As you already know, many factors affect the chemical, physical and biological characteristics of a water body. Events that humans have no control over, such as the weather or the geology of the area, create some of these factors. Human activities are responsible for other factors. Other webpages (River Uses and Human Impacts On A Watershed) have discussed some of the impacts human activities have on aquatic ecosystems. This webpage discusses how people can determine the health of a water body and keep track of its improvement or degradation.
When we try to determine the health of a water body or its water quality, we evaluate the water bodies chemical, physical and biological characteristics. For example, a simple evaluation might consist of measuring the pH, temperature and aquatic insect members of a water body. Certain fluctuations in water quality characteristics are normal and dependent on seasons, time of day, or location of the testing site. Other fluctuations can be a result of human activities within a watershed that impact the chemistry, physical nature or biological inhabitants of the water.
The chemical, physical and biological health of waters are so important that they are protected by the Federal Water Pollution Control Act. This legislation's purpose is the restoration and maintenance of the integrity of the nation's waters. A classification system was developed to help with the implementation of this law. Each water body is assigned to an intended use. These class uses are sometimes simplified to Drinkable, Swimmable and Fishable. The class determines the water quality standard according to measurements of criteria such as dissolved oxygen, fecal coliform content, color and odor. A water body that serves as a source of drinking water would belong to a class that has much stricter water quality standards than one that is used for the irrigation of inedible crops. The water quality standards for drinking water are the same for all states and are administered by the Environmental Protection Agency (EPA). For the other classes, state standards must be equal to or more restrictive than federal standards. Acceptable standards and water quality testing procedures are usually determined by state agencies involved in public health or environmental protection.
Water quality monitoring happens when water quality surveys are performed on a regualar basis for a specific purpose on a particular body of water. Water quality monitoring involves recording data about these various characteristics and usually involves analyzing and interpreting these data. Monitoring helps ensure that a water body is suitable for its determined use. It can also be used for protective purposes to prevent degradation or to upgrade the class.
What kind of information do water quality monitors look for? There are many aspects of a water body that can be measured or observed and provide helpful information. Some of the measurements and observations are easy to make; others are much more complicated. In the discussion that follows we will emphasize measurements and observations that have fairly simple procedures and can be conducted either at the sampling site or in most post elementary school laboratories. This is not a comprehensive list of possible parameters - it is merely a sampling. See the references at the end of the page to learn the procedures for conducting these tests.
One of the simplest ways to learn more about a water body is to use the senses. Observing color, flow, streambank condition, wildlife evidence, types of vegetation, debris and signs of human activity provide information. What odors do you smell? - mustiness, gasoline, organics, chemicals, dead fish, rotten eggs? Can you hear flowing water, drain discharge, fish jumping, waterfowl or boats? Using the senses is not only a good way to gather information, but can also help decide what and where to monitor.
When monitors gather information in a systematic and formal way, they are doing watershed surveys. A watershed survey usually involves combining existing information about sources of pollution with observations of potential sources of pollution such as sewage treatment plants, landfills and residential areas. Usually monitors will use a map to help guide the survey.
Water temperatue is a characteristic that can vary widely and is influenced by a number of variables including geographic location, shading, water source, thermal discharges, water body size and depth. Temperature has a great influence in determining what organisms can survive in a water body. Temperature directly affects the amunt of oxygen that can be dissolved in water; the rate of photosynthesis by algae and larger aquatic plants; the metabolic rates of aquatic organisms; and the sensitivity of organisms to toxic wastes, parasites and diseases. Salmon and trout and the prey they depend upon survive best in cool, oxygen-rich waters.
Human activities influence water temperature. The webpage Human Impacts On A Watershed discusses the effects of thermal pollution and streamside clearing, both of which can create changes in water temperature. Soil erosion raises water temperature by increasing the amount of suspended solids in the water. Suspended solids make water cloudy. Cloudy water absorbs more radiation (and warmth) from the sun than clear water does.
The flow rate of moving water is influenced by topography, rainfall, structures and aquatic vegetation. Typically, fast moving water is well oxygenated. Slow flows allow pollutants to collect and oxygen to be depleted. Inconsistent flows can disrupt invertebrate and fish nesting areas.
When substances such as silt, microorganisms, plant fibers, sawdust, wood ashes, chemicals, coal dust and plankton are suspended in water, they make it cloudy. Transparency is a measure of how cloudy water is. Plankton and soil erosion are the most common sources of low transparency.
The decreased transparency of turbid waters can have both positive and negative consequences for aquatic life. It depends on the source and degree of suspended particles. For example, plankton, a valuable food sources for fish, causes decreased transparency. It may be easier for some fish to hide themselves from predators in turbid waters. Very low transparency, on the other hand, can be detrimental to aquatic llife in a number of ways.
Water contains both hydrogen (H+) and hydroxyl (OH-) ions. The pH reading of a solution is an expression of the concentration of hydrogen (H+) ions. It is used to describe the acidity of a solution. The pH scale ranges from 1 (very acidic) to 14 (very basic).
Pure deionized water is considered neutral. It has an equal concentration of hydrogen and hydroxyl ions and has a pH of 7. If a sample has a pH less than 7 it is considered acidic. If it has a pH greater than 7 it is considered basic or alkaline. pH is logarithlmic, so that a single unit change in pH reflects a 10 fold change in hydrogen ion concentration or acidity. The pH of a water body is affectd by its age, geology and the chemicals discharged into it by communities and industries.
Human activities also affect the pH of water bodies in other ways. Acid precipitation is the result of nitrogen oxide gases and sulfur dioxide combining with water in the atmosphere to produce nitric and sulfuric acids. These gases are produced and released into the atmosphere during the burning of fossil fuels such as gas, oil and coal. Driving a car, heating a home, producing coal-fired electricity and manufacturing products involve the burning of fossil fuels and contribute to the production of acid rain. Acid precipitation falls into water bodies and makes some of them acidic. Runoff from acidic soils also contributes to acid waters. Water bdies that have limestone geology are less susceptible because the alkaline carbonates of limestone help neutralize the effects of acid precipitation.
Most aquatic organisms survive best within a limited pH range. Even small changes in pH are harmful to pH sensitive species. Most fish can tolerate pH values of about 5.0 to 9.0. pH values outside that range can create problems for reproduction and survival. Amphibians are particularly susceptible to acid waters. Acid waters in conjunction with some metals such as aluminum, lead and copper create an even more toxic environment than either of the substances alone.
Acid precipitation can also corrode structues by slowly eating away at the exposed stone, metal and paints. Unpolluted rain has a pH of around 5.6 (slightly acid). The average rain and snowfall in most states eat of the Mississippi River measures between 4 and 5 on the pH scale. Some individual storms go as low as 3.0. Although there are ways to reduce the amount of harmful gases entering the atmosphere, there are no easy solutions to the problem of acid precipitation.
Alkalinity refers to the ability of a solution to resist changes in pH. Alkalinity buffers waters against dramatic changes in pH. Adding a weak acid or base to a buffered solution will cause only slight changes in the pH; however, adding the same weak acid or base to an unbuffered solution can cause dramatic changes in pH. The main sources of natural alkalinity are rocks which contain carbonate, bicarbonate and hydroxide compounds. Borates, slilcates and phosphates also may contribute to alkalinity. Waters flowing through limestone typically have good buffering capacity. Waters flowing through granite areas, like most of New England, typically have low alkalinity and poor buffering capacity.
Alkalinity helps fish and aquatic life because it protects against pH changes and makes water less vulnerable to acid rain. When alkalinity falls below 2 mg/l the pH of waters can change easily. During the spring alkalinity is especially important for protecting aquatic organisms in their early life stages from large amounts of acidic snowmelt and runoff.
Aquatic organisms cannot survive without oxygen. Only oxygen-rich waters can support a broad variety of aquatic organisms. Remember, a wide variety of organisms (biodiversity) helps preserve stability in an ecolgical system. Waters with low amounts of dissolved oxygen can support only limited amounts and types of aquatic organisms. The best trout and salmon streams are cool and well oxygenated. Catfish and carp dominated aquatic systems are typical of waters with low levels of oxygen.
Dissolved oxygen comes from a variety of sources. The action of waves and water tumbling over rocks helps mix oxygen in the atmosphere with moving water. Plants also release oxygen into the water as a byproduct of photosynthesis during daylight hours, but plants and animals also use oxygen during respiration and produce carbon dioxide. Both oxygen and carbon dioxide are more soluble in water at low temperatures than at high ones. Large amounts of carbon dioxide are a sign of accumulating organic material and a low dissolved oxygen. Human activities have great potential to influence dissolved oxygen levels because they are so closely linked to temperature and nutrient levels. Increased nutrients (like phosphorus and nitrogen) stimulate algal growth. eventually the algae die and accumulate. Animal waste, sewage, food and paper industry discharges, agricultural and urban runoff, in addition to the dead algae, create a large amount of organic material. Bacteria and fungi use oxygen to break down this organic material and cause the biochemical oxygen demand within the sytstem to incease. Biochemical oxygen demand refers to the amount of oxygen required by microorganisms to oxidize an amount of organic materials. A high demand lowers the availabilty of dissolved oxygen in the water.
When oxygen is consumed by aerobic bacteria, there is less available for other aquatic organisms. Only organisms, such as carp, midge flies and leeches, that are tolerant of low dissolved oxygen levels will survive. This reduces the diversity within the system, creating a system that is less stable ecologically.
Cool trout and salmon waters generally contain oxygen concentrations above 5 mg/l (=ppm). Waters which are at least 90% saturated with dissolved oxygen are considered healthty (unless they are superasaturated due to cultural eutrophication). Waters with less than 90% saturation may have large amounts of eoxygen demanding materials.
Phosphorus is sometimes called a limiting factor for aquatic plant life because the amount of phosphorus has great influence over plant growth. Phosphorus exists in aquatic ecosystems in several forms. Phosphorus is part of plant and animal tissue. Phosphorus also exists dissolved in water. It can also attach to tiny particles of silt and sediment. Plants take up free phosphorus from the soil and water. Animals get it from eating plants.
Phosphous can enter water bodies in many different ways. Because phosphorus is part of plant and animal tissue, phosphorus is released into the water when aquatic plants and animals die and decompose. Phosphorus from animal and human waste also enters water bodies with agricultural and residential runoff. Inadequately treated sewage from wastewater treatment plants and septic tanks contains phosphorus. Because it is part of many soils, phosphorus washes with rain and snow into water bodies when the soil surface is disturbed, such as when the vegetation is removed during farming or construction. Many fertilizers used on agricultural lands and on lawns contain phosphorus. Any phosphorus that is not taken up by the plants in the fields or lawns can wash into water bodies along with surface runoff. Remember that wetlands serve to hold nutrients. When wetlands are destroyed and organic rich soils are disturbed, nutrients that have accumulated over years are released. Industries release phosphous from cleaning compounds and other wastes. Phosphorus also comes from phosphorus rich rocks.
In some systems phosphorus can become a problem because it causes an overabundance of plant material that creates a disruption in the overall system. Algae in aquatic systems require phosphorus. Algal blooms are typical of waters with excess nutrients. Algal blooms cause water to become green and thick with algae. Algal blooms are often a sign of cultural eutrophication. Natural eutrophication is the natural aging process of water bodies. Over thousands of years, open water bodies gradually collect phosphorus, sediment, algae, protozoans, rooted aquatic vegetation and other forms of life. As the algae flourish more and more, bacterial levels increase, oxygen levels drop, fish die and the basin begins to fill with plants. Eventually the pond becomes more like a swamp. After more time the swamp fills in and becomes a forest. Cultural eutrophication occurs when human generated wastes which include excess phosphorus speed up the aging process by accelerating algal blooms, depleting oxygen, etc. A limited diversity of organisms can survive the low oxygen levels of eutrophic ponds and lakes. Only the most tolerant organisms can then live and reproduce.
Water contains microbes, tiny organisms such as bacteria, algae and protozoans, that are too small to see without a microscope. Pathogenic microbes, such as some bacteria, viruses and parasites, in drinking water can cause diseases in humans. In order for waters to be safe for drinking and swimming, they must be checked for the presence of harmful microbes. These pathogens are difficult to detect in water because there aren't many of them, they are difficult to grow and they can't survive very long outside a human or animal body. Water quality monitors looking for harmful microbes check for total coliform or fecal coliform bacteria.
