cive230 lec 10 - water pollution

negative effects of solid pollution

greater turbidity (compromises drinking water and recreation), lower light infiltration (decreases photosynthetic activity), disrupts/creates new sediment deposits (fundamentally altering the benthic habitat)

negative impacts of salt pollution

poses threat to agricultural uses

negative impacts of volatile organic compounds

toxins

negative impacts of oxygen demanding materials

renders waterways uninhabitable for natural species

negative impacts of nutrients (NOx, NHx, P)

biostimulation / eutrophication

eutrophication

excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen

quantitative measures of water quality

• pH

• Turbidity (NTU - Nephelometric Turbidity Units)

• Dissolved Oxygen (D.O.) [mg/L]

• Temperature [◦C]

• Concentrations [mg/L] of solids, nutrients, etc.

quantitative models to measure water quality

• Atmospheric chemistry and the formation of acid precipitation

• Natural resistance to acidity in waterways

• Models of runoff and its impacts

• Models to estimate the quantity of oxygen consuming materials

• Models to predict the natural replenishment of dissolved oxygen ((D.O.) in natural waterways

acid rain

rainfall made sufficiently acidic by atmospheric pollution (NOx, SOx) that it causes environmental harm, typically to forests and lakes - pH value below 5.6

why is rainwater naturally acidic

due to the presence of carbon dioxide in the atmosphere - when carbon dioxide dissolves in rainwater, it forms carbonic acid, which lowers the pH of the water

main sources of SOx in Canada and USA?

Industrial sources and electric utilities (Canada), electric utilities, fuel combustion, and industrial sources (USA)

main sources of NOx in Canada and USA?

transportation, industrial sources, and electric utilities (Canada), transportation, electric utilities, and fuel combustion (USA)

buffering

the natural ability of some lakes to resist changes in pH - presence of “bicarbonate” molecule acts as a strong “alkaline” buffer - H+ reacts with bicarbonate ions (HCO3-) to form carbonic acid (H2CO3), effectively removing H+ from the solution and raising the pH

Impacts of Surface Transport

• Collect solids, metals, petroleum etc.

• Cause erosion

• Influence natural habitats

• Require investments infrastructure to manage/contain

influences on quantity and speed of

runoff

amount of impervious area

hydrograph

graph that describes runoff as a function of time

impacts of increased impervious area

• Faster rise in water runoff rate

• Higher speed runoff

• Lower baseline flow

• Greater peak / baseline ratio

what does “hot, fast, and dirty” runoff mean

runoff water is hotter than groundwater (heat transferred from surfaces), fast due to the high peak and shorter tail of runoff in an urbanised area on the hydrograph, and dirty due to the pollutants picked up

what is a combined sewer overflow

when the capacity of combined sewer systems (sanitary and stormwater) are overwhelmed during heavy rainfall or snowmelt, untreated or partially treated stormwater and sewage is discharged into waterways

effects of higher speed runoff

creates greater erosive forces, compromising structures, utilities, etc. and introduces more solids into waterways

biostimulation

• Major algae growths

• Red tide

• Reduced photosynthetic activity

• Displacement of natural flora

influences on dissolved oxygen

• temperature (inversely proportional)

• Salts (Cl- are inversely proportional)

• Barometric pressure (proportional)

biochemical oxygen demand

Presence of organics and other oxygen consuming materials that reduce oxygen content and compromise water quality

water pollutants

• solids

• salts

• toxic/heavy metals (zinc, lead)

• pesticides

• VOC

• oxygen demanding materials

• nutrients

• heat

• pathogens

• arsenic

• emerging contaminants

oxygen sag curve

The oxygen sag curve obtained by plotting the concentration of dissolved oxygen in a river into which sewage or some other pollutant has been discharged against the distance downstream from the sewage outlet. The presence of sewage reduces the oxygen concentration of the water in the river and increases the biochemical oxygen demand (BOD). Microorganisms present in the river water decompose the organic matter in the sewage and use all the available oxygen leading to a reduction in oxygen concentration.

sections of xygen demand sewage curve

clean zone, decomposition zone, septic zone, recovery zone, clean zone