Natural Water Chemistry Water Quality Parameters Temperature - Dissolved Oxygen (DO) - pH Alkalinity - Hardness Nitrates and Phosphates - Turbidity Conductivity - Temperature Affects: Water density Gas solubility Chemical reaction rates Organism growth rates
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Chemical reaction rates
Organism growth rates
… Changes in seasonal/diurnal air temperature
… Thermal stratification in lakes
… Size and temperature of inflows
… Residence time (lakes)
… Heated industrial effluent
… Runoff from asphalt/pavement
cold-blooded aquatic organisms
Predicts that growth rate will double if temperature increases by 10˚C (18˚F) within their "preferred" range.
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.
Saltwater from entry
Freshwater from stream
and river runoff.
Long residence time
Modified from Hood Canal Dissolved Oxygen Project, Collias, UW, PRISM 2005
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.
(e.g.: via acid rain)
Liberation of Al, metals
Smaller, weaker fish
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.
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
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.
Redfield Ratio: 106:16:1
The U.S. EPA has set a maximum contaminant level for NO3- in drinking water of 10 parts per million (ppm)
Blue green algae
From US EPA
Mississippi River drainage basin – 41% of US landmass.
Image from Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC, January 2003
From NCAT (Nat’l Center for Appropriate Technology)
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
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).
Reduce soil erosion
Reduce emissions – WWTP/industry
“murky” the water is
Soluble organic compounds
MODIS Image from NASA
Causes of highly
Effects of highly
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 –
Conductivity of natural waters depends upon:
Ion characteristics (mobility, valence, concentration)
Size of watershed
Some artificial factors that can affect conductivity:
Urban runoff (especially road salt)
Salt present in 1L water