Eutrophication case studies

Question 1

What causes seasonal hypoxia off the coast of Oregon?

Answer 1

The Oregon coast experiences seasonal hypoxia due to upwelling-driven phytoplankton blooms.
In summer, upwelling brings nutrients and iron to the surface, fueling phytoplankton and krill.
When upwelling stops, phytoplankton die and decompose on the seafloor, consuming oxygen.

🦀 Crabs and bottom-dwelling fish cannot escape, leading to die-offs.

Question 2

What causes hypoxia in the Gulf of Mexico?

Answer 2

The Gulf of Mexico’s hypoxic zone (~6,334 square miles) forms mainly due to excess nutrients (especially nitrogen and phosphorus) from farms, cities, and wastewater entering via the Mississippi River.

In spring and summer, these nutrients fuel large phytoplankton blooms.
When algae die and sink, microbial decomposition consumes oxygen, creating low-oxygen conditions.

🐟 Hypoxia alters fish diets, growth, reproduction, and habitat use, especially affecting commercial species like shrimp.

Question 4

How has eutrophication affected the Southampton Water Estuary?

Answer 4

The estuary is monitored using automatic water quality sensors. In 2019, large algal blooms were recorded involving:
- Phaeocystis globosa (creates surface organic slicks)
- Rhizosolenia delicatula
- Mesodinium rubrum (caused red tides)

Question 5

What are the effects of eutrophication in The Fleet Lagoon?

Answer 5

Eutrophication in The Fleet Lagoon has led to the presence of toxic shellfish, making seafood unsafe to eat. The shellfish contain paralytic shellfish toxins (PSTs), produced by harmful algal blooms, which can pose serious health risks to humans.

Question 6

What caused the 2023 eutrophication crisis in Lough Neagh?

Answer 6

In Summer 2023, cyanobacteria (blue-green algae) blooms were visible from space. Causes included:
- Agricultural runoff
- Urban sewage discharges
- High N and P levels (nutrient pollution)
- Storm overflows: 28% of all overflows in NI drain into rivers feeding the lough

Consequences:
- 80% drop in migratory winter birds
- 66% drop in insect/snail species
- Major decline in fish
- Toxic, thick algal blooms