4.4. Water Quality Chemical and Physical Factors. Dissolved Oxygen

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1 ater Quality Chemical and Physical Factors How do we determine quality? Factors such as size, color, and flavor might be used to determine the quality of an apple. The intended "use" is another factor that is important when judging the quality of apples. Some varieties of apples are good for baking, others for eating, and still others are good for making applesauce. Water quality is determined by a number of chemical, physical, and biological factors. The designated "use" is also important when judging the quality of water. High-quality drinking water with 0.4 ppm chlorine would not be high-quality water for a goldfish. Most fish cannot live in water with even small amounts of chlorine. Brook trout and brown trout cannot survive in water with more than 0.02 ppm chlorine. The ability of an organism to survive and reproduce in an aquatic ecosystem depends upon the quality of the water. The water quality depends on certain physical, chemical, and biological conditions. Water is polluted when substances are present in the water in amounts that are harmful to the organisms living in or using the water. In this section we will study some of the conditions that affect the water quality of aquatic ecosystems. Such studies are not simple. Changing one condition will often cause other conditions to change. For example, a change in temperature will affect the amount of dissolved oxygen that the water can hold. Synergistic effects also occur. Some chemicals are more poisonous when certain other chemicals are present. Keeping this in mind, let's investigate water quality. O B J E C T I V E S Identify chemical and physical factors that affect water quality. Relate the temperature of the water to the level of dissolved oxygen (DO). Contrast ecosystems with hard and soft water. Evaluate the condition of an aquatic ecosystem based on chemical and physical conditions. Dissolved Oxygen Aquatic organisms do not break water molecules apart to get oxygen for respiration. The oxygen they absorb, through their skin or special respiratory structures, is oxygen gas (O2) that is dissolved in the water dissolved oxygen (DO). Dissolved oxygen enters water by diffusion from the atmosphere. When water is mixed with air as it falls over rocks and waterfalls, the level of DO is greatly increased. Standing or slow-moving bodies of water have lower DO levels than fast-flowing water or bodies of water with wave action. The types of organisms in a pond or lake may be limited by the amount of DO. This is not usually a problem for organisms living in a rapidly flowing stream with clean water. Photosynthesis in algae and aquatic plants produces oxygen, which increases the level of dissolved oxygen during daylight hours. At night and on cloudy days, the oxygen level falls as all organisms, including algae and aquatic plants, use oxygen for respiration. The water at the bottom of a deep lake has very little DO. Decomposers use any oxygen that reaches the bottom by diffusion. Water polluted with organic matter has less dissolved oxygen than clean water because the bacteria and other decomposers use much of the Students measure the dissolved oxygen level of the water in the creek. 305

2 oxygen for the process of decay. When there is not enough oxygen for decomposers, other decomposers not dependent on oxygen take over the job of decomposition. The waste products produced by these organisms give the water an unpleasant odor. Dissolved oxygen may be the most important factor affecting aquatic organisms. A large variety of organisms usually indicate water with a high level of DO. Fewer types of organisms are found in water with low levels of DO. Many of these, such as the water boatmen, are air-breathers and must come to the surface to breathe. A balanced aquatic ecosystem usually contains between 5 and 10 ppm of DO near the surface. Only a few species of fish can survive in water with less than 4 ppm DO. Carp and catfish may be able to survive in water with only 1 or 2 ppm DO, but they will be more active if the DO level is higher. Bluegill, bass, and pike need at lest 4 ppm DO. Trout and salmon require much higher levels of DO, usually 6 ppm or more. Dissolved oxygen is not a problem for organisms living in this fast-flowing creek. Temperature and Dissolved Oxygen Solubility is the ability of a substance to dissolve in a liquid. The solubility of a gas decreases as the temperature of the liquid increases. Maximum Level of DO (ppm) Over Temperature ( C) 30 Temperature ( C) After several warm and cloudy days, the dissolved oxygen level may drop to dangerously low levels in this weedy Florida lake. 306 As the temperature of the water increases, the water retains less DO. In contrast, cooler water can hold more DO. Fish, such as trout and salmon which require high levels of DO, are found in cold water. Warm water fish, like carp and catfish, can survive in water with very low levels of DO. Fish are cold-blooded animals. As the temperature of the water rises, the body temperature of cold-blooded animals increases. As the temperature increases, more oxygen is needed to maintain their normal bodily functions. The warmer water may not hold enough oxygen to supply the fish's needs. The insufficient amount of DO found in some water now causes more fish kills than any other single event, including oil spills. Most water used by factories, especially electrical power plants, is used for cooling. Pollution occurs when hot water is dumped into aquatic ecosystems. The warmer water cannot hold as much DO. Water quality standards strictly limit industrial activities that increase the temperature of a natural aquatic ecosystem. To meet the requirements, some companies build cooling towers or holding reservoirs that permit the water to cool before it enters the natural aquatic ecosystem.

