Traditionally stream and river quality assessments have been conducted based solely on chemical analysis to analyze the impact of land use change on water quality. While variables such as pH, dissolved oxygen, hardness and concentrations of metals, soluble chemicals, nutrients, and organics were typically measured, other extremely valuable information regarding biological species diversity and overall habitat quality was lacking.
More recently, scientists have recognized the need to incorporate this biological data in order to create a comprehensive investigation of watershed quality and response to change. This biological line of investigation is important because chemical assessments could not assess the effect of a particular pollutant after settling in the system, and could only accurately measure its short-term effects.
Biological methods take into account a variety of ecological indicators like topography, soil structure, water table levels, and surrounding vegetation and present a more conclusive picture of a watershed. These ecological variables are useful in measuring long-term effects and the ability of the water system to respond to major stress events. The Ohio EPA has highlighted the following as primary components of biological integrity:
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Using ecological parameters is extremely valuable in assessing non-point pollution. With no known discharge sites and unknown times of origin, non-point pollution becomes very difficult to assess. Therefore, it is in the best interest of the planner, developer, and landowner to recognize the need for incorporating biological data into watershed assessments.
Measuring chemical variables has been the traditional approach to water quality assessments. A few common chemical parameters for investigating water quality conditions are found below.
Variable | Description | Example of Cause/Impact |
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Available Oxygen |
The amount of molecular oxygen dissolved in water is an important measure of habitat availability for aquatic organisms. Low levels of oxygen result from the introduction of organic waste pollution which increases the rate of eutrophication and decreases the suitability for aquatic animal life. Sources include: agricultural runoff, urban runoff, and wastewater treatment plants. | |
pH |
pH is a unit that expresses the strength of a solution based on its acidic or basic properties. Aquatic organisms can only function in a particular range of pH, and become forced to relocate when the surrounding water changes. Pollution from burning fossil fuels increases the amounts of sulfur and nitrogen oxides introduced into the water, thereby increasing the overall acidity. | |
Turbidity |
The amount of suspended material in water can be measured by collecting the solids or assessing the relative light transmission of the suspension. The increased opaqueness is caused by increased sediment which negatively affect many aquatic organisms. Both algal production and fish reproduction and feeding can become diminished and some organisms, like shell-fish (continual filter-feeders) can become choked by sediment and eventually die in heavily turbid waters. | |
Toxic Organic Compounds |
There are many chemicals that have the capacity to travel throughout a waterway. Many of these are pollutants and can cause significant distress to the surrounding habitat. Solutions such as oil or antifreeze enter a watershed from nearby runoff sources and directly poison the surrounding aquatic environment. With appropriate riparian vegetation, large surge concentrations of these chemicals can be prevented from directly entering the water. | |
Heavy Metals |
Industrial effluents are major sources of heavy metals, and aquatic environments are extremely sensitive to even the smallest concentrations of these materials. Serious abnormalities have been reported in many aquatic organisms. Arsenic and mercury are two common examples of heavy metals, but other similar substances and compounds can also have significant effects on an aquatic community. | |
Nutrients |
Additional nutrients, such as phosphorus and nitrogen, are added to streams by many avenues, but primarily through human sewage, animal waste, fertilizers and erosion. This area of water quality monitoring is greatly affected by both urban and agricultural human practices. Runoff from any inadequately covered lands can increase these nutrient loads and result in eutrophication of the nearby aquatic habitat. |
Although these chemical variables are useful to monitor impacts, they only provide a short-term picture of water quality at a sampled site and each can only represent a portion of a complete assessment. A couple disadvantages of using only chemical indicators include:
Chemical testing is much more applicable for point source pollution where industrial contamination is suspected.
Animal waste, including manure and urinary waste can enter streams directly when livestock wade in and around the water. Animals also trample streambanks and damage fish habitat. Animal wastes deposited in waterbodies can accelerate eutrophication and contaminate water used for fishing, swimming, and drinking. Streambank fencing is one way to protect streams from this type of livestock damage (See best management practices).
Areas under construction are usually devoid of any surface vegetation and topsoil and remain bare for extended periods of time. This process allows for extremely high quantities of subsoil to runoff into surrounding stormwater systems where receiving waters eventually accumulate large sediment loads. This increase in sediment decreases the amount of light penetrating through the water and thereby decreases the diversity and productivity of aquatic organisms.
Crops planted on the edge of streams can create many problems with soil stability. With heavy farm machinery for planting and harvesting and heavy rainfall, increased soil compaction and bank erosion will result over time and the soil will be pushed into the stream thereby increasing sediment load and decreasing the area of the bank. Planting close to a stream edge should be avoided; area around the stream should be maintained with adequate trees and vegetation along the bank (See best management practices).
