Dissolved Oxygen and Water Quality

Transcription

1 Dissolved Oxygen and Water Quality Introduction to Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Dissolved Oxygen You can't tell by looking at water that there is oxygen in it (unless you remember that chemical makeup of a water molecule is hydrogen and oxygen). But, if you look at a closed bottle of a soft drink, you don't see the carbon dioxide dissolved in that until you shake it up and open the top. The oxygen dissolved in lakes, rivers, and oceans is crucial for the organisms and creatures living in it. As the amount of dissolved oxygen drops below normal levels in water bodies, the water quality is harmed and creatures begin to die off. Indeed, a water body can "die", a process called eutrophication. Although water molecules contain an oxygen atom, this oxygen is not what is needed by aquatic organisms living in natural waters. Dissolved oxygen refers to the small amount of oxygen gas (O 2 ), up to about ten molecules of oxygen per million of water, is actually dissolved in water. Oxygen enters a stream by diffusion from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge. This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive. Dissolved oxygen and water quality Rapidly moving water, such as in a mountain stream or large river, tends to contain a lot of dissolved oxygen, whereas stagnant water contains less. Bacteria in water can consume oxygen as organic matter decays. Thus, excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen deficient situation that can cause a water body "to die." Aquatic life can have a hard time in stagnant water that has a lot of rotting, organic material in it, especially in summer (the concentration of dissolved oxygen is inversely related to water temperature), when dissolved oxygen levels are at a seasonal low. Water near the surface of the lake is too warm for them, while water near the bottom has too little oxygen. Conditions may become especially serious during a period of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely result from problem.

2 Dissolved oxygen, temperature, and aquatic life As this chart shows, the concentration of dissolved oxygen in surface water is controlled by temperature and has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved oxygen concentration is high. In summer and fall, when the water temperature is high, the dissolved oxygen concentration is low. Photosynthesis is the process by which plants make food from the sun. During this process, plants release oxygen. Therefore, the presence of aquatic plants can increase dissolved oxygen levels and be beneficial for the health of the water. However, excessive plant growth, particularly algae, can decrease dissolved oxygen levels. This is became the algae tend to grow rapidly a phenomenon known as an algal bloom and then die off quickly. When the algae die, the bacteria that break it down consume oxygen, lowering dissolved oxygen levels and decreasing water quality. Measuring Dissolved Oxygen Dissolved oxygen is measured using an electronic probe. The units are mg / L. A reading of 0 2 indicates there are very low, and possibly deadly levels of dissolved oxygen. A reading of 3 5 means levels are somewhat low, and may be stressful to some aquatic organisms. A reading of 6 or above indicates a normal, healthy level of dissolved oxygen.

3 ph and Water Quality Introduction to Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. ph ph is a measure of the acidic or basic (alkaline) nature of a solution. It is the hydrogen ion (H+) concentration that determines ph of a solution. A water molecule is made up of hydrogen ion (H+) and a hydroxide ion (OH ): H + + OH = H 2 0. ph is determined and recorded as a number between 0 and 14. Distilled (pure)water has a ph of 7 which is neutral. This means that the level of H + and OH ions in pure water are equal.if the level of H+ ions increases, the substance is considered an acid and the ph number is below 7. If the level of OH ions increases, the substance is considered to be alkaline or base and the ph number is above 7. An acid has a range of 0 to any numerical value below 7. For example, 6.9 would be a weak acid. A base has a range of any numerical value above 7 to 14 with 7 being a neutral value. A one unit change in the ph, from 4 to 3, is a ten fold change in how acidic the substance has become. This means that a ph of 3 is ten times more acidic than a ph of 4. ph and water quality In the United States, the ph of most natural water systems range from , but wide variations can occur due to increases in the atmosphere of nitrogen oxides and sulfur dioxides from automobile and coal fired power plant emissions. These oxides are converted to nitric and sulfuric acids in the atmosphere and fall to earth as acid rain or snow. This acidic precipitation can adversely lower the ph of aquatic ecosystems. In dead zones, where the carbon dioxide levels are high and dissolved oxygen levels are very low, carbonic acid forms causing ph to become acidic.

