Understanding Eutrophication, Aquifers, and Groundwater Contamination
Eutrophication of Surface Water
Eutrophication occurs when a river, lake, or reservoir becomes enriched with nutrients. This can be a natural process or caused by human activities (anthropogenic). An excess of nutrients leads to abundant plant growth, which, upon dying and decaying, reduces water quality. This decomposition process consumes large amounts of oxygen, making the water unsuitable for most living organisms and severely damaging the ecosystem.
Natural Water Purification: Water has a capacity to self-purify, ridding itself of pollution discharges (organic matter) without significant changes to its characteristics. This process is carried out by microorganisms in the water and soil. This capacity depends on:
- Nature of the contaminant (composition)
- Contaminant quantity: The self-purification process is only effective if the contamination does not exceed its capacity.
- Health status of the aquatic environment (dissolved oxygen, photosynthetic organisms, the level of aquatic life)
Dissolved oxygen is essential for the survival of all aquatic organisms.
Aquifers: Groundwater Reservoirs
An aquifer is a geological formation that allows water to move through its pores and cracks, making it accessible for human use. Aquifers are recharged by rainfall that percolates through soils, sands, etc., and are stored in permeable rock formations that contain or carry water.
Types of Aquifers:
- Free Aquifers: The storage layer is in direct contact with the surface. The water is at atmospheric pressure.
- Confined Aquifers: These are separated from the surface by an impermeable layer. Water pressure is greater than atmospheric pressure.
- Hanging Aquifers: These are disconnected from the main groundwater body.
Water Quality in Aquifers
If calcareous soils dominate, the water will be hard; if volcanic soils dominate, the water will be soft. Groundwater is generally suitable for human consumption because it undergoes natural filtration. However, anthropogenic pollution can cause quality problems.
Contamination of Groundwater
Because groundwater is a hidden resource, preventing and monitoring pollution is more difficult than with surface water due to its inaccessibility. Contamination can persist for many years due to the slow rate of water movement. Efforts must focus on eliminating the source of pollution (domestic, agricultural, industrial, nitrogen fertilizers, and pesticides). A lack of awareness of its hidden nature exacerbates the problem.
Sources of Groundwater Contamination:
Spread from the surface:
- Pollution from leachate from waste deposited on the surface.
- Contamination from agricultural activities (fertilizers, pesticides, and irrigation).
- Pollution induced by the flow of contaminated surface water into a well.
- Domestic wastewater contamination from septic tanks or treatment systems in areas favorable to infiltration, such as recharge areas.
- Impoundments: Accumulation of liquids from various sources.
- Saline intrusion due to alterations in the flow regime.
Differences between Groundwater and Surface Water Pollution
