Primary Production and Eutrophication Flashcards
What is eutrophication?
The increase of nutrients in an aquatic ecosystem that stimulates the growth of aquatic plants and algae (change from lower to higher primary productivity)
What produces the vast amount of oxygen on Earth?
Phytoplankton
What are the cause variables of eutrophication?
Nutrients, mainly N and P
Describe the process of eutrophication.
2 CAUSES
- Fertilisers (agriculture runoff) -> provides minerals, esp. nitrates
- Sewage (residential and urban runoff) -> provides minerals, esp. phosphates
Leads to EUTROPHICATION
Then leads to ALGAL BLOOM
2 consequences of algal blooms
- Competition for light, meaning plants die
- Consumers cannot consume algae fast enough so algae die
Leads to DETRITUS
Means there are more DECOMPOSERS
These use up oxygen by aerobic respiration (increased biological oxygen demand, BOD)
2 consequences
- Aerobes die (invertebrates, fish, etc.)
- Anaerobic bacteria thrive, releasing ammonium, methane, hydrogen sulfide
What do anaerobic bacteria release and why is this bad?
Chemicals such as ammonium, methane and hydrogen sulfide which are toxic to marine life
What is the biological oxygen demand?
The dissolved oxygen necessary for decomposition processes to happen - aerobes die when there is not enough oxygen the meet this demand
How long does natural eutrophication take to occur?
Thousands of years
How long does cultural or man-made eutrophication take to occur?
Decades
Describe the eutrophic state of lakes.
Extremely high concentrations of phosphorous and chl a and poorer water clarity.
Shallow lakes often muddy and contain an abundance of aquatic plants
What are lakes?
Inland basins full of water with a large surface area
What is the experimental lakes system?
A unique research area encompassing 58 formerly lakes in Ontario, Canada. Allows testing of different environmental and human influences on lake systems. Originally, this was started to deal with the issue of algal blooms, and decipher which nutrients led to strong algal growth. This led to the banning of phosphates in detergents.
What was a suggested way to fight eutrophication in lakes?
Introduction of fish
Where was the removal of fish tested to examine the effects on eutrophication? What were the results?
Long Lake, Michigan, US - Bass were removed from a section of the lake
Biological cascade - More Bass means less zooplanktivorous fishes, meaning an increase in zooplankton and so less phytoplankton. Less phytoplankton means there are no algal blooms and water clarity is increased.
When is eutrophication more likely to occur and why?
Summer - there is stratification of water which prevents oxygen reaching the benthos and organic matter cannot decompose. A lack of oxygen for benthic aerobic species can lead to hypoxia and death for those that have low mobility or are sessile. Can also cause migration of mobile organisms.
What is usually the limiting factor in coastal waters?
Nitrogen
What areas are naturally eutrophic in coastal waters?
Deltas and salt marshes
What increases productivity in coastal areas?
Upwelling
What are dead zones?
Area where dissolved oxygen is low and plants and animals struggle to survive
Where is the largest dead zone in the world?
The largest dead zone in the world lies in the Arabian Sea, covering almost the entire 63,700-square mile Gulf of Oman.
What is the 2nd largest dead zone?
The second largest sits in the Gulf of Mexico in the United States, averaging almost 6,000 square miles in size.
Why might climate change make dead zones or eutrophic conditions worse?
More rainfall means more nutrient runoff from urban, residential or agricultural areas. Also, warmer waters means greater stratification of the water column. This means that vertical mixing cannot occur as easily and oxygen cannot reach the deepest areas of the water column. As organic material is deposited there (extra detritus from dead algae, plants and faecal waste) the available oxygen is used in decomposition and aerobic organisms die, or, if mobile, migrate.
What algae produce toxins which result in amnesic shellfish poisoning?
Pseudo-nitzchia
What algae produce toxins which result in paralytic shellfish poisoning?
Alexandrium
What algae produce toxins which result in diarrhetic shellfish poisoning?
Dinophysis
How do harmful algal blooms cause issues for humans?
- Can lead to shellfish poisoning (amnesic, paralytic, diarrhetic)
- May contaminate drinking water
- Economic loss through loss of fish, reduced tourism
- Reduced aesthetic value
