2-4- 3: Water Pollution

Transcription

1 2-4- 3: Water Pollution A"er this lecture, you should be able to: Iden6fy the various types of pollu6on (Unit 2-3) and describe their poten6al sources and effects with respect to water. Explain how dissolved oxygen measurements can be used to assess overall water quality in an ecosystem. Explain how nutrients, such as nitrogen and phosphorus, which are essen6al to living organisms, can nega6vely impact aqua6c ecosystems. Explain how sedimenta6on effects both aqua6c and terrestrial ecosystems. Evaluate the different variables that affect surface water and ground water.

2 Water Pollution Degrada6on of water quality Based on: Intended use of the water How far the water departs from the norm Its effects on public health Its ecological impacts Primary water pollu6on problem is the lack of clean, disease free drinking water Outbreaks of waterborne disease affects several billion people worldwide All segments of society may contribute to water pollu6on Increasing popula6on may cause: Introduc6on of more pollutants Increased demands on finite water resources Water pollutants include Heavy metals Sediment Certain radioac6ve isotopes Heat Fecal coliform bacteria Phosphorus Nitrogen Sodium, and other useful (even necessary) elements Pathogenic bacteria and viruses

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4 Water Pollution Standards EPA sets thresholds and limits on some but not all pollutants 700 iden6fied drinking water contaminants

5 Waterborne Diseases Primary water pollu6on problem globally Effects vary from an upset stomach to death Example cholera Early 1990s - widespread suffering and death in South America US EPA thresholds levels: 200 cells/100 ml water for swimming 0 cells/100ml water for drinking water North America is not immune to outbreaks of waterborne disease Fecal coliform bacteria used as indicator of disease Escherichia coli (E. coli) is deadly to humans - outbreaks result from ea6ng contaminated meat

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7 Dissolved Oxygen Bacteria in stream decompose organic mayer Decomposi6on requires oxygen More bacteria decomposi6on = less oxygen in the water available to fish and other organisms Oxygen can be decreased to point where aqua6c organisms die off BOD (Biological Oxygen Demand) Amount of oxygen required for biochemical decomposi6on Measure of the amount of oxygen consumed by microorganisms as they break down organic mayer Rou6nely measured as part of water quality at waste water treatment plants A stream with an low dissolved oxygen (DO) is considered polluted Source of organic mayer include: Natural sources Agricultural runoff Urban sewage US EPA defines the threshold for water pollu6on alert as DO levels of less than 5 mg/l

8 Biochemical Oxygen Demand (BOD) Three zones are iden6fied a"er a spill Pollu6on zone High BOD Ac6ve decomposi6on zone Dissolved oxygen content reaches a minimum Recovery zone Dissolved oxygen increases and the BOD is reduced

9 Eutrophication Two important nutrients that cause water pollu6on are phosphorous and nitrogen Highest levels found in agricultural areas Process by which a body of water develops a high concentra6on of nutrients Nutrients cause a large growth in aqua6c plants and photosynthe6c bacteria and algae Use up dissolved oxygen High popula6ons of bacteria and algae naturally die off Input of organic mayer into water- more nutrients Oxygen content lowered to point where aqua6c organisms die

10 Eutrophication Oligotrophic lake Lake with rela6vely low concentra6on of nutrients required by life Clear water Low abundance of aqua6c life Eutrophic lake Lake with high concentra6on of nutrients O"en with mats of algae and murky water Abundance of life Cultural eutrophica6on Human processes that add nutrients to water Solu6on - ensure that high concentra6ons of nutrients do not enter water use phosphate- free detergents control nitrogen runoff dispose or reuse treated wastewater advanced water treatment methods

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12 Sediment Sediment consis6ng of rock and mineral fragments Ranging in size from gravel (>2mm) to finer sand, silt and clay to even finer par6cles Cause sediment pollu6on By volume and mass, greatest water pollutant Two fold problem Erosion Reduces the quality of water resource it enters Land use effects erosion and sedimenta6on Forested areas more stable Agricultural prac6ces can lead to large soil loss Large quan66es of sediment lost during construc6on phase of urbaniza6on

13 Surface Water Pollution Too much of an undesirable or harmful substance flows into a body of water Substance exceeds the natural ability of that water body to: Remove the undesirable material Dilute it to a harmless concentra6on Convert it to a harmless form Point source Pollutant Dis6nct and confined Pipes from municipal or industrial sites that empty into a stream or river Nonpoint source Diffused and intermiyent Ex: runoff Influenced by land use, climate, hydrology, topography, na6ve vegeta6on, and geology Difficult to monitor and control Two tradi6onal approaches to dealing with surface water pollu6on are To reduce the sources To treat the water to remove pollutants or convert them to forms that can be disposed of safely Two new approaches are Nanotechnology Uses extremely small par6cles to capture heavy metals in water Urban run- off naturaliza6on

14 Groundwater Pollution ~Half of all people in US depend on groundwater for drinking Long believed to be pure and safe to drink Can be contaminated from a number of sources May become worse as human popula6on pressures increase Pollu6on leaking from buried gasoline tanks from service sta6ons Wide spread problem Thousands of old tanks removed and surrounding groundwater and soil treated Disposal of soil, Vapor extrac6on of water Use of microorganisms (bioremedia6on) The hazard presented by a par6cular groundwater pollutant depends on: Concentra6on or toxicity of the pollutant Degree or exposure of people or other organisms to the pollutant

15 Principles of Groundwater Pollution Important points about groundwater pollutants: Some pollutants, such as gasoline, are lighter than water and float on the groundwater Some pollutants have mul6ple phases: liquid, vapor, and dissolved Some pollutants are heavier than water and sink or move downward through groundwater Method used to treat must take into account the physical and chemical proper6es of the pollutant and how these interact with water Emphasis should be on preven6ng pollutants from entering groundwater in the first place

16 End- of- Lecture Objectives Iden6fy the various types of pollu6on (Unit 2-3) and describe their poten6al sources and effects with respect to water. Explain how dissolved oxygen measurements can be used to assess overall water quality in an ecosystem. Explain how nutrients, such as nitrogen and phosphorus, which are essen6al to living organisms, can nega6vely impact aqua6c ecosystems. Explain how sedimenta6on effects both aqua6c and terrestrial ecosystems. Evaluate the different variables that affect surface water and ground water.