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Natural Water Chemistry

Natural Water Chemistry

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Natural Water Chemistry

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  1. Natural Water Chemistry

  2. Water Quality Parameters • Temperature - Dissolved Oxygen (DO) - pH • Alkalinity - Hardness • Nitrates and Phosphates - Turbidity • Conductivity • -

  3. Temperature Affects: Water density Gas solubility Chemical reaction rates Organism growth rates Conductivity pH Dissolved Oxygen

  4. Temperature – naturally variesbecause of… … Changes in seasonal/diurnal air temperature … Thermal stratification in lakes … Size and temperature of inflows … Residence time (lakes)

  5. Temperature – artificially variesbecause of… … Heated industrial effluent … Runoff from asphalt/pavement … Deforestation

  6. Q10 rule cold-blooded aquatic organisms Predicts that growth rate will double if temperature increases by 10˚C (18˚F) within their "preferred" range.

  7. Dissolved Oxygen (DO) DO is the measurement of oxygen dissolved in water and available for fish and other aquatic life. Indicates health of an aquatic system. Can range from 0-18 ppm. Most natural water systems require 5-6 ppm to support a diverse population. Varies with time of day, weather, temperature.

  8. Increase in organic waste Increase in algae/plant vegetation Decrease in DO available to organisms Leads to changes in ecosystem as organisms needing lots of DO are replaced by organisms needing little. Dissolved Oxygen (DO)

  9. Hood Canal, Wash. DO Hood Canal

  10. Sill Saltwater from entry point. Freshwater from stream and river runoff. Highly stratified Slow-circulating Long residence time

  11. Hood Canal Jan Apr Jun Sept Dec Modified from Hood Canal Dissolved Oxygen Project, Collias, UW, PRISM 2005

  12. Potential causes • Natural • increased sunlight or other climate factors • increased nutrient availability • Changes in ocean properties • Changes in river input (e.g.: drought) • Changes in weather conditions • Artificial • human loading of nutrients or organic material • Changes in river input (eg: diversion)

  13. pH - p(otential of) H(ydrogen) pH = -log [ H +] Determines the solubility of nutrients (PO4-3, NO3-, C) and heavy metals (Fe, Cu, etc) Determines availability of these chemicals for use by aquatic life. In natural water systems, determined largely by geology and soils.

  14. Sea water due to humic acid Limestone, marble, CO3 rich Pure rain, snow pH of natural waters Modified from

  15. Factors that affect pH • Algal blooms • Bacterial activity • Water turbulence • Chemicals flowing into the water body • Sewage overflows • Pollution

  16. How pH affects aquatic life Decreasing pH (e.g.: via acid rain) ▼ Liberation of Al, metals ▼ Toxic conditions ▼ Chronic stress ▼ Smaller, weaker fish

  17. Alkalinity Alkalinity refers to the capability of water to neutralize acid. Buffering capacity – resistance to pH changes. Common natural buffer: CO3 (carbonates – like limestone). Protects aquatic life. Commonly linked to water hardness. In natural systems: 50 – 150 mg/L as CaCO3. Limestone outcrop

  18. Hardness Reflects dissolved carbonate minerals. Mostly of concern for drinking water standards. Metals precipitate out of solution. Create scale/hard water deposits High alkalinity  Hard water From USGS

  19. Nitrates and Phosphates Nitrate (NO3-) naturally-occurring form of nitrogen found in soil. Forms by microbial decomposition of fertilizers, plants, manures or other organic residues Plants uptake nitrates (Spinach a good source). Phosphate (PO4-3) naturally occurs in rocks and minerals. Plants uptake weathered-out elements and compounds. Animals ingest plants. Water soluble. Redfield Ratio: 106:16:1

  20. Nitrates • Artificial sources: • Livestock • manure/urine • Failing septic • systems • Synthetic fertilizers • Can lead to: • eutrophication of natural water systems (overproduction of vegetation) • Blue baby syndromne The U.S. EPA has set a maximum contaminant level for NO3- in drinking water of 10 parts per million (ppm)

  21. Phosphates • Artificial sources: • Sewage • Laundry, cleaning fluids • Synthetic fertilizers • Can also lead to eutrophication of natural water systems (overproduction of vegetation) Blue green algae

  22. 1990 and 1999 comparison of Nitrates in Great Lakes From US EPA

  23. Hypoxia in the Gulf of Mexico Gulf of Mexico Mississippi River drainage basin – 41% of US landmass.

  24. Hypoxia in the Gulf of Mexico Hypoxic waters Image from Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC, January 2003

  25. Hypoxia in the Gulf of Mexico From NCAT (Nat’l Center for Appropriate Technology)

  26. Global distribution of oxygen-depleted coastal zones. Annual = yearly events (summer or autumnal stratification) Episodic = occurring at irregular intervals > one year Periodic = occurring at regular intervals < one year Persistent = all-year-round hypoxia Sources: Boesch 2002, Caddy 2000, Diaz and others (in press), Green and Short 2003, Rabalais 2002

  27. Source: Patrick Heffer, Short Term Prospects for World Agriculture and Fertilizer Demand 2002/03 - 2003/04 (Paris: International Fertilizer Industry Association (IFA), December 2003); IFA Secretariat and IFA Fertilizer Demand Working Group, Fertilizer Consumption Report (Brussels: December 2001); historical data from Worldwatch Institute, Signposts 2002, CD-ROM, compiled from IFA and the U.N. Food and Agriculture Organization, Fertilizer Yearbook (Rome: various years).

  28. Solutions?? Wetland restoration Reduce fertilizers Reduce soil erosion Reduce emissions – WWTP/industry

  29. Turbidity Measures how “murky” the water is Estimates: Mineral fraction Organics Inorganics Soluble organic compounds Plankton Microscopic organisms MODIS Image from NASA

  30. Turbid Causes of highly waters • In open waters, phytoplankton • Closer to shore, particulates Resuspended bottom sediments (wind) • Organic detritus from stream and/or wastewater discharges. • Dredging operations • Channelization • Increased flow rates • Floods • Too many bottom-feeding fish (such as carp) • Hippos

  31. Turbid Effects of highly waters • Modify light penetration • Increase sedimentation rate • Smother benthic habitats • Settling clay particles can suffocate • newly hatched larvae • Fine particulate material also can • damage sensitive gill structures • Decrease organism resistance to disease • Prevent proper egg and larval development • Macrophyte growth may be decreased • Reduced photosynthesis can lead to lower daytime release of oxygen

  32. From

  33. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Conductivity Ability of a substance to conduct an electrical current. In water, conductivity determined by types and quantities of dissolved solids. (Commonly called Total Dissolved Solids = TDS) Current carried by ions (negatively or positively charged particles). Eg: NaCl(aq) = Na + + Cl – Cl- Cl- Cl- Cl- Cl- Na+ Na+ Na+ Na+ Cl- Cl- Cl- Cl- Cl- Na+ Na+ Cl- Cl- Cl- Cl- Cl- Na+ Na+ Cl- Cl- Cl- Cl- Na+ Cl- Na+ Na+ Na+ Cl-

  34. Conductivity Conductivity of natural waters depends upon: Ion characteristics (mobility, valence, concentration) Water temperature Geology Size of watershed Evaporation Some artificial factors that can affect conductivity: Wastewater Urban runoff (especially road salt) Agricultural runoff

  35. Electrical Conductivity and TDS From Salt present in 1L water