Nitrate Nitrogen
Nitrate is a nutrient for plant growth that dissolves readily in water. Common sources for nitrate include commercial and manure-based fertilizers, wastewater treatment plants, and faulty septic systems. Also, some nitrate is rained out of the atmosphere downwind from sources such as coal-fired power plants and forest fires.
The Virginia Water Quality Standard [1] for nitrate is 10 parts per million (ppm) when the concentration is expressed as nitrate nitrogen. (One part per million is equivalent to one milligram per liter of water.) This standard was established to protect human health. Drinking waters with levels greater than ten ppm pose a risk to human health from methemoglobinemia, also known as “blue baby” syndrome. Infants are particularly susceptible to this disease that interferes with their breathing.
Nitrate may also affect the health of fish, plants, and other life in rivers. As a nutrient, nitrate stimulates plant growth. In fact, all plants need some nitrate in order to grow at all! However, when nutrient levels stimulate too much plant growth (including algae), the river becomes an unhealthy place. The excessive plant growth does more than just take up space; it causes changes in dissolved oxygen. Decaying plant material lowers dissolved oxygen levels leading to foul tastes, odors, and occasional fish kills. In their report, “Nutrients in the Nation’s Water – Too Much of a Good Thing? [2]”, the United States Geological Survey found that rivers in areas of the country with little human impact had less than 0.6 ppm nitrate nitrogen.
The Virginia Water Quality Standards [1] are intended to protect all state waters for recreation, wildlife, the growth of a balanced population of aquatic life, and the production of edible and marketable fish and shellfish. However, no numeric criteria for nitrate currently exist to protect the health of freshwater aquatic life.
Phosphate
Phosphate is a form of phosphorus that acts as a nutrient for plant growth. Because of its nutrient value, phosphate is a common part of lawn and agricultural fertilizers which may enter rivers through erosion of the land surface. Other sources for phosphate include wastewater treatment plants and faulty septic systems. No significant atmospheric sources for phosphate are known.
Phosphate may affect the health of fish, plants, and other life in rivers. As a nutrient, phosphate stimulates plant growth. In fact, all plants need some phosphate in order to grow at all! However, when nutrient levels stimulate too much plant growth (including algae), the river becomes an unhealthy place. The excessive plant growth does more than just take up space; it causes changes in dissolved oxygen. Decaying plant material lowers dissolved oxygen levels leading to foul tastes, odors, and occasional fish kills. In their report, “Nutrients in the Nation’s Water – Too Much of a Good Thing? [2]”, the United States Geological Survey found that rivers in areas of the country with little human impact had less than 0.1 part per million phosphate. (One part per million is equivalent to one milligram per liter of water.)
The Virginia Water Quality Standards [1] are intended to protect all state waters for recreation, wildlife, the growth of a balanced population of aquatic life, and the production of edible and marketable fish and shellfish. However, no numeric criteria for phosphate currently exist to protect the health of freshwater aquatic life.
Ammonia Nitrogen
Ammonia is a gaseous form of nitrogen that dissolves in water. Most people are familiar with ammonia as a cleaning agent. In river waters, common sources for ammonia include commercial and manure-based fertilizers, wastewater treatment plants, and faulty septic systems. Ammonia is commonly converted to other forms of nitrogen (such as nitrate) by natural processes involving bacteria and other microorganisms in healthy rivers.
Ammonia is toxic to fish and other types of aquatic life. The Virginia water quality standard [3] is designed to protect aquatic life and, as a result, is complicated by the fact that ammonia’s toxicity depends on both the temperature and pH of the water. Chronic (or long-term) levels above 3.0 parts per million (ppm) clearly violate the water quality standard. (One part per million is equivalent to one milligram per liter of water.) However, lower levels may also violate the standard depending upon the pH and temperature of the water. For specific guidance, consult the numeric criteria tables that relate pH, temperature, and total ammonia levels. These tables can be found in the State Water Control Board’sWater Quality Standards document [4].
Dissolved Oxygen (DO)
DO is an important measure of stream water quality. Oxygen in stream systems comes from the atmosphere and from plants as a result of photosynthesis. Aquatic organisms need DO to live. Minimal DO level of 5 mg/l is usually required to maintain healthy growth and activity. The DO criteria for natural trout waters are a minimal DO reading of 6.0 mg/L with a daily average of 7.0 mg/L (www.deq.state.va.us/wgs [5] pg4). The DO capacity of water is limited by the temperature and salinity of the water and the atmospheric pressure (or altitude). Cold water holds more oxygen than warm water and water holds less oxygen at higher altitudes. The DO levels in and below riffles areas, or moving water are typically higher than pooled or slow moving water. DO levels fluctuate seasonally and over a 24-hour period, typically with the highest DO readings at midday to early afternoon, and the lowest reading in the early morning before the sun rises. DO is highest in the early afternoon because aquatic plants are in the Photosynthesis mode which means they are taking in CO2 and releasing Oxygen (this also raises the pH). At night these plants are in the Respiration mode and just like us they take in oxygen and release CO2 which also lowers the pH.
