| Abbreviation | Explanation |
| Ch1 | chlorophyll |
| cm | centimeter (0.01 m or 0.39 inch) |
| DIC | dissolved inorganic carbon (CO2 + HCO3- + CO32-) |
| DOC | dissolved organic carbon |
| e- | electron |
| g | gram (0.001 kg) |
| gal | gallon (3.79 liters) |
| GH | General Hardness. See page 185 |
| h, hr | hour |
| ha | hectare (2.47 acres) |
| HS | humic substances |
| IFAS | Institute of Food and Agricultural Sciences (Univ. of Florida, Gainesville) |
| inches (“) | 2.54 cm |
| Kcal | kilocalorie (unit of energy = 1,000 calories) |
| kg | kilogram (1,000 g or 2.2 lbs) |
| KH | carbonate hardness. See page 91 |
| 1 | liter (0.26 gal) |
| µeq | microequivalent |
| µg | microgram (0.001 mg) |
| µm | micrometer (0.001 mm or 1 micron) |
| µM | micromolar (0.001 mM) |
| µmhos | measure of specific conductance [µmhos/cm = (R of 0.00702 N KC1 ÷R of sample) X 1000] where R is the electrical resistance in ohms |
| µmol | micromole (molecular wt. of compound in µg); for example, a µmol of CuS04, which has a molecular wt. of 160, would by 160 µg |
| µmol/m2/s | measure of light quantitation (see explanation on page 147) |
| M | molar (moles/liter) or (g/l divided by the compound’s molecular wt) |
| m | meter (3.3 feet) |
| meq | milliequivalent = 1,000 µeq |
| mg | milligram (0.001 g) |
| min | minute |
| mM | millimolar (0.001 M) or 1 millimole/l |
| mm | millimeter (0.1 cm or 0.001 meter) |
| mmhos | measure of specific conductance = 1,000 µmhos (see µmhos above) |
| mo. | month |
| mV | millivolt |
| mT | metric ton (1,000 kg) |
| NH4-N | ammonium nitrogen (1 NH4-N = 1.29 NH4) |
| nm | nanometer (0.001 µm) |
| NO2-N | nitrite nitrogen (1 NO2-N = 3.28 NO2) |
| NO3-N | nitrate nitrogen (1 NO3-N = 4.43 NO3) |
| PO4-P | phosphate phosphorus (1 PO4-P = 3.07 PO4) |
| ppm | parts per million (can mean either mg/l or mg/kg) |
| RNA | ribonucleic acid |
| RUBISCO | ribulose bisphosphate carboxylase/oxygenase (major photosynthetic enzyme for ‘fixing’ carbon) |
| wt. | weight |
mg/l v. Molarity v. Equivalents
Molarity defines the concentration of a compound in solution, plus adjusts for that compound’s weight. In some instances, it is a better term than mg/l or ppm when comparing one compound with another. Table II-1 on page 9 compares the toxicities of several metals based on molarity– not identical mg/l. An investigator would probably not compare, for example, lead (Pb) and chromium (Cr) using a 1 mg/l solution of each. This is because Pb has an atomic wt. that is almost four times greater than Cr’s (i.e., 207 v. 52). If an investigator used 1 mg/l solutions for toxicity testing, organisms would be exposed to almost 4 times more Cr atoms than Pb atoms. This is an ‘unfair’ comparison heavily biased to make Cr look more toxic than Pb. For Table II-1, however, the investigator compared toxicity on a molar basis. He/she probably used 1 mM solutions (i.e., 207 mg/l of Pb and 52 mg/l of Cr) to conclude– correctly– that Pb was more toxic to fish than Cr.
Related terms meq and µeq are further refinements. They not only adjust for the atom’s weight, but its electrical charge. In instances where electrical charge influences something like binding or electrical conductivity, this term is most appropriate. For example, every mg of DOC is said to bind 1 µeq of metal (see page 15). We must assume that each mg of DOC has a fixed number of negative charges, so how much metal it binds will be influenced by the metal ion’s electrical charge (i.e., valence). Thus, the copper ion (Cu2+) will bind to two negative charges, whereas the aluminum ion (Al3+) will instead bind to three negative charges. In this example, a µeq of Cu is 32 µg- copper’s atomic wt (in µg) of 64 ÷ 2, while a µeq of Al is 9 µg- aluminum’s atomic wt (in µg) of 27 ÷ 3. Thus, a mg of DOC will bind 32 µg of copper but only 9 µg of aluminum.
Examples of the overall relationship of mg/l to molar concentration to equivalents are: