The County of Dorsetshire
OS Map Grid Ref: ST721015
see also Towns & Villages of Dorset
The county of Dorset is well watered by the Stour, Frome, Piddle, Liddon, Yeo, and other lesser rivers.
The Frome and Piddle emptying into Poole Harbour are fine examples of chalk streams while the Stour drains more complex geology to empty with the Wiltshire and Hampshire Avon into Christchurch Harbour. These three major Dorset river systems all run in a south-easterly direction.
Dorset has no significant lakes or other bodies of fresh water but the vast Poole Harbour, separated from the sea by only a narrow channel and the Fleet Lagoon behind Chesil Beach compensate for this.
Dorset's rivers, including the Frome and the Piddle are home to the river water dropwort (Oenanthe fluviatilis) with its finely divided light green leaves. Although it is common in the rivers of Southern England, the English populations are important as they are more common than anywhere in North-Western Europe to which the plants are confined.
The plant life of youthfull mountain rivers is dominated by mosses and algae on the rocks and boulders but the lowland rivers of Dorset support a wide variety of higher plants.these plants are adapted to life within, on the surface, and on the margins of the watercourse. The plant communities vary with the type of the river and along its course.
The plants not only create a variety of habitats for invertibrates, fish birds and mammals but have a pronounced effect on the flow of the water and on the sediments which it carries. Although some of the fresh weed is consumed by animals, only a small proportion is consumed by either the vertibrate or invertibrate fauna. Rather the submerged higher plants provide a large surface area on which algae, grazed by invertibrates, grow in the spring and summer. In the autumn and the winter, the aquatic plants not only decay themselves to provide winter sustenance for invertibrates, but they also trap leaves shed in the autumn which would otherwise be flushed dowstream by the flow.
CHALK STREAMS (e.g.; the Frome and the Piddle)
Water Crowfoot (Ranunculus fluitans) grows spectacularly in the spring along winterbourne sections of the rivers shows spectacular growth. Its growth assumes a different form in the summer as the winter streams dry out. Common (Nasturtium officinale) and Fool's Watercress (Apium nodiflorum) may also be found in the streams and on their margins.
Downstream, where the flow persists, the dark green mass of water crowfoot dominates the water while the white arial flowers form a haze across the surface of the water during spring and summer. The lesser water parsnip (Berula erecta) favours areas near the bank which are shaded by treesand slow-flowing silted areas are occupied by elongated light green beds of water starwort (Callitriche marginata).
Further dowstream the variety of plants which emerge from the water and inhabit the river bank increases. They include branched bur-reed (Sparganium erectum) and reed canary grass (Phalaris arundinacea) and reed sweet grass (Glyceria maxima syn. Poa aquatica). Above the water they provide resting places for insects while below they offer refuges from the force of the mid-stream flow for invertibrates.
On the river banks, comfrey (Symphytum officinale), greater willow herb (Epilobium hirsutum), meadowsweet (Spiraea Ulmaria), purple loosestrife (Lythrum salicaria) and other wild flowers provide an ever-changing display of colour.
The fauna (animal life) of any location is determined by the prevailing environmental conditions so the type of river and the site of the location along its course are important in determining the animal community which is found. The range of invertebrate species is, however, also subject to pollution and other forms of environmental stress (the sensitivity of invertebrate animals to stress has been used as a means of monitoring rivers).
Dorset's streams and rivers support a wide range of insects and all the major groups are represented; alderflies (Megaloptera), beetles (Coleoptera), bugs (Hemiptrea), caddis flies (Trichoptera), dragonflies and damselflies (Odonata), mayflies (Ephemeroptera), stoneflies (Plecoptera) and the true flies (Diptera). The non-insect invertebrate fauna are represented by the crustaceans (Malacostraca), flatworms (Tricladida), leeches (Hirudinea), mussels (Bivalvia), snails (Gastropoda) and true worms (Oligochaeta).
Many high quality sites in the middle reaches of Dorset's rivers include over a hundred species of invertebrate animals. The life-cyles of these creatures range from a few weeks to over two years.
see also: Rivers
FROME
LIM
The river rises in Devon and crosses into Dorset to tumble through Lyme Regis before spilling onto the beach.
MOORS RIVER
PIDDLE
STOUR
RIVERS
DORSET
Rivers
Bridges
Mills
Towns & Villages
CORNWALL
DEVON
DORSET
HAMPSHIRE
ISLE OF WIGHT
SOMERSET
WILTSHIRE
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