No two high energy river sections look alike – particle size and stability on the river bed dominate both the physical and biological character of a section. (Image NE)

High energy river sections largely occur in the uplands or in hillier parts of lowland England, and can exhibit a range of water chemistries and trophic conditions. These sections include boulder-strewn rapids as well as active shingle river sections where gravel shoals are continually eroded, deposited and reworked. The stability and particle size of river substrates strongly influences the species that are supported. Stable boulders and cobbles favour the growth of mosses and liverworts and invertebrates associated with them, particularly in the humid

Riparian tree cover creates humid conditions that support diverse invertebrate communities. (Image NE)

conditions created by tree-shading and ravines and gorges. Shifting gravel substrates support algal communities and invertebrate species adapted to the instability, whilst exposed gravel shoals that stabilise in-channel margins support diverse beetle assemblages. The fish community in high-energy sections

Small fish, like this bullhead (Cottus Gobio), dominate the high-energy river sections.

is naturally dominated by salmon, brown trout and eel along with a range of smaller species such as bullhead and stoneloach. These rivers have been degraded by straightening, flood embankments, flow regulation from headwater impoundments, loss of natural riparian vegetation (including trees), pollution, abstraction and non-native species.