Where boat traffic is not too heavy, they can support much wildlife, often bringing it into urban settings. Some little-used canals are of international importance for their aquatic flora and invertebrates. Most farm ditches are of little interest, but those in areas that were once wetlands (for example in coastal and floodplain grazing marshes) can often be rich in plants and invertebrates, providing a refuge for species that were once more widespread.

Tamed rivers

Natural rivers are dynamic, forming braids, shingle bars and riffles and gradually eroding the outer curve of meanders, causing them to migrate across their floodplain over time. They can have both shallow vegetated margins and river cliffs, and may be choked in places with woody debris and logjams. Of interest in themselves, these features also provide habitat for a multitude of species. For example, cliffs provide nesting habitat for sand martin and kingfisher, loose un-vegetated shingle supports diverse invertebrates and may be used by nesting little ringed plover and common sandpiper. Shingle bars also sometimes support montane or heath species washed down from the mountains. Woody debris creates pools and modifies the flow, catching silt and providing shelter, shade and spawning sites for fish, while emerging branches provides perches for the adult terrestrial stage of mayflies, stoneflies and caddisflies (often referred to as river flies) and dragonflies and damselflies. Woody debris also slows the water flow, reduces bank erosion and stabilises the river bed.

However, few rivers in the UK (particularly in England and Wales) show fully functioning natural processes. River systems have been modified for centuries though water impoundment (for mills) and abstraction, flood defences, canalisation, effluent disposal and energy creation schemes. Both diffuse pollution (general inputs of nutrients, soil and pollutants such as sewage, herbicides and pesticides, often from agricultural sources) and point pollution (pollution from single sources such as industry, or single pollution events such as an oil spillage) can have major effects on the health of rivers and water bodies. Water courses have been deepened, straightened and embanked to allow water to flow away more rapidly to reduce flooding and to allow navigation – but this has also ripped apart natural systems by cutting rivers and streams off from their floodplains and preventing the natural processes that provide habitat for wildlife and regulate water flow downstream. The lack of riverine wet woodland, together with people’s propensity to tidy up nature has also greatly reduced the amount of woody debris, and intensive cultivation of river catchments has resulted in soil run-off and polluted waters.

Conservation

Recognition of these issues has led to the development of catchment scale management plans to reduce pollution and restoration schemes that reinstate river meanders, allow woody debris to be left remove or circumvent barriers to fish migration and remove nutrient-laden silt (for example from lowland lakes). The next step is to restore natural dynamics and allow the rivers themselves to undertake the engineering.

Water bodies are particularly sensitive to climate change (which is likely to lead to warmer temperatures, intensified storm events and drought) which may exacerbate existing problems. Future river restoration needs to combine ecological restoration with wider policies relating to climate change, such as the reinstatement of functional floodplains.

How you can help

We have started to recognise that healthy wetlands are important, not just for wildlife, but also for us. River and floodplain restoration projects carried out by local Wildlife Trusts are aiding these vital habitats. You can support this work by joining your local Wildlife Trust.

You can help reduce the strain on our streams and rivers by reducing your own water use, in the house and in the garden. Tips for saving water include turning off the tap when brushing your teeth, or washing fruit and veg in a bowl rather than under a running tap.

Check out your local water company website, as many companies now offer water saving tips and also devices – for example, see Anglian Water’s advice on using water wisely.