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Environmental DNA: What is it and why does it matter

Understanding the number and size of animal species in a specific ecosystem is an important part of environmental management and conservation. However, traditional methods of tracking animal species are time-consuming and sometimes of questionable accuracy. Environmental DNA offers a new method for tracking animal species within an ecosystem. A tracking method that is more comprehensive and also less time-consuming than existing ones.

The USGS describes environmental DNA as follows. Environmental DNA (eDNA) is organismal DNA that can be found in the environment. Environmental DNA originates from cellular material shed by organisms (via skin, excrement, etc.) into aquatic or terrestrial environments that can be sampled and monitored using new molecular methods. Such methodology is important for the early detection of invasive species as well as the detection of rare and cryptic species.

So, part of the beauty of eDNA is its ability to yield a wealth of information about species that are hard to detect by traditional survey methods.

Before eDNA

Traditional methods of monitoring animals in a particular location include looking for signs, visual sightings, and camera traps.  However, all of these methods provide low reliability when tracking secretive or low-density species. Visual sightings and looking for signs like footprints or feces are manpower intensive, and they also require constant monitoring over long periods to get quality datasets. However, even over time, these methods will fail in detecting some species. 

Camera traps eliminate the need for the onsite presence of observers. However, the resulting information is heavily dependent on camera locations