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Nonpoint Source Water Pollution

Nonpoint Source > Watershed Assessment > Water Monitoring and You > Common Watershed Parameters Common Watershed Parameters

Watershed groups in Indiana collect data on a wide variety of water quality parameters. While there are many parameters that groups can choose from, many groups will choose a few to concentrate on, in order to better utilize their resources. While there are several parameters described here, there are also many others that can be worthwhile to look into that are not covered. Work with your watershed specialist to determine what parameters are best for your group’s goals.

Some water quality parameters have Federal or State water quality standards while others have suggested benchmarks. For more information about a parameter’s standard or suggested benchmark, please reference Water Quality Standards in the Indiana Administrative Code.

Table of Contents


One of the most widely used herbicides in the Unites States, atrazine is used to control grassy weeds in crop fields. Because of its chemical properties and widespread use as an herbicide, concerns have been raised over the risks it poses for aquatic organisms and humans. These risks are most pronounced in agricultural watersheds where atrazine is commonly applied and the majority of residents draw drinking water from private wells. Atrazine is regulated by the U.S. Environmental Protection Agency (U.S. EPA). Under the Safe Drinking Water Act, U.S. EPA has determined that an annual average of no more than 3 parts per billion (ppb) of atrazine may be present in drinking water.

Atrazine is relatively expensive to sample for, so most of Indiana’s watershed groups do not collect data on it. Several independent studies have found atrazine in the drinking water supply across the Midwest, including Indiana. Skeptics of the herbicide’s safety believe the standard in the Safe Drinking Water Act needs to be revised. U.S. EPA has recently announced it is undertaking a review of recent atrazine studies to determine if more regulation is needed.

Those concerned about atrazine in their drinking water should use a filter certified by NSF International to meet American National Standards Institute Standard 53 for volatile organic compound (VOC) reduction and therefore capable of significantly reducing many health-related contaminants, including atrazine.

More information about Atrazine:

Biological Oxygen Demand

Biological oxygen demand (BOD) is a measure of the oxygen used by bacteria to decompose a waste. A high BOD level indicates lots of bacteria in the water, which also indicates organic pollution. Nitrates and phosphates in a body of water can contribute to high BOD levels. Nitrates and phosphates are plant nutrients and can cause plant life and algae to grow quickly. This contributes to the organic waste in the water, which is then decomposed by bacteria, resulting in a high BOD level. Common nitrate and phosphate sources include urban and agricultural fertilizers or human and animal waste.

The temperature [PDF] of the water can also contribute to high BOD levels. For example, warmer water usually will have a higher BOD level than colder water. As water temperature increases, the rate of photosynthesis by algae and other plant life in the water also increases. When this happens, plants grow faster and die faster. When the plants die, they sink to the bottom and are decomposed by bacteria. The bacteria require oxygen for the decomposition process, raising the BOD at that location.

High BOD and related low levels of dissolved oxygen are found in Indiana waterways and, most famously, in the “dead” zone in the Gulf of Mexico.

More information about Biological Oxygen Demand:


Conductivity measures the ability of water with dissolved particles to carry an electric current. This ability depends on the presence of ions: their total concentration, mobility, and valence. Conductivity measurements can help estimate the sample size necessary for other chemical analyses, determine the amount of chemical reagents or treatment chemicals to be added to a water sample, and other specific applications. From a nonpoint source standpoint the parameter can give the watershed coordinator an idea of the total dissolved solids in a sample. However, as most watershed groups are interested in sediment that has not dissolved, conductivity is not always useful to watershed groups.

Dissolved Oxygen

Dissolved oxygen (commonly abbreviated on forms as DO) found in water is essential to healthy streams and lakes. The dissolved oxygen measurement can indicate the level of pollution in the water is and how well the water can support aquatic plant and animal life. Generally, a higher dissolved oxygen level indicates better water quality. If dissolved oxygen levels are too low, some fish and other organisms may not be able to survive (see macroinvertebrates).

Much of the dissolved oxygen in water comes from oxygen in the air that has dissolved in the water. Some of the dissolved oxygen in the water is a result of photosynthesis of aquatic plants. Stream turbulence may also increase dissolved oxygen levels when air is trapped under rapidly moving water, dissolving the oxygen into the water. In addition, the amount of oxygen that can dissolve in water depends on temperature [PDF]. Colder water can hold more oxygen than warmer water. Similarly, a difference in dissolved oxygen levels may be apparent at different depths of the water if there is a significant change in water temperature.

