Coastal eutrophication

Question 1

What is eutrophication?

Answer 1

The enrichment of an environment with nutrients and associated production of undesirable effects.

Question 2

What are the stages of eutrophication?

Answer 2

1. increase in plant nutrient concentration (nitrates & phosphates) in natural waters
2. increase in nutrient concentration & increase in plant (algal) production
3. leads to: changes in sp composition, abnormal algal blooms, toxic algal species, deoxygenation, adverse effects on fish & invertebrates, changes in structure of benthic communities

Question 3

Where are the natural levels of nutrients in the sea from? (4)

Answer 3

1. plant & animal decomposition
2. animal excretion (NH4, urea, PO4)
3. air-sea exchange (rain, aerosols)
4. oceanic mixing

Question 4

Which human activities add to natural nutrient additions into the sea?

Answer 4

1. domestic wastes
2. agricultural runoff of excess fertiliser
3. animal wastes from intensive livestock rearing
4. aquaculture
5. industrial

Question 5

What is sewage?

Answer 5

A mixture of all liquid domestic wastes - including human body waste, faecal matter, urine, domestic household wastes, chemical/industrial wastes.
oxygen demanding pollutant.

Question 6

What reduces biological oxygen demand (BOD)?

Answer 6

Dilution of sewage.

If further dilution is not possible then SEWAGE TREATMENT is needed. This involves providing favourable conditions for accelerated bacterial degradation of the org matter.

Question 7

What are the types of sewage treatment?

Answer 7

• preliminary treatment: screening large objects, maceration & grit removal. iron bars 5-10cm spacing, removes wood, paper, bottles
• primary treatment (sedimentation): suspended solids separated out as sludge
• secondary (biological) treatment: dissolved and colloidal organics are oxidised in presence of micro-organisms
• tertiary treatment: used when high quality effluent is required. it may involve removal of further BOD, bacteria, suspended solids, toxic compounds and nutrients.

Question 8

What are the consequences of sewage disposal?

Answer 8

1. Sewage sludge: from primary/secondary treatment processes - organic enrichment - increase BOD
2. Organic discharges: following secondary an to lesser extent tertiary treatment - increase BOD
3. Plant nutrients: enrichment of ammonium and phosphate
4. Public health: microflora i.e. bacteria protozoa, fungi etc

Question 9

What are the impacts of anthropogenic nutrients on the estuarine ecosystem?

Answer 9

• water quality deteriorates due to increasing nutrient loading
• this promotes large algal blooms and production of chlorophyll a
• the algal blooms shift to a more harmful species and oxygen content of the water decreases, resulting in fish kills and change in benthic flora
• reduction in oxygen coincides with CO2 production, and promotes chem reactions leading to pH decline
• influencing factors include nutrients and susceptibility of environment to eutrophication

Question 10

What is hypoxia? What is the effect on benthic fauna?

Answer 10

When dissolved oxygen <2mg/L

Benthic fauna show aberrant behaviour

If DO <0.5mg/L, there is mass mortality

Question 11

What is anoxia?

Answer 11

When DO content is zero