Eutrophication Flashcards
(15 cards)
Eutrophication
Excess nutrients in estuaries cause hypernutrification
A perturbation of a marine ecosystem that appreciably degrades the health or threatens the sustainable human use of that ecosystem
How does it occur
Eutrophication can be regarded as occuring in stages:
- Increase in plant nutrient conc
- Increase in nutrient conc and an increase in plant production
Increases lead to
Changes in species composition
Abnormal blooms of algae
Toxic algal species
Deoxygenation
Adverse effects on fish and invertebrates
Changes in structure of benthic communities
Nutrient loads from estuary to coastal
Nutrient pollution, defined as excess amount of N and P in aquatic systems
One of the leading causes of water quality impairment
Stages of eutrophication
Excess nutrients
Excess algal growth, can lead to harmful algal blooms
Reduction in sunlight
Algal death
Bacteria digest the dead plants, use up remaining O, and give off C dioxide
If they can’t swim away, fish and other wildlife become unhealthy or die without O
Sewage discharge
Sewage in an inclusive term, a mixture of all liquid domestic wastes
- human body waste, faecal matter, urine, domestic household wastes, chem/industrial wastes
It is an O demanding pollutant
Sewage treatment
Preliminary treatment: screening large objects, maceration and grit removal. Iron bars remove big things
Primary, suspended solids separated out as sludge
Secondary, dissolved and colloidal organics are oxidised in presence of microorgs
Tertiary, used when high quality effluent is required. It may involve removal of further BOD, bacteria, suspended solids, toxic compounds and nutrients
Sewage spills
Dry spills are illegal when untreated wastewater spills straight out into rivers and seas when there is no rain.
Legal spilll, allowed when there has been heavy or prolonged rainfall
Recording sewage discharge
Monitored using water level sensors which detect releases at designated points
Allows untreated sewage into the environment
Sensors measure the start of overflow and end which gives duration
Spill counting starts when the first discharge occurs
Any discharge in the first 12 hours counted as 1 spill
Any discharge in the next 24 hour blocks are each counted as 1 additional spill per block
Counting continues until there is 24 hours with no spill
Conceptual model of eutrophication
Arrows indicate interactions between different ecological compartments
A balanced ecosystem is characterized by:
- A pelagic food chain, which effectively couples production to consumption and minimises the potential for excess decomposition,
- Natural species composition of plankton and benthic organisms
- If appropriate a natural distribution of submerged aquatic vegetation
- Nutrient enrichment results in changes in the structure and function of marine ecosystems
Dead Zone
A more common term for hypoxia, reduced level of O in the water
Baltic sea is hypoxic and most studied but an inland sea
Expanding OMZ
Intermediate depths within the ocean
Far reaching impacts on ecosystems because important mobile macro-organisms avoid or cannot survive in hypoxic zones
Oxygen decreases in the 300 to 700m layer is 0.09 to 0.34 umol/kg per year
Reduced oxygen levels may have dramatic consequences for ecosystems and coastal economies
Coast of Oregon
Dead zone
Upwelling in summer bring up large number of krill
Fuels large phytoplankton blooms, large number of krill
When it stops and phyto die and sink and their decomposition leads to low oxygen
Crabs and other bottom fish die as cannot move out of the hypoxic zone
Gulf of Mexico
Dead zone
6,334 square miles
Excess nutrients from cities, farms and other sources in upland watersheds drain into the Gulf and simulate phyto growth during the spring and summer
Hypoxic water effects
Alter fish diets
Growth rates
Reproduction
Habitat use and availability of commercially harvested species
