Ecology

Rivers and Streams

About Rivers and Streams

Rivers are an important freshwater drinking source for humans, livestock and wildlife. The complex natural systems have been gradually altered by human activity over time but still provide an important habitat for aquatic and terrestrial organisms.

The physical and chemical conditions of a river determine the habitat and the species living within it. Rivers have different flow rates depending on many conditions such as steepness of the landscape, rainfall rates and water depth. Seasonal changes also cause changes in water depth and flow rate over the course of the year. The physio-chemical properties of a river, including light availability, temperature and chemical properties will also determine which species can survive there. Typically, faster flowing rivers contain more dissolved oxygen which increases biodiversity.

Water quality is reduced by human inputs such as from sewage, agricultural runoff and industrial pollution. These inputs increase when it rains. Water quality determines the species living within a river as many species have different tolerance levels to pollution.

Riverbed Species

The larval stages of many mayflies, caddisflies, dragonflies, beetles and other insects live abundantly in riverbeds along with worms, crustaceans and molluscs. These are all known as macroinvertebrates and can be discovered by carrying out a kick sample. Different species of macroinvertebrates are tolerant to different pollution levels, making them a direct indicator of water quality.

Macroinvertebrates provide a food source for fish, birds and mammals.

: Burrowing mayfly nymph (Ephemeridae) and snipe fly larvae (Athericidae)

: Flay-headed mayfly nymph (Heptageniidae)

: Free living green caddisfly larvae (Rhyacophilidae)

: Net spinning caddisfly nymph (Hydropsychidae)

: Large red damselfly

Aquatic plants and fish

Aquatic plants such as lilies, weeds, reeds and algae are mostly found in areas of low flow rates. Many are rooted to mud or rocks in the riverbed. They provide dissolved oxygen and shelter for fish and macroinvertebrates. If light and nutrient inputs to a river are high, plants and algae may grow at excessive rates. The resulting algal bloom reduces light availability, causing plants to die and decompose. Decomposition results in anoxic conditions, causing fish and macroinvertebrate deaths. This process is known as eutrophication.

Riverbanks

Many terrestrial plants are suited to wet conditions, so they are attracted to riverbanks. They can provide shelter for mammals and nesting opportunities for birds. Some species to look out for include:

Common reed (Phragmites australis)
Common bulrush (Typha latifolia)
Common clubrush (Schoenoplectrus lacustris)
Hemlock water dropwort (Oenenthe crocata)
Hemp agrimony (Eupatorium cannabinum)
Meadowsweet (Filipendula ulmaria)
Alder (Alnus glutinosa)

Look out for invasive Himalayan balsam which grows in large clumps on riverbanks, it is a particular problem across South-Central Wales and along the Great Glamorgan Way route. Visit our page on Himalayan balsam to find out how to identify and remove it.

Mammals

Terrestrial mammals rely on freshwater sources such as rivers, lakes and ponds for drinking water. However, many mammals have adapted to living in water such as by having waterproof fur and closing noses allow them to stay in the water for longer. Other adaptations like webbed feet and muscular tails make them strong swimmers. Many of these species are now endangered due to land-use change as their habitat is becoming reduced. Some of the mammalian species that rely on rivers include:

European water vole (Arvicola amphibius)
Eurasian Otter (Lutra lutra)
Eurasian Water shrew (Neomys fodiens)
American mink (Neovision vision)
Daubenton’s bat (Myotis daubentoniid)

Otters live in the River Taff, which runs parallel to the Great Glamorgan Way route. Otters are shy and nocturnal but sometimes can be seen on the riverbank or swimming in rivers. An otter’s webbed feet and strong tails aids it with swimming, as well as their closing nose and ears which keep out water.

Birds

There are many species of bird which can be seen near freshwater such as rivers, lakes and ponds. Some hunt for fish and others make nests near the water’s edge. Some species such as swans and ducks are excellent swimmers. Other species such as herons and ibises have long legs and toes which allow them to wade on soft mud. Smaller species including kingfishers are more likely to be seen in flight over the water. Here are some species to look out for on the Great Glamorgan Way: