water pollution
any chemical, biological, or physical change in water quality that has a harmful effect on living organisms
- e.g. infectious bacteria, inorganic & organic chemicals, excess heat
how scientists monitor water quality
- bacterial counts; drinking water should not contain any colonies per 100mL; safe swimming water should not have more than 200 colonies per 100mL
- chemical analysis: checking inorganic/organic chemicals, sediment content, and turbidity
- indicator species
bacterial source tracking
new field of science that uses molecular biology techniques to determine subtle differences in strains of bacteria based on their host
biological oxygen demand
the amount of dissolved oxygen consumed by aquatic decomposers
point-source v. nonpoint-source pollution
point source: discharge pollutants at specific locations; easy to identify, monitor, and regulate
- drain pipes, ditches, sewer lines, factories
nonpoint source: scattered and diffused; cannot be traced back to any single site of discharge; difficult and expensive to identify/control
- runoff from croplands & livestock feedlots
leading sources of water pollution
- agriculture: erosion/overgrazing, fertilisers, pesticides, excess salt (from irrigation)
- industries
- mining
recovery from pollution in STREAMS
- combination of dilution & biodegradation if stream’s flow is not reduced due to damming, agricultural diversion, drought
- breakdown of pollutants by bacteria –> oxygen sag curve; organisms that have high oxygen demand die
sag curve
graph that shows how the concentration of dissolved oxygen in a body of water changes over distance from a point of pollution
factors of how great a sag curve is
- volume of stream
- volume of wastes entering
- flow rate
- temperature
- pH levels
factors of severe pollution in the ganges river, india
- religious beliefs, cultural traditions
- poverty
- little economic development
- large population size
why are lakes less effective at diluting pollutants?
- lakes are often lentic/still bodies of water with little to no flow
- lakes are stratified into layers with little vertical mixing; may take 100yrs to flush/change water in lakes
- lakes are more vulnerable to runoff contamination
- chemical concentrations biomagnify through the food webs in lakes
eutrophication
when a body of water receives too many nutrients, which leads to an overgrowth of algae and other microorganisms
natural vs cultural eutrophication
- natural: natural nutrient enrichment of lakes, depends on composition of surrounding drainage basin, enrich abundance of desirable organisms
- cultural: human-caused, near urban or agricultural areas, can lead to significant pollution problems, also in coastal waters/estuaries/bays due to runoff
“blooms” of organisms reducing lake productivity
- algae overgrowth –> less sunlight
- algae overgrowth –> increases bacteria, decreases DO –> fish die –> if it gets bad enough, anaerobic bacteria take over
how to reduce cultural eutrophication
- banning/limiting phosphates in detergents
- using advanced treatment methods to remove nitrates & phosphates from wastewater
- using soil conservation methods to reduce runoff
how to clean up lakes
- removing excess weeds
- controlling plant growth
- pumping air through lakes to avoid oxygen depletion
Why is groundwater especially vulnerable to contamination?
- groundwater cannot effectively cleanse itself and dilute/disperse pollutants
- groundwater flows very slowly
- cleansing is slow bc of low DO, cold water temperature, less population of decomposing bacteria
- degradable wastes may take 100s of years to cleanse; nondegradables stay forever
- groundwater pollution is a low-risk ecological ecological issue, but a high-risk human health issue
Effects of nitrates in ground water
- prevalent in agricultural areas
- nitrates convert to nitrites in the body —> can cause cancer
- in babies under 6mo, high levels of nitrites can lead to blue baby syndrome, where blood cannot cary sufficient oxygen to the cells
Degradable pollutants (examples)
raw sewage, sludge, oil, some industrial wastes
- high levels of degradation occur in deep-water areas and rivers/streams with high flow rate
coastal pollution
- 40% of the world’s population lives on or within 100km from the coast; this puts a tremendous burden on wetlands, estuaries, coral reefs, mangrove swamps
- sewage is often dumped into the sea without treatment; beach pollution, shellfish contamination
- extensive nonpoint runoff has caused seasonal, large oxygen-depleted zones in temperate coastal waters due to oxygen depletion
preventing coastal pollution
- reduce number and size of oxygen-depleted zones
- reduction of nitrogen inputs
- planting forests & grasslands to soak up excess nitrogen
- restore costal wetlands
- improve sewage treatment
- require further reduction of NOx emissions
- use forms of renewable energy to replace fossil fuels
london dumping convention 1972
100 countries agreed to not dump highly roxic pollutants & radioactive wastes into the open sea
- by 1994, it became a permanent ban
oysters’ roles in water pollution
- oysters filter algae and silt
- over-harvesting, coupled with two parasitic oyster diseases reduced the oyster population to about 1% of its population in chesapeake bay
- introduction of disease-resistant oysters into chesapeake bay could help to recover the population and filter pollution faster
causes of oil pollution in oceans
- released from day-to-day activities
- off-shore oil wells, leaks from pipelines and storage tanks, tankers being washed out, loading/unloading of tankers
- most oil pollution comes from on-land activities
