Trace Biomonitoring · Sampling Guidance

Creating your
sampling strategy

Deciding where to take your samples, where to take your subsamples, and how many samples to take, is project specific and dependent on budget, goals, and habitat type. Generally, the more samples you take, the more representative your data will be. But, locating your samples strategically can cut down on costs and maximise results.

Number and location of samples

A few rules of thumb for choosing number of samples and locations of samples:

Still waterbodies — ponds & lakes

Still waterbodies, such as ponds and lakes, create more localised areas of eDNA. Therefore, in ponds and small lakes, you should aim to filter water from all distinct microhabitats, and space your samples roughly every 50m around the perimeter.

For larger lakes, you should aim for a minimum of 1 sample per 200m of shoreline to maximise your chances of capturing rare or elusive species, and capturing representative data. It is important to also place samples in areas where eDNA might accumulate, such as in sheltered bays or water inflows.

On tighter budgets, or for particularly big lakes, subsamples can be used to maximise the amount of eDNA collected in order to reduce the number of samples required (see advice below).

Moving waterbodies — rivers & streams

In faster moving waterbodies, such as rivers, eDNA travels and mixes more readily. Therefore, sample sites should be spread further apart than on still waterbodies to increase the chances of detecting species unique to the sites.

How far you space your samples will depend on how fast flowing the river is. Here are a few rules of thumb:

Slow moving streams (flow velocity <0.3m/s)

Space samples roughly 100–200m apart.

Medium rivers (flow velocity 0.3–0.8m/s)

Space samples 200–500m apart.

Fast rivers (flow velocity >0.8m/s)

Space samples 500m–1km apart.

It is also important to sample above and below any significant tributaries, as these can dilute eDNA in the main river as well as introducing new DNA.

If you are specifically targeting species that you know to be rare or sparse (such as white-clawed crayfish or water voles), then tighter spacing between samples is recommended.

Subsamples

When using our biodiversity services, subsamples are an important part of the sampling protocol (subsamples are less important if you are targeting bacteria/pollution tracking, but still good practice).

Subsampling simply refers to the act of collecting multiple small samples of water from each sampling site, and pooling them together into your main sample. By doing this, you maximise the amount of DNA you collect, and capture a representative sample by including areas where DNA may become localised or trapped (e.g. in pools or riffles of rivers).

To subsample effectively, you should aim to take around 10-15 small samples within one sampling bag. This can either be done by dipping the sampling bag into the water at multiple points, or you can use a small container or plastic water bottle (sterilised) to collect and decant into the bag. We have a range of equipment, including sampling poles for extending reach, available at an additional cost. Alternatively, you can use the syringe to draw water directly from the waterbody, and move each time you take up a new syringe of water, to subsample. If you are getting into a river to sample, just ensure you start downstream and move upstream as you go, to avoid contaminating the sample with DNA from your boots/waders.

Important note on equipment sterilisation

If re-using equipment such as sampling poles, these should be disinfected between sites using a 10% solution of bleach and tap water.

Where you take your subsamples will depend on your specific goals and the accessibility of your site. As a general rule of thumb:

Rivers

Subsamples should be collected along the width (e.g. some from the left bank, middle, and right bank of the sample location), and should include any riffles or pools nearby.

Lakes & ponds

A subsample can be taken every 10–20 metres along a stretch of shoreline.

Need help planning your sampling strategy?

Creating yoursampling strategy

Number and location of samples

Subsamples

Creating your
sampling strategy