Nutrient Pollution

Question 1

What is nutrient pollution and what are the main sources?

Answer 1

The most ubiquitous form of water pollution
Mainly caused by inputs of nitrates and phosphates
Sources
- Agricultural runoff
- Waste from aquaculture facilities
- Domestic sewage
- Industrial effluents
- Atmospheric inputs (fossil fuel burning, bush fires etc.)

Question 2

What are the main urban nutrient sources?

Answer 2

Domestic sewage
- massive urban discharge
- 10.8g N per person per day
- 2.18g P per person per day
Industrial waste
- may be locally important depending on the type of industry
- e.g. brewing effluent contains 156mg N L-1, 20mg P L-1

Question 3

What are the main rural nutrient sources?

Answer 3

Drainage water percolating through farm land
Animal slurry
Forestry operations
Erosion of surface soils
Locally (poor septic tanks)

Question 4

What is the primary source of inorganic nutrient addition to aquatic ecosystems?

Answer 4

Agricultural runoff from fertilisers and effluent from secondary sewage treatment plants - rich in N and P

Question 5

What is the annual cycle in lakes with regards to nutrients?

Answer 5

Lakes - slow moving or still water (little aeration)
In summer in deeper lakes, water becomes stratified
- upper layers of warm water heated by sun
- warm upper layer (epilimnion) is less dense than cold bottom water (hypolimnion)
- thermocline separates the two non mixing layers
- temperature drops suddenly as you pass below the thermocline
In summer - photosynthesis in warm upper layer allows phytoplankton to grow, and use up nutrients
- nutrients deplete and phytoplankton die
Autumn/Winter - Upper layer cools, cool water sinks and water and nutrients mix

Question 6

What happens to the annual nutrient cycle if an area is affected by nutrient pollution?

Answer 6

Phytoplankton growth increases, nutrient levels in upper layer do not become depleted and algal blooms consist after summer

Question 7

What is the Redfield ratio and what is the major limiting factor in FW systems?

Answer 7

Phytoplankton require N and P in relative proportions 7:1 (Redfield ratio)
Major limiting nutrient in FW is phosphate

Question 8

What are the five defining nutrient status terms in water systems?

Answer 8

Dystrophic - brown water lakes
Oligotrophic - low nutrient levels
Mesotrophic - medium nutrient levels
Eutrophic - high nutrient levels
Hypertrophic - very high nutrient levels

Question 9

What is the directive that defines eutrophication and what is the definition?

Answer 9

Urban Waste Water Treatment Directive (91/271/EEC)
enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned

Question 10

What is the difference between natural and cultural eutrophication?

Answer 10

Natural - a process that occurs as a lake or river ages over a period of hundreds of thousands of years
Cultural - a process that occurs when humans release excessive amounts of nutrient: shortens the rate of ageing to decades

Question 11

What is the major limiting nutrient in marine waters?

Answer 11

Nitrogen

Question 12

What is the difference between point and diffuse sources of nutrification?

Answer 12

Point - inflow into the lake or stream is localised e.g. sewage, industrial effluent, deliberate eutrophication (fish farming)
Diffuse - Entry of organic pollutants occurs along a significant length of lake or river margin e.g. agricultural seepage, aerial pollution

Question 13

What species are characteristic of oligotrophic waters and what species for eutrophic? (phytoplankton)

Answer 13

Olgiotrophic - desmids (Chlorophyta) and Golden algae (Chrysophyta)
Eutrophic - colonial cyanobacteria, chlorococcales (unicellular green algae) and centric diatoms (Bacillariophyta)

Question 14

What does an increase in phytoplankton productivity mean to the rest of the food web?

Answer 14

^ phytoplankton = zooplankton less grazing impact
= decreased visibility
= v in piscivorous fish
= ^ zooplanktivorous fish
= v zooplantkon more phytoplankton
= algal bloom

Question 15

What is the major impacts of eutrophication?

Answer 15

Oxygen sensitive organisms decline and biodiversity decreases
Eventually no fish and very little benthic invert life is supported
Toxic algal blooms can occur (particular problem in marine ecosystems)
- some dinoflagellates can produce nerve toxin
- toxin can build up in tissues of shell fish
- can lead to paralytic shellfish poisoning in humans if ingested
- Can also lead to poisoning and death of aquatic organisms (fish, shellfish, birds)
- can cause human illnesses such as gastroenteritis, liver disease and skin irritation

Question 16

What is the most common cause of FW HABs?

Answer 16

HAB = harmful algal bloom

Cyanobacteria (blue-green algae) can cause death to animals drinking from lakes and rivers

Question 17

What is the result of the rapidly growing bacterial populations that occur when algae begin to die?

Answer 17

Rapidly growing bacterial populations need exponentially increasing amounts of oxygen
Once dissolved oxygen levels become too low, fish and many freshwater inverts die, thus adding more organic matter
As oxygen disappears, anaerobic bacteria produce methane, hydrogen sulfide and ammonia
Bacterial respiration increases carbonic acid
In all but the most depleted waters, tubificid worms, midge larvae and mosquito larvae replace oxygen loving inverts

Question 18

Why may HABs be getting worse?

Answer 18

Natural species dispersal
Human-related factors 
- increased nutrient inputs and eutrophication
- transport in ballast water
- climactic shifts
- increased observations

Question 19

Facts and figures on Marine dead zones

Answer 19

Whole ecosystem hypoxia
200 dead zones worldwide
- Gulf of Mexico 18,000km^2
- Baltic Sea 120,000km^2
Number of dead zones doubled every decade since the 1960s
Problem expected to worsen as sea temperatures rise
Occur close to highly populated areas
Increased levels of nutrients enter water from agricultural run off, sewage and rainwater containing nitrous oxides (fossil fuel combustion)

Question 20

What factors cause dead zones in oceans?

Answer 20

Nutrients in ocean usually quickly diluted
Waves and currents oxygenate water
Conditions that can lead to a dead zone forming
- areas of limited water circulation (estuaries and bays)
- mouths of large polluted rivers
- supply of nitrogen
- stratification (stops oxygenated surface water mixing with deeper waters)
Many dead zones dissipate over winter when strong winds break up stratification