3 Cooling towers at this nuclear power plant allow the water to cool before it is returned to the river. Rainbow Falls, Hawaii In which of these rivers would you more likely find fish with gas bubble disease? Can There Be Too Much Oxygen! We have already seen that the amount of gas that can be dissolved in the water is dependent upon the temperature. When a liquid holds all of the gas that can be dissolved at a given temperature, it is saturated. If it holds less than it can possibly hold, the amount of gas dissolved is described as the percent oxygen saturation. For example, if water holds half of the DO that it can hold at a given temperature it is 50 percent saturated. Under certain conditions more gas is dissolved in water than normally would be dissolved at a given temperature. When this situation occurs, the water is supersaturated. Supersaturation of water usually occurs in rivers below dams or waterfalls. As water falls it mixes with air, and in the deep pool below the dam or waterfall, the pressure increases. The dissolved gases diffuse across the fish's gills, and the gases come out of solution forming bubbles in the blood vessels or the body tissues. This condition is known as gas bubble disease. This condition is most likely to occur in spring when large amounts of cold water flow over the dam or waterfall. Fish that do not die of gas bubble disease are frequently in a weakened state and often die of other diseases. A healthy aquatic ecosystem should have water that is between 80 and 125% oxygen saturation. A low saturation level indicates that there is a demand for DO, perhaps due to decaying vegetation or untreated sewage. The amount of oxygen consumed (demanded) by microorganisms Yellowstone Falls,Wyoming. Did You Know Several times a year fish, crabs, and shrimp come ashore in Alabama's Mobile Bay. It happens on warm, still nights when the DO level is low.the rising tide brings the hypoxic (low oxygen) water toward the shore, and the fish swim ahead of it. When the fish reach shallow water, they are an easy catch for local residents who call it a jubilee. Gas Bubble Disease. 307

4 and combined with chemicals in the water is called the biochemical oxygen demand (BOD). If the BOD is 5 mg/l or higher, the water quality is poor. ph,.. Milk of Magnesia The ph Scale:The color distribution of the chart represents the indicator colors of phydrion paper that is used to determine the ph of liquids. Bleach Ammonia ph Scale Baking-Soda Distilled Water Tomatoes Carrots j Vinegar Lemon Battery juice Acid! icoia 1 II Normal Rain ACID RAIN ALKALINE/BASIC UIUIIU For background information on ph, visit: water, u sgs.gov/ed u/. ACIDIC Few organisms live in water with a ph lower than 4 or higher than 9. Although some organisms live in water with a very low or very high ph, most species have a narrow range of ph where they can grow and reproduce. Some species are very sensitive to small changes in ph and a sudden change in the ph can be deadly. The ph of water often determines the kinds of animals and plants that can live there. Water with a ph between 6.5 and 8.2 usually supports a good variety of plant and animal life. At 6.5 snails and tadpoles begin to die, salmon and trout reproduction declines, and mayfly and caddisfly populations decline. At 5.5 the decomposers begin to die. A ph above 9.0 can be harmful to salmon, trout and perch. The ph of the water is affected by several factors. Lakes and ponds are usually basic (alkaline) when they are first formed. Living organisms produce carbon dioxide during respiration. When organisms die, more carbon dioxide is produced during the process of decay. Carbonic acid is formed when carbon dioxide combines with water. The higher the amount of carbonic acid dissolved in the water, the lower the ph. C02 H20 H2C03 carbon dioxide water carbonic acid V H2C03 HCO3" 2H+ C03 2 carbonic acid bicarbonate ion hydrogen carbonate ion Water entering aquatic ecosystems from industries may contain chemicals that alter the ph. Accidents involving trains and trucks 308

