What We're Measuring and Why
The five-year trends analysis of the Clark Fork–Pend Oreille Watershed water quality monitoring program mentions several physical and chemical water quality measurements. You may be wondering why these measurements are important and what they tell us about water quality and the health of the watershed. Below are brief explanations that may help answer some of these questions. For general watershed definitions and terms go to the Glossary. If you would like more detailed information, please contact us.
TERMS
- Algae
- Ash-Free Dry Weight (AFDW)
- Chlorophyll-a
- Conductivity
and Total Dissolved
Solids
- Copper
- Nonpoint Sources
- Periphyton
- pH
- Point Sources
- Secchi
disk
- Soluble Reactive Phosphate
- Total
Nitrogen
- Superfund
- Temperature
- Total
Soluble Inorganic
Nitrogen
- Total
Phosphorus
- Total
Recoverable
Metals
- Turbidity
- Zinc
TERMS
Total Nitrogen (TN) - Nitrogen is plentiful in the natural environment and almost 80 percent of the earth's atmosphere consists of nitrogen gas (N2). However, plants and animals usually need nitrogen in other chemical forms before they can use it. Just as water has a cycle and takes on different forms (evaporation from the ocean, condensation into clouds, precipitation as rain or snow, and is then carried back to the ocean again by rivers and streams), nitrogen also has a cycle and changes forms. Total Nitrogen is a measurement of all forms of nitrogen in a water sample. It is important for scientists to know how much Total Nitrogen is in the water and to see whether or not the levels and forms of nitrogen are changing over time. Too much nitrogen in the water can lead to excessive plant growth and nitrogen in certain forms can be harmful or even toxic to aquatic life.
Total Soluble Inorganic Nitrogen (TSIN) - As mentioned above, nitrogen comes in many different forms and this is one type. Although scary to look at, this term should be somewhat familiar, as it is Total Nitrogen (explained above) with two words added: soluble and inorganic. Soluble simply means capable of being dissolved (in water for example), and inorganic is generally thought of as being compounds composed of elements other than carbon. So then, Total Soluble Inorganic Nitrogen is a measurement of all forms of nitrogen that are capable of being dissolved and do not contain carbon. Why do we care? These forms of nitrogen are particularly easy for aquatic plants to use. Monitoring their levels is important in understanding how plant and algae growth may be affected by these forms of nitrogen in the water.
Total Phosphorus (TP) - Like nitrogen, phosphorus can take on many forms and is constantly changing. Unlike nitrogen, phosphorus is much more limited in the water under normal conditions. Total phosphorus is a measurement of all forms of phosphorous in a water sample. Too much phosphorus in the water can lead to excessive plant growth and potentially toxic conditions for aquatic life.
Soluble Reactive Phosphate - When measuring water samples for total phosphorus, it is not known how much of the total phosphorus is in a form available to plants. In order to find this out, scientists have water samples analyzed for Soluble Reactive Phosphate which are the forms of phosphorus most available to plants in the water. Why do we care? These forms of phosphorus are likely to be the biggest contributors to excessive plant growth and provide scientists with yet another piece of the water quality puzzle.
Algae (Periphyton) - Periphyton is a complex combination of algae and microbes attached to underwater surfaces in almost all aquatic ecosystems. It serves as an important food source for aquatic bugs, some fish, and it can absorb contaminants. Periphyton is also an important indicator of water quality and can be measured to help monitor changes over time.
Ash-Free Dry Weight (AFDW) - Another common assay in stream ecology is that of AFDW, which determines the total amount of carbon containing material present in a sample. All living things and many of their wastes contain carbon, so knowledge of sample carbon content is useful because it gives an estimate of the total biological activity in the stream ecosystem. AFDW samples are placed in a 60oC drying oven for a minimum of 48 hours in order to remove all the excess water. Next, the samples are weighed and put in the 550oC muffle furnace for four hours. The intense heat of the muffle furnace completely vaporizes all organic carbon containing compounds in the samples-- hence the term 'ash-free'. Next the samples are allowed to cool. Then they are re-wetted, and placed back in the drying oven for another 48 hours. The final step in the process is to reweigh the samples to determine their final weight, and the difference between the initial and final weights represents the total weight of the organic matter contained in the sample.
