Environmental impacts: water-related impacts
The environmental impact of an activity can be measured using indicators linked to climate change (greenhouse gas emissions), the destruction of the ozone layer and human toxicity in the soil and air. Several of these environmental indicators are also linked to water management, both as a resource and as a biotope. Taking a global view of the environmental impact of a product or activity means taking into account its impact on water consumption, aquatic ecotoxicity and the eutrophication of marine and fresh water.
Managing water resources
Water consumption
Under the combined effect of global warming and increasing use in human activities, freshwater resources are becoming increasingly scarce. Yet freshwater is a precious resource, accounting for only 3% of the planet's water, 2/3 of which is in the form of ice. Most water consumption is linked to agricultural activity (58%). The production of drinking water is the second largest consumer. In France, the average consumption of drinking water is around 150 litres per person per day, but only 1% of drinking water is actually drunk! So 99% of the drinking water consumed in France is used for hygiene, cooking, watering the garden and washing the car. These figures clearly point the way to more sustainable water management in developed countries, including agroecology and water-saving practices in the home.
Depletion of surface and ground water
Water resources are diminishing as a result of their intensive use by mankind: more water is being withdrawn from groundwater than is naturally returning to it through infiltration. Furthermore, the water withdrawn for human activities is not returned to its original environment: water withdrawn from rivers is discharged into the sea and therefore permanently lost to watercourses; groundwater does not return to the water tables. Worse still, some water tables in coastal areas, overexploited for agricultural purposes, fill up with salt water and become unusable.
Global warming and droughts are not the only causes of the failure of water tables to replenish naturally. Deforestation, the development of river banks, the concreting of land through the construction of buildings, car parks and roads, as well as the ploughing and leaching of land by intensive farming, all lead to waterproofing of the soil: water no longer infiltrates, but evaporates or runs off directly into the sea. During periods of heavy rain, flooding is increasingly frequent, without any benefit to water reserves. Finally, in desert areas, fossil aquifers that are no longer replenished continue to be exploited and inexorably drained.
Aquatic ecotoxicity
As a major environmental protection issue, sustainable water management means combating water pollution, and particularly the degradation of groundwater and surface water by chemicals. Pesticides, herbicides and antifungals used in conventional farming infiltrate the soil and enter the groundwater. These pollutants also accumulate in surface water. Aquatic ecotoxicity is also caused by heavy metal pollution (mercury, lead, arsenic, cadmium), which comes from industrial activities and transport. Water pollution by toxic products leads to the disappearance of species and general degradation of the ecosystem.
Eutrophication of water
Eutrophication, a major environmental problem, results in an imbalance in the ecosystem due to an excessive input of nutrients into surface waters. This excessive supply of nutrients leads to the disproportionate growth of certain plant species. Ultimately, the eutrophication process leads to deoxygenation of the environment. As a result, biodiversity is reduced or even eliminated. Although based on the same principle, a distinction is made between eutrophication of freshwater and eutrophication of marine waters.
Eutrophication of fresh water
Combating the eutrophication of freshwater is one of the key levers for sustainable development. Over-fertilisation of rivers, lakes and freshwater bodies is the result of agricultural pollution (particularly nitrogen and phosphorus from manure and fertilisers) and urban pollution (wastewater discharges). As a result of eutrophication, continental surface waters age prematurely: algae and aquatic plants proliferate, leading to an increase in decomposed organic matter, and therefore accelerated sedimentation. Oxygen levels fall in water, resulting in a significant loss of biodiversity, leading to the death of the environment. The eutrophication of fresh water can occur naturally over thousands of years. But human activity accelerates this ageing process, allowing it to occur in just a few decades.
Eutrophication of marine waters
Well-known on the French north-west coast of Brittany with the problematic proliferation of green algae, the phenomenon of eutrophication of marine waters is one of the challenges of sustainable management of water and aquatic ecosystems on our planet.
The localised demographic explosion of a species of algae can lead to the poisoning of large marine fauna. Furthermore, the proliferation of algae due to the over-fertilisation of marine waters prevents light from penetrating the ecosystem, hindering photosynthesis and therefore oxygen production. Oxygen resources are depleted all the faster as the activity of organisms that decompose organic matter (protozoa in particular) is increased. The environment rapidly becomes anoxic, i.e. devoid of oxygen and therefore of life.
In the specific case of the green algae that washes up on the coast of Brittany, there is also a health problem for humans and terrestrial fauna, linked to the toxic gases that emanate from their decomposition.
In conclusion, the environmental impacts linked to water are many and varied. To assess the overall impact of an activity, it is essential to take into account its water consumption, aquatic ecotoxicity and water eutrophication. The increasing scarcity of freshwater resources is a major problem, exacerbated by global warming and the intensive use of water in human activities. Water pollution caused by chemicals and heavy metals is leading to the disappearance of species and the degradation of ecosystems. Finally, the eutrophication of water, whether fresh or marine, destabilises ecosystems and threatens biodiversity. Sustainable water management is therefore essential if we are to preserve our environment.
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