Environmental impacts: impacts related to water
THEenvironmental impact of an activity can be measured using indicators, linked in particular to climate change (GHG emissions), to the destruction of the ozone layer, to human toxicity in the soil and in the air. Several of these environmental indicators are also linked to the management of water, as a resource and as a biotope. Considering the environmental impact of a product or an activity in a global manner therefore requires taking into account their impact on water consumption, aquatic ecotoxicity, or even the eutrophication of marine waters and fresh waters.
Water resources management
Water consumption
Under the combined effect of global warming and increasing use in human activities, freshwater resources are becoming scarce. However, fresh water is a precious resource, which represents only 3% of the water on the planet, 2/3 of which is in the form of ice. [i] The largest part of water consumption is linked to agricultural activity (58%). The production of drinking water is the second point of consumption. In France, the average consumption of drinking water is around 150 liters per day and per inhabitant, [ii] but only 1% of drinking water is drunk! 99% of the drinking water consumed in France is therefore consumed for hygiene, cooking, watering the garden and washing cars. These figures clearly provide courses of action for more sustainable water management in developed countries: among them, the practice of agroecology and daily actions to save water at home.
Rarefaction of surface water and groundwater
Water resources are decreasing as a result of their intensive use by humans: the quantity of water taken from groundwater is greater than the water that naturally returns there by infiltration. Moreover, water taken for human activities is not returned to its original environment: water taken from rivers is discharged into the sea and therefore permanently lost to waterways; groundwater does not return to groundwater. Even worse, some groundwater located in coastal areas, which are overexploited for agricultural activities, fill up with salt water and become unusable.
Global warming and drought episodes are not the only causes of the lack of natural filling of groundwater. Deforestation, the development of river banks, the concreting of soils through the construction of buildings, car parks and roads, as well as the ploughing and leaching of land in intensive agriculture waterproof the soil: water no longer seeps in, it evaporates or flows directly into the sea. During episodes of heavy rains, floods are more and more frequent without benefiting water supplies. Finally, in desert areas, fossil aquifers, which no longer fill up, continue to be exploited and to be emptied inexorably.
Aquatic ecotoxicity
A major challenge in terms of environmental protection, sustainable water management involves fighting against water pollution, and in particular against the degradation of groundwater or surfaces by chemical products. Plant protection products are the main culprits of aquatic ecotoxicity: they are pesticides, herbicides and antifungals used in conventional agriculture, which 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 in turn comes from industrial activities and transport. Water pollution by toxic products leads to the disappearance of species and the general degradation of the ecosystem.
Eutrophication of water
A major environmental problem, water eutrophication results in an imbalance in the ecosystem due to an excessive supply of nutrients in surface water. This excessive supply of nutrients in fact leads to the disproportionate growth of certain plant species. At its end, the eutrophication process leads to deoxygenation of the environment. The consequence is a decrease or even the disappearance of biodiversity. Although based on the same principle, a distinction is made between the eutrophication of fresh waters and the eutrophication of marine waters.
Eutrophication of fresh water
Fighting against the eutrophication of fresh water is one of the essential levers of sustainable development. Over-fertilization of rivers, lakes and freshwater bodies results from agricultural pollution (in particular nitrogen and phosphorus from manure and fertilizers) and urban pollution (wastewater discharges). As a result of eutrophication, continental surface waters experience premature aging: algae and aquatic plants proliferate, causing an increase in decomposed organic matter, and therefore accelerated sedimentation. The oxygen content decreases in the waters of the lake, with the consequence of a significant loss of biodiversity, until the environment dies. The phenomenon of eutrophication in lakes can take place naturally over thousands of years. But human activities accelerate this aging process to the point where it can occur in only a few decades.
Eutrophication of marine waters
Well known on the Breton coast with the problem 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 localized population explosion of an algae species can in fact cause the intoxication of large marine fauna. In addition, the proliferation of algae due to the over-fertilization of marine waters prevents light from entering the ecosystem, hindering photosynthesis and therefore the production of oxygen. Oxygen resources are depleted all the more quickly as the activity of organisms that decompose organic matter (protozoa in particular) is increased. The environment quickly becomes anoxic, that is to say devoid of oxygen, and therefore of life.
In the specific case of green algae that wash up on the Breton coast, there is also a health problem for humans and for terrestrial fauna, linked to the toxic gases that emanate from their decomposition.
In conclusion, the environmental impacts associated with water are numerous 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 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, leads to the disappearance of species and the degradation of ecosystems. Finally, the eutrophication of waters, whether fresh or marine, unbalances ecosystems and threatens biodiversity. Sustainable water management is therefore essential to preserve our environment.
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