Water Quality Monitoring Data Parameters
What do water quality monitoring parameters mean? Testing of physical parameters, including temperature, dissolved oxygen, pH and conductivity is performed to see if any changes have occurred over time. These parameters can be measured to find out the quality of the water in a particular waterbody.
The acidity or alkalinity of water is expressed by a measurement called pH. The pH scale ranges from 0-14. A pH of 7 is neutral, with levels below 7 indicating acidity, and levels above 7 indicating alkalinity. When pH is outside the range of 5.5 to 8.5, most aquatic organisms become stressed and populations of some species can become depressed or disappear entirely. Rapid pH fluctuations can also stress aquatic organisms. Acidity can aggravate toxic contamination problems. The pH of the waters we tested ranged from 6.76 to 9.4, with an average of 7.97. This indicates moderately high alkalinity from the limestone-rich geology of the area, and provides a natural protection against acid precipitation.
Dissolved Oxygen and Temperature
Dissolved oxygen (D.O.) is necessary for most aquatic life. Oxygen dissolves into water from atmospheric exchange (especially wave turbulence) and through the photosynthesis of aquatic plants and algae. However, there is a maximum limit to the amount of D.O. the water can hold, called a saturation limit. Cold water can hold more D.O. than warm water. The closer the D.O. is to saturation at a particular temperature, the better the water quality.
Because the density of water varies with temperature, relatively deep lakes can vertically stratify into zones with different temperatures. In stratified lakes, the surface waters may be much warmer than bottom waters in the summer. Vertical mixing does not occur between zones. In winter, surface water is slightly colder than bottom water.
Oxygen content can also vary within a lake, depending on depth and season. In stratified lakes during summer, oxygen in water near the bottom often drops to low levels or disappears entirely in all but lakes of the highest quality. Fish and other organisms can recover from short exposure to low D.O., but prolonged exposure to levels less than 2 milligrams per liter (mg/l, the same as parts per million) can permanently harm or kill fish. Generally, warm water fish need at least 5 mg/l of D.O., and cold water fish need at least 7 mg/l for good growth and survival. Larval and juvenile fish are more sensitive, and need even higher D.O. levels than adult fish. Excessive nutrients and the respiration and decay of the plant life they stimulate, as well as some other types of pollution, can consume oxygen faster than it is produced, robbing the water of dissolved oxygen.
We conduct comprehensive monitoring in the spring because lakes are unstratified and well mixed from top to bottom by wind-generated currents. As a result, water quality components such as nitrogen and phosphorous are easiest to sample and analyze. We record temperature readings simply to ensure that a lake is not stratified, and to allow us to determine percent saturation of oxygen. Except for a few instances just above the bottom, D.O. was close to saturation in all lakes and streams. The Watershed Council occasionally measures late summer or late winter D.O. in selected lakes to determine the maximum extent of oxygen depletion.
Water Clarity, Color, and Chlorophyll-A
The more algae or sediment in water, the less clear it is. Clarity is also described by terms like turbid, cloudy, or muddy. Generally, the clearer the water, the fewer the nutrients and the better the water quality. Waters which are not clear may be less productive, because sunlight cannot penetrate deeply. Muddy waters also clog fish gills, smother spawning beds, inhibit the sight and feeding of many fishes, and can reduce angling success. The clarity of water is a simple and valuable way to assess water quality. We measure water clarity using a Secchi Disc, a weighted disc eight inches in diameter painted black and white in alternating quarters.
Water clarity is often highest in winter and early spring, when cold temperatures inhibit algae growth. However, "algae blooms" also occur in most lakes at some time during spring. As a result, clarity varies greatly, from several feet in small inland lakes, to about 50 feet in large inland lakes and bays of the Great Lakes. Secchi Disc readings are also collected weekly throughout the summer in lakes participating in the VLM program.
Chlorphyll-a is a pigment found in all green plants, including algae. Measuring the amount of chlorophyll-a in water provides a measure of the amount of phytoplankton, which is directly related to the nutrient level. Phytoplankton is extracted from the water with a filter device, and the filter membranes are analyzed in a laboratory to determine the amount of chlorophyll-a.
