Water Quality Testing Parameters | Missouri Department of Natural Resources - Chuyên Trang Chia Sẻ Kiến Thức Thời Trang Mới Nhất

Water quality data are used to describe the condition of a waterbody, to help understand why a condition exists, and to provide some clues as to how it may be improved. Water quality indicators include physical, chemical and biological measurements. The following list includes the testing parameters the department uses to determine the water quality in Missouri.

Acidity of water is its capacity to react with a strong base to a designated pH. Acidity is a measure of a combined property of water and can be interpreted in terms of specific substances only when the chemical composition of the sample is known (19th Edition, Standard Methods, 1995).

The alkalinity, or the buffering capacity, of a stream refers to how well it can neutralize acidic pollution and resist changes in pH. Alkalinity measures the amount of alkaline compounds in the water, such as carbonates, bicarbonates and hydroxides. These compounds are natural buffers that can remove excess hydrogen ions (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Ammonia (Nitrogen as Ammonia)

Ammonia, or NH3, is one of the most important pollutants in the aquatic environment because of its highly toxic nature and its prevalence in surface water systems. It is discharged in large quantities in industrial, municipal and agricultural waste waters.

Bicarbonate alkalinity is a specific subset of alkalinity. It is determined by a calculation that takes into account the alkalinity value and the pH measured in the field at time of sample collection.

The biological oxygen demand, or BOD, is the amount of oxygen consumed by bacteria in the decomposition of organic material. It also includes the oxygen required for the oxidation of various chemicals in the water, such as sulfides, ferrous iron and ammonia. While a dissolved oxygen test tells you how much oxygen is available, a BOD test tells you how much oxygen is being consumed.

BOD is determined by measuring the dissolved oxygen level in a freshly collected sample and comparing it to the dissolved oxygen level in a sample that was collected at the same time but incubated under specific conditions for a certain number of days. The difference in the oxygen readings between the two samples in the BOD is recorded in units of mg/L.

Unpolluted, natural waters should have a BOD of 5 mg/L or less. Raw sewage may have BOD levels ranging from 150 – 300 mg/L (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Carbonaceous biochemical oxygen demand, or CBOD, measures the amount of demand that is oxidized by carbon. CBOD is a fraction of the BOD that excludes the nitrogenous oxygen demand by the addition of nitrogen inhibitors during the analysis (19th Edition, Standard Methods, 1995).

The chemical oxygen demand, or COD, is used as a measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. For samples from a specific source, COD can be related to BOD, organic carbon or organic matter.

Chlorides are salts resulting from the combination of the gas chlorine and various metals. Chloride is one of the major components of road salt, also known as rock salt. Most chlorides in water come from salt, or sodium chloride (NaCl), applied to pavement to melt ice. Other sources of chloride are wastewater treatment discharges, water softeners, storm sewers, animal feed, fertilizers and underground aquifers.

Chloride is soluble and can enter surface and groundwater easily. Although non-toxic at low levels, elevated levels of chloride in waterbodies can have a detrimental effect on freshwater ecosystems. High chloride levels are toxic to aquatic life. Some invasive species (e.g., Eurasian water milfoil) are more tolerant of high chloride levels and can outcompete native organisms.

High levels of chloride can also lead to stratification in lakes and ponds, resulting in oxygen depletion and fish kills. High chloride concentrations can restrict water use for consumption in domestic and public supply wells, and affect the quality necessary for many industrial uses (Missouri Stream Team Level 1 Volunteer Water Quality Monitoring Training Notebook).

Algae is a fundamental producer in the food web of freshwater ecosystems. Artificially elevated nutrient levels can cause algae to grow in excess causing ecological and aesthetic problems in lakes and streams. Algae occurs in two general types. One is as growth directly to the substrate, or bottom material, called periphyton. The other is free-floating in the water column and is called phytoplankton.

Relative amounts of algae, whether in the form of periphyton or phytoplankton, can be quantified by the analysis of chlorophyll a contained in the algae in a sample. Samples for chlorophyll a (the most predominant form of chlorophyll) analysis are collected by running water through a filter. For phytoplankton, a measured amount of water from the waterbody is run through the filter. For periphyton, a known area from either natural or artificial substrate is scraped and rinsed through the filter. Phytoplankton chlorophyll a is reported in units of µg/L and periphyton chlorophyll a is reported in units of mg/m2. Staff uses fluorometry methods of analyzing chlorophyll a.

Conductivity is a measure of how well water can pass an electrical current. It is an indirect measure of the presence of inorganic dissolved solids, such as chloride, nitrate, sulfate, phosphate, sodium, magnesium, calcium, iron and aluminum. The presence of these substances increases the conductivity of a body of water. Organic substances, like oil, alcohol and sugar, do not conduct electricity very well, and thus have a low conductivity in water.

Inorganic dissolved solids are essential ingredients for aquatic life. They regulate the flow of water in and out of organisms’ cells and are building blocks of the molecules necessary for life. A high concentration of dissolved solids, however, can cause water balance problems for aquatic organisms and decrease dissolved oxygen levels (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Cyanotoxins are produced by cyanobacteria (blue-green algae) within the cyanobacterial cell and are released into the waterbody when the cyanobacterial cell dies or ruptures. Health effects from cyanotoxins range from mild skin irritations to more serious illnesses or death. The most common cyanotoxins are microcystins, cylindrospermopsin, anatoxin and saxitoxin.

Dissolved oxygen, or DO, is vital to supporting the aquatic life in that particular waterbody. DO will fluctuate daily and is affected by many factors:

Temperature: Oxygen is more easily dissolved in cold water, so colder water will have higher DO, and warmer water will have lower DO.
Flow: Oxygen concentrations vary with the volume and velocity of water flowing in a stream. Faster flowing white water areas tend to be more oxygen rich because more oxygen enters the water from the atmosphere in those areas than in slower, stagnant areas.
Aquatic Plants: The presence of aquatic plants in a stream affects the dissolved oxygen concentration. Green plants release oxygen into the water during photosynthesis. Photosynthesis occurs during the day when the sun is out and ceases at night. Thus in streams with significant populations of algae and other aquatic plants, the dissolved oxygen concentration may fluctuate more drastically, reaching its highest levels in the late afternoon. Because plants, like animals, also take in oxygen, dissolved oxygen levels may drop significantly by early morning.
Altitude: Oxygen is more easily dissolved into water at low altitudes than at high altitudes.
Dissolved or suspended solids: Oxygen is also more easily dissolved into water with low levels of dissolved or suspended solids.
Human Activities Affecting DO:
- Removal of riparian, or streambank, vegetation may lower oxygen concentrations due to increased water temperature resulting from a lack of shade and increased erosion of bare soil.
- Typical urban human activities may lower oxygen concentrations. Runoff from impervious surfaces bearing salts, sediments and other pollutants increases the amount of suspended and dissolved solids in stream water.
- Organic wastes and other nutrient inputs from sewage and industrial discharges, septic tanks and agricultural and urban runoff can result in decreased oxygen levels. Nutrient inputs often lead to excessive algal growth. When the algae die, the organic matter is decomposed by bacteria. Bacterial decomposition consumes a great deal of oxygen.
- Dams may pose an oxygen supply problem when they release waters from the bottom of their reservoirs into streams and rivers. Although the water on the bottom is cooler than the warm water on top, it may be low in oxygen if large amounts of organic matter have fallen to the bottom and have been decomposed by bacteria.

Usually streams with high dissolved oxygen concentrations (greater than 8 mg/L for Ozark streams) are considered healthy streams. They are able to support a greater diversity of aquatic organisms. They are typified by cold, clear water, with enough riffles to provide sufficient mixing of the water. In streams impacted by any of the above factors, summer is usually the most crucial time for dissolved oxygen levels because stream flows tend to lessen and water temperatures tend to increase. This can cause fish kills and stress for other aquatic life.

Dissolved Oxygen Solubility Tables – USGS

(1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Human and animal wastes carried to stream systems are sources of pathogenic or disease-causing, bacteria and viruses. The disease-causing organisms are accompanied by other common types of nonpathogenic bacteria found in animal intestines, such as fecal coliform bacteria, enterococci bacteria, and Escherichia coli, or E. coli, bacteria.

Fecal coliform, enterococci and E. coli bacteria are not usually disease-causing agents themselves. However, high concentrations suggest the presence of disease-causing organisms. Fecal coliform, enterococci and E. coli bacteria are used as indicator organisms; they indicate the probability of finding pathogenic organisms in a stream.

The department uses the IDEXX Colilert® and Quanti-Tray® system for detection and counting of E. coli and total coliforms. The method can be applied to ambient fresh waters, drinking waters and wastewaters. The EPA-approved Colilert® method is based on Defined Substrate Technology®. The product utilizes nutrient indicators that produce color and/or fluoresce when consumed by total coliforms and E. coli. After the reagent is added to the sample and incubated for 24 hours, the number of total coliform and E. coli can be determined. These numbers are used to determine compliance with water quality standards, facility permit limitations, state regulations and as an indicator of fecal contamination.

To measure indicator bacteria, water samples must be collected in sterilized containers. The samples are forced through a filter and incubated at a specific temperature for a certain amount of time. The resulting colonies that form during incubation are counted and recorded as the number of colony producing units per 100 mL of water (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods) .

Water hardness is the sum of calcium and magnesium concentrations, expressed as mg/L of calcium carbonate. These minerals naturally become dissolved in water as it passes through rock and soil. Human sources can include runoff, and municipal and industrial discharges. Humans and animals need these minerals to stay healthy, however when they are in excess in a waterbody it can affect the toxicity of metals such as lead, cadmium, chromium and zinc.

The effects of metals in water and wastewater range from beneficial to troublesome to dangerously toxic. Some metals are essential, others may adversely affect water consumers, wastewater treatment systems, and receiving waters depending on concentration (19th Edition, Standard Methods, 1995).

Not all metals are acutely toxic in small concentrations. The “heavy metals” include copper, iron, cadmium, zinc, mercury and lead. These are the most toxic to aquatic organisms. Some water quality characteristics that affect metal toxicity include temperature, pH, hardness, alkalinity, suspended solids, redox potential and dissolved organic carbon. Metals can bind to many organic and inorganic compounds, which reduces the toxicity of the metal. The primary mechanism for toxicity to organisms that live in the water column is by uptake of dissolved metals across the gills. This is not to say that particulate metal is nontoxic, only that particulate metal appears to exhibit substantially less toxicity than does dissolved metals (U.S. EPA).

Metals can be in different forms and are analyzed accordingly:

Dissolved – represent the bioavailable fraction of metals in the water column (June 1996 U.S. EPA, The metal Translator: Guidance for Calculating a Total Recoverable Permit Limit from a Dissolved Criterion).
Total: Includes all metals, inorganically and organically bound, both dissolved and particulate. The total value will give an unrealistically high value for those metals that are biologically available to aquatic organisms.

Nitrogen is important to all life. Nitrogen in the atmosphere or in the soil can go through many complex chemical and biological changes. It can be combined into living and non-living material and return back to the soil or air in a continuing cycle called the nitrogen cycle.

Nitrogen occurs in natural waters in various forms, including nitrate, nitrite and ammonia. Nitrate is the most common form tested. Test results are usually expressed as nitrate-nitrogen, or NO3-N, which simply means nitrogen in the form of nitrate. Ammonia is the least stable form of nitrogen and thus difficult to measure accurately. Nitrite is less stable and usually present in much lower amounts than nitrate.

Nitrate → Nitrite → Ammonia → Organic Nitrogen

(Stable) → → →→ → →→ → → (Unstable)

These compounds are interrelated through the process of nitrification, the biological breakdown of ammonia to nitrate. In this process nitrite is produced as an intermediate product.

(1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Nitrate, or NO3-, generally occurs in trace quantities in surface water. It is the essential nutrient for many photosynthetic organisms and has been identified as the growth limiting nutrient. Nitrate is a less serious environmental problem since it can be found in relatively high concentrations while being relatively nontoxic to aquatic organisms. When nitrate concentrations become excessive, however, and other essential nutrient factors are present, eutrophication and associated algal blooms can be become a problem (Fundamentals of Aquatic Toxicology, 1985).

Nitrite, or NO2-, is extremely toxic to aquatic life, however, is usually present only in trace amounts in most natural freshwater systems because it is rapidly broken down to nitrate. In sewage treatment plants using nitrification processes to convert ammonia to nitrate, the process may be impeded, causing discharge of nitrite at elevated concentrations into receiving waters.

The conversion process is affected by several factors, including pH, temperature, dissolved oxygen, number of nitrifying bacteria and presence of inhibiting compounds. Total ammonia in wastewater treatment systems can impede the conversion of nitrite to nitrate, causing nitrite to accumulate.

Organic nitrogen and ammonia can be determined together and have been referred to as “Kjeldahl nitrogen, or TKN,” a term that reflects the technique used in their determination (19th Edition, Standard Methods, 1995).

