TENDUA - Association for biodiversity conservation

Newsletter n°11 - March 2014

Nitrates and eutrophication of rivers and others water bodies

Eutrophication is a long-term natural phenomenon that converts, during thousands of years, a water plan into a meadow and then in a forest. The eutrophication reveals that the capacity of self-purification of a healthy aquatic environment has reached its limits, either punctually or a chronic way.

Natural eutrophication of a body of water, natural reserve of Kaluga region, Russia
Natural eutrophication of a body of water, natural reserve of Kaluga region, Russia
© M. Dupuis

Indeed, a healthy environment contains a good biodiversity with full of nutrients, fish, and thus a good oxygen rates in water.

However, pollutants and other external fertilizers used in agriculture, flow naturally into the nearest water plans ... Fertilizers allow crops to grow faster; in water, they have the same effect on algae and other aquatic plants which, in fact, grow and compete for oxygen with other species. The natural balance is upset, the ecosystem is impoverished, plants and algae are gaining ground: it’s eutrophication. Many of our lakes are affected by this phenomenon today mainly due to additional pollution such as agricultural spraying and industrial and urban waste (laundry, household products ...).

Solution : inverse the process

As usual, there are various ways of control and mitigation (“déseutrophisation”). The technology exists but, obviously, the individual responsibility and the political courage are absent. Examples of what could be done:
* Reduce the use of pesticides : when they arrive in the watercourse, they kill many organisms, or, by limiting the “higher” plants, they can contribute to aggravate or induce eutrophication ;
* conduct agronomic soil analysis and focus on natural fertilizers ;
* reduce the use of eutrophic pollutants from the upper watershed ;
* develop watershed that restore hedged farmland networks, banks, hedges and grass strips, sufficient in size and consistent with the terrain and soils (soil study); Stormwater runoff can promote the training of nutrients such as phosphorus that are better retained if the soil infiltration capacity is restored ;
* protect and restore buffer zones (ideally combining a riparian forest with grass strips) between fields and rivers ;
* replace all the phosphates from detergents with anti-limestone agents with no impact on the environment;
* better removal of nitrogen and phosphorus in wastewater treatment plants (which can be equipped with methods of denitrification and phosphorus removal).

So, when do we begin ???

Green algae in the Bay of Douardenez
Green algae in the Bay of Douardenez
Green algae (Ulva) preferentially feed on nitrogen that is in low quantities in the marine environment, in particular from spring to autumn. In confined coastal areas, more or less continuous contributions of nitrates, natural chemicals involved in the nitrogen cycle, are coming from rivers flowing directly into the marine environment. These nitrates then promote excessive growth of green algae. - © L.Mignaux

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