Assessment of Water Pollution Levels Using Biological Methods

Using Bioindicators

1. Scientific Basis

Black Fly Larvae (Family Simuliidae)

One of the simplest methods for assessing water quality is to collect and analyze key bioindicators (such as aquatic insects and other organisms). This method is cost-effective and not overly complex, yet it helps to provide an overall picture of the quality of aquatic environments. However, when implementing this method, we need to pay attention to the following issues:

Since this method is designed for quick and simple execution, it can only accurately detect significant changes in water quality. Minor changes in water quality or identifying pollution sources fall outside the scope of this process.

2. Assessing Water Quality through Large Macroinvertebrates

Macroinvertebrates refer to visible invertebrate organisms that can be observed with the naked eye. In freshwater environments, they are typically found in the form of insects (or their larvae), crustaceans, mollusks, snails, various worms, and other types. However, in most water bodies, insect larvae are predominant, making them useful organisms for evaluating water quality. Macroinvertebrate species are closely related to their habitats.

Macroinvertebrates

Therefore, if the quality of a water body changes, it takes a long time for the population structure to recover. Thus, identifying the species present in the water body allows us to ascertain its quality at the time of the survey.

Caddisfly Larvae (Order Trichoptera)

3. Interpreting Collected Data

• When using the collected data on macroinvertebrates to interpret the water quality, it is essential to consider all the following aspects:
• The diversity level of these organisms in the sample.
• The percentage ratio of each species in the sample.
• The number of organisms per unit area.
• The diversity level of the sample (including the three aspects above).
• The pollution tolerance level of the organisms in the sample.

Factors Affecting Water Quality Can Be Divided into Three Major Groups

Clams (Class Bivalvia (Pelecypoda))

– Physical factors: changes in flow rate, temperature, sedimentation due to erosion, or construction works affect the riverbeds. The impacts of physical factor changes can vary from reducing the number of individual organisms to decreasing the diversity of populations in that area.

– Organic and Nutrient Pollution: from livestock waste, fertilizers. These types of pollution often lead to a reduction in biodiversity in the surveyed area and an increase in the number of species that can directly consume organic waste. Organic and nutrient pollution can also cause “algal blooms” (explosions in algal numbers in water bodies) and increase the populations of some other aquatic organisms. Some macroinvertebrate species may be completely eliminated from the aquatic environment, replaced by species that can survive in low dissolved oxygen (DO) conditions.

Crane Fly Larvae (Family Tipulidae)

– Toxic Substances: including chemicals such as chlorine, acids, metals, pesticides, and oil. It is challenging to generalize the effects of toxins on macroinvertebrates because their tolerance levels vary by species. However, toxins are often the cause of the complete disappearance of macroinvertebrates from the aquatic environment.

According to traditional methods of assessing water quality using bioindicators, samples must be collected accurately and carefully. Typically, each sample requires about one hour for collection and preservation. Sample analysis takes approximately several days with expensive equipment. This process yields scientifically robust and high-quality results.

Crayfish (Order Decapoda)

The new method of the Water Watch Biological Monitoring Project is simpler and faster. Samples are collected and analyzed on-site with inexpensive equipment to detect pollution levels ranging from moderate to heavy. If analyses indicate that water quality is low, further sampling upstream will be conducted to identify the source of pollution.

4. Necessary Tools

• Despite the many different sampling methods, the most commonly used sampling tools are nets and drag nets. The basic tools can be listed as follows:
• A nylon drag net with an area of 4 square feet.
• A pot or paper plate.
• A macroinvertebrate identification guide.
• A report form for recording results.

Damselfly Nymphs (Order Odonata)

When the samples are lifted from the water, they are placed on the surfaces of the paper plate or pot for easy observation, then sorted into groups and data collected as mentioned in the data interpretation section, and filled into the report form.

If after analysis we assess the water quality as poor (heavily to moderately polluted), additional sampling is needed to identify the pollution source. The following steps will be taken:

Step 1: Sample from a point upstream about 1 mile (1.6 km) from the previous sampling point.

Step 2: If the analysis results indicate pollution levels remain poor, repeat Step 1. If pollution levels improve (moderate to good), proceed to Step 3.

Step 3: Sample downstream of the last sampling point (with closer intervals) until the point of quality decline is detected. The source of pollution will be located somewhere near this point; re-survey the discharge sources in this area to identify the cause.

Dobsonfly Larvae (Family Corydalidae)

5. Macroinvertebrate Groups Used to Indicate Environmental Pollution Levels

• Pollution-sensitive group (will disappear or severely decline in number when water sources are polluted).
• Intermediate group (appears in areas beginning to be polluted).
• Pollution-tolerant group (can be present in polluted areas).

6. Note that this process is intended for non-intensive studies; thus, it provides only relatively accurate information. The application of this process will yield the following results:

• Quick, on-site assessment of water quality, allowing for further upstream studies to identify pollution issues.
• Low-cost tools and expenses for the research process, enabling non-profit research organizations to self-fund.
• Amateur researchers can effectively collect samples and conduct analyses.

7. Groups of Organisms Sensitive to Pollution

• Dragonfly Nymphs (Order Odonata)

  Caddisfly Larvae (Order Trichoptera)

• Dobsonfly Larvae (Family Corydalidae)
• Mayfly Nymphs (Order Ephemeroptera)
• Water Penny Beetle Larvae (Family Psephenidae)
• Riffle Beetles (Family Elmidae)
• Stonefly Nymphs (Order Plecoptera)
• Other Snails (Class Gastropoda)
• Beetle Larvae (Order Coleoptera)
• Damselfly Nymphs (Order Odonata)
• Dragonfly Nymphs (Order Odonata)
• Scuds (Order Amphipoda)
• Crayfish (Order Decapoda)
• Sowbugs (Order Isopoda)

• Scuds (Order Amphipoda)

  Clams (Class Bivalvia (Pelecypoda))

• Crane Fly Larvae (Family Tipulidae)
• Aquatic Worms (Phylum Annelida and others)
• Pouch Snails (Class Gastropoda)
• Black Fly Larvae (Family Simuliidae)
• Leeches (Class Hirudinea)
• Midge Larvae (Family Chironomidae)

Kentucky Water Watch
Translation by: Lê Hoàng Việt