There are several reasons why a stream may have low dissolved oxygen. Temperature, turbulence, and the time the sample was taken could all contribute to the reading. Pollution may also have an impact. Similar to biological oxygen demand, dissolved oxygen is impacted by the same types of nonpoint sources and flow regimes.

E. coli

Escherichia coli (E. coli) is one member of a group of bacteria known as fecal coliform bacteria. Since this bacteria has an easy and economical test, E. coli is used as an indicator organism to identify the potential for the presence of pathogenic organisms in a water sample. Pathogenic organisms can present a threat to human health by causing a variety of serious diseases, including infectious hepatitis, typhoid, gastroenteritis, and other gastrointestinal illnesses. E. coli can come from the feces of any warm-blooded animal. Wildlife, livestock and domestic animal defecation, as well as manure fertilizers, previously contaminated sediments, combined sewer overflows, and failing or improperly sited septic systems are common sources of the bacteria. E. coli pollution found between rain events may signal issues that may need to be addressed.


Flow is the volume of water (measured in cubic feet) that passes a point in a stream over a measured period of time (usually seconds). Watershed projects should collect base and high flows, as both indicate different things about water quality. Base flow correlates to dry weather. Water quality problems found during base flow are likely from pollution that can enter streams without the aid of run-off. These may include point sources, malfunctioning or straight-pipe septic systems, and accidental or purposeful releases into a waterway. High flow occurs during rain events, indicating water quality problems could be caused by nonpoint source pollution. Flow data is a necessity for calculating pollutant loads.


Habitat is measured using an index called the qualitative habitat evaluation index (QHEI). The QHEI is composed of six metrics including substrate composition, instream cover, channel morphology, riparian zone and bank erosion, pool/glide and riffle-run quality, and map gradient. Observations of stream conditions along a 200 foot (61 meter) reach are recorded on the QHEI datasheet. Each metric is then scored individually then summed to provide the total QHEI score. The QHEI score generally ranges from 20 to 100.

As discussed below in “Macroinvertebrates,” habitat is necessary for aquatic life to thrive, and measuring the diversity of this life can give the watershed coordinator important trend information about a water body. Some of the QHEI metrics can also provide clues about possible water quality problems.

  • If the riparian zone lacks mature bushes and trees to shade the stream, temperatures may increase.
  • Areas of bank erosion can increase sediment loads to the stream.
  • Poor pool/glide and riffle-run quality may be caused by sedimentation of the stream channel. If poor pool and riffle quality is combined with a very low gradient, the stream may lack turbulence and the dissolved oxygen level may be impacted.

More information about Habitat:


Benthic macroinvertebrates are defined as “aquatic invertebrates that live in the bottom parts of our waters. They make good indicators of watershed health because they live in the water for all or most of their lives, stay in areas suitable for their survival, are easy to collect, differ in their tolerance to amount and types of pollution, are easy to identify in a laboratory, often live for more than one year, have limited mobility, and are indicators of environmental condition.” (U.S. EPA, 2007) Pollution-sensitive organisms such as mayflies, stoneflies, and caddisflies are more susceptible to the effects of physical or chemical changes in a stream than other organisms. These organisms act as indicators of the absence of pollutants. Pollution-tolerant organisms such as midges and worms are less susceptible to changes in physical and chemical parameters in a stream. The presence or absence of such indicator organisms is an indirect measure of pollution.

The benthic community in the streams is evaluated using IDEM’s macroinvertebrate Index of Biotic Integrity (mIBI). The mIBI is a multi-metric index that combines several aspects of the benthic community composition. As such, it is designed to provide a complete assessment of a creek’s biological integrity. The mIBI consists of ten metrics which measure the species richness, evenness, composition, and density of the benthic community at a given site. The mIBI is calculated by averaging the classification scores for the ten metrics. mIBI scores of zero to two indicate the sampling site is severely impaired; scores of two to four indicate the site is moderately impaired; scores of four to six indicate the site is slightly impaired; and scores of six to eight indicate that the site is non-impaired.

mIBI impairment can be caused by lack of habitat, water pollution, or a combination of the two. For more information about macroinvertebrates, see: Hoosier Riverwatch Manual and IDEM’s Biological Studies Section


Nitrogen is an element needed by all living plants and animals to build protein. In aquatic ecosystems, nitrogen is present in many forms:

  • Nitrate forms when nitrogen combines with oxygen. Nitrates may come from fertilizers, sewage, and industrial waste. Eutrophication can occur in lakes and ponds when nutrients such as nitrogen and phosphorus are added to a body of water. These nutrients usually come from run-off from farmlands and lawns, sewage, detergents, animal wastes and leaking septic systems. High levels of nutrients in a body of water may cause plant life and algae to flourish. As the plants grow they can choke out other organisms. Algae blooms may eventually cover the water's surface. These plant populations produce oxygen in the upper levels of the water. However, when the plants die and fall to the bottom, they are decomposed by bacteria using a large quantity of the dissolved oxygen in lower levels. Bodies of water with high levels of nitrates usually have high biological oxygen demand (BOD) levels due to the bacteria consuming the organic plant waste and subsequent low dissolved oxygen levels.
  • Ammonia-nitrogen is an inorganic dissolved form of nitrogen and is the preferred form for algae and plant growth. Ammonia is the most reduced form of nitrogen and is found in water where dissolved oxygen is lacking. Common sources of ammonia to waterways include fertilizers, human and animal waste, and industrial byproducts.
  • Total Kjeldahl Nitrogen is named after the Kjeldahl technique for measuring the amount of organic nitrogen contained in water. The organic nitrogen concentration is actually the total Kjeldahl nitrogen concentration minus the ammonia concentration. Organic nitrogen in water may indicate excessive organic pollution from the watershed. Animal and human waste, decaying organic matter and live organic material like tiny algae cells can cause organic nitrogen pollution.


Phosphorus is usually present in natural waters as phosphate. Phosphates are present in fertilizers and laundry detergents and can enter the water from agricultural run-off, industrial waste and sewage discharge. Phosphates, like nitrates, are plant nutrients. When too much phosphate enters the water, plant growth flourishes.

Phosphates also stimulate the growth of algae which can result in an algae bloom. These large plant populations produce oxygen in the upper levels of the water. When the plants die and fall to the bottom they are decomposed by bacteria, consuming much of the dissolved oxygen in the lower levels. Bodies of water with high levels of phosphates usually have high biological oxygen demand (BOD) levels and subsequent low dissolved oxygen levels.

  • Ortho-Phosphate is a dissolved form of phosphorus. Sources can include failing septic systems, animal waste, fertilizers, decaying plants and animals and re-suspension from the substrate.
  • Total Phosphorus is a measurement that includes ortho-phosphate and undissolved forms of phosphorus. As phosphorus attaches to soil, the primary source of particulate phosphorus is soil loss or erosion from the land. Total phosphorus is often a problem in agricultural watersheds.


It is important to know the temperature of the water each test site because it could help predict or confirm other conditions of the water. For example, the water temperature has a direct influence on other water quality factors such as dissolved oxygen, biological oxygen demand (BOD), as well as on the survival of some aquatic species.

The metabolic rates of aquatic organisms increase in warm water. Since metabolism requires oxygen, some species may not survive if there is not enough oxygen in the water to meet their needs. Water temperature may also affect the reproductive rates of some aquatic species; some species may not be able to reproduce in warmer waters. Since bacteria and other disease causing organisms grow faster in warm water, the susceptibility of aquatic organisms to disease in warm water increases as well.

Sudden increases in temperature may be a result of the discharge of large amounts of warm water from urban or industrial areas, known as thermal pollution. Sudden changes in water temperature may cause thermal shock in some aquatic species and result in death. Thermal pollution, even if gradual, may disrupt the ecosystem balance, potentially eliminating heat intolerant species from that area.

Total Suspended Solids

Total Suspended Solids (TSS) includes all particles suspended in water that can be trapped by a filter. Although it’s commonly collected to estimate the scale of sediment run-off from the watershed, TSS includes much more than just soil. TSS can include inorganic materials like industrial waste, and organic materials like dead plants and animal matter, live organisms and sewage. Large amounts of TSS can reduce water clarity, reduce light availability necessary for plant growth, and harm fish and other aquatic organisms. Sediment can clog fish gills and fill in spawning and other habitat areas. High TSS can also cause an increase in water temperature as the particles trap heat from the sun. Additionally, high TSS measurements can indicate high levels of nutrients, bacteria, metals and other chemicals since many of these pollutants attach to sediment. TSS even has an economic impact, since it has to be filtered out of surface water used as a drinking water source.


Turbidity is a measure of the degree to which the water loses its transparency due to the presence of suspended particulates. Turbidity is measured in NTUs: nephelometric turbidity units. The instrument used for measuring it is called nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample. In lakes turbidity is measured with a secchi disk.

This black and white disk is dropped in the water attached to a rope. The depth that the disk reaches before it disappears from sight is recorded. This provides an estimation of the turbidity level in the lake. Sources of turbidity are similar to total suspended solids (TSS). Watershed groups wishing to calculate loads for suspended solids should collect TSS rather than turbidity; the latter cannot be extrapolated into a load, nor easily converted to TSS.