Oxygen in water is available to the plants and animals that live there only if it is dissolved. Dissolved oxygen or DO can range in concentration from 0 to 14.6 parts per million in water. This is also equivalent to a weight-based measure, milligrams per liter (or mg/l). The amount of oxygen that can be dissolved in water is inversely related to temperature - that is as the water temperature gets higher, the amount of oxygen that can be dissolved in the water goes down. It is also possible under some circumstances to have oxygen levels above 14.6 mg/l. This can happen where water goes over a dam or other structure that causes unusual amounts of mixing. The more oxygen that is in the water, the more diversity can be expected in the plants and animals found in the water.
Pollutants that make DO go down (besides heat) are any organic wastes such as animal or human sewage or any chemicals that will be decomposed by bacteria in the water. The growing bacteria that break down either the organic or chemical wastes consume oxygen for their reproduction and thus take oxygen out of the water and away from the other plants and animals.
BOD is a lab test that measures the total amount of oxygen per unit volume of water required to bacterially oxidize (stabilize or break-down) the organic matter in the water. Samples are incubated under standard conditions for periods of 5, 10, 20 or 30 days. The standard test is for 5 days. The higher the BOD, the more oxygen depletion will take place.
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Many pollutants enter nearby waterways by efficient movement across surfaces These surfaces do not allow for penetration and percolation which would normally occur in a well vegetated, open-soil area. Heavy concentrations of pollutants can enter a water system during storm events where a large amounts of water flow across impervious areas and flushes the compounds into the local river or stream. Pollutant levels from non-point sources can be decreased by supplying adequate vegetative ground cover throughout the riparian area (See best management practices).
Sediment from nonpoint sources is the most widespread pollutant of surface water. Turbidity is the measure of the amount of suspended material in water and is determined by the relative light transmission of the suspension. Turbidity is an important consideration because it greatly reduces algal populations by inhibiting sunlight and slowing photosynthesis, changes heat radiation, has harmful effects on benthic fish and plants, and compromises most of water's major beneficial uses. The concentrations of suspended sediment in streams can be highly variable and are influenced by many factors, including the following: rainfall intensity and duration, soil condition, geology, topography, and present vegetation. Concentrations are measured in milligrams per liter (mg/l)
There are two typical scales used to measure turbidity, percent transmission and optical density. Percent transmission, or transmittance, varies from 0-100% and is based on the amount of light that is able to penetrate through the water sample. Optical density, or absorbance, is based on a logarithmic scale ranging from 2-0 where 2 represents the most turbid and 0 represents the least. A transmittance value of 50% corresponds to about a 0.3 absorbance value.
A wastewater treatment plant is where sewage goes from individual households and businesses. It removes a large percentage of the organic wastes (BOD) and sediments from the sewage and then discharges them into a local stream. Even so, the volume of the discharge can still cause a major pollution problem. You can find out more about what is in a wastewater sewage treatment plant at https://en.wikipedia.org/wiki/Sewage_treatment
pH measures the acidity of the water. Thescale goes from 0 to 14 with 7 being neutral and numbers below 7 representing additional acidty and numbers above the lack of acid or "basic" conditions. Most organisms thrive in water that is near neutral.
As the amount of acidity increases, the impacts on aquatic life also increase. The acidity is toxic to aquatic life, contributes to the release of toxic metals into solution, and weakens the shells and skeletons of biota.
Major sources of acidity are industrial wastes and deposition of acids from air pollution (acid rain), The figure below shows some common items and their place on the pH scale. It also shows the levels at which various biota are impacted by acidity.
This index is designed to measure the aquatic vertebrate community and the surrounding conditions by using fish species as indicators. Overall, there are 12 fish community variables that can be broken down into three main categories: species richness and composition, trophic composition, and fish abundance and condition. By assessing the variables within these parameters, scientists can compare a sampled site with a relatively undisturbed site with similar geographical and climatic conditions. With this rationale, the only variable would be stressors resulting from human development and disturbance. The following table lists the 12 variables measured in the IBI and their applicability depending on particular sites.
