Pollution from the river basins

[Ian West and Tonya West – Geology of the Wessex Coast ]

The Solent Estuarine System consists of Southampton Water, the West Solent, the East Solent and Spithead, Portsmouth, Langstone and Chichester Harbour, all of which are drowned Pleistocene river systems. The Solent River extended from west to east at a time when sea-level was low and the English Channel was dry. As the sea level continues to rise, we need to appreciate the influence of the rivers which now feed the modern day Solent waterways.

Much of the pollution which enters the Solent originates upstream in the river basins, where agricultural methods, reliant on synthetic fertilisers containing nitrogen and phosphorus, have intensified continuously since the Industrial Revolution. At each stage, innovations in farming techniques brought about huge increases in crop yields. This tremendous rise in food production and the consequent increase in cultivated land has sustained a global population that has quadrupled in size over the span of a single century.

While these chemicals have helped increase food production, they have also brought about a gigantic increase in reactive nitrogen levels throughout the environment. Excess levels of nitrogen and phosphorus have caused the once-beneficial nutrients to become pollutants and roughly half the nitrogen in synthetic fertilisers now escapes the fields where it is applied, finding its way into the soil, air, rainfall and rivers of the region. Soil bacteria convert nitrogen from fertiliser into toxic nitrates which rainstorms and irrigation systems carry into groundwater and river systems.

Accumulated levels of nitrogen and phosphorus harm terrestrial and aquatic ecosystems by loading them with excess nutrients, a process known as eutrophication which is a causal factor in the toxic algae blooms affecting our rivers and coastal waters. As excessive organic matter decomposes in aquatic environments, it can bring about oxygen depletion, creating ‘dead zones’ within bodies of water where nothing can survive. Nitrogen accumulation in water and on land threatens biodiversity and the health of native plant species and natural habitats. In addition, fertiliser application in soil leads to the formation and release of nitrous oxide, one of the most harmful greenhouse gases.

With the global population continuing to increase, the tension will continue to grow between agricultural growth and the ecological health of the land upon which humans depend. Our farmers are now well aware of the damage caused by fertiliser run-off and it is to be hoped that the management techniques now promoted by The Environment Land Management initiative will bring about a substantial improvement to water quality in our rivers and coastal waters.

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