Scientists in many different fields – be it wildlife biology, epidemiology, sociology, psychology, anthropology, environmental science, etc. – may spend a significant amount of time “in the field”.
What being “in the field” entails will vary significantly depending on the occupation. For example, wildlife biologists may spend a lot of time in jungles or wetlands, while epidemiologists may be in villages in the developing parts of the world, studying emerging diseases. Sociologists and psychologists may consider “the field” to be the very neighbourhoods you live in!
Why are these scientists in the field? Well, a major reason is to collect samples. Sample collection is a vital part of fieldwork. In this article, we will be going over sample collection – its methods, its different types, and more.
Sample Collection: Definition and Importance
Let's begin with the definition of sample collection.
Sample collection (in environmental science) refers to the collection of specimens from the environment.
These specimens can be biotic or abiotic. What does this mean?
Biotic specimens are living organisms (e.g. animals, plants, fungi, microorganisms) in an ecosystem.
Abiotic specimens are the non-living components (e.g. air, soil, water) in an ecosystem.
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.
The presence or absence of certain freshwater invertebrates can indicate the level of pollution. For example, stonefly nymphs are only found in clean, unpolluted waters. In contrast, rat-tailed maggots are only seen in heavily polluted waters.
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.
- 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.
- Next, they collect the samples in the field.
- 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:
| Risk | Mitigation |
| Adverse weather conditions | - Check the weather forecast in advance
- Wear appropriate clothing
|
| Slipping and falling | - Wear suitable footwear
- Pay attention to your surroundings
|
| Falling into flowing water | - Stay away from river banks
- Pay attention to your surroundings
|
| Allergic reactions from plant stings | - Wear long sleeves and trousers
- Bring allergy medication
|
Sample Collection: Types, Location, and Methods
When planning your sample collection, you need to determine the following:
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.
During the wet season, water levels are high and forests often flood. Crocodilians spread out and hide more than during the dry season. So, conducting random crocodilian sampling during the wet season would yield inaccurate population densities.
Systemic Sampling
In systematic sampling, samples are taken at regular intervals.
These intervals could refer to time (for example, sampling a stream every hour) or distance (for example, collecting samples every 10m along a transect).
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:
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
Quadrats are frames placed in an area to designate sample collection sites.
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.
Measuring Equipment | Purpose |
| Surber Samplers | Collecting aquatic samples from river beds |
| Pitfall Traps | Collecting invertebrates, amphibians, and small reptiles from the ground |
| Sweep Nets | Disturbing invertebrates on leaves |
| Beating Trays | Collecting invertebrates fallen from leaves |
| Light Traps | Attracting insects at night |
| Tüllgren Funnel | Collecting arthropods from soil samples |
Fig. 2 – A light trap setup. Source: Wikimedia Commons
And this table details equipment suitable for measuring abiotic factors.
| Abiotic Factor | Measuring Equipment |
| Light Intensity | Light meter |
| Temperature | Thermometer |
| Humidity | Hygrometer |
| pH | Handheld digital probe or indicator solution |
| Wind Speed | Anemometer |
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.
When crocodilians are captured, they are marked by 'scute clipping'. This involves clipping their dorsal scute (a rigid plate near their head). These plates won't grow back, so animals who are scute clipped as hatchlings can be identified if they are recaptured decades later.
Simpson's Biodiversity Index incorporates both species richness and species abundance.
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.
| Species | n | n(n-1) |
| Birch | 7 | 7 x (7-1) = 42 |
| Alder | 12 | 12 x (12-1) = 132 |
| Oak | 3 | 3 x (3-1) = 6 |
| Holly | 4 | 4 x (4-1) = 12 |
| TOTAL | N = 26 | ∑ n(n-1) = 192 |
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!
Sample Collection - Key takeaways
- Sample collection in environmental science refers to the collection of specimens from the environment.
- Sample collection helps scientists understand the ecosystem and find evidence to support their theories.
- The most prominent types of sample collection are random and systematic sampling.
- Sampling locations need to be safe, accessible, and suitable. Sampling location is determined using transects or quadrats.
- Sample collection involves specialised equipment and making biotic measurements using your data.
- For laboratory use, samples may need to be reduced, but remain representative of the whole sample.
1. Nuffield Foundation, Invertebrate indicators of pollution, Practical Biology Student Sheet, 2010
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