Natural Water Chemistry

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Natural Water Chemistry
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Water Quality Parameters

• Temperature - Dissolved Oxygen (DO) - pH
• Alkalinity - Hardness
• Nitrates and Phosphates - Turbidity
• Conductivity
• -

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Temperature
Affects Water density Gas solubility Chemical
reaction rates Organism growth
rates Conductivity pH Dissolved Oxygen
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Temperature naturally variesbecause of
Changes in seasonal/diurnal air temperature
Thermal stratification in lakes Size and
temperature of inflows Residence time (lakes)
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Temperature artificially variesbecause of
Heated industrial effluent Runoff from
asphalt/pavement Deforestation
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Q10 rule
cold-blooded aquatic organisms
Predicts that growth rate will double if
temperature increases by 10C (18F) within their
"preferred" range.
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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)
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Hood Canal, Wash. DO
Hood Canal
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Sill
Saltwater from entry point. Freshwater from
stream and river runoff. Highly
stratified Slow-circulating Long residence time
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Hood Canal
Jan
Apr
Sept
Jun
Dec
Modified from Hood Canal Dissolved Oxygen
Project, Collias, UW, PRISM 2005 http//www.hoodca
nal.washington.edu/observations/historicalcomparis
on.jsp
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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)

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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.
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pH of natural waters
Modified from www.waterwatch.org http//www.vic.wa
terwatch.org.au/fortheteacher/manual/sect4f.htm
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Factors 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 life
Decreasing pH (e.g. via acid rain) ? Liberation
of Al, metals ? Toxic conditions ? Chronic
stress ? Smaller, weaker fish
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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
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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 http//water.usgs.gov/owq/news.html
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and
Nitrates
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 106161
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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)
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Phosphates

• Artificial sources
• Sewage
• Laundry, cleaning fluids
• Synthetic fertilizers
• Can also lead to eutrophication of natural water
  systems (overproduction of vegetation)

Blue green algae
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1990 and 1999 comparison of Nitrates in Great
Lakes
From US EPA http//www.epa.gov/glnpo/monitoring/li
mnology/SprNOx.html
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Hypoxia 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 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 Mexico
From NCAT (Natl 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 gt one year Periodic
occurring at regular intervals lt one
year Persistent 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??
Wetland restoration
Reduce fertilizers
Reduce soil erosion
Reduce emissions WWTP/industry
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Turbidity
Measures how murky the water
is Estimates Mineral fraction Organics Inorgani
cs Soluble organic compounds Plankton Microscopic
organisms
MODIS Image from NASA http//rapidfire.sci.gsfc.na
sa.gov/
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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

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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

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From waterontheweb.org http//waterontheweb.org/un
der/waterquality/turbidity.html
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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-
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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
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EC TDS
(µS/cm) (mg/L)

Divide Lake Divide Lake 10 4.6
Lake Superior Lake Superior 97 63
Lake Tahoe Lake Tahoe 92 64
Grindstone Lake Grindstone Lake 95 65
Ice Lake 110 79
Lake Independence Lake Independence 316 213
Lake Mead Lake Mead 850 640
Atlantic Ocean Atlantic Ocean 43,000 35,000
Great Salt Lake Great Salt Lake 158,000 230,000
Dead Sea ? 330,000

Electrical Conductivity and TDS
From wateronthweb.org http//www.waterontheweb.org
/under/waterquality/conductivity.html
Salt present in 1L water
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