102 THE


DART ESTUARY -environmentally speaking


The beautiful Dart estuary is the tidal reach of the River Dart - stretching out approximately 9 miles from the weir above Totnes to Dartmouth. Starting as a trickle on Dartmoor, here the freshwaters of the river meet and mix with the saltwaters of the sea – the precise definition of an estuary not just a river. by Nigel Mortimer, Estuaries Officer South Devon AONB


W


ith the size and character of the River Dart’s water


catchment area, the Dart estuary is particularly freshwater dominated and is part of the reason why the waters of the estuary are frequently cloudy or turbid, hiding its under- water treasures from casual view. Sometimes the unexpected snort of a seal taking a breath reminding us that there is a whole other word down there! Watching the birdlife stabbing,


probing and sieving for food over the extensive estuarine mudflats, it is all too easy to imagine how the bed of the whole estuary is equally featureless but in reality there are hidden rocky reefs and outcrops, shallows and depths, sandy and stony areas, seaweed jungles – not to mention the water column itself and manmade structures and paraphernalia that we’d expect from a rich maritime port and harbour history. Being so freshwater dominated, most of the ‘food’ and nutrients that support this estuarine ecosystem


wash and flow down from the wider water catchment area – a watery conveyor belt flow of natural debris such as leaves, twigs, branches and dead stuff as well as the less-natu- ral washings and discards for our houses, streets, gardens, parks and farmland. As the downstream flow reaches the wider channel of the estuary, it slows and its carrying capacity declines so that much of this debris sinks to the bed; here it is gradually broken down by an untold population of microorganisms that release its life supporting nutrients into the estuary. There are so many, that three teaspoons of estuarine mud may hold as many bacteria as the entire human population – so many that they use up all the oxy- gen at the surface and those thriv- ing below survive on a chemistry quite alien to our own. This is why mudflats are quite naturally black and smelly just below the surface! Whilst these mudflats can, let’s


face it, be quite disgusting to our sensitivities, they are very much the lifeblood of the estuary. Seaweeds


thrive on the nutrients released and many many worms, shrimps, clams and even fish feed on the microorganisms; animals that then support the interconnected food web of the estuary culminating in the sights of the seals and ospreys or even the occasional glimpse of a kingfisher, dolphin or otter! The Dart estuary is quite a busy place to see these animals but if you are lucky enough to see them, do give them the space and respect they deserve, and remember all the other animals, plants, seaweeds and micro-heroes further down their food chain that they ultimately depend upon. Driven by the spin of the earth and pull of the sun and moon, the twice daily tides have a huge impact on the life in, on and around the estuary. Life on the shores must cope with the constant challenge of being underwater and then periods of exposure – possibly to the baking sun, drying wind, or freezing depths of winter. And life throughout has to cope with the ever-changing salinity as the tides push the zone of the


“The informed choices that we make should not just be kept for when we’re out on or by the waters but even at home when we’re wondering what to do with the fat in pan, how much detergent to add to the washing or how much fertiliser the roses really want. “


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