Eutrophication

Question 1

What is Eutrophication?

Answer 1

Eutrophication is the excessive growth of plants in water bodies due to high levels of nutrients, primarily phosphorus and nitrogen, often resulting from human activities

Question 2

What is
- Hypoxia
- Anoxia
- And dead zone

Answer 2

• Hypoxia occurs when dissolved oxygen (DO) levels in water drop below 2-3mg/L
• Anoxia is when DO is below 0.2mg/L
• Dead zones are sustained hypoxic or anoxic areas where oxygen levels are too low to support marine life.

Question 3

Factors affecting oxygen levels

Answer 3

Oxygen levels in water are influenced by factors like photosynthesis, respiration, mixing, temperature, metabolic activity, salinity, pressure, and stratification.

Question 4

Nutrient Cycling in Coastal Waters

Answer 4

Nutrients in coastal waters undergo cycling processes including photosynthesis, respiration, sediment interactions, denitrification, anaerobic ammonium oxidation, and nitrogen fixation.

Question 5

Sources and Sinks of Nutrients:

Answer 5

Nutrients enter coastal waters from various sources such as upwelling, rivers, runoff, point source pollution, atmospheric deposition, submarine groundwater discharge, and sediment release.

Question 6

Photosynthesis and Respiration

Answer 6

Photosynthesis increases oxygen levels through the production of carbohydrates and oxygen, while respiration decreases oxygen levels through the breakdown of organic matter.

Question 7

Mixing and Temperature:

Answer 7

Mixing of water columns replenishes oxygen, influenced by factors like wind, storms, topography, and bathymetry. Temperature affects both oxygen solubility and metabolic activity of organisms.

Question 8

Salinity, Pressure, and Stratification:

Answer 8

Salinity decreases oxygen solubility, pressure impacts oxygen retention, and stratification, caused by temperature and salinity differences, creates physical barriers to mixing, affecting oxygen distribution.

Question 9

Short history of Eutrophication

Answer 9

Over the 20th century, nutrient input to coastal waters doubled for nitrogen and phosphorus, with agriculture contributing around 50-55%. Efforts from the 1970s to 1990s focused on point-source pollution, but eutrophication problems persist due to non-point source pollution.

Question 10

Where is Eutrophication occuring?

Answer 10

Eutrophication-associated dead zones are globally distributed, affecting areas like the Gulf of Mexico, Baltic Sea, Venice Lagoon, Brittany Coast, and China Coast

Question 11

What are the Effects of Eutrophication?

Answer 11

Eutrophication leads to oxygen depletion, chemical changes in hypoxic/anoxic conditions, and harmful algal blooms, affecting water clarity, submerged aquatic vegetation, and biodiversity.

Question 12

What is a seasonal scenario ?

Answer 12

High river flow into coastal waters increases nutrient and organic material delivery, causing stratification and hypoxia. There’s a positive correlation between river flow and the size of hypoxic zones.

Question 13

Baltic Sea and Gulf of Mexico

Answer 13

Both the Baltic Sea and the Gulf of Mexico face eutrophication issues due to nutrient influx, impacting oxygen levels and marine life.

Question 14

What Can Be Done?

Answer 14

Prevention strategies include improved understanding, engineering solutions, managing nutrient delivery from terrestrial environments, and implementing realistic territorial projects.

Question 15

How do nutrients reach the coastal zones?

Answer 15

7 main sources of nutrients
- Upwelling
- Rivers
- Runoff
- Point source pollution
Atmospheric deposition
- Submarine Groundwater Discharge
- Phosphorus release from sediment

Question 16

How do nutrients reach coastal zones?

Answer 16

Nutrients, including nitrogen, phosphorus, and silicate, are delivered to coastal zones primarily by rivers, which supply significant quantities of these substances. The riverine source of reactive nitrogen is now double its pre-industrial supply, and phosphorus inputs have also increased.

Question 17

What role do surface sediments play in the cycling of phosphate?

Answer 17

In aerobic conditions, surface sediments act as a sink for phosphate, as it strongly adsorbs onto iron and manganese oxides. However, in anoxic conditions, these sediments become a source of phosphate due to the reduction of iron and manganese oxides, releasing the phosphate previously adsorbed onto them.

Question 18

What are the key processes involved in nutrient cycling in coastal waters?

Answer 18

Photosynthesis consumes nutrients, respiration releases them, sediments can act as sources or sinks depending on conditions, denitrification and anaerobic ammonium oxidation lead to nitrogen loss, while nitrogen fixation introduces nitrogen into the system

Question 19

What affects water oxygen levels?

Answer 19

Photosynthesis increases oxygen, while respiration decreases it. Mixing helps replenish oxygen, but low mixing can cause hypoxia. Factors include wind, storms, temperature, and salinity affecting solubility, metabolic activity, and stratification.