Beauty is Not Only Skin Deep - The Ecology of the Dart
The River Dart is a waterway we all love, flowing from the moor to the sea at Dartmouth.
Its beauty and tranquillity are hard to beat - but under this calm surface there is a complex and remarkable ecosystem we hardly ever consider.
The Dart is an estuary – a place where a fresh water river flows into a tidal inlet. This means fresh and salt water are mixing together, which ensures a high level of nutrients are present in the water, one of the main reasons for the rich ecology.
The river that feeds into the estuary starts with two - East Dart and West Dart, which meet, rather surprisingly, at Dartmeet on the moors. The two rivers well up through the acid soils of the moor and begin from the bogs for which the area is famous.
From there the River Dart flows to Totnes, where it runs over the weir just past Dartington and meets the tidal inlet. It runs from moor to sea over a course 28 miles long. It drains from an area covering 47,500 hectares, a third of the size of Greater London.
Its sides are generally very steep and the lower river especially is subsequently a ‘flash’ river valley. This means any rainfall makes its way into the river very quickly – putting the river at high risk of pollution, as any problems on land are quickly washed into the river system.
As the river becomes tidal – and salty - after flowing over the weir at Totnes there are some saltmarshes. These form in tidal areas where mud builds up which is uncovered at high tide. Plants take hold and create a stable but very wet area. Saltmarshes are vital to the ecology of the river, as they are hunting grounds for many species and also the nurseries for many too, due to the plant life giving both food and shelter. Recent research indicates that Salt Marshes are carbon sinks – soaking up greenhouse gases – making their retention and protection even more important.
The Dart is officially a ‘drowned river valley’ or ‘ria’. The Dart Valley was formed over millions of years by rivers running down to the sea. This valley was then flooded when the ice sheets melted 12,000 years ago at the end of the last ice age raising the world’s sea levels by 120 metres.
12,000 years sounds like a long time to us – in geological terms it’s an eye-blink. Think of the 4.7 billion year history of our world as a single day. In that time frame, 12,000 years would equate to 0.2 seconds.
So our beautiful Dart, which seems timeless in its beauty and tranquillity, is incredibly young (geologically speaking).
The river is, as previously stated, an ecosystem, built around an incredible complexity - each part depending on others.
Starting from the smallest, the river is full of bacteria, diatoms and algae. All three are incredibly widespread and vital in the ecosystems of the world’s oceans.
There are huge numbers of these in the river. Mind bogglingly huge. In two teaspoons of river mud there are more than 8 billion bacteria – more bacteria than there are people on planet earth.
In fact the Environment Agency will often receive calls from concerned rivers users about ‘sewage’ which is in fact massive amounts of algae in bloom – it often looks brown and can also produce a foam which looks rather disgusting. If you see it remember it’s just another miracle of nature.
Many of the river’s creatures depend on these tiny, often single-celled creatures and their abundance - thanks to the rich nutrients created by the mixing of sea and fresh water - is one of the main reasons the Dart is so rich in wildlife.
The river is simply teeming with life – its population of invertebrates - from the crabs children try to catch off Dartmouth’s Embankment to nymphs, flies and other creatures which fill every available niche.
Countless birds, including goosander, dipper and grey wagtail, along with kingfishers, cranes, swans, ducks, buzzards and many others populate the banks of the river - it is a twitcher’s paradise and no mistake.
Part of the reason for this is the flies, bugs and other almost invisible creatures, but it’s also down to the huge deposits of rich mud that are revealed every low tide.
Full of worms and other creatures, its like a huge buffet is revealed every low tide for a host of birds and other creatures to feast to their heart’s content.
Populations of salmon and many other breeds of fish also live in the Dart along with seals and otters – the cute pin-ups of river life.
These creatures are the ones we remember if we are lucky enough to see them, along with the beautiful bird life, but it is worth remembering that they are on top of a massive food chain that is all supported by the rich and complex ecology and geography of the River Dart.
The river is once again supporting oyster beds as well as other shellfish producers – the river was too polluted during the 1960s and 70s and production stopped. Their return is an indication of the clean-up that the river has seen in the last thirty years – and it requires the dedication of all users of the river to ensure it continues in that way.
It perhaps goes without saying that the River Dart is an amazing, beautiful place, which all of us are guilty of taking for granted sometimes. To look at the ecology and geography behind its beauty is to appreciate it all the more – the river is a miracle we all get to share.
First Published May/June 2012 By The Dart
