For fish, no single environmental factor affects their development and growth more than water temperature. Many biological processes such as spawning and egg hatching are geared to annual temperature changes.
Warm water holds less oxygen than cool water, so it may be saturated with oxygen but still not contain enough for survival of aquatic life. For example, salmon eggs are large and need more oxygen than other fish eggs. That is why salmon lay eggs in cool flowing streams. Some chemical compounds are also more toxic to aquatic life at higher temperatures.
| Hatching salmonids: | approximately 9 degrees centigrade |
| Adult salmon: | approximately 12 degrees centigrade |
| Sucessful salmonid spawning has occurred in waters between 2 to 21 degrees centigrade. However, for a stream or river to be rated Class A, temperatures should not exceed 18 degrees centigrade. Temperatures which exceed 21 degrees are not acceptable. | |
Reasons for Natural Variation
Like terrestrial animals, fish and other aquatic organisms need oxygen to live. Oxygen can be present in the water, but at too low a concentration to sustain aquatic life. Dissolved oxygen (DO) is a critical water quality parameter indicating the health of an aquatic system. DO is the measurement of oxygen dissolved in water and available for fish and other aquatic life.
| Optimal | Acceptable | Poor |
|---|---|---|
| 9 mg/l | 7-8 mg/l | 3.5-6 mg/l |
| Levels below 3.5 mg/l are likely fatal to salmonids. | Generally, a DO level of under 5 mg/l is stressful to most vertebrates and cause mortality to some invertebrates. | |
Reasons for Natural Variation
Oxygen is produced during photosynthesis of plants and consumed during respiration and decomposition. Because it requires light, photosynthesis occurs only during daylight hours. Respiration and decomposition, on the other hand, occur 24 hours a day. This difference alone can account for large daily variations in DO concentrations. DO concentrations steadily decline during the night and are the lowest just before dawn, when photosynthesis resumes. Always measure DO at the same time of day. Other sources of oxygen include the air and inflowing water sources. More oxygen dissolves into water when wind stirs the water. Rivers and streams deliver oxygen, especially if they are turbulent. Turbulence mixes water and air (aeration).
Another physical process that affects DO concentrations is the relationship between water temperature and gas saturation. Cold water can hold more gas - that is DO - than warmer water. Warmer water becomes "saturated" more easily with oxygen.
Seasonal changes also affect dissolved oxygen concentrations. Warmer temperatures during summer speed up the rates of photosynthesis and decomposition. When all the plants die at the end of the growing season, their decomposition results in heavy oxygen consumption. The DO of an estuary is always changing and relates to water temperature, salinity, sample depth, weather, tide and season.
| Temperature degrees C | Oxygen Solubility (mg/L) |
|---|---|
| O | 14.6 |
| 5 | 12.8 |
| 10 | 11.3 |
| 15 | 10.2 |
| 20 | 9.2 |
From this you can see: the colder the water temperature, the greater the level of dissolved oxygen and why it is important to take the temperature and DO measurements at the same time.
Expected Impact of Pollution
To the degree that pollution contributes oxygen-demanding organic matter (like sewage or lawn clippings) or nutrients that stimulate growth of organic matter, pollution causes a decrease in average DO concentrations.
Why is it important?
The pH of water determines the solubility and biological availability of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.). For example, in addition to affecting how much and what form of phosphorus is most abundant in the water, pH also determines whether aquatic life can use it. Metals tend to be more toxic at lower pH, because they are more soluble.
Expected Impact of Pollution
pH
Acid conditions caused by acid rain are highly detrimental to aquatic macroinvertebrates and fish. If pH declines below 6.5, few salmon eggs hatch and aquatic insect levels drop. pH levels should not vary from natural conditions more than .2 due to human activities.
| When pollution results in higher productivity, for example, from increased temperature or excess nutrients, pH levels increase. Although these small changes in pH are not likely to have a direct impact on aquatic life, they greatly influence the availability and solubility of all chemical forms and may aggravate nutrient problems. | Acid Rain Lakes that have received too much rain with a low pH (acid rain), lose their buffering capacity. Acid rain is not considered to be a significant problem in the Puget Sound lowlands. |
Generally, during the summer months in the upper portion of a productive or eutrophic lake, pH will range between 7.5 and 8.5. In the bottom of the lake or in less productive (oligotrophic) lakes, pH will be lower, 6.5 to 7.5 perhaps. This is a very general statement to provide an example of the differences you might measure.
Why are they important?
Nutrient Concentrations
| Nutrients in water serve the same basic functions as nutrients in a garden. They are essential for growth. In a garden, growth and productivity are considered beneficial, but this is not necessarily so in water. The additional algae and other plant growth encouraged by the nutrients may be beneficial up to a point, but may easily become a nuisance. The main nutrients of concern are phosphorus and nitrogen. |
Phosphates and nitrates are associated with many nonpoint pollution sources, such as livestock manure and urine, failing septic systems and synthetic fertilizers. (Synthetic fertilizers release their nutrients more rapidly than the slower-acting organic ones like compost and composted manure.) Excessive nutrient loads can artifically stimulate plant growth resulting in algal blooms which speed up the aging process of aquatic systems.
Reasons for Natural Variation.
The total input of nutrients varies through time, depending upon land use and other factors. During the winter, high rainfall causes increased runoff of organic matter such as leaves, twigs, grass and other debris. Because decomposition of this organic matter releases nutrients, it constitutes an important and beneficial source of nutrient loading.
Nutrient concentrations also may vary with the depth of the water. For example, near the top, algae growth may cause higher nutrient concentrations. As you move deeper in the water there is less algae and less nutrients. Near the bottom of a lake or deep stream, available nutrient concentrations may be higher because that is where many of the materials end up.
