The environmental impact of an activity can be measured through indicators linked in particular to climate change (GHG emissions), ozone layer destruction, and human toxicity in soils and air. Several of these environmental indicators are also linked to water management, both as a resource and as a biotope. Considering the environmental impact of a product or activity in a holistic way therefore requires taking into account their impact on water consumption, aquatic ecotoxicity, or the eutrophication of marine and fresh waters.
Managing water resources
Water consumption
Under the combined effect of global warming and growing use in human activities, fresh water resources are becoming scarce. Yet fresh water is a precious resource, representing only 3% of the water present on the planet, two-thirds of which is in the form of ice. The largest share of water consumption is linked to agricultural activity (58%). Drinking water production is the second largest use. In France, average drinking water consumption is around 150 litres per day per inhabitant, but only 1% of drinking water is actually drunk. These figures point to actions for more sustainable water management in developed countries: among them, the practice of agroecology and everyday habits to save water at home.
Depletion of surface water and groundwater
Water resources are decreasing under the effect of their intensive use by humans: the quantity of water drawn from aquifers exceeds the water that naturally returns to them through infiltration. Moreover, the water drawn for human activities is not returned to its original environment. Worse still, some coastal aquifers, overexploited for agricultural activities, fill with salt water and become unusable.
Global warming and drought episodes are not the only causes of the lack of natural replenishment of aquifers. Deforestation, riverbank development, the concreting of soils through the construction of buildings, car parks and roads, as well as ploughing and leaching of land in intensive agriculture, make soils impermeable: water no longer infiltrates, it evaporates or runs off directly to the sea.
Aquatic ecotoxicity
A major issue in environmental protection, sustainable water management involves fighting water pollution, and particularly the degradation of groundwater or surface water by chemical products. Plant protection products are the main cause of aquatic ecotoxicity: these are the pesticides, herbicides and fungicides used in conventional agriculture, which seep into soils and penetrate underground aquifers. Aquatic ecotoxicity also stems from 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 the general degradation of the ecosystem.
Eutrophication of waters
A major environmental problem, water eutrophication manifests as an imbalance in the ecosystem due to an excessive supply of nutrients in surface waters. This excessive nutrient input leads to the disproportionate growth of certain plant species. At its end point, the eutrophication process leads to deoxygenation of the environment, resulting in a decline, or even disappearance, of biodiversity. A distinction is made between freshwater eutrophication and marine eutrophication.
Freshwater eutrophication
The over-fertilisation of rivers, lakes and freshwater bodies results from agricultural pollution (notably nitrogen and phosphorus from manure and fertilisers) and urban pollution (wastewater discharge). Because of eutrophication, inland surface waters undergo premature ageing: algae and aquatic plants proliferate, leading to an increase in decomposed organic matter and therefore accelerated sedimentation. The oxygen content decreases, resulting in a significant loss of biodiversity. Human activities accelerate this ageing process to the point of making it occur in just a few decades.
Marine eutrophication
Well known on the Breton coast with the problematic proliferation of green algae, the phenomenon of marine eutrophication is one of the challenges of sustainable management of water and aquatic ecosystems. The localised population explosion of an algae species can cause the poisoning of large marine fauna. Moreover, the proliferation of algae due to over-fertilisation prevents light from penetrating the ecosystem, hindering photosynthesis and therefore oxygen production. The environment quickly becomes anoxic, that is, devoid of oxygen, and therefore of life.
In conclusion, the environmental impacts linked to 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. Sustainable water management is therefore essential to preserve our environment.