A DO test measures the amount of oxygen dissolved in the water. A DO measurement, however, does not measure the amount of DO the water is capable of holding at the temperature at which it was tested. Table 1.1 illustrates the potential DO concentrations in waters based on temperature of the water. For this project DO is measured in mg/l using a WTW multi parameter. The DO probe is filled with a potassium chloride (KCl) solution and has a selectively permeable membrane that allows DO to pass from the stream water into the salt solution. The DO that has diffused into the KCl solution changes the electric potential of the salt solution that is read in mg/l.
The Winkler titration method has served as the standard for measuring DO. For this project this method will be used as a check for the accuracy of the DO probe. DO is not measured directly in the Winkler method. Instead, the oxygen in the water sample is used to convert some of the test chemicals from one form to another that can be easily measured. The conversion occurs during the mixing and settling steps referred to as “fixing” the sample, in which free iodine is produced in direct proportion to the amount of oxygen in the original sample. The free iodine appears as a yellow to brown color in the “fixed” sample. To determine the amount of free iodine, the sample is titrated with a measurable amount of sodium thiosulfate (of a specific concentration), until the brown or yellow iodine color disappears. This endpoint is difficult to see, so starch is added near the end of the titration (while some yellow color remains) to enhance color change at the endpoint. Starch produces a strong blue-purple color while free iodine is still present but instantly turns colorless when the titration is complete. The amount of sodium thiosulfate required is directly proportional to the amount of free iodine in the “fixed” sample, and therefore is directly proportional to the amount of DO in the original sample.
The Virginia Water Quality Standards [1] are intended to protect all state waters for recreation, wildlife, the growth of a balanced population of aquatic life, and the production of edible and marketable fish and shellfish. The minimum DO standard for the majority of the streams west of the Blue Ridge is 4.0 mg/l. For Put & Take Trout Waters it is 5.0 mg/l and 6.0 mg/l for Natural Trout Waters.
pH
pH is a measure of how acidic or basic (alkaline) the water is. The pH scale measures the logarithmic concentration of hydrogen (H+) and hydroxide (OH–) ions, which make up water (H+ + OH– =H20). When both types of ions are in equal concentration, the pH is 7.0 or neutral. Water with a pH below 7 is acidic (there are more hydrogen ions than hydroxide). When the pH is above 7.0, the water is basic (alkaline) (there are more hydroxide ions than hydrogen ions). Since the pH scale is logarithmic, a drop in the pH by 1.0 unit is equivalent to a 10-fold increase in acidity. i.e., a water sample with a pH of 5.0 is 10 times as acidic as one with a pH of 6.0, and pH 4.0 is 100 times as acidic as 6.0. Therefore, a change in pH of one whole unit is quite a significant change.
In the Shenandoah Valley to take in account for the limestone geology, pH readings below 6.5 and above 9.5 are in violation of the Virginia Water Quality Standards (www.deq.state.va.us/wqs/ [1]). A range of pH 6.5 to 8.0 is optimal for most organisms. pH outside this range reduces the diversity in the stream because it stresses the physiological systems of most organisms and can reduce reproduction. Toxic metals trapped in sediment are released into the water at lower ph levels and “available” for absorption by aquatic plants and animals. Photosynthesis by aquatic plants removes carbon dioxide (CO2) from the water, which can significantly increase pH. Activities in the watershed may affect pH. Increased leaching of soils during snowmelt of heavy precipitation affect pH downstream. Changes in pH can also be caused by atmospheric deposition (acid rain), human activities and nature itself.
A pH meter measures the electric potential (millivolts) across an electrode when immersed in water. Therefore, pH meters can display results in either millivolts (mV) or pH units. For this project, results are recorded in pH units using a WTW multi parameter.
Temperature
Temperature affects feeding, reproduction and metabolism of aquatic animals, even a week or two if high temperatures may make stream unsuitable for sensitive aquatic organisms, even though temperatures are within tolerable levels throughout the rest of the year. Not only do different species have different requirements, but optimum habitat temperatures may change depending on the stage of life. Water has a very high heat capacity, which makes it resistant to changes in temperature. Compared to other substances, a large amount of heat is required to raise the temperature of one gram of water by 1 C. This physical property of water moderates daily and seasonal climatic changes in temperature.
The Virginia Water Quality Standards [1] are intended to protect all state waters for recreation, wildlife, the growth of a balanced population of aquatic life, and the production of edible and marketable fish and shellfish. The maximum temperature standard for the majority of the streams west of the Blue Ridge is 31 degrees C. For Put & Take Trout Waters it is 21 degrees C and 20 degrees C for Natural Trout Waters.
Turbidity
Turbidity is a measure of water clarity. When the river is muddy, soil solids increase turbidity by mixing with the water and becoming suspended. During high flow, soil solids may erode from the land surface or become re-suspended from sediment on the river bottom. Another source of turbidity is free-floating algae cells that grow when high nutrient levels exist in the river.
Turbidity is also an indirect measurement of one of the leading problems with the health of our nation’s rivers – sediment. Sediment can cover fish eggs, smother habitat on the river bottom, and impede fish feeding. When it remains high for long periods of time, turbidity can prevent aquatic plants from getting sunlight and producing oxygen through photosynthesis.
The Virginia Water Quality Standards [1] do not include any guidelines for turbidity. However, as a general guide, water begins to appear cloudy when the turbidity is greater than 5 nephelometric turbidity units (NTU.)