Clear water lets light penetrate more deeply in a body of water than does murky water. The light allows photosynthesis to occur and oxygen to be produced.
Clarity is affected by algae, soil particles, and other materials suspended in the water. The clarity of lakes, estuaries and slow, deep rivers is measure with a Secchi disk.
Reasons for Natural Variation
Generally, water will be at its clearest during cool weather and at its murkiest with warm temperatures and increased algae growth.
Rainstorms also may affect clarity. Erosion from rainfall, runoff, and high stream velocities may result in higher concentrations of suspended particles in inflowing streams and therefore decrease clarity.
Expected Impact of Pollution
Pollution tends to reduce water clarity. Watershed development and poor land use practices cause increases in erosion, organic matter, and nutrients, all of which cause increases in suspended particulates and algae growth.
In general, we expect an increase in pollution along the course of a river, from its headwaters to its mouth. (See summary chart to follow the downstream trends.) chart.Why is measuring turbidity important?
Turbidity is the measurement of the light scatttering properties of water. Suspended solids (including total dissolved solids) in water can reduce the transmission of light either through absorption or scattering. High turbidity can have a strong negative effect
Reasons for Natural Variation
Rivers naturally carry large amounts of silt, clay and detritus from their watersheds. Moving water carries more suspended solids than still water. Waves and tides can cause turbidity.
Optimal Levels
Total solids are the sum of the dissolved solids (from soluble rocks and soil) and the suspended solids (silts, clays, plankton, etc.) contained in a water sample. Human activities can increase these levels. In the Nisqually River, glacial activity brought on by warm weather can greatly increase total solids loads. Rapid changes in total solids levels are stressful to fish.
Optimal Levels
Why is it important?
Total suspended solids (TSS) concentrations and turbidity both indicate the amount of solids suspended in the water, whether mineral (e.g., soil particles) or organic (e.g., algae). However, the TSS test measures an actual weight of material per volume of water, while turbidity measures the amount of light scattered from a water sample (more suspended particles cause greater scattering).
Reasons for Natural Variation
TSS and turbidity values vary for two main reasons - one physical, the other biological. Heavy rains and fast-moving water are erosive. They can carry enough dirt and debris to make even an unpolluted inflowing stream look muddy.
Phytoplankton may also increase turbidity in slow moving rivers and streams.
In lakes, the most important reason for variation in these parameters is caused by seasonal changes in algae growth. Warm temperatures, prolonged daylight, and release of nutrients from decomposition may cause algae blooms that increase turbidity or TSS concentrations.
Why is it Important?
Fecal coliform bacteria are microscopic animals that live in the intestines of warm-blooded animals. They also live in the waste material or feces excreted from the intestinal tract. When fecal coliform bacteria are present in high numbers in a water sample, it means that the water may have received fecal matter from one source or another. Although not necessarily agents of disease, fecal coliform bacteria indicate the potential presence of disease-carrying organisms. Fecal coliform is measured in colonies per 100 ml.
Reasons for Natural Variation
Unlike the other conventional water quality parameters, fecal coliform bacteria are living organisms. They multiply quickly when conditions are favorable for growth and die in large numbers when they are not. For example, although winter rains may wash more fecal matter from urban areas into a lake, cool water temperatures may cause many of the organisms to die. Direct exposure to sunlight is also lethal to bacteria, so die off may be high even in the warmer water of summertime.
Expected Impact of Pollution
A water system heavily polluted by nutrients may have very low concentrations of fecal coliform bacteria. Possible sources of fecal coliform may be cow manure used as agricultural land fertilizers, pet waste, failing septic systems, or leaking sewer lines. Storm water runoff in urbanized areas has been found to be surprisingly high in fecal coliform bacteria concentrations.
Optimal Levels and Water Quality Standards
Human Sanitation Levels
Biochemical oxygen demand is a measure of how much oxygen is consumed by the decomposition of organic materials (algae and other dead aquatic plants). Large volumes of decomposed organic materials can cause a biochemical oxygen demand which lowers dissolved oxygen to levels dangerous for fish. Massive fish kills (death by suffication) result.
Optimal Levels
Why is it important?
Chlorophyll is the green pigment in plants that allows them to create energy from light - to photosynthesize. By measuring chlorophyll, you are indirectly measuring the amount of photosynthesizing plants found in a sample. Chlorophyll is a measure of all green pigments whether they are active (alive) or inactive (dead). Chlorophyll a is a measure of the portion of the pigment that is still active; that is, the portion that was still actively respiring and photosynthesizing at the time of sampling.
Reasons for Natural Variation
Sunlight, temperature, nutrients, and wind all affect algae numbers and therefore chlorophyll concentration. During the spring when water begins to warm, the days are sunnier, and nutrients are still plentiful, the first outbreak or "bloom" of algae may occur. As the days become warmer and sunnier, algae will continue to grow. The total amount of algae growth may be limited by the available supply of nutrients.
Wind also can impact algae populations. A good strong wind may mix the water in a lake or river, causing an immediate decrease in algae concentrations as they become mixed throughout the water column. On the other hand, the wind also may cause a release of nutrients into the water system by stirring up nutrient-laden bottom sediments. Then, after the wind dies down, the number of algae and the chlorophyll concentration may increase.
As summer turns to fall and temperature and sunlight decrease, algae concentrations will decrease as well. Often, in deeper lakes where temperature stratification has occurred, there will be a fall algae bloom when the layers of water mix again and nutrients are released to the entire water columnf
Algae populations, and therefore chlorophyll concentrations, vary greatly with water depth. Algae must stay within the top portion where there is sunlight to be able to photosynthesize and stay alive. As they sink below the sunlit portion, they die. The increase in nutrients caused by pollution usually results in more algae.