5 sometimes result in chemical spills that affect the ph of the water. For example, a massive detergent spill from a tanker truck did not affect the aquatic insect life in a small creek nearby, but it caused the death of more than 32,000 fish. There are many places where coal has been removed from the ground by strip mining. Some coal deposits and the surrounding rock formations contain sulfur. When the sulfur is exposed to air and water, sulfuric acid is formed. For many years after the mining has ceased, sulfuric acid is produced with each rain. Acid mine drainage, from abandoned coal mines, is the single biggest pollutant of Pennsylvania's streams. Over 2,400 miles of streams don't meet water quality standards because of acid mine drainage. S 02 SO, sulfur oxygen 2SO2 sulfur dioxide oxygen sulfur dioxide 2H2O 2H2SO4 water sulfuric acid Acid lakes are formed in the old strip mine pits. During heavy rains, these lakes overflow and drain into nearby creeks. Old strip mine lakes lie in the watershed of Cedar Creek, near Columbia, Missouri. As many as sixty thousand fish have been killed when a lake overflows, and a slug of acid moves down the creek. Once the acid is diluted, fish once again move up the creek from the Missouri River. These fish will be the next victims when heavy rains cause another acid lake to overflow. Two rivers in western Pennsylvania show the effect of ph on an aquatic ecosystem. The Little Conemaugh River that runs through Johnstown, PA, once supported trout, bass, pike, shad and pickerel. Now most of the river is severely polluted with large amounts of acid mine drainage. The upper reach of Stoneycreek River, a tributary of the Little Conemaugh, has benefited from mine reclamation. The upper Stoneycreek now supports 22 species offish, including brook, brown and rainbow trout and smallmouth, spotted and rock bass. Strip mining can be done without damage to nearby streams. To prevent the formation of acid, the sulfur minerals left behind must be covered with soil. This reduces the amount of acid in the runoff. These new lakes can be stocked for fishing, and plantings can be made to provide more habitats for wildlife. Streams that drain watersheds with rocks and soils containing natural buffers may have a ph greater than 7. A buffer is a substance that, when placed in water, prevents large changes in the ph. Buffers neutralize the acids that enter the water. The alkalinity is a measure of the buffering capacity of the water. Freshwater aquatic ecosystems with an alkalinity between 100 and 200 ppm will have a stable ph. Little Conemaugh River 309

6 Hardness The rocks and soil in the watershed also determine the hardness of a body of water. If the area contains granite rocks that do not dissolve easily, the water will contain few minerals. Water that lacks certain minerals is said to be soft water. Water with a hardness of less than 10 ppm can support very little plant or animal life. In areas where there is limestone, the carbonic acid in the water dissolves the calcium and magnesium compounds from the rocks. Water that contains high levels of calcium and magnesium is said to be hard water. Calcium is essential for the making of cell walls in plants, and shells and bones in animals. Magnesium is an element in the chlorophyll molecule. Hard water also contains mineral compounds that act as buffers. Aquatic ecosystems in streams and lakes with hard water are less affected by acid rain than those aquatic ecosystems that contain soft water. The buffers prevent large changes in ph that would harm the aquatic organisms. The water test most used by industry is the total hardness test. Minerals in the water interfere with many industrial processes. The manufacture of steel and synthetic rubber requires water with less than 50 ppm calcium carbonate. It is often necessary for industries to "soften" the water or remove excess minerals. Nitrates and Nitrites Most fertilizers, used by farmers and homeowners, contain nitrates (NO3~). All nitrates are soluble in water. When it rains, the nitrates from fields and lawns are carried into nearby streams and lakes. Another major source of nitrates is sewagg^produced" by humans and other animals. One cow produces waste equal to the sewage produced by 4.5 humans. Nitrogen is also released by the decomposition of organic matter. [See Section 1.7, Nitrogen Cycle, page 31]. The nitrates in a body of water are nutrients for algae and aquatic plants. This increased growth of algae and build-up of dead plant material causes an increase in the BOD and lowers the DO level of the water. The EPA has identified nitrogen as the main factor causing low oxygen levels (less than 3 ppm) in the western part of Long Island Sound. Unpolluted waters generally have a nitrate-nitrogen level below 1 ppmrfast-flowing water will prevent the growth of floating aquatic plants and plankton algae even when nitrate levels are high. In the lower reaches where the water is warmer and slower moving, the nitrate causes abundant growth of algae, an algal bloom. The algae die and settle to the bottom and their decay causes the DO level to fall. The abundant growth of algae in this stream indicates a high level of nutrients.the nutrients come from malfunctioning septic systems in addition to animal waste and fertilizers in run-off. 310

