Natural Water Chemistry.ppt
Transcript of Natural Water Chemistry.ppt
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Natural Natural WaterWater
Chemistry Chemistry
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Water Quality ParametersWater Quality ParametersTemperature - Dissolved Oxygen (DO) - pH
Alkalinity - HardnessNitrates and Phosphates - Turbidity
Conductivity-
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TemperatureTemperature
Affects:Water densityGas solubilityChemical reaction ratesOrganism growth ratesConductivitypHDissolved Oxygen
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… Changes in seasonal/diurnal air temperature
… Thermal stratification in lakes
… Size and temperature of inflows
… Residence time (lakes)
Temperature – naturally variesTemperature – naturally variesbecause of…because of…
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… Heated industrial effluent
… Runoff from asphalt/pavement
… Deforestation
Temperature – artificially variesTemperature – artificially variesbecause of…because of…
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Q10 rulecold-blooded aquatic organisms
Predicts that growth rate will double if temperature increases by 10˚C (18˚F) within their "preferred" range.
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Dissolved Oxygen (DO)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.
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Dissolved Oxygen (DO)Dissolved Oxygen (DO)Increase in organic waste
Increase in algae/plant vegetation
Decrease in DO available to organisms
Leads to changes in ecosystem asorganisms needing lots of DO are replaced by organisms needing little.
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Hood Canal, Wash. DOHood Canal, Wash. DO
HoodCanal
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Sill
Saltwater from entrypoint.
Freshwater from streamand river runoff.
Highly stratified
Slow-circulating
Long residence time
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Hood Canal
Modified from Hood Canal Dissolved Oxygen Project, Collias, UW, PRISM 2005http://www.hoodcanal.washington.edu/observations/historicalcomparison.jsp
Jan Apr DecSeptJun
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Potential causesPotential causesNatural
• 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)
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pHpH - - p(otential of) H(ydrogen)
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.
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pH of natural waterspH of natural waters
Modified from www.waterwatch.orghttp://www.vic.waterwatch.org.au/fortheteacher/manual/sect4f.htm
due to humic acid
Limestone, marble, CO3 richPure rain, snow
Sea water
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Factors that affect pHFactors that affect pH• Algal blooms • Bacterial activity • Water turbulence • Chemicals flowing into the water body • Sewage overflows • Pollution
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How pH affects aquatic lifeHow pH affects aquatic life
Decreasing pH (e.g.: via acid rain)
▼Liberation of Al, metals
▼Toxic conditions
▼Chronic stress
▼Smaller, weaker fish
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AlkalinityAlkalinityAlkalinity 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
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HardnessHardnessReflects 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 USGShttp://water.usgs.gov/owq/news.html
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andandNitrate (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-outelements and compounds.
Animals ingest plants.
Water soluble.
Redfield Ratio: 106:16:1
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NitratesNitrates
The U.S. EPA has set a maximum contaminant level for NO3
- in drinking water of 10 parts per million (ppm)
Artificial sources:• Livestock manure/urine• Failing septic systems• Synthetic fertilizers
Can lead to:eutrophication of natural water systems (overproduction of vegetation)
Blue baby syndromne
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Artificial sources:• Sewage• Laundry, cleaning fluids• Synthetic fertilizers
Can also lead to eutrophication of natural water systems (overproduction of vegetation)
PhosphatesPhosphates
Blue green algae
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1990 and 1999 comparison 1990 and 1999 comparison of Nitrates in Great Lakesof Nitrates in Great Lakes
From US EPAhttp://www.epa.gov/glnpo/monitoring/limnology/SprNOx.html
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Hypoxia in the Gulf of MexicoHypoxia in the Gulf of Mexico
Gulf of Mexico
Mississippi River drainage basin – 41% of US landmass.
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Hypoxia in the Gulf of MexicoHypoxia in the Gulf of Mexico
Hypoxic waters
Image from Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC, January 2003
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Hypoxia in the Gulf of MexicoHypoxia in the Gulf of Mexico
From NCAT (Nat’l Center for Appropriate Technology)http://www.ncat.org/nutrients/hypoxia/hypoxia.html
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Global distribution of oxygen-depleted coastal zones. Annual = yearly events (summer or autumnal stratification)Episodic = occurring at irregular intervals > one yearPeriodic = occurring at regular intervals < one yearPersistent = all-year-round hypoxia
Sources: Boesch 2002, Caddy 2000, Diaz and others (in press), Green and Short 2003, Rabalais 2002
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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).
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Solutions??Solutions??
Wetland restoration Reduce fertilizers
Reduce emissions – WWTP/industryReduce soil erosion
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TurbidityTurbidity
Measures how “murky” the water is
Estimates:
Mineral fractionOrganicsInorganicsSoluble organic compoundsPlanktonMicroscopic organisms
MODIS Image from NASAhttp://rapidfire.sci.gsfc.nasa.gov/
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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
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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
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From waterontheweb.orghttp://waterontheweb.org/under/waterquality/turbidity.html
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ConductivityConductivity
Ability of a substance to conduct an electrical current.
In water, conductivity determined by types and quantities of dissolvedsolids. (Commonly called Total Dissolved Solids = TDS)
Current carried by ions (negatively or positively charged particles).
Eg: NaCl(aq) = Na + + Cl –
Cl-Na+Na+
Na+
Na+
Na+ Cl-
Cl-
Cl-
Cl-
Na+Cl- Cl- Cl- Cl-
Na+Na+ Na+Na+ Na+Na+ Na+Na+
Cl- Cl- Cl- Cl-Na+ Na+ Na+Na+
Cl- Cl- Cl- Cl-Na+ Na+ Na+Na+
Cl- Cl- Cl- Cl-Na+ Na+ Na+ Na+Na+
Na+Na+
Na+ Na+
Na+ Na+
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ConductivityConductivity
Conductivity of natural waters depends upon:
Ion characteristics (mobility, valence, concentration)Water temperatureGeologySize of watershedEvaporation
Some artificial factors that can affect conductivity:WastewaterUrban runoff (especially road salt)Agricultural runoff
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EC TDS(μS/cm) (mg/L)
Divide Lake 10 4.6Lake Superior 97 63Lake Tahoe 92 64Grindstone Lake 95 65Ice Lake 110 79Lake
Independence 316 213Lake Mead 850 640Atlantic Ocean 43,000 35,000Great Salt Lake 158,000 230,000Dead Sea ? ~330,000
Electrical Conductivity
and
TDS
From wateronthweb.orghttp://www.waterontheweb.org/under/waterquality/conductivity.htmlSalt present in 1L water
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