WATER QUALITY

1. WATER QUALITY http://h2o.enr.state.nc.us/

2. What is Water Quality? • EPA defn:”Water Quality defines the goals for a waterbody by designating its uses, setting criteria to protect those uses, and establishing provisions to protect the water from pollutants.” • Requirement for compliance with Clean Water Act (1977) • Two main parts:(1) designated uses of the water body (e.g., recreation, water supply, aquatic life, agriculture)(2) water quality criteria to protect designated uses (numeric pollutant concentrations and narrative requirements) • Website with 50 States WQ Standards:http://www.epa.gov/waterscience/standards/states/

3. INDICATORS How Measure Water Quality? • Did you ever stop to wonder how we get our information on the condition of our Nation's streams, lakes, estuaries, and coastal waters? On whether these waters are safe enough to swim in, fish from, or use for drinking or irrigation purposes? Monitoring provides this basic information. There are many ways to monitor water conditions. To monitor the constituents in water, sediments, and fish tissue -- such as levels of dissolved oxygen, suspended sediments, nutrients, metals, oils, and pesticides -- monitoring specialists perform chemical measurements. Physical measurements of general conditions such as temperature, flow, water color, and the condition of stream banks and lake shores are also important. Biological measurements of the abundance and variety of aquatic plant and animal life and the ability of test organisms to survive in sample water are also widely used to monitor water conditions. • Monitoring can be conducted for many purposes. Five major purposes are to: 1. characterize waters and identify changes or trends in water quality over time; 2. identify specific existing or emerging water quality problems; 3. gather information to design specific pollution prevention or remediation programs 4. determine whether program goals -- such as compliance with pollution regulations or implementation of effective pollution control actions -- are being met; and 5. respond to emergencies, such as spills and floods.

4. Desirable Properties of an Indicator • EPA definition:” An indicator is a sign or signal that relays a complex message, potentially from numerous sources, in a simplified and useful manner. An ecological indicator is defined here as a measure, an index of measures, or a model that characterizes an ecosystem or one of its critical components.” http://www.epa.gov/bioindicators/ • Based on scientific principles related to ecosystem response to stressors • Capable of indicating presence of stressors prior to significant loss of habitat • Diagnostic of identity and magnitude of stressors • Useful for making management decisions • Useful as one of a suite of indicators

5. Upper Middle Lower Monthly vs continuous monitoring

6. Temperature & pH Lecture 1

7. Temperature Scales • Fahrenheit: 32 – 212 F (180 units) • Celsius: 0 – 100 C (100 units) • Kelvin: 273.15 – 373.15 K, where absolute zero = -273.15 C. (SI unit) • http://en.wikipedia.org/wiki/Fahrenheit • http://en.wikipedia.org/wiki/Celsius • http://en.wikipedia.org/wiki/Kelvin

8. 1 F = 5/9 C 1 C = 9/5 F

9. Thermometer • http://en.wikipedia.org/wiki/Thermometer • thermo (Gk) = heat, meter (Gk) to msr • Secondary thermometers – are calibrated at a number of fixed temperatures (e.g. NIST traceable). • Mercury-, alcohol-filled, digital, Infra-red.

10. Expansion of “liquid”: mercury (Hg). Health issues – clean up requires special caution, Disposal concerns, Hg becoming increasingly prevalent in environment. http://www.epa.gov/region1/eco/mercury/spillstherm.html • Bi-metal strip: • Thermistor: a type of resistor used to measure temperature changes, ΔR = kΔT, where ΔR = change in resistance ΔT = change in temperature k = first-order temperature coefficient of resistance http://en.wikipedia.org/wiki/Thermistor

12. Digital IR thermometer • An infrared thermometer is a non-contact temperature measurement device. Infrared Thermometers detect the infrared energy emitted by all materials -- at temperatures above absolute zero, (0°Kelvin)-- and converts the energy factor into a temperature reading.

13. pHH+ ion concentration

14. pH pH is defined as minus the decimal logarithm of the hydrogen ion activity in an aqueous solution. By virtue of its logarithmic nature, pH is a dimensionless quantity. pH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+). Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations. The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement. Pure water is said to be neutral. The pH for pure water at 25 °C (77 °F) is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.  In natural waters pH will vary between 4-10, with marine waters generally between 7.5-9. Because marine waters are well “buffered”, you will calibrate using pH 7 and pH 10 standards. pH is commonly measured by means of a combined glass electrode, which measures the potential difference, or electromotive force, E, between an electrode sensitive to the hydrogen ion activity and a reference electrode, such as a calomel electrode or a silver chloride electrode. 

15. Each pH step, there is 10x change in H+ concentration. Therefore entire scale there is a 1014 change (100 trillion) Marine waters http://en.wikipedia.org/wiki/PH

16. Why is the pH well buffered? Dissolved Carbon Dioxide Dissolved carbon dioxide in seawater occurs mainly in three inorganic forms (see Figure next slide): free aqueous carbon dioxide (CO2(aq)), bicarbonate (HCO3-), and carbonate ions (CO32-).  A minor form is true carbonic acid (H2CO3) whose concentration is less than 0.3% of [CO2(aq)]. The sum of [CO2(aq)] and [H2CO3] is denoted as [CO2]. The majority of dissolved inorganic carbon in the ocean is in the form of HCO3- (>85%). At typical surface seawater pH of 8.2, the speciation between [CO2], [HCO3-], and [CO32-] hence is 0.5%, 89%, and 10.5%, showing that most of the dissolved CO2 is in the form of HCO3-  http://www.eoearth.org/article/Marine_carbonate_chemistry

