Diatoms serve as excellent indicators of water pollution because their communities respond predictably to changes in water quality, especially nutrient enrichment.
Why Diatoms Are Effective Indicators
Diatoms are single-celled algae with intricate silica cell walls. Their suitability as biological indicators stems from several key characteristics:
- High Sensitivity to Nutrient Changes: As stated in the reference, diatoms are highly sensitive to changes in concentrations of nutrients (phosphorus, nitrogen and silica). These nutrients, when present in excess due to human activities, act as pollutants for water. Different diatom species have varying tolerances and requirements for these nutrients. When nutrient levels change, the composition of the diatom community shifts, with sensitive species declining and tolerant or nutrient-loving species increasing.
- Predictable Responses: The specific types of diatoms present in a water body can tell scientists a lot about its condition. For instance, a shift towards species known to thrive in high-nutrient environments indicates nutrient pollution (eutrophication).
- Widespread Distribution: Diatoms are found in almost all aquatic environments, from rivers and lakes to wetlands and even damp soils, making them readily available for sampling.
- Sessile Nature: Many diatoms live attached to surfaces (like rocks or plants), meaning they reflect the water quality conditions at that specific location over time, rather than just fleeting conditions in the water column.
- Tolerance to Pollutants (relative): The reference also notes that diatoms can have high tolerance to pollutants compared with other organisms. This tolerance means they can often survive in polluted conditions where other, less resilient organisms might die off. While sensitive species disappear, tolerant species persist, ensuring that a diatom community is still present and available for analysis, even in degraded environments. This contrasts with their sensitivity to nutrient levels, which drives the changes in species composition that scientists monitor.
- Measurable in Laboratories: Diatom samples are relatively easy to collect and process. Their silica cell walls preserve well, even in sediment cores, allowing for historical water quality analysis. The analysis involves identifying and counting the different species present, which is measurable in the laboratories.
Using Diatoms for Water Quality Monitoring
Monitoring water quality using diatoms typically involves:
- Sample Collection: Gathering samples of diatoms attached to surfaces in the water body.
- Laboratory Processing: Cleaning the samples to isolate the silica cell walls (frustules).
- Identification and Counting: Using microscopes to identify the different diatom species present and count their relative abundances.
- Data Analysis: Comparing the observed community composition to known lists of species and their environmental preferences (e.g., nutrient tolerance indices).
Practical Insights:
- Changes in diatom community diversity and species composition provide a detailed picture of the water body's health. A diverse community with many sensitive species indicates good quality water, while a less diverse community dominated by pollution-tolerant species suggests degraded conditions.
- Diatom analysis can complement chemical monitoring by providing information about the cumulative effects of pollution over time, rather than just instantaneous conditions.
By examining the diatom community, scientists can assess the ecological health of aquatic ecosystems and track changes caused by pollution, making them invaluable tools in water resource management.