Organic nitrogen is the byproduct of living organisms. It includes such natural materials as proteins and peptides, nucleic acids and urea, and numerous synthetic organic materials. Typical organic nitrogen concentrations vary from a few hundred micrograms per liter in some lakes to more than 20 mg/L in raw sewage (19th edition, Standard Methods, 1995).

Phosphorus is often the limiting nutrient for plant growth, meaning it is in short supply relative to nitrogen. Phosphorus usually occurs in nature as phosphate. Phosphate that is bound to plant or animal tissue is known as organic phosphate. Phosphate that is not associated with organic material is known as inorganic phosphate. Both forms are present in aquatic systems and may be either dissolved in water or suspended (attached to particles in the water column). Inorganic phosphate is often referred to as orthophosphate or reactive phosphorous. It is the form most readily available to plants, and thus may be the most useful indicator of immediate potential problems with excessive plant and algal growth.

Testing for total phosphorous (both inorganic and organic phosphate) provides you with a more complete measure of all the phosphorus that is actually in the water (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

pH is an important factor for aquatic life. If the water in a stream is too acidic or basic, it can disrupt aquatic organism’s biochemical reactions and either harm or kill the organisms.

pH measures the hydrogen (H+) ion concentration of a substance and is expressed on a scale ranging from 1 to 14. When the H+ concentration is equal to the hydroxide (OH-) concentration it is considered neutral. A solution with a pH less than 7 has more H+ activity than OH-, and is considered acidic. A solution with a pH value greater than 7 has more OH- activity than H+, and is considered basic. The pH scale is logarithmic, meaning that as you go up and down the scale, the values change in factors of 10. A one-point pH change indicates the strength of the acid or base has increased or decreased tenfold.

Streams generally have pH values ranging between 6 and 9, depending upon the presence of dissolved substances that come from bedrock, soils and other materials in the watershed.

Changes in pH can change the aspects of water chemistry. For example, as pH increases, smaller amounts of ammonia are needed to reach a level that is toxic to fish. As pH decreases, the concentration of bioavailable metals may increase because higher acidity increases their ability to be dissolved from sediments into the water (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Total solids is a measure of the suspended and dissolved solids in a body of water. Thus, it is related to both conductivity and turbidity. To measure total suspended and dissolved solids, a sample of water is placed in a drying oven to evaporate the water, leaving the solids. To measure dissolved solids, the sample is filtered before it is dried and weighed. To calculate the suspended solids, the weight of the dissolved solids is subtracted from the total solids (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Sulfates can be naturally occurring or due to human impacts. Naturally occurring sources include breakdown of plant material, groundwater passing through rocks or soil containing minerals, and atmospheric deposition. Human sources include mine drainage, fertilizer runoff, wastewater discharges, and industrial discharges from tanneries, pulp mills, and textile mills. Sulfates, in conjunction with chlorides and water hardness, can affect the solubility of metals and other substances in water.

Water temperature is a controlling factor for aquatic life. It controls the rate of metabolic activities, reproductive activities, and therefore, life cycles. If stream temperatures increase, decrease or fluctuate too widely, metabolic activities may speed up, slow down, malfunction or stop altogether.

There are many factors that can influence the water temperatures and they can fluctuate seasonally, daily and even hourly, especially in smaller-sized streams. Spring discharges and overhanging canopy of stream vegetation that provides shade help buffer the effects of temperature changes. Water temperature is also influenced by the quantity and velocity of stream flow. The sun has much less effect in warming the waters of streams with greater and swifter flows than of streams with smaller, slower flows.

Temperature also affects the concentration of dissolved oxygen in a water body. Oxygen is more easily dissolved in cold water. (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods).

Turbidity is a measure of the cloudiness of water. Cloudiness is caused by suspended solids (mainly soil particles) and plankton (microscopic plants and animals) that are suspended in the water column. Moderately low levels of turbidity may indicate a healthy, well-functioning ecosystem, with moderate amounts of plankton present to fuel the food chain.

However, higher levels of turbidity pose several problems for stream systems. Turbidity blocks out the light needed by submerged aquatic vegetation. It also can raise surface water temperatures above normal because suspended particles near the surface facilitate the absorption of heat from sunlight, resulting in lowered dissolved oxygen. Suspended soil particles may carry nutrients, pesticides and other pollutants throughout a stream system, and they can bury eggs and benthic organisms when they settle. (1991, Streamkeeper’s Field Guide: Watershed Inventory and Stream Monitoring Methods)