Environmental Sampling Methods

You’ve read your sources, written your hypotheses, planned your experiment… now it's time to carry it out! To achieve this, you will need to do some environmental sampling. Environmental sampling is about observing the traits of a specified environment. There are many different sampling methods – how you choose to sample your environment will depend on the nature of your habitat and study species. 

Environmental Sampling Methods Environmental Sampling Methods

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Table of contents

    The Importance of Environmental Sampling

    Samples and data from the natural environment can be used as evidence to support scientific theories. Sampling enables statistical analysis, which is key to backing up a hypothesis.

    Environmental sampling can be used to identify rare species or detect harmful microbes.

    Environmental sampling needs to be considered reliable. Your experiment report will need to show exactly what you did, where and how.

    Types of Environmental Sampling

    When studying an environmental area, often, very little is known about the site. Several approaches can be taken for sampling; sometimes, more than one can be applied at a time. We will explore three environmental sampling methods: random, systematic, and stratified.

    Random Sampling

    Random sampling is used where every member of a population is equally likely to be included, such as daisies in an unmanaged field.

    It is essential to make sure that your samples are unbiased. This can be done by using a random number generator to select numbers or using grid references.

    Suppose you are estimating how many daisies there are in a field. You are making 20 quadrat measurements and multiplying your averages to match the total area of the field. When making your measurements, you are drawn to a patch of the field with lots of daisies. You decide to make a measurement there. This is biased sampling.

    Biased sampling leads to over-representation or under-representation of the variable and is frowned upon in science.

    Systematic Sampling

    Systematic sampling is used where the study area includes an environmental gradient, such as a sand dune system. Transects are lines placed along the gradient and are used to make regular measurements.

    Systematic sampling shows how an ecosystem changes along a gradient.

    Stratified Sampling

    Stratified sampling is used where the sample area can be subdivided. After dividing, proportionate random observations are taken from each population subsection.

    To put this into context, imagine that a field has 70% ryegrass cover and 30% clover cover. To perform stratified sampling, take 70% of your samples from the ryegrass zones and the remainder from the clover zones.

    Environmental Sampling Techniques

    Before we begin this section, let's review some critical quantitative measures.

    • Species population: a group of individuals of the same species living in an area.

    • Species richness: the number of different species present in an ecosystem

    • Species distribution: how a population is spatially arranged

    • Biodiversity: the variety of life in an ecosystem

    Knowing these quantitative measures will help you carry out environmental sampling effectively.

    Quadrats

    Quadrats are used to assess vegetation coverage and frequency in a study site. They can be used in random, systematic and stratified sampling. There are two types: frame and point.

    Quadrats can be used to measure biotic factors related to population size, species richness, species distribution, and biodiversity.

    Biotic factors are any living organism that has an effect on the ecosystem.

    When sampling with a quadrat, it's essential to know the species distribution. A sparser distribution requires a larger quadrat size.

    To learn more about this, see our article on Quadrats!

    Transects

    Transects are lines laid out on the ground. Either the transect is continuous, where observations are made constantly, or interrupted, where measurements are made at regular intervals. Transects are frequently used in systematic sampling.

    Species Lists and the ACFOR Scale

    ACFOR stands for: abundant, common, frequent, occasional and rare.

    Species lists and the ACFOR scale can be used to determine the presence and abundance of different species. Understanding species richness and biodiversity is essential.

    Measuring Animal Taxa in and on the Soil

    There are two main methods for measuring invertebrates in the soil: pitfall traps and Tüllgreen funnels.

    • Pitfall traps are small containers sunk into the soil for running or crawling invertebrates to fall into.

      Before installing pitfall traps, it's vital to recognise species distribution.

    • Tüllgreen funnels are used to extract invertebrates from soil samples in the lab. The sample is placed in a funnel above a perforated disc, and the whole apparatus is placed under an electric lightbulb. The temperature rise and drying effect encourage the invertebrates to move downwards through the perforated disc into a collecting vessel below.

    Either method can be employed to measure biotic factors related to population size, species richness, species distribution, and biodiversity of animal taxa on the soil surface and in the soil.

    Measuring Animal Taxa on Leaves

    Invertebrates living on leaves can fly, so they must be collected with different methods.

    • Sweep nets are robust nets used to disturb non-woody vegetation. The net is moved in a figure-of-eight motion.

    • Beating trays are white sheets placed on the ground below branches of woody vegetation. A strong stick is used to shake the branches so invertebrates fall onto the sheet.