17. bicarbonate H2CO3

18. This world map of ocean acidity shows that ocean pH varies from about 7.90 to 8.20 but along the coast one may find much larger variations from 7.3 inside deep estuaries to 8.6 in productive coastal plankton blooms and 9.5 in tide pools. The map shows that pH is lowest in the most productive regions where upwellings occur. It is thought that the average acidity of the oceans decreased from 8.25 to 8.14 since the advent of fossil fuel (Jacobson M Z, 2005). http://www.seafriends.org.nz/oceano/seawater.htm

19. Anthropogenic CO2 Since the beginning of the industrialization, the oceans have taken up about 50% of the anthropogenic CO2 produced by fossil fuel burning and cement-manufacturing (cf. greenhouse gases). The carbon dioxide dissolves in seawater, produces hydrogen ions and neutralizes carbonate ions (CO32-): CO2 + H2O + CO32- → 2 HCO3- Buffering by the carbonate – bicarbonate system maintains seawater in near equilibrium wrt pH at this time.

21. pH electrodes • The most common type of pH electrodes are the "glass" electrodes. They consist of a special glass membrane that is sensitive to variations in pH, as pH variation also changes the electrical potential across the glass. • In order to be able to measure this potential, a second electrode, the "reference" electrode, is required. Both electrodes can be present in a "combined" pH electrode, or two physically-separate electrodes can be used.

22. pH electrode function • 2 electrodes – glass and reference • The glass electrode consists of a glass shaft on which a bulb of a special glass is mounted. The inner is usually filled with 3 Mol/Litre aqueous KCl and sealed. Electrical contact is provided by a silver wire immersed in the KCl. • The reference electrode, which traditionally used silver chloride (AgCl) has been superseded by the kalomel (mercurous chloride, HgCl2) electrode which uses mercuric chloride (HgCl) in a potassium chloride (KCl) solution • A pH meter measures essentially the electro-chemical potential between a known liquid inside the glass electrode (membrane) and an unknown liquid outside. Because the thin glass bulb allows mainly the agile and small hydrogen ions to interact with the glass, the glass electrode measures the electro-chemical potential of hydrogen ions or the potential of hydrogen. To complete the electrical circuit, also a reference electrode is needed. Note that the instrument does not measure a current but only an electrical voltage.  glass reference electrodes

23. Simple test of pH probe • The voltage produced by one pH unit (say from pH=7.00 to 8.00) is typically about 60 mV (milli Volt) • In contact with different pH solutions a typical glass electrode gives, when compared to the reference electrode, a voltage of about 0 mV at pH 7,  increasing by 60 mV per pH unit above 7, or decreasing by 60 mV per pH unit below 7. Both the slope, and the intercept of the curve between pH and generated potential, are temperature dependent. • Test of pH probe accuracy is to see if mV reading differs approx by 180mV between pH 7 and pH 4 or 10 calibration solutions (3 x 60mV steps).

24. Calibration • Insert pH probe in pH 7 calibration solution, should read pH 7 and 0mV • Rinse with next solution, typically pH 10, and calibrate to 10, mV reading should be about 180mV • People assume pH measurements are accurate, however many potential errors exist. There can be errors caused by the pH-sensitive glass, reference electrode, electrical components, as well as externally generated errors, see: http://stason.org/TULARC/science-engineering/chemistry/26-2-How-do-pH-electrodes-work.html • A pH meter should not be used in moving liquids of low conductivity (thus measuring inside small containers is preferable). • Remember also that the calibration solutions consist of chemical buffers that 'try' to keep pH levels constant, so contamination of your test vial with a buffer is really serious

25. Calibration Solutions • Today, most pH meters are minicomputers that measure the voltage and translate them into pH values at the correct temperature under the most adverse conditions. These meters with glass electrodes are now calibrated with buffer solutions (resistant to changes in pH) that can be traced to standards at the NIST. • Typical standard buffers include: • potassium hydrogen phthalate (pH = 4.01) • disodium hydrogen phosphate + potassium dihydrogen phosphate (pH = 7.00) • borax (pH = 10.01) • The pH values are at 25°C and accurate to ±0.002. http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=pHTheory.htm&ID=560

26. Calibration & Care • Frequent calibration and adjustment of pH meters are necessary. To check the pH meter, at least two standard buffer solutions are used to cover the range of interest. The pH meter should be on for at least 30 minutes prior to calibration to ensure that all components are at thermal equilibrium, and calibration solutions should be immersed for at least a minute to ensure equilibrium.  • First use the buffer at pH 7, and adjust the zero (or the intercept). Then, after thorough rinsing with water, use the other buffer to adjust the slope. This cycle in repeated at least once, or until no further adjustments are necessary. Many modern pH meters have an automatic calibration feature,which requires each buffer only once. • But electrodes do not have eternal life (usually 2 years) and need to be replaced when they drift unacceptably or take unusually long to settle. • Caring for a pH meter depends on the types of electrode in use. Study the manufacturer's recommendations. When used frequently, it is better to keep the electrode moist. However for prolonged periods, it is recommended to moist it with a solution of potassium chloride at pH=4 or in the pH=4.01 acidic calibration buffer. pH meters do not like to be left in distilled water. 

27. Lab • Check temperature on 2 Sondes in same bucket. • Read temperature on a number of thermometers in same bucket, compare results – what is the error between “instruments” • Calibrate a pH meter, measure pH of 4 water samples (0, 10, 20, 30 ppt salinity)