Algae (Chlorophyll-a) - Chorophyll-a is a specific pigment that occurs in plant cells and is used to measure the amount (sometimes referred to as the biomass) of algae in water samples. The AFDW test and the chlorophyll-a test are often run in tandem with one another. The chlorophyll-a test measures only living phytoplankton, while the AFDW measures all organic matter. When quantities of these very tiny algae become so numerous (sometimes referred to as an algae bloom), they use up so much of the available oxygen in the water that it can create toxic conditions for fish and bugs (because they can't breathe). Like many water quality measurements taken over time, scientists are looking at chlorophyll-a to see if any changes can be seen, what these changes mean to the health of a water body and why they are occurring.
Total Recoverable Metals - Metals exist in water as both dissolved and solid particles. When water samples are analyzed for total recoverable metals, it can be thought of as measuring metals in both the dissolved and solid forms. The term recoverable is used to describe a type of laboratory procedure which has to "dissolve" the metals that are in a solid form (maybe sticking to particles of sediment for example) by using strong acids and then measuring them as dissolved metals. In this way the sample is measured for all metals or total recoverable metals. Why do we care? Metals in different forms have different effects on the environment. For example, if metals in a solid form end up settling to the bottom of lakes, rivers, or streams, they can affect the creatures that live there (including humans who may eat things that live there!).
Copper - In certain forms copper is extremely toxic to fish and algae. Ironically, scientists sometimes add a form of copper known as copper sulfate to kill aquatic weeds and algal blooms when they threaten the overall health of a water body (see chlorophyll-a above). Most of the pipes in houses are copper and it is a common part of wastewater discharges to waterbodies, especially wastewater from metal mines (like those near Butte, Montana, and the headwaters of the Clark Fork River). For these reasons, copper has been monitored in the Clark Fork-Pend Oreille watershed.
Zinc - Too much zinc can be harmful to both aquatic and human life. Because most zinc enters the environment as the result of human activities such as mining, purifying of zinc, lead, and cadmium ores, steel production, coal burning, and burning of wastes, it is important to monitor the levels of zinc in the watershed.
Secchi disk - The Secchi disk is used to measure how deep a person can see into the water of lakes and large rivers. It is generally an 8-inch diameter metal disk painted in alternate black and white quadrants. The disk is lowered into the water until the observer loses sight of it. The disk is then raised until it reappears. The depth of the water where the disk vanishes and reappears is the Secchi disk reading. Secchi Disk measurements are important to understanding how water clarity may be affected by algae and sediment at different times of the year.
Temperature - Certain types of fish and aquatic organisms need cold water temperatures to thrive. Temperature is monitored to observe changes from month to month, season to season, and overall trends from year to year. Temperature may also directly affect the amount and location of aquatic plant growth.
pH - How acidic or basic something is measured by its ph factor. pH is measured on a scale from 0 to 14, with 7 being neutral. Fresh water generally has a pH between 6.0 and 8.5. If the pH of water becomes too high (basic) or too low (acidic), aquatic organisms begin to die. At extremely high or low pH levels all aquatic life will die. pH is probably the single most important factor initiating all chemical reactions in water.
Conductivity and Total Dissolved Solids - Conductivity is a measure of how well water can transmit an electrical current. In the Clark Fork watershed, conductivity is primarily used to determine the mineralization of water (commonly called total dissolved solids). Information from the amount of total dissolved solids can be used to determine changes in water at different times of the year and can also be used to determine certain physiological effects on plants and animals.
Turbidity - Turbidity refers to how clear the water is. The greater the amount of total suspended solids in the water (not to be confused with total dissolved solids above), the murkier it appears and the higher the measured turbidity. The major source of turbidity in the open waters of most lakes is typically floating organisms. Closer to the shores of lakes and in rivers and streams, turbidity is more likely a result of clay and silt particles from erosion, runoff, and resuspended bottom sediments. Turbidity can greatly affect water quality in many ways. Some examples include reducing the amount of light available for plant growth, damaging sensitive gill structures in fish and aquatic organisms, as well as increasing their susceptibility to disease, and preventing proper egg and larval development.
Superfund - A program administered by the Environmental Protection Agency to locate, investigate, and clean up the worst uncontrolled and abandoned toxic waste sites in the nation.
Point Sources - Sources of pollution you can actually point your finger at are point sources. Some examples include pipes, ditches, channels or tunnels that directly discharge to surface waters. Typical point sources include discharges of wastewater from factories and sewage treatment plants.
Nonpoint Sources - Sources of pollution you cannot actually point your finger at are nonpoint sources. Some examples include large fields or farmland without proper best management practices in place, roads (paved and unpaved), and atmospheric deposition that do no not directly discharge to surface water through pipes, ditches, channels or tunnels.