Introduction
Total solids, TS, is a measure of all the suspended, colloidal, and dissolved solids in a sample of water. While turbidity looks at the lack of clarity due to suspended solids in a body of water, total solids includes dissolved salts such as sodium chloride, and solid particles such as silt and plankton. An excess of total solids in rivers and streams is a very common problem. The Environmental Protection Agency’s National Water Quality Inventory1 has concluded that siltation, one of the primary contributors to total solids, is the most common pollutant of the streams and rivers they sampled.
Many factors can contribute to the total solids in water. Soil erosion is a large contributor. An increase in water flow or a decrease in stream-bank vegetation can speed up the process of soil erosion and contribute to the levels of suspended particles such as clay and silt. Naturally occurring rocks or minerals in the soil such as halite, NaCl, or limestone, CaCO3, may also dissolve into the water, adding to the total solids.
Total solids can also come from various types of runoff. Agricultural runoff often contains fertilizers and suspended soil particles. Other sources include industrial waste, effluent from water treatment plants, and urban runoff from parking lots, roads, and rooftops.
Bottom-dwelling aquatic organisms, such as catfish, can contribute to the total solids in the water by stirring up the sediment that has built up on the bottom of the stream. Organic matter such as plankton or decaying plant and animal matter that are suspended in the water will also add to the total solids in a stream.
Dissolved solids often make a significant contribution to the amount of total solids in water. In fact, the mass of the dissolved solids is sometimes higher than the mass of the suspended particles. Dissolved solids in freshwater samples include soluble salts that yield ions such as calcium, chloride, bicarbonate, nitrates, phosphates, and iron.
If the level of total solids is too high or too low, it can impact the health of the stream and the organisms that live there. High levels of total solids will reduce the clarity of the water. This decreases the amount of sunlight able to penetrate the water, thereby decreasing the photosynthetic rate. Reduced clarity also makes the water less aesthetically pleasing. While this may not be harmful directly, it is certainly undesirable for many water uses. When the water is cloudy, sunlight will warm it more efficiently. This occurs because the suspended particles in the water absorb the sunlight which, in turn, warm the surrounding water. This leads to other problems associated with increased temperature levels.
As previously mentioned, dissolved solids often make a large contribution to total solids. The correct balance of dissolved solids in the water is essential to the health of aquatic organisms for several reasons. One reason is that many of these dissolved materials are essential nutrients for the general health of aquatic organisms. Another reason is that the transport of ions through cellular membranes is dependent on the total ionic strength of the water. Too many dissolved salts in the water can dehydrate aquatic organisms. Too few dissolved salts, however, can limit the growth of aquatic organisms that depend on them as nutrients.
1 From the EPA’s Office of Water web site at water.epa.gov
Objectives
- Determine the total solids in a sample of water from a stream or lake.
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This experiment is #4 of Water Quality with Vernier. The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.