Variable Measured | Type of Site | |
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1. | Total Number of Species | H W B |
2. | Number of Darter Species | H W |
Percent Round-bodied Suckers | B | |
3. | Number of Sunfish Species | W B |
Number of Headwater Species | H | |
4. | Number of Sucker Species | W B |
Number of Minnow Species | H | |
5. | Number of Intolerant Species | W B |
Number of Sensitive Species | H | |
6. | Percent of Tolerant Species | H W B |
7. | Percent of Omnivorous Species | H W B |
8. | Percent of Insectivorous Species | H W B |
9. | Percent of Top Carnivores | W B |
Percent of Pioneering Species | H | |
10. | Number of Individuals | H W B |
11. | Percent of Hybrids | W B |
Number of Simple Lithophilic Species | ||
12. | Percent of DELT Anomalies | H W B |
Type of Site: H-Headwater, W-Wading, B-Boat
IBI scores can range from 12-60 depending on the amount of disturbance that has taken place at and around the sampling site. Possible scores range from:
DELT-Deformities, eroded fins, lesions, and tumors
IBI criteria as taken from Ohio EPA 1987aMaximum Score of 12(variables) * 5(highest score) = 60
Minimum score of 12(variables) * 1(lowest score) = 12
The invertebrate community index (ICI) is very similar to the IBI and measures the health of the macroinvertebrate community. This index is comprised of 10 metrics where sampled sites are also compared to relatively undisturbed sites with similar geographical features. Both IBI and ICI are useful tools for biological measuring of aquatic environments, but IBI is often the preferred method; fish are generally longer lived and can therefore represent environmental changes over a longer period of time.
Variable Measured | |
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1. | Total Number of Taxa |
2. | Total Number of Mayfly Taxa |
3. | Total Number of Caddissfly Taxa |
4. | Total Number of Dipteran Taxa |
5. | Percent of Mayflies |
6. | Percent of Caddisflies |
7. | Percent of Tribe Tanutarsini Midges |
8. | Percent of Other Dipterans and Non-insects |
9. | Percent of Tolerant Organisms |
10. | Total Number of EPT Taxa |
EPT- Ephemroopters, Plecoptera, and Trichoptera (specific types of invertebrate taxa); ICI criteria as taken from Ohio EPA 1989
Modeled after IBI, ICI can receive a score of 6, 4, 2, or 0 depending on the undisturbed site comparison. Each site can therefore range between:
The qualitative habitat evaluation index (QHEI) gives scientists a quantitative assessment of physical characteristics of a sampled stream similar to IBI and ICI biological data. QHEI represents a measure of instream geography. By combining evaluations of QHEI and IBI, for example, researchers can gain a well-rounded perspective of both the physical and biological conditions of a particular stream site. This comprehensive assessment is critical for evaluating disturbance and land use practices. There are six variables which comprise this index (represented in the following table).
Metric | Metric Component | Best Possible Score |
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Substrate |
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20 | |
Instream Cover |
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20 | |
Channel Morphology |
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20 | |
Riparian Zone |
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10 | |
Pool Quality |
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12 | |
Riffle Quality |
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8 | |
Map Gradient |
10 | ||
TOTAL | 100 |
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Metrics for QHEI:
Substrate: This metric includes two components, substrate type and substrate quality.
Silt cover is the extent to which the substrate is covered by silt. Silt heavy means that nearly all of the stream bottom is layered with a deep covering of silt. Moderate includes extensive coverings of silts, but with some areas of cleaner substrates. Normal silt cover includes areas where silt is deposited in small amounts along the stream margin or is present as a "dusting" that appears to have little functional significance. Silt free substrates are those that are exceptionally clean of silt.
Instream Cover: The first half of instream cover is the type that is present. Any cover that is in more than five percent of the sampling area should be noted, but should not be counted if in areas of the stream that are too shallow (usually <20 cm) to make it useful. Instream cover amount can be categorized by: extensive, moderate, sparse, or nearly absent. Extensive cover is that which is present in greater than 75 percent of the sampling area. Moderate is about 25%-75%, Sparse is less than 25%, and Nearly Absent is when no large patch of any type exists anywhere in the sampling area.
Channel Morphology: Relates to quality of the stream with regard to creation and stability of macrohabitat. This includes: channel sinuosity, channel development, channelization, and channel stability.
Riparian Zone: This metric measures the quality of the riparian buffer zone of floodplain vegetation, including riparian zone width, floodplain quality, and extent of bank erosion. To score each component, one looks downstream and averages both the left and right banks.
Pool Quality: Pool quality consists of three areas: maximum depth of pool or glide, current type, and morphology.
Riffle Quality: If no riffles exist, a zero should be recorded. If not, riffle quality consists of three areas:
Back to QHEI Table Map Gradient: Calculated from USGS 7.5 minute topographic maps by measuring elevation drop through the sampling area. First, the stream length is measured between the first contour line upstream and the first contour line downstream of sampling site and then dividing the distance by the contouring interval. A minimum distance of one mile should be used if contours are "packed" together.