Sample Collection

Sample Collection: Definition and Importance

Let's begin with the definition of sample collection.

These specimens can be biotic or abiotic. What does this mean?

Sample Collection in Research

Sample collection is vital to environmental research. It allows scientists to learn more about ecosystems.

For example, taking samples from a stream can determine how polluted it is, and whether each native species is present.

Collecting samples from the environment also helps scientists find evidence to support their theories. The evidence turns the scientist's idea into a fully-fledged, accepted theory.

Sample Collection: Procedure

When planning out their sample collection, scientists follow a specific procedure.

1. Firstly, the scientists write a sample collection plan. This details where and when the samples will be taken, and why they need to be collected.
2. Next, they collect the samples in the field.
3. Finally, they ensure that the samples collected are safely contained until they are ready to be used.

It's important to follow this specific procedure for ethical reasons. Planning out what you're going to do, instead of wandering into an ecosystem and thoughtlessly grabbing specimens, will minimise disturbance and damage to the ecosystem. Safely containing samples – especially if they are live animals – prevents further distress and risk to life. Plus, it prevents any major change or degradation before analysis (there's more about this later on, so keep reading).

Plus, planning ahead gives us time to make a risk assessment. These identify potential risks and how to mitigate against them. For example:

Sample Collection: Types, Location, and Methods

When planning your sample collection, you need to determine the following:

• Type of sample collection

• Sampling location

• Sampling methods

Types of Sample Collection

The two most prominent types of sample collection are random and systemic.

Random Sampling

In random sampling, every member of the population has an equal chance of being sampled. Random sampling is likely to produce unbiased results that are representative of the population.

However, it's not without its issues. Random sampling is time-consuming, so it's best suited to a small sampling area. Furthermore, random sampling needs to take the behaviour of the target species into account.

Systemic Sampling

In systematic sampling, samples are taken at regular intervals.

Systematic sampling is quicker and easier than random sampling, but may lead to skewed results if the population exhibits an undetected pattern.

Sample Collection Location

Sampling locations should be:

• Safe

• Accessible

• Suitable for your investigation

Once you have determined your sampling location, you need to gather the right equipment.

Sampling Location

A transect is a line placed across a habitat. It's useful in sampling locations that experience an environmental gradient (a change in abiotic factors that influences the organisms present).

There are two kinds of transects: line and belt.

• Line transects are one-dimensional transects. Every individual who touches the line is identified and counted.

• Belt transects use a rectangular area instead of a line. They supply more data than a line transect, but are more time-consuming to use.

Either kind of transect can be continuous or interrupted.

• Continuous transects record every individual that touches the transect. They provide a high level of detail, but are very time-consuming to use. As a result, they're only suitable for short distances.

• Interrupted transects record individuals at regular intervals. Using an interrupted transect is much quicker, but doesn't provide as much detail as a continuous transect.

Quadrats

Fig. 1 – An open frame quadrat, covering 1m². Source: Wikimedia Commons

There are three types of quadrat used in environmental science:

• Open frame quadrats consist of a simple square frame, typically 1m² in size. They're particularly useful for sampling rocky areas, as the open frame allows for easy lifting and inspection.

• Grid quadrats consist of a square frame with many smaller square 'grids' within (normally 25 or 100). They're ideal for use in areas with thick vegetation.

• Point quadrats are very different from the other two quadrats; they consist of a T-shaped frame containing 10 long pins. The quadrat is pushed towards the ground. Organisms hit by the pins are identified and counted.

Sampling Methods

When determining your sampling method, you need to determine the equipment needed, and biotic measurements you will make.

Sampling Equipment

This table provides a summary of equipment used for sampling biotic factors.

Fig. 2 – A light trap setup. Source: Wikimedia Commons

And this table details equipment suitable for measuring abiotic factors.

Biotic Measurements

There are many ways to quantify the biotic and abiotic components of an ecosystem.

The DAFOR scale is a useful way to obtain an estimation of species abundance in a relatively short space of time. It's mostly used to determine vegetation abundance based on coverage. DAFOR stands for the coverage values identified:

• (D)ominant: >75% coverage

• (A)bundant: 51-75% coverage

• (F)requent: 26-50% coverage

• (O)ccasional: 11-25% coverage

• (R)are: 1-10% coverage

The Lincoln Index is used to calculate the population size of a certain animal species by utilising the 'capture, mark, recapture' method. Several animals are captured, marked in some way, then released. At a later data, more animals are captured. The proportion of marked animals that are recaptured allows scientists to estimate the population size.

Simpson's Biodiversity Index incorporates both species richness and species abundance.

$D=1-\left(\sum _{n(n-1)}/N(N-1)\right)$

Where:

• D: diversity index (from 0 'no diversity' to 1 'infinite diversity')

• N: total number of all organisms

• n: number of individuals of a particular species

Let's do a worked example.

D = 1 – (192 ÷ 26(26-1))

D = 1 – (192 ÷ 650)

D = 0.70

Sample Collection in the Laboratory

When collecting samples for laboratory use, they need to be carefully monitored to make sure that they do not degrade or significantly change before analysis. That's one of the reasons why it's important to follow sample collection procedure!

Often, collected samples are too large or unwieldy for use in the lab, so they must be reduced in size. These reduced samples are portions of the larger sample that are deemed representative of the whole.

Once the reduced sample is adequately prepared for analysis, it is considered to be a test sample. Any subdivisions of this test sample are referred to as test portions. These are the final parts of the sample that will be used in the test.

Hopefully you now know a bit about the methods and types of sample collection that scientists might carry out in “the field” now. Maybe you're even using what you've learnt to plan your next fieldtrip!

^{1. Nuffield Foundation, Invertebrate indicators of pollution, Practical Biology Student Sheet, 2010}