Human Impact on Aquatic Ecosystems Notes

Human Impact on Aquatic Ecosystems

Introduction

• Understanding the multifaceted human impact on aquatic ecosystems is essential for conservation and managing marine and freshwater habitats.

Threats to Marine Habitats

• There are numerous threats to aquatic ecosystems, including:
  • Nutrient runoff from land
  • Increasing ocean acidity
  • Marine extinctions
  • Microplastics in the food web
  • Introduction of new species
  • Managing stressors and marine heatwaves
  • Physical damage to habitats
  • Sediment deposition from the land
  • Sea level rise
  • Loss of predator species

Key Concepts in Human Impact

1. Run-off of Sediments

• Sources: Construction, mining, and logging lead to increased sediment run-off.
• Consequence: Increased turbidity (cloudiness in water) prevents sunlight penetration, reducing photosynthesis and ecosystem productivity.
• Impact on Fauna: Sediments can clog fish gills, leading to suffocation and eventual death.

2. Saltwater Intrusion

• Causes: Over-extraction of aquifers faster than natural recharge, predominantly due to agricultural irrigation.
• Effect: Movement of saline water into freshwater aquifers, detrimental to plants reliant on freshwater.
• Challenge: Positive feedback loop where increasing salinity forces farmers to pump more water, further degrading the water quality.

3. Ocean Acidification

• Process: CO2 diffusion into oceans increases acidity as it reacts to form carbonic acid.
• Impact on Marine Life: Acid binds to carbonate ions required by marine organisms for shell formation, weakening shells and increasing vulnerability to stress.

4. Climate Change and Ocean Warming

• Driving Factor: Primarily caused by fossil fuel combustion.
• Effect on Oceans: Ocean absorbs excess heat, leading to coral stress and bleaching, and contributing to biodiversity loss.

5. Eutrophication from Fertilizer Run-off

• Process: Excess nutrients from agricultural fertilizers (nitrogen and phosphorus) enter water bodies, triggering rapid algae blooms.
• Consequences: Thick algae blooms obstruct sunlight; subsequent die-off leads to oxygen depletion due to decomposition by bacteria, harming aquatic life.

6. Dams and Their Impact

• Function: Serves as sediment traps, reducing downstream nutrient flow essential for aquatic life.
• Negative Effects: Can erode coastlines and disrupt natural migration and spawning of fish such as salmon.

7. Destruction of Mangroves

• Importance: Mangroves host high biodiversity, providing essential nursery habitats for fish and preventing coastal erosion.
• Consequences of Destruction: Loss of critical ecosystem services leads to habitat degradation, flooding, and decline in marine populations.

8. Overfishing

• Impact: Advances in fishing technology allow for excessive and unregulated fishing, leading to significant fish stock declines.
• Bycatch: Unintentional capture of non-target species contributes to the decline of vulnerable populations.

9. Loss of Keystone Species

• Definition: Keystone species play a critical role in maintaining ecosystem structure and function.
• Consequences of Loss: The extinction of these species can lead to trophic cascades resulting in biodiversity loss.

10. Invasive Species

• Characteristics: Non-native species introduced by human activities which often compete successfully against native species.
• Impact: Disruption of local food webs, decreased biodiversity, and increased vulnerability of native species to extinction (e.g., lionfish in the Florida Keys).

Conclusion

• The cumulative human impacts on aquatic ecosystems highlight the essential need for comprehensive management strategies and conservation efforts to protect these vital habitats and their biodiversity.