Indicator Species (DP IB Environmental Systems & Societies (ESS))

Indicator Species

• Indicator species are organisms that are used to assess the quality of an environment or indicate the presence of specific environmental conditions, including pollution

• Different groups of organisms, including invertebrates, plants, and algae, can serve as indicator species in polluted waters:

Fresh water pollution invertebrate indicator species

   1. Invertebrates

• Bloodworms (Chironomidae): bloodworm (the aquatic larvae of midges) are commonly found in polluted waters, especially those contaminated with organic matter - their presence indicates low dissolved oxygen levels and high organic pollution

• Tubifex worms: tubifex worms also thrive in polluted waters with high organic content and low oxygen levels - their abundance suggests degraded water quality

   2. Plants

• Common Reed (Phragmites australis): this tall perennial grass is tolerant of high nutrient levels, such as nitrates and phosphates, often found in eutrophic or polluted waters

• Duckweed (Lemnaceae family): duckweed is a small floating plant that thrives in nutrient-rich waters, including those polluted with agricultural runoff or sewage effluents

   3. Algae

• Blue-green Algae (Cyanobacteria): excessive nutrients, particularly nitrogen and phosphorus, can trigger harmful algal blooms dominated by blue-green algae - these blooms are often associated with nutrient pollution and indicate degraded water quality

• Indicator species in aquatic ecosystems can also provide valuable insights into unpolluted or clean waters - examples include:

   1. Invertebrates

• Stonefly nymphs (Plecoptera): stoneflies are sensitive to water pollution and are often found in well-oxygenated, clean streams and rivers - their presence indicates good water quality

• Mayfly nymphs (Ephemeroptera): mayflies are also highly sensitive to pollution and require clean, well-oxygenated water - their presence is indicative of unpolluted aquatic habitats

   2. Plants

• Water Crowfoot (Ranunculus spp.): water crowfoot is a plant species commonly found in clean, well-oxygenated freshwater streams and rivers its presence indicates good water quality and suitable habitat conditions for other aquatic organisms such as fish

   3. Algae

• Diatoms: diatoms are a diverse group of algae, and their presence in high diversity and abundance is often associated with clean, well-oxygenated waters

• These are just a few examples of indicator species commonly used in water quality assessments

• By studying the presence, abundance, and diversity of these organisms, scientists and environmental professionals can gain insights into the pollution levels and overall health of aquatic ecosystems

  • It is important to note that the selection of indicator species may vary depending on the specific region, ecosystem, and type of pollution being assessed

• Monitoring the presence or absence of these organisms helps to assess the condition of water bodies and aids in conservation and management efforts to improve water quality and protect clean, unpolluted waters

Dave Huth from Allegany County, NY, USA, CC BY 2.0, via Wikimedia Commons

Indicator species such as the stonefly nymph can tell you that water is clean, but not how clean

Potential Limitations of Using Indicator Species

• Although using indicator species is a fairly simple and cost-effective method of determining whether a habitat is polluted or not, it has some drawbacks

  • For example, it can't give accurate numerical (quantitative) figures for exactly how much pollution is present

  • In addition, the presence or absence of indicator species can also be affected by factors other than pollution (e.g. the presence of predators or disease)

• If more detailed information on pollution levels is required, non-living indicators can be used instead

  • For example, dissolved oxygen meters and chemical tests can be used to very accurately determine the concentration of dissolved oxygen in the water and can be used to show changes in levels of water pollution over time

Biotic Indices

• A biotic index is a tool used to assess the overall health and pollution levels of an ecosystem based on the presence, abundance, and diversity of indicator species within a community

• It provides an indirect measure of pollution by evaluating the impact on different species according to their tolerance, diversity, and relative abundance

Photo by Jonny Gios on Unsplash 

   A biotic index allows environmental scientists to assess the health of an ecosystem

   Step 1 = Selection of Indicator Species

• Indicator species are selected based on their known sensitivity or tolerance to pollution

• These species are representative of different ecological niches and are used to evaluate the impact of pollution on the ecosystem

   Step 2 = Sampling and Data Collection

• Sampling is conducted at different sites within the water body being assessed

• The presence, abundance, and diversity of indicator species are recorded

   Step 3 = Calculation of Biotic Index

• The collected data is used to calculate a biotic index value, which is a numerical score or rating that reflects the overall quality of the ecosystem

• The index is based on factors such as species diversity, tolerance values, and relative abundance

   Step 4 = Interpretation of Biotic Index

• The biotic index is then interpreted to determine the pollution level of the ecosystem

• Higher biotic index values indicate cleaner or less polluted waters, whilst lower values indicate higher pollution levels

• For example, the Trent Biotic Index is a widely used biotic index for assessing freshwater pollution

  • It focuses on macroinvertebrates (insects, crustaceans, molluscs) as indicator species

  • The index assigns tolerance values to different species based on their known sensitivity to pollution

  • By sampling macroinvertebrate communities at various sites in a river, the relative abundance and diversity of pollution-sensitive and pollution-tolerant species are determined

  • These data are then used to calculate the Trent Biotic Index score, which provides an assessment of water quality and pollution levels in the river

  • If the Trent Biotic Index score for a particular section of the river is high, it suggests a healthy and less polluted ecosystem, as it indicates the presence of a diverse community of pollution-sensitive macroinvertebrates

  • Conversely, a low Trent Biotic Index score indicates poor water quality and higher pollution levels, as pollution-tolerant species dominate the community

• There are many different types of biotic indices that can be calculated to study different types of water pollution

  • For example, the Fine Sediment Sensitivity Index can be calculated to help identify occurences of sediment pollution in freshwater systems

• These biotic indices provide a valuable means to evaluate and monitor the impact of pollution on aquatic ecosystems, aiding in conservation efforts and guiding water management strategies