Presentation on theme: "Natural Water Chemistry. Water Quality Parameters Temperature - Dissolved Oxygen (DO) - pH Alkalinity - Hardness Nitrates and Phosphates - Turbidity Conductivity."— Presentation transcript:
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 Conductivity pH Dissolved Oxygen
… Changes in seasonal/diurnal air temperature … Thermal stratification in lakes … Size and temperature of inflows … Residence time (lakes) Temperature – naturally varies because of…
… Heated industrial effluent … Runoff from asphalt/pavement … Deforestation Temperature – artificially varies because of…
Q 10 rule cold-blooded aquatic organisms Predicts that growth rate will double if temperature increases by 10˚C (18˚F) within their "preferred" range.
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.
Dissolved Oxygen (DO) 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.
Hood Canal, Wash. DO Hood Canal
Sill Saltwater from entry point. Freshwater from stream and river runoff. Highly stratified Slow-circulating Long residence time
Hood Canal Modified from Hood Canal Dissolved Oxygen Project, Collias, UW, PRISM JanApr Dec SeptJun
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)
pH - pH - p(otential of) H(ydrogen) Determines the solubility of nutrients (PO 4 -3, NO 3 -, 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.
pH of natural waters Modified from due to humic acid Limestone, marble, CO3 rich Pure rain, snow Sea water
Factors that affect pH Algal blooms Bacterial activity Water turbulence Chemicals flowing into the water body Sewage overflows Pollution
How pH affects aquatic life Decreasing pH (e.g.: via acid rain) Liberation of Al, metals Toxic conditions Chronic stress Smaller, weaker fish
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
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
and Nitrate (NO 3 - ) 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 (PO 4 -3 ) naturally occurs in rocks and minerals. Plants uptake weathered-out elements and compounds. Animals ingest plants. Water soluble. Redfield Ratio: 106:16:1
Nitrates The U.S. EPA has set a maximum contaminant level for NO 3 - 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
Artificial sources: Sewage Laundry, cleaning fluids Synthetic fertilizers Can also lead to eutrophication of natural water systems (overproduction of vegetation) Phosphates Blue green algae
1990 and 1999 comparison of Nitrates in Great Lakes From US EPA
Hypoxia in the Gulf of Mexico Gulf of Mexico Mississippi River drainage basin – 41% of US landmass.
Hypoxia in the Gulf of Mexico Hypoxic waters Image from Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC, January 2003
Hypoxia in the Gulf of Mexico From NCAT (Natl Center for Appropriate Technology)
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
Source: Patrick Heffer, Short Term Prospects for World Agriculture and Fertilizer Demand 2002/ /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).
Turbidity Measures how murky the water is Estimates: Mineral fraction Organics Inorganics Soluble organic compounds Plankton Microscopic organisms MODIS Image from NASA
Causes of highlywaters 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
Effects of highlywaters 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
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 - Na+ Cl - Na+ Cl - Na+ Cl - Na+ Cl - Na+ Cl - Na+
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
ECTDS (μS/cm)(mg/L) Divide Lake104.6 Lake Superior9763 Lake Tahoe9264 Grindstone Lake9565 Ice Lake11079 Lake Independence Lake Mead Atlantic Ocean43,00035,000 Great Salt Lake158,000230,000 Dead Sea?~330,000 Electrical Conductivity and TDS From wateronthweb.org Salt present in 1L water