Eutrophication

Define eutrophication

the process of nutrient enrichment, increased organic matter, and subsequent ecosystem degradation

What are the main effects of eutrophication?

• excessive plant growth

• excessive algal growth

General increase of primary production suffocates ecosystem

When was eutrophication most severe in NA?

1960s and 1970s

• sewage dumping (phosphorus)

• fertilizer and agriculture runoff (nitrogen + phosphorus)

• detergents (phosphates)

Why is phosphorus so hard to get rid of, and what are some methods?

Attaches to sediment so even if all phos. in water is used up, levels can raise again from the sediment phos.- will take years to equilibriate

Can either dredge sediment ($$)  or use phosphate binders (even worse)

List some limiting nutrients

Phosphate, Nitrogen, Iron, potassium, carbon

How is CO2 effected by algal blooms?

CO2 in water drops during summer due to algal blooms (gets used up in photosynthesis) 

CO2 increases as bloom dies off, into the winter

Why are summer conditions are good for algal blooms?

1. warm water temps- increases metabolic rates

2. increased sunlight- more time for photosynth

3. nutrient availability- summer activities increase nut. avail. 

4. stable water column - warm water at the top reduces mixing in the column, and traps nutrients up in the warm sunny areas

is more primary productiity good for the rest of the ecosystem?

Yes to a point but then it all collapses- high nutrient density is not sustainable

how do large predatory fish impact algal blooms?

If they are present, they will consume the plankivore, meaning more plankton (to eat algae) and a decrease in algal, but vice versa if absent

What are some stressors on local water ecosystems?

• Agriculture

• cottages

• sport fishing

• high nutrients

• few predators

• lots of minnows

• few daphnia

• lots of phytoplankton

• few weed beds 

how can we keep watershed healthy?

1. awareness of fertilizer use

2. maintaining riparian areas along the shore

3. protecting wetlands

4. introducing predatory fish

What are the problems caused by eutrophication?

1. dense blooms are typically made of noxious algal (cyanobacteria), ruin water quality

2. blooms limit light penetration- reduces native plant growth

3. decrease in avail.co2 due to high photosynthesis- increases pH for a while

4. Hypoxia- causes dead zones

What are some examples of hypoxic zones?

Lake erie or the gulf of mexico

describe how dead zones work

agriculture runoff and sewage cover water, preventing access to air → algal blooms on top, dies and sinks to the bottom, decay process uses all available o2 → oxygen deprived lower water layer, kills all other life

How is erie’s deadzone worse than gulf of mexicos?

Stratified by just temperature, not by salinity and temp

less water circulation, no fresh/salt mixing so water settles out faster and creates larger dead area

How are cyano bacteria toxic to humans?

Neurotoxin, hepatotoxin (liver), dermatoxin (skin)

Why are cyanobacteria so common for eutrophic lakes?

They are nitrogen fixers- if nitrogen becomes the limiting nutrient, they can produce their own and bloom more