Imaginez une rivière, coulant librement, ses eaux regorgeant de vie. Puis, une usine déverse ses eaux usées non traitées dans le cours d'eau. Cet afflux soudain de polluants plonge le fragile écosystème de la rivière dans le chaos. C'est là qu'intervient le concept de **sag de l'oxygène**.
Le sag de l'oxygène fait référence à une **diminution temporaire des niveaux d'oxygène dissous (OD)** dans un cours d'eau ou une rivière se produisant en aval d'un point de pollution. Cette diminution n'est pas simplement un léger creux ; elle peut être suffisamment grave pour nuire à la vie aquatique et même entraîner la mort d'écosystèmes entiers.
**Voici comment se déroule le sag de l'oxygène :**
**Les conséquences d'un sag de l'oxygène sont considérables :**
**Solutions pour lutter contre le sag de l'oxygène :**
Le sag de l'oxygène nous rappelle cruellement l'importance du maintien de la qualité de l'eau. En comprenant ce phénomène et en prenant des mesures proactives pour le prévenir et l'atténuer, nous pouvons protéger nos rivières et garantir leur santé pour les générations futures.
Instructions: Choose the best answer for each question.
1. What is the oxygen sag? a) An increase in the dissolved oxygen levels in a river. b) A temporary decrease in the dissolved oxygen levels in a river. c) A permanent decrease in the dissolved oxygen levels in a river. d) The natural fluctuation of dissolved oxygen levels in a river.
b) A temporary decrease in the dissolved oxygen levels in a river.
2. What causes the oxygen sag? a) An increase in the amount of dissolved oxygen in the water. b) The decomposition of organic waste by microorganisms. c) The release of harmful chemicals into the water. d) The natural flow of the river.
b) The decomposition of organic waste by microorganisms.
3. What is BOD? a) Biochemical Oxygen Demand b) Biological Oxygen Demand c) Bacterial Oxygen Demand d) Bio-Organic Demand
a) Biochemical Oxygen Demand
4. What is a major consequence of the oxygen sag? a) Increased fish populations. b) Improved water quality. c) Fish kills due to lack of oxygen. d) Enhanced biodiversity in the river.
c) Fish kills due to lack of oxygen.
5. Which of the following is NOT a solution to combat oxygen sag? a) Wastewater treatment. b) Pollution prevention. c) Increasing industrial discharge. d) River restoration.
c) Increasing industrial discharge.
Instructions:
Imagine a river that receives wastewater discharge from a nearby factory. The factory produces a significant amount of organic waste, contributing to a severe oxygen sag in the river.
Task:
**Analysis:** * **Fish Kills:** The severe oxygen depletion caused by the factory's discharge will lead to fish kills, as they struggle to survive in low-oxygen conditions. * **Impact on Aquatic Organisms:** Other aquatic organisms, such as insects, invertebrates, and plants, will also be negatively affected by the oxygen sag. These organisms form the base of the food web, and their decline will have a ripple effect throughout the ecosystem. * **Ecosystem Imbalance:** The oxygen sag disrupts the natural balance of the river ecosystem, leading to the dominance of pollution-tolerant species and the decline of sensitive species. This imbalance weakens the ecosystem's resilience to future disturbances. **Proposed Solutions:** 1. **Wastewater Treatment:** The factory should install an effective wastewater treatment plant to remove organic matter and other pollutants before discharging wastewater into the river. This significantly reduces the BOD load entering the river. 2. **Pollution Prevention:** The factory should implement measures to reduce the generation of organic waste in its production process. This could include using less water-intensive production methods, recycling and reusing materials, and adopting cleaner production technologies. 3. **River Restoration:** The local authorities could implement river restoration projects to improve the river's health. This could involve planting riparian buffer zones to filter pollutants, restoring degraded habitats, and controlling invasive species that compete with native plants.
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