    Either method can be employed to measure biotic factors related to population size, species richness, species distribution, and biodiversity of animal taxa on foliage and flying invertebrates.

    Mark, Release and Recapture Method

    Samples of invertebrates or small mammals are taken from the population, counted, and then marked.

    Later, a second sample is taken. The total number of individuals, and the total number of marked individuals, are recorded.

    The Lincoln Index is the equation used to estimate the population size.

    The Lincoln Index is a formula used to estimate animal population sizes based on two independent sets of observed cases.

    Population = number of animals in 1st sample x number of animals in 2nd samplenumber of marked animals in 2nd sample

    The mark, release and recapture method makes several assumptions, such as random mixing and no migration.

    Aquatic Sampling Methods

    Aquatic sampling techniques include using a pond net. The net is used to agitate the water, dislodging invertebrates, then ending with a scooping motion to collect the animals in the net.

    If the bed of the water body is stony or sandy, you can use 'kick-sampling' - lightly disturb the bed with your heel to dislodge benthic organisms, such as clams, oysters, worms etc.

    Benthic organisms are a complex community of deep-sea dwellers.

    Larger invertebrates can be collected using a surber sampler (a net that sits on the water). The sampler is placed downstream, so flowing water directs the macroinvertebrates into a collecting net.

    Net-based methods can assess biodiversity, species richness, and population size.

    Colonisation media is an artificial substance placed in an aquatic habitat to assess the rate of colonisation by different organisms. A range of materials should be used to provide additional surface areas. The colonisation media is placed in the aquatic habitat and assessed regularly.

    This method can be used to determine species distribution and biodiversity.

    Abiotic Factors

    Abiotic factors are non-living components of ecosystems.

    An ecosystem's abiotic factors can affect biodiversity and species distributions. Many species are adapted to certain abiotic conditions and cannot survive elsewhere. So, measuring abiotic factors indicates the living conditions of organisms in the habitat.

    Abiotic factors include temperature, pH, humidity, light intensity, and soil type.

    These factors can also be measured in freshwater ecosystems. The main factors are:

    • Temperature (impacts metabolism)
    • Velocity (impacts growth)
    • pH (affects species present)
    • Oxygen concentration (affects species present)
    • Nutrients (affects biodiversity)
    • Light (determines primary production)
    • Substrate (impacts growth and community structure)

    Environmental Soil Sampling Methods

    Soil plays a vital role in ecosystem functioning. It provides environments and nutrients for plants, filters water, prevents flooding, promotes biodiversity and stores carbon.

    Soil is the uppermost level of the Earth's crust, consisting of organic matter, minerals, gases, and water.

    Studying the soil and its edaphic factors is key to understanding ecosystems.

    Edaphic factors are the soil properties that affect the organisms living in the soil environment.

    Measuring edaphic factors helps scientists understand ecosystem structure and the impacts of climate change.

    Edaphic factors include soil temperature, water content, pH, soil structure, and salinity.

    On-site Sampling

    Soil sampling can take place on-site or off-site. On-site sampling methods are used to see how the soil interacts with its physical environment.

    Soil Infiltration Rate

    A rapid soil infiltration rate is desirable for plant growth.

    • Use a mallet to bang an infiltration tube into the ground until it forms a seal.

    • Pour water into the tube until it reaches a standardised level.

    • Use a stopwatch to record how long it takes for the water to infiltrate.

    • If necessary, add more water to reach the standardised level.

    • The infiltration time depends on the soil's composition and compaction.

    Off-site Sampling

    Off-site methods are used when the soil needs to be weighed or analysed closely. For the following techniques, soil samples are removed from the ground with a trowel … and the landowner's permission!

    Soil pH

    Soil pH can limit the plants and microorganisms present.

    • Soil pH can be measured with a handheld digital probe.
    • Or, place some soil into a test tube. Add barium sulphate, distilled water and indicator solution.
    • pH alters the community composition.

    Soil Texture

    Soil texture influences the plants that can grow in the soil.

    • Soil texture is measured by the different proportions of sand, silt and clay.
    • This affects compaction and community composition.

    A high soil moisture content is desirable for plant growth.

    • Weigh a fresh soil sample, allow it to dry, and then weigh it again.
    • The difference between the two masses is the soil moisture content, which can be expressed as a percentage.
    • You can dry the soil sample using an oven at 105°C or leave it to dry overnight.

    The humus content of soil influences plants fertility.

    Humus is the dark organic matter of soil, made up of decomposing plant and animal matter.