Some types of coliform bacteria naturally coexist with pathogens inside the intestines of both warm and cold blooded animals. These bacteria are beneficial in the intestines of humans and other animals and aid in digestion. The term total coliform bacteria includes all coliform bacteria that come from the gut of vertebrates as well as from soil dwelling bacteria. Fecal coliform bacteria are only present in the intestines of warm blooded animals. E. coli is a type of fecal coliform that is commonly monitored by state health labs. Fecal coliform bacteria can create intestinal problems. However, they are not, themselves, usually considered pathogenic. Their importance is that their presence indicates that excrement from humans or other warm blooded animals has contaminated a water source. Unprocessed toilet wastes, farm animal wastes and pet waste that make it into a water supply or swimming area can contaminate that water body. Untreated overflow from wastewater treatment plants or sewer systems can discharge contaminated wastewater into a lake, river or estuary. Faulty septic tanks also allow harmful bacteria to pass untreated into another water body. Diseases such as hepatitis, dysentery, typhoid fever and ear infections can be contracted in water with high fecal coliform counts.
Bioindicators are organisms whose presence, absence or condition provides information about environmental quality. Every organism has particular environmental requirements for it to be healty and reproduce successfully. The presence or absence of healthy populations of organisms within their habitats is a sign of particular environmental characteristics. The advantage of using bioindicators over chemical and physical tests to evaluate water quality is that the presence of living organisms inherently provides information about water quality over time. Chemical and physical tests give information that is accurate only at that moment the sample is taken. The presence of a mixed population of healthy aquatic insects, mussels or fish usually indicates that the water quality has been good for some time. The absence of bioindicators at a site that appears good according to chemical and physical sampling might prompt further investigation for toxics or periodic insults to water quality. Imagine that pulses of toxics enter a particular stream or river only for short periods of time. When the chemical tests are taken downstream they might be taken at the wrong time and miss the toxics. The lack or poor conditions of bioindicators might provide a clue that someting like this was happening.
In streams and rivers, water quality monitors often look for benthic macroinvertebrates to get an idea of water qualtity. Benthic macroinvertebraes include aquatic insects, worms, shellfish, crustaceans and other animals without backbones that are large enough to see without a microscope and live at the bottom of a water body. Many species of mayfly nymphs, casddisfly larvae, water pennies and stonefly larvae, for example, can survive only in swift, cool, well oxygenated water. Their presence at a sampling site is generally a sign of good water quality. Black fly larvae, midges, leeches and aquatic worms on the other hand, are quite tolerant of pollution. They can be found in waters of both good and poor quality. If they are the only types of macroinvertebrates found at a site, chances are the site is silty and has low dissoved oxygen. Such conditions might represent a polluted first order stream or a downsteam site near the mouth of a river.
Aside from using the presence or absence of certain indicator species to determine water quality, both the number of different species and the EPT richness can provide even more information. The three most polllution intolerant orders of aquatic insects are the Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies). The first letter of each order gives the index its name - EPT. The higher the percentage of these pollution intolerant species in relation to the percentage of tolerant species at a site, the better the water quality.
The health of resident fish species will be indicative of overall water quality. Condition is determined by comparing the length of the fish to its weight. The heavier the fish for its length, the better the condition. Fisheries biologists also look at scales under a microscope to learn about age and growth history of a fish.
Freshwater mussels, like aquatic insects, serve as bioindicators. Each species of mussel has different environmental requirements. Some species like Elliptio complanata, the Eastern Elliptio Mussel, are more pollution tolerant than species like Margaretifera margaretifera, the Pearlshell Mussel. Freshwater mussels are filter feeders who use an incurrent siphon to pump water into their shell where they use gills to simultaneously retrieve oxygen and extract food from the flowing water. Because they move so slowly, mussels must be able to obtain their food and oxygen from one spot. If their habitat becomes inundated with polllution such as toxics or silt, some of them will most likely perish.
Perhaps the most interesting aspect of freshwater mussel natural history is reproduction. Larval mussels, called glochidia attach to the gills or scales of fish. The glochida develop for a while attached to the fish and eventualy drop back to the bottom. The glochidia do not seem to harm the fish. Scientists think that the mussel glochidia will only survive attached, in some cases, to particular species of host fish. For example, the Pearlshell Mussel mentioned above usually uses salmon and trout as a host. If obstacles such as dams, poor water quality, or overfishing interfere with the survival of the fish, they are likely also interfering with the survival of the mussels. Because freshwater mussels can live for decades, their presence or absence can provide even more information about the history of water quality at a site. Their longevity may be how they continue to survive with such a risky reproductive strategy.