Environmental Sampling Methods

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.

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.

Stratified Sampling

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

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

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.

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

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

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.

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.

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.

$Population=numberofanimalsin1stsamplex\frac{numberofanimalsin2ndsample}{numberofmarkedanimalsin2ndsample}$

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.

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.

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.

Abiotic Factors

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.

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.

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

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

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.

Soil Moisture Content

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.

Humus content

The humus content of soil influences plants fertility.

• 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.

Environmental Microbiology Sampling

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.

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