Algae, sediments, and other suspended or dissolved materials in the water can impart color as well as turbidity. Algae can impart a green or yellowish color to the water. Slight brownish or tea-colored staining can be caused by organic compounds in wetlands. Slight staining is often evident when a stream discharges into clear, unstained lake waters. This staining is not harmful, and should not be confused with sediment pollution. Many waters in Northern Michigan experience a phenomena called marl turbidity (caused by a chemical precipitate of tiny calcium carbonate particles), which imparts a milky-green color to the water. Very clear, deep waters are generally some shade of blue because that wavelength of visible light is absorbed least by water, and some of the blue light entering the water is reflected back up to the surface (sort of the same reason the sky looks blue). Suspended sediment (soil particles) cause waters to be slightly milky brown to dark chocolate brown, depending on the amount.
The ability of water to conduct electricity is termed conductivity. Charged particles called ions, such as chloride (Cl?) or calcium (Ca+), that become dissolved in water supply the means for water to conduct electricity. Rain water has very low conductivity (near 0 microsiemens/cm) while sea water has very high conductivity (~50,000 µS/cm). As conductivity measures the dissolved ionic content of water it is also commonly used as a measure of total dissolved solids. Because our lakes and streams contain a lot of soluble minerals (called hardness) and high alkalinity (from carbonate ions), the conductivity is fairly high. Readings ranged from 176 to 656 µS/cm, with an average of 286. Lakes with conductivity greater than 400 µS/cm include: Spring, St. Clair, Ellsworth and Wilson. Conductivity is an easy and accurate way to measure the level of dissolved substances, but cannot indicate what the substances are. A steady increase of conductivity over a period of years is usually indicative of pollution occurring.
Chloride, a component of salt, is one of the common anions found in freshwater and thus chloride levels are directly related to conductivity. Due to the marine origin of bedrock in Northern Michigan, chloride is present in the ground water, usually in concentrations less than 12 mg/l. Surface waters seem to have a normal level of 4 mg/l. Even slight increases in chloride concentration can have a subtle impact on aquatic ecosystems, but most fish and other large aquatic organisms are not directly affected until concentrations reach 1,000 mg/l or more.
Chlorides are common in many products associated with human activities. Chloride is a "mobile ion," meaning it is not removed by chemical or biological processes in the soil and ground water. Increasing chloride levels or levels above expected natural background amounts can indicate impacts from human activities. Chloride levels in our lakes and streams have ranged from 1.0 mg/l to 82.9 mg/l with an average of 7.7 mg/l. Lakes with levels exceeding 20 mg/l include: Spring, Round (Emmet County), Bass, and St. Clair.
Nitrogen and Phosphorus
Elements required for the growth of plants are called nutrients. Nitrogen, phosphorus, and carbon are the three most important nutrients for aquatic plants. Because all the large lakes and streams in our service area have high levels of carbonate, carbon is not a nutrient of concern and was not part of the comprehensive monitoring.
Nitrogen and phosphorus occur in many chemical forms. Only the inorganic forms are generally useable by algae and rooted aquatic plants for growth. The organic forms are those that are, or have recently been, incorporated into the bodies of living organisms. Because these nutrients can undergo complex reactions and change form quickly, testing the total amount of all forms is considered the most reliable way to evaluate nutrient status of a lake or stream.
Nitrogen is a major component of all plant and animal matter and a very abundant element throughout the earth's surface. Some plants, including blue-green algae, have the ability to "fix" nitrogen directly from the atmosphere. As a result, nitrogen levels are highly variable in lakes and streams. In the first two field seasons we tested for the nitrate and ammonia forms of nitrogen. Although these are the most common forms of nitrogen and the most useable by aquatic plants, significant amounts of nitrogen can be present in other forms. In 1995 we began determining the total amount of nitrogen in the water, allowing us to better compare nitrogen levels from year to year and to calculate the ratio of nitrogen to phosphorus.
Phosphorus is the most important nutrient for productivity in surface waters because it is usually in shortest supply relative to nitrogen and carbon. A water body is considered phosphorous limited if the ratio of nitrogen to phosphorous is greater than 15:1. Phosphorus is normally found at concentrations less than 10 micrograms per liter (ug/l = parts per billion) in high quality surface waters.
Unfortunately, nitrogen and phosphorus are released into the environment as a result of many human activities. For instance, septic tank effluent contains about 15,000 and 50,000 ug/l of phosphorus and nitrogen respectively. Nutrient pollution is the most serious threat to the water quality of northern Michigan's lakes and streams. Since the inception of the monitoring program in 1987 total nitrogen in our lakes and streams has ranged from 0.125 to 1.9 mg/l (parts per million) and total phosphorus from 1 to 42.8 ug/l (parts per billion).