    • Weigh a dry sample soil sample, burn off the humus in the soil, and then weigh it again.

    • The difference between the two masses is the humus content, which can be expressed as a percentage

    • The easiest way to burn off the humus is by using a furnace or a Bunsen burner.

    Microbiology sampling in the environment locates and identifies microbial populations. This can be key for environmental research or even investigating disease outbreaks.

    Environmental microbiology sampling is complex, but the main sampling techniques are summarised here.

    METHODHOW DOES IT WORKBENEFITSDRAWBACKS
    Swab-Rinse Method

    A cotton swab is dipped into a neutraliser and rubbed against the test area. The swab is returned to the neutraliser. 1ml of the medium is acquired and plated onto a petri dish.

    Agar is added for enumeration.

    This method is suitable for small sampling sites or uneven areas with cracks and crevices.Microorganism numbers may be altered in the neutraliser if the time between sampling and plating is too long.
    Rinse MethodThe surface is immersed in a sterile fluid and then agitated to detach microorganisms. This method is more accurate and precise than the swab method because the entire surface is sampled.The rinse method is the most accurate for enumerating viable microorganisms.The contaminant may not be soluble. It could also become trapped in the equipment.
    Agar Contact MethodA plate is gently placed onto selected surfaces to acquire samples and then incubated. This method is the easiest and most convenient sampling method. It can show continuous growth where discrete counting is too difficult.This method is not suitable for uneven surfaces.
    Direct Surface Agar Plating MethodSterile agar is pipetted onto the study area, evenly spread, and then incubated in a high humidity chamber. After incubation, the agar circles are flooded with staining aqueous solution and left at room temperature before counting.This method is the best for enumerating particulates containing viable microorganisms.Relatively hot agar may kill some contaminants and lead to small colonies being overlooked.

    Enumeration is the complete ordered listing of items.

    Environmental Sampling Methods - Key takeaways

    • Environmental sampling is essential because it helps us study the environment. Sampling needs to be reliable.

    • There are three types of sampling: random, systematic and stratified.

    • Environmental sampling techniques include quadrats, transects, species lists, the ACFOR scale, mark/release/recapture methods, and measuring abiotic factors.

    • Soil plays a crucial role in ecosystem functioning. Soil infiltration rate can be measured on-site. pH, humus content, moisture content and soil composition can be studied off-site.

    • Microbiology sampling is a complex field. Different sampling methods are suited to other sampling conditions.


    1. AQA, Environmental Science Specification. 2017

    2. Christina Simkanin, Using historical data to detect temporal changes in the abundances of intertidal species on Irish shores, Journal of the Marine Biological Association of the UK, 2005

    3. Chunlong Zhang, Fundamentals of Environmental Sampling and Analysis, 2007

    4. Dr Stefano Panzeri, Scholarpedia, 2008

    5. Field Studies Council, Sampling - The Basics, 2022

    6. Robert Angelotti, A Direct Surface Agar Plate Laboratory Method for Quantitatively Detecting Bacterial Contamination on Non-Porous Surfaces, 1958

    7. The Royal Society, Soil structure and its benefits: An evidence synthesis, 2020

    8. Sagar Aryal, Pour Plate Technique- Procedure, Advantages, Limitations, 2019

    9. Somayeh Ramandi, Evaluation of Swab and Rinse Sampling Procedures and Recovery Rate Determination in Cleaning Validation Considering Various Surfaces, Amount and Nature of the Residues and Contaminants, 2020

    10. Viroxy Labs, Environmental Monitoring Surface, 2022

    Frequently Asked Questions about Environmental Sampling Methods

    What is environmental sampling?

    Environmental sampling is the observation of the traits of a specified environment.

    How are environmental samples taken?

    Environmental samples are taken using measurement equipment such as transects and quadrats. There are also different methods for estimating population sizes, including the ACFOR Scale and the Lincoln Index.

    What is environmental sampling used for?

    Environmental sampling is used to collect data to support scientific theories, identify rare species or detect harmful microbes.

    What are the methods of environmental sampling?

    The three environmental sampling methods are random, systematic and stratified.

    What are environmental samples in microbiology?

    Environmental samples are used in microbiology to locate and identify microbial populations.

    Test your knowledge with multiple choice flashcards

    This type of sampling is used where every member of a population is equally likely to be included.

    This type of sampling is used where there is an environmental gradient.

    This type of sampling is used where the sample area can be subdivided.

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    Team Environmental Science Teachers

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