7 Water that is used for drinking should be tested for nitrates. The national drinking water standard for nitrate-nitrogen is 10 ppm. Wells can be contaminated with nitrates from fertilizers and sewage.'nitrate levels, in the water of farm wells, and wells in areas with septic systems, canjaa high enough to cause the death of infants. Special bacteria in the baby's digestive system change nitrate to nitrite. Nitrites enter the bloodstream causing a condition called methemoglobinemia (met-hemo-glo-bin-emia). When nitrites are present, oxygen cannot combine with hemoglobin. The "blue baby" condition that results is sometimes fatal. Phosphates Phosphorus, in the form of phosphates (PO^3), is a plant nutrient and stimulates the growth of algae and aquatic plants. In most aquatic ecosystems the phosphate level is low, and this makes it the "growthlimiting" factor for aquatic plants and algae.^the maximum, level of phosphates recommended for rivers and streams is 0.1 ppm. A level of 0.03 ppm increases the growth of algae and plants in ponds and lakes. Inorganic phosphates, the type found in fertilizers used by farmers and homeowners, are attracted to soil particles and organic matter in the soil. When erosion occurs, the soil particles with the attached phosphates enter the water. Organic phosphates are present in human and animal wastes. Phosphates are also present in some detergents and wastewater from certain industrial processes. Many states have banned or limited the use of phosphates in detergents. Turbidity Carol Browner, head of the EPA during the Clinton Administration, said that the products of soil erosion are our greatest water-quality problem. Soil erosion increases the turbidity the solid particles suspended in the water. The phosphates attached to the particles and the nitrates dissolved in the water increase the growth of plankton algae, which also increases the turbidity. As the turbidity increases, less light penetrates the water and photosynthesis decreases. There may be abundant life in the turbid water of some rivers, but there is less diversity of species than there is in the clearer water upstream. Suspended particles create problems for aquatic life. They clog the gills of fish and smother the benthic organisms. Fish eggs and the larvae of clams, crabs, and aquatic insects that are coated with silt do not develop. Water Quality Chemical and Physical Factors Erosion makes water in this stream turbid and smothers aquatic organisms. 31!

8 QUESTIONS FOR STUDY AND DISCUSSION: 1. Define the following terms: algal bloom alkalinity / biochemical oxygen demand (BOD) buffer ' VOCABULARY dissolved oxygen, ph " gas bubble disease phosphates J hard water \^ polluted methemoglobinemiav^ reclamation*"-"' nitrates soft water ^-" nitrites solubility ^ x List three types of factors that affect water quality. 3. Under what.conditions is oxygen considered a pollutant? 4. Why are studies of aquatic ecosystems often complicated? Dissolved Oxygen ^y. What is the source of oxygen used by aquatic organisms? (3. What are the two major sources of the dissolved oxygen in water? /. Explain why the level of oxygen is low when the water is polluted with organic matter. 8. What is the minimum amount of DO that you would expect to find in an aquatic ecosystem with a large variety of ojganisms? Temperature and Dissolved Oxygen H. What is the relationship between the temperature of a liquid and the amount of gas that can be dissolved in the liquid? id. Give two reasons why fish may not be able to get as much oxygen as they need if the water is warm. Can There Be Too Much Oxygen? 11 / Describe the condition that exists when fish get j gas bubble disease. 12. Give the location and the time of year when gas bubble disease usually occurs. 13. What is the range of saturation levels that indicates a healthy aquatic ecosystem? supersaturation ^ synergistic effects " turbidity J ph 14^ Give the ph range that supports a good variety of organisms. 15/ Explain why the ph of a body of water changes jas, it ages. 16. Explain why fish kills sometimes occur in streams that receive water from abandoned coal mines. 17/ What is the relationship between the alkalinity level and the ph of a stream? Hardness 18. What determines the hardness of a body of water? 1-S. Compare water in a lake within a watershed that has granite rocks with the water in a lake j within a watershed that has limestone. 20. Why will hard water be affected less by acid rain than soft water? Nitrates and Nitrites 21. How will excess nitrates affect a body of water? 22. List three problems caused by excess algae growth. 2 2L^ Explain why a high level of nitrates in water can be dangerous. Phosphates 24/ How do excess phosphates affect lakes and streams? 25.>/What is the connection between erosion and phosphate levels in a stream? Turbidity 2 6,^Describe the effects of turbidity on an aquatic ecosystem. 312 Water Quality Chemical and Physical Factors