Chemical Parameters：化学参数.docx

Chemical Parameters for Water StudypH pH = potential of HydrogenpH is a measure of the dissolved hydrogen ion concentration H+ in water. It is found by determining the negative log of the hydrogen ion concentration.pH = -log H+Its counterpart is pOH which is a measure of the dissolved hydroxide ion concentration OH- in water. It is found by determining the negative log of the hydrogen ion concentration.pOH = -log OH-Pure water ionizes to form equal amounts of hydrogen and hydroxide ions:HOH H+ + OH The concentration of each ion in a solution of pure water is 1 X 10 -7 M (moles per liter). Since the log of this number is -7, the pH is 7 and the pOH is also 7. Pure water has a neutral pH because the concentration of hydrogen and hydroxide ions are equal. This leads to the pH scale (and its counterpart pOH scale) with 7 in the middle. A concentration of 10-6 is more concentrated than 10-7. 10-5 is more concentrated than 10-6 and so on.Concentration pHpOH Concentration 0 0 1 2 3 4 5 6 7 7 6 5 4 3 2 1 8 9 10 11 12 13 14 8 9 10 11 12 13 14 High Concentration High Concentration Low Concentration Low Concentration 100 M 10-1M 10-2 M 10-3M 10-4 M 10-5M 10-6 M 10-7M 10-8 M 10-9M 10-10 M 10-11M 10-12M 10-13M 10-14 M 10-14 M 10-13M 10-12 M 10-11M 10-10 M 10-9M 10-8 M 10-7M 10-6 M 10-5M 10-4 M 10-3M 10-2M 10-1M 100M pH Ranges and Aquatic Life pHAcidic 0 _7_14 BasicBacteria 1_13Aquatic Plants 6.5 _13Carp, Suckers, Catfish, 6_13some invertebrates Bass, Crappie 6.5 _9Snails, Mussels 7 _9Amphibians 5 _9Most others 6.5 _ 7.5/parameters.phpRain is naturally acidic (pH 5.0 6.0) due to the absorption of carbon dioxide in the atmosphere. Usually a lowered pH (more acidic) has greater affect on aquatic organisms. Toxicity of many compounds increases at lower pH and the solubility of metals (aluminum, copper) also increases at lower pH. Both have a direct effect on the viability of aquatic organisms. SourcesEarth Force Water Quality Standards/assets/files/Water%20Quality%20Testing/Water%20Quality%20Parameters.pdfUS EPA Acid Rain/acidrain/effects/surface_water.htmlDissolved OxygenOxygen (O2) is an essential element for most living things. The air that we breathe is about 20% oxygen (the rest being mostly nitrogen gas). Out of 100 molecules of air, 20 of them will be oxygen or 20 parts per hundred (pph).Gases dissolve in water at very low concentrations and are affected by changes in temperature (and pressure). Leave an open soda out overnight and it goes flat. The increase in temperature has caused most of the dissolved carbon dioxide to escape. Cooler temperatures mean higher concentrations of dissolved gases. The concentration of dissolved gasses is measured in parts per million (ppm or milligrams/Liter), not parts per hundred. In most streams, dissolved oxygen is not a problem due to the mixing of the water with air in riffle zones and readings of 8 to 12 ppm are common. In pools the level might be lower and in cut-off oxbows near the stream, the level of dissolved oxygen may approach zero. Various levels of dissolved oxygen are needed for different organisms. Most game fish, for example, need higher levels than bottom dwelling fish such as catfish.In aquatic systems the amount of dissolved O2 is also dependent on time of day, season, shade or sun conditions (all related to temperature differences), aquatic plant activity (production of oxygen gas but usually found in lakes and ponds), decomposition of organic material (aerobic decomposition uses up oxygen), stream velocity and other factors.ConductivityConductivity is a measure of the dissolved ions in solution. Water is a good solvent and most metal salts will dissolve to some degree in water. If salts dissolve, ions form in solution as illustrated below:CaCl2 Ca+2 + 2 Cl-1Metal salts are found in nature in the form of rocks (limestone is calcium carbonate, gypsum is calcium sulfate) and soil constituents, both of which can leach into the water. Additional salts come from fertilizers, road salts, wells and industrial sites to name a few.Not all rocks will dissolve in water, however. Sandstones of Eastern Kentucky are made mostly of silicon dioxide which is insoluble. There are regional differences in conductivity around the state.Pure water will have a conductivity of zero. Ocean water will be in the thousands. The conductivity test indicates the presence of dissolved salts in the water but it does not identify the salts.AlkalinityRelated to pH is the alkalinity of a system. Alkalinity refers to the ability of a system to resist changes in pH. For freshwater systems, this usually means that the concentration of carbonate ions in water is relatively high (other ions also contribute to alkalinity specifically the hydroxide ion OH- , and the hydrogen carbonate ion HCO3-1). The carbonate ions are present in nature in the form of calcium carbonate or magnesium carbonate, both of which are found in carbonate rocks i.e. limestone, dolomite, marble. Calcium carbonate is slightly soluble in water, especially if the water is acidic i.e. from rain.CaCO3 Ca +2 + CO3-2In water, the carbonate ion (CO3-2) is able to bind with excess hydrogen ions (additional acid) to