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Algae Analysis Under the Microscope: A 'Biological Indicator' of Water Quality

In water-source protection, lake and reservoir monitoring, aquaculture, wastewater treatment, and ecological research, algae are among the most frequently 'watched' subjects. They are tiny, yet they sensitively reflect the health of a water body—and to see them clearly, count them accurately, and identify them correctly, the microscope is what does the job. This article systematically introduces the groups, significance, methods, metrics, and equipment requirements of algae analysis.

1. What Are Algae

The algae discussed here mainly refer to phytoplankton—microscopic organisms that live in water bodies and can photosynthesize. Common groups include:

Cyanobacteria (blue-green algae): prokaryotes; some species produce harmful substances such as microcystins and readily form blooms;

Green algae: single-celled or colonial, a common indicator of water-body fertility;

Diatoms: cell walls made of silica, with delicate and varied forms, and an important group for water-quality evaluation;

Dinoflagellates, cryptomonads, euglenoids, golden algae, yellow-green algae, and so on.

Different groups have different adaptability to the environment, so 'who dominates' is itself important information.

2. Why Conduct Algae Analysis

1. Water sources and water plants

Monitoring the populations and numbers of harmful algae such as cyanobacteria to give early warning of blooms and safeguard water supply—algal metabolites also cause taste-and-odor problems.

2. Lake, reservoir, and river monitoring

Using algal community structure, quantity, and diversity to evaluate water quality and the degree of eutrophication—one of the core indicators of biological assessment.

3. Aquaculture

Judging water-body fertility, feed abundance, and the risk of an 'algae crash' from the algal phase (water color), to guide fertilization and aeration.

4. Wastewater treatment and ecological restoration

Assessing treatment effectiveness and the state of aquatic ecological recovery.

5. Scientific research

Research directions such as biodiversity, primary productivity, and the carbon cycle.

3. How to Conduct Algae Analysis

The standard workflow is roughly: sampling, fixation, concentration and making up to volume, then identification and counting under the microscope.

1. Sampling

Use a water sampler to take a quantitative water sample, or collect by towing a net per the specified mesh (such as a No. 25 plankton net). Sampling points, depths, and times should be fixed to facilitate longitudinal comparison.

2. Fixation

Generally Lugol's solution (iodine–potassium iodide) is added on site to fix the sample, stabilizing algal morphology and aiding preservation.

3. Concentration and making up to volume

Concentrate by static settling or centrifugation, and make up to a known volume, to facilitate conversion of the count per unit volume of water.

4. Identification and counting

This is the most critical step:

Identification: based on features such as cell morphology, size, chromatophores, flagella and mode of movement, and cell walls (such as the valve ornamentation of diatoms), determine to the genus or species level;

Counting: use a plankton counting chamber (such as a 0.1 mL chamber) or a hemocytometer, tally individuals by field of view or by square, and convert to 'cells/L.'

4. Core Metrics

Quantity: cell density (cells/L), reflecting abundance;

Biomass: converted from cell volume into biomass (such as mg/L), which better reflects the 'amount of matter' than counting alone;

Dominant species: the species with the highest proportion of the count, often determining the water-body state;

Diversity index: such as the Shannon-Wiener index, reflecting community stability;

Chlorophyll a: as a supplementary indicator, positively correlated with algal biomass.

5. Requirements for the Microscope

Optical configuration: a biological microscope plus phase-contrast (or brightfield) objectives; low magnification (4×/10×) to find the field, high magnification (40×) and oil (100×) to see details;

Measurement and imaging software: to measure cell length and width, archive images, and assist counting;

Illumination and imaging quality: algal cells are small with fine structures, so image sharpness directly determines identification accuracy;

Stability: during long counting sessions, a stable light path and a solid stage markedly improve efficiency.

6. Reading Water Quality from Algae

The algal community is like a mirror:

When diatoms and green algae dominate with good diversity, it usually indicates a relatively healthy water body;

When cyanobacteria proliferate, it is often a signal of eutrophication, accompanied by toxin and taste-and-odor risks;

A single, low-diversity community may indicate pollution or ecological imbalance.

Therefore, long-term, fixed-point algae monitoring can detect trends in a water body earlier than a single set of physicochemical indicators.

7. Key Identification Points for Common Groups

Cyanobacteria: cells have no chromatophores (pigment dispersed in the cytoplasm), no flagella but capable of gliding movement, and many species have a gelatinous sheath; Microcystis is mostly colonial, while Anabaena is filamentous;

Green algae: contain chloroplasts and are varied in form (single-celled, colonial, filamentous), such as Scenedesmus, Chlorella, and Spirogyra;

Diatoms: the cell wall consists of two overlapping siliceous valves, with radial or pennate ornamentation on the valve—an important basis for identification;

Dinoflagellates: mostly have two flagella, one transverse and one longitudinal, with a transverse and a longitudinal furrow, and some species have plates;

Cryptomonads and euglenoids: larger cells with pronounced movement; euglenoids often have an eyespot at the front end.

When identifying, combine cell morphology, size, and professional literature atlases, and use a higher-magnification objective or staining to confirm when necessary.

8. Precautions

Sampling and fixation must be standardized; otherwise cells deform during preservation and become hard to identify;

Counting must have sufficient statistical data, and the selection of fields of view should be random, avoiding 'looking only at the large and obvious ones';

Different groups need to be identified with specialized literature atlases, and taxonomic experts should be consulted when necessary;

Numerical conversion must use a unified basis (concentration factor, counting-chamber volume), otherwise longitudinal comparison loses meaning.

Conclusion

Algae analysis 'reveals the big in the small'—with a single microscope, you can read the story of the water. For monitoring agencies, water plants, and aquaculture enterprises, it is an indispensable biological perspective beyond physicochemical testing.

(For microscopy and imaging solutions related to algae analysis, feel free to contact us.)