Читать книгу Taming the Flood: Rivers, Wetlands and the Centuries-Old Battle Against Flooding - Jeremy Purseglove - Страница 33

Additional benefits of tree-lined streams, in reducing the effects of nitrates and phosphates in the water and in shading out the choking growth of summer weed in a river bed, which may otherwise necessitate further expensive dredging, have been recognized by Dutch and German scientists for over a decade.⁸ The only green thing about many of our English rivers nowadays is profuse algal growth in the water, which results from an excess of fertilizer leaching off arable fields straight into the stream. Traditional drainage has accelerated this problem in two ways: by promoting farming methods which require high levels of fertilizer, and by stripping out the buffer of vegetation between the riverside and the fields. It is not uncommon for tractors to slide into a stream as they attempt to cultivate every last scrap of land beside a watercourse. This approach has led to overexploitation of stream systems. Until 1986, the steeply graded banks of one river in arable country were regularly sprayed with the approved chemical 2-4-D amine, in order to reduce the nettles, which were less good at holding the banks than slow-growing grasses, but for which perfect conditions had been established by abundant nitrogen leaching off the fields. As is so often the case in operations which go wrong, over-heavy management went hand in hand with a haphazard lack of supervision. The spraying boat, affectionately known as the ‘Black Pig’, would set off on its regular journey up the river without any adjustment on the spraying nozzle. Consequently, once the motor was started, the spray was meted out indiscriminately to riverside walls, fishermen, lovers on the bank, and nettles alike.

It is estimated that for every pound farmers spend on fertilizer on their fields, they can expect the rain to wash away a good fifty pence-worth. But the real cost of such waste is not only monetary. Water is extracted for drinking purposes from many of our lowland rivers, and high nitrate levels in drinking water can lead to illness in bottle-fed babies. Thus, while land-drainage departments promote agricultural intensification, other departments in the same water authority have to spend more public money in expensive plant to treat the water, in order to comply with EEC regulations on nitrate levels. Further expense to the water authority in cleaning up river pollution caused by silage effluent is yet another consequence of high-gear monocultural farming, encouraged by land drainage.^fn5

Peat shrinkage. The Holme Post, Cambridgeshire, showing levels of shrinkage between 1848 and 1932. © Cambridgeshire Libraries