keep them from increasing the concentration of hydrogen ions and decreasing the pH.CO3-2 + H+1 HCO3-1This ability to absorb excess acid in a system is called buffering. (Aspirin is often buffered because it is an acid and can cause excess acid in the stomach. Antacids such as Tums and Rolaids contain calcium carbonate to reduce excess stomach acid buffers). Streams and lakes in Kentucky are usually well buffered and low pH is not a problem. There are regional differences due to the underlying geology of the region.Alkalinity is measured in parts per million (ppm) of calcium carbonate. Levels from 20 200 ppm are common in streams. In central Kentucky readings in the range of 100 200 ppm show relatively high alkalinity and buffering capacity.Alkalinity represents buffering capacity mainly due to carbonate, hydrogen carbonate and hydroxide ions in solution. On another note:The presence of carbonate rocks also increases the Hardness of water. Hardness is due to the calcium ions (Ca +2) and magnesium ions (Mg +2) in the water. Hard water increases the residue left behind as water evaporates the “scale” on your shower head or teapot.ChlorideChlorides are salts resulting from the combination of the gas chlorine with a metal. Some common chlorides include sodium chloride (NaCl) and magnesium chloride (MgCl2). Chlorine alone as Cl2 is highly toxic and it is often used as a disinfectant. In combination with a metal such as sodium it becomes essential for life. Small amounts of chlorides are required for normal cell functions in plant and animal life. Chloride is the main extracellular anion in animals, including humans. It is a highly mobile ion that easily crosses cell membranes and is involved in maintaining proper osmotic pressure, water balance, and acid-base balance in animal tissues. Recent studies indicate that the chloride ion also plays an active role in renal function, neurophysiology, and nutrition.Chlorides may get into surface water from several sources including: rocks containing chlorides; agricultural runoff; wastewater from industries; oil well wastes; effluent wastewater from wastewater treatment plants, and road salting. Chlorides can contaminate fresh water streams and lakes. Fish and aquatic communities cannot survive in high levels of chlorides. The table below shows the effects of chlorides on fish:Chloride Above These Levels Can Be ToxicShort Exposure (ppm)Long Term Exposure (ppm)Species2540400Snails6570430Fathead minnow6740900Rainbow trout8000800Channel catfish8390850CarpPublic Drinking Water Standards require chloride levels not to exceed 250 ppm. Criteria for protection of aquatic life require levels of less than 600 ppm for chronic (long-term) exposure and 1200 ppm for short-term exposure. Although chloride is an essential element for maintaining normal physiological functions in all aquatic organisms, elevated or fluctuating concentrations of this substance can be detrimental. More specifically, exposure to elevated levels of chloride in water can disrupt osmoregulation in aquatic organisms leading to impaired survival, growth, and/or reproduction. Because excess chloride is most frequently actively excreted from animal tissues via the kidneys or equivalent renal organs to achieve osmoregulatory balance, the bioaccumulation potential of chloride is low. Several factors such as dissolved oxygen concentration, temperature, exposure time and the presence of other contaminants influence chloride toxicity. Sources:EPA British Columbia.bc.ca/wat/wq/BCguidelines/chloride/chloride.htmlRiver Assessment Monitoring Project/ww/ramp/default.htm/ww/ramp/rmcl.htm/ww/ramp/rmtests.htmTurbidityTurbidity is a measure of the relative clarity of water, and is based upon the number of suspended particles present, and the resulting level of light transmission through the liquid. Water with no suspended particles, such as distilled water, has a turbidity of zero, high level of light transmission, and is, simply put, easy to see through. As the number of suspended particles in the water increases, the greater the turbidity, the lower the level of light transmission, and the harder it becomes to see through the water.There is a natural level of turbidity found in watersheds, with particulate inputs from natural erosion, organic decay, and algae. In urban areas, however, levels of turbidity are often unnaturally high due to sediment from runoff, storm water, waste discharge, algal growth, and the disturbance of ground sediments from storm events. High levels of turbidity are associated with lower water quality. Some of the direct and indirect impacts of increased water turbidity include: Increased water temperature and reduced oxygen levels (high turbidity water holds more heat) Photosynthesis levels decrease as light cannot be transmitted to lower levels of the water columno Inhibited growth of submerged aquatic plants that can no longer receive light and consequent effects on the species that are dependent upon these primary producers Increase in levels of suspended particles in the water can clog gills, smother bottom dwelling organisms, and reduce available habitat for aquatic life. Suspended particles can protect