|
| Stream Monitoring | Creating the Context Default |
|
Creating the Context Home Research Focus Background Info Research Methods Data Submission Results of Study Data Analysis Conclusion Further Research Guided Research Research Question Background Info Research Methods Data Submission Results of Study Data Analysis Conclusion Further Research Research Values Student Research Doing Research Publish View Tools Discussions Stream Teams Water Links |
Water is sometimes called the universal solvent because so many things can dissolve in it. As water interacts with the atmosphere, biosphere, rocks, and soil in a watershed, many materials are dissolved and carried away. Total dissolved solids (TDS) include all suspended solids that may or may not pass through a filter. Some dissolved solids come from organic sources such as leaves, silt, plankton, industrial waste and sewage. Some dissolved solids come from inorganic materials (such as rocks and air) which may contain calcium bicarbonate, nitrogen, iron phosphorus, sulfur, and other minerals. Many of these materials form salts. Salts are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Ions are particles that have a positive or negative charge. A constant level of minerals in the water is necessary for aquatic life. Changes in the amounts of dissolved solids can be harmful because the density of total solids determines the flow of water into and out of an organism's cells. Many of these dissolved solids contain chemicals, such as nitrogen, phosphorus, and sulfur, that are the building blocks of molecules necessary for life. Concentrations of total dissolved solids that are too high or too low may limit growth and lead to the death of many aquatic organisms. High concentrations of dissolved solids may also reduce water clarity, contribute to a decrease in photosynthesis, combine with toxic compounds and heavy metals, and lead to an increase in water temperature. High concentrations in drinking water may give the water an unpleasant taste and could result in a laxative effect. Sources of harmful dissolved solids are many such as: runoff from urban areas; road salts used on streets in the winter; fertilizers and pesticides used on lawns and farms; wastewater from sewage treatment plants; decayed plant and animal matter; construction that disturbs the soil; and clear-cutting trees which leads to increased soil erosion. HOW TO MEASURE TOTAL DISSOLVED SOLIDS There are two common ways to measure the amount of total dissolved solids in a sample of water. The first method requires an extremely sensitive balance that can measure to the nearest .0001 gram. A 100mL sample of water is carefully collected from the middle of a stream. A 300mL beaker is carefully weighed. The water sample is poured into the beaker and allowed to evaporate in an oven at 103oC. Allow the beaker to cool to room temperature before weighing. The beaker is then weighed again. Be careful not to touch the beaker with your hand as the oils and moisture on your hand will add weight to the beaker. The first weight is subtracted from the second weight and multiplied by 10,000 to determine the mg/liter of total dissolved solids in the sample. Another, simpler method requires the use of a Hach Pocket Pal TDS
meter. This meter works by measuring the electrical conductivity of the
water. Conductivity increases as the amounts of salts and other dissolved
solids increase in the water. Conductivity and TDS are two different but
related tests. One can be calculated from the other by multiplying or dividing
by a certain fixed number. Pocket Pal TDS meters give an approximate result
+10%.
Listed below are the directions for how to use a Pocket Pal TDS meter.
|
| © 1996-2006 PathFinder Science |