4 Excessively high and low phs can be detrimental for the use of water. Certain chemicals, like detergents (ammonia), can cause the ph of water to increase. High ph causes a bitter taste, water pipes and water using appliances become encrusted with deposits, and it depresses the effectiveness of the disinfection of chlorine, thereby causing the need for additional chlorine when ph is high. Low ph water will corrode or dissolve metals and other substances. Pollution can change a water's ph, which in turn can harm animals and plants living in the water. For instance, water coming out of an abandoned coal mine can have a ph of 2, which is very acidic and would definitely affect any fish crazy enough to try to live in it! By using the logarithm scale, this mine drainage water would be 100,000 times mor acidic than neutral water so stay out of abandoned mines! The ph scale:

5 Introduction to Water Quality Nitrates/Phosphates and Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Nitrates/Phosphates (Nutrients) Both nitrogen and phosphorous are elements that living things need to grow and survive. These nutrients are beneficial when they are present in the right amount, but can pollute water if they are in excess (too much). Nitrates are a chemical form of nitrogen found in water.normally only small amounts are found naturally, but an increase in nitrate levels can come from many man made sources such as septic (sewer) systems, fertilizer runoff and improperly treated wastewater. As nitrates increase, they act as a plant nutrient and cause an extreme increase in plant growth. As the plant material dies and decomposes, the bacteria that breaks down the plants uses up lots of oxygen. As a result, dissolved oxygen levels decrease, which can hurt fish and other aquatic life. Phosphates are a chemical form of phosphorous found in water. Sources of phosphates include septic tanks, runoff from feedlots, runoff from agriculture and waste water treatment plants. Like with nitrates, if phosphate levels are too high there is an increase in the growth of aquatic plants, especially algae. This is sometimes called an algal bloom. With the increase in algal growth and decomposition, the dissolved oxygen levels will decrease.detergents with phosphates were a prime source of pollution before manufacturers developed phosphate free alternatives. The EPA suggest that unpolluted waters shall have less than 0.1mg/l of phosphates and shall contain less than 1 mg/l of nitrates.

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8 Introduction to Water Quality Temperature and Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Temperature The temperature of an aquatic ecosystem is very important because it can affect: 1. dissolved oxygen levels; 2. the rate at which algae and aquatic plants photosynthesize; 3. the metabolism of aquatic organisms (metabolism is all of the things an organism does to stay alive) 4. how aquatic organisms are affected by different pollutants, parasites and pathogens. Cold water can hold more dissolved oxygen than warm water. One of the man made problems associated with water quality is thermal (heat) pollution. Thermal pollution is when warm water is added into an aquatic ecosystem. Sources include industries such as power plants, and also storm drain runoff which has been warmed on streets, parking lots and sidewalks. In addition, human activities such as cutting down trees, the removal of vegetation around the water, and construction can lead to an increase in water temperature. These practices can increase erosion (when soil is washed away by moving water) which increases sediments (dirt) in the water. As sediments increase, the water becomes turbid, or cloudy. Cloudy water absorbs more of the sun's rays which increases the water temperature.

9 Increases in temperature can change aquatic plants.. As the temperature increases, the rate of photosynthesis increases. Photosynthesis is the process by which plants use energy from the sun to make food. When plants photosynthesize, they give off oxygen. Some photosynthesis is good for water. But if the water is too warm, then there is one type of plant that grows a lot algae! Algae can grow so thick that it blocks out the sun, and kills all the other plants. This is called an algal bloom. When the plants and algae die, bacteria break them die. The bacteria use up all the oxygen in the water decomposing the dead plants. This causes low oxygen levels and poor water quality.

10 Introduction to Water Quality Runoff and water quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Runoff Runoff is the water that flows over the ground after a heavy rain. Most of the rainfall in forested areas is soaked into soils, is stored as groundwater, and slowly makes its way to streams through springs. Flooding is less common in these more natural conditions because water soaks into the ground, which lessens the amount of runoff into a stream during the storm. As areas of land that drain into small rivers are urbanized (built up with houses and roads), much of the vegetation (plants) is replaced by man made surfaces. These are sometimes called impervious surfaces, which means they are not permeable to water; water cannot soak into them. Impervious surfaces reduce the amount of water returning to the groundwater. In fact, they cause more stormwater runoff to occur. This runoff is collected by drainage systems such as storm sewers (as shown in this picture), and ditches, which carry runoff directly to streams. In areas in which people have built towns and city, water arrives much more quickly into streams, causing more flooding.

11 Runoff from agricultural land (and even our own yards) can carry excess manure or fertilizer into streams, lakes, and groundwater supplies. These substances contain nitrogen and phosphorus, nutrients that have the potential to degrade (lower) water quality. Why is stormwater runoff a problem? As it flows over the land surface, stormwater picks up pollutants that may include sediment, nutrients (from lawn fertilizers), bacteria (from animal and human waste), pesticides (from lawn and garden chemicals), metals (from rooftop and roadways), and petroleum by products (from leaking vehicles). Pollution originating over a large land area without a single point of origin and generally carried by stormwater is considered non point source pollution. In contrast, point source pollution is pollution that originates from a single source, such as a factory or landfill. Polluted stormwater runo can be harmful to plants, animals, and people.

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13 Introduction to Water Quality Bioindicators and Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Bioindicators Bio means life. A bioindicator is a living organisms that indicates (shows) if a body of water is clean or polluted. One type of bioindicators are aquatic macroinvertebrates. Aquatic means they live in the water. Macro means they are big enough to see without a microscope. Invertebrate means they don t have a backbone this includes things like insects and crustaceans. These organisms often live in the water as larva (babies), and then turn into adults and leave the water. If there is a lot of diversity (different types) of macroinvertebrates it usually means the water is healthy. If there is not a lot of diversity of macroinvertebrates, it may mean the water is polluted. If you find more than 22 species of macroinvertebrates, you have excellent water quality. If you find species, you have good water quality. If you find species, you have fair water quality. If you find less than 11 species, you probably have poor water quality. Where to find bioindicators You can find aquatic macroinvertebrates in a lot of different places lakes, ponds, streams, and rivers. When looking a stream, you want to look in a wide variety of places by the edge of the stream and in the middle, where the water is moving fast and where it forms pools and does not move a lot. One of the best places to look is in riffle area this is where the water is moving quickly, usually over rocks. You can find the macroinvertebrates by picking up rocks, or by scraping a net along the rocks or the bottom of the stream. Types of Macroinvertebrates There are three groups of macroinvertebrates: First, there are macroinvertebrates that are pollution intolerant (high quality). They cannot tolerate (live with) pollution. This means if there is any pollution, they will die. If you find lots of these macroinvertebrates, you know your stream must be healthy. They need lots of oxygen, a neutral ph, and cool water to live. Here are some examples of these macroinvertebrates: Mayflies Stoneflies Caddisflies

14 The second group of macroinvertebrates are somewhat pollution tolerant (middle quality). They can tolerate some pollution, but not too much. If there is a lot of pollution, they will die. Here are some examples of these macroinvertebrates: Dragonflies Damselflies The third group of macroinvertebrates are pollution tolerant (low quality). They can tolerate lots of pollution. They can live with very little oxygen, low or high phs, and warmer water. If you only find these macroinvertebrates, there is a good chance your water is polluted. Here are some examples of these macroinvertebrates: Mosquitoes Midges

15 Introduction to Water Quality Turbidity and Water Quality Is it safe for drinking? Can fish and other aquatic life thrive in streams and lakes that are affected by human activities? What is the water quality? To answer these questions, it is helpful to understand what "water quality" means, how it is determined, and the natural processes and human activities that affect water quality. Water quality is a measure of the usefulness of water for a particular purpose based on certain physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to standards and guidelines to decide if the water is suitable for a particular use. Turbidity Turbidity is the measure of relative clarity (clearness) of a liquid. It is an characteristic of water and is an expression of the amount of light that is scattered by material in the water when a light is shined through the water sample. The higher the intensity of scattered light, the higher the turbidity. Material that causes water to be turbid (unclear) include clay, silt, dead leaves, algae, soluble colored compounds, and plankton and other microscopic organisms. Turbidity makes water cloudy or opaque. Turbidity reported in nephelometric turbidity units (NTU). During periods of low water flow (base flow), many rivers are a clear green color, and turbidity is low, usually less than 10 NTU. During a rainstorm, sediments (dirt) from the surrounding land are washed into the river making the water a muddy brown color, indicating water that has a high turbidity. Also, during high flows, water is moving faster, which ca stir up material from the stream bed (the bottom of the stream), causing higher turbidites. Turbidity and water quality High turbidity levels stop light from penetrating (going through) the water. This can kill aquatic plants, and the organisms that rely on those plants for food. In streams, increased sedimentation can occur (more dirt in the water), and can result in harm to habitat areas for fish and other aquatic life. Sediments in the water provide attachment places for other pollutants, notably metals and bacteria. For this reason, turbidity readings can be used as an indicator of potential pollution in a water body.

16 Turbidity and human health Excessive turbidity, or cloudiness, in drinking water is aesthetically unappealing, and may also represent a health concern. Turbidity can provide food and shelter for pathogens (bacteria and viruses that cause diseases). If not removed, turbidity can promote regrowth of pathogens in the distribution system, leading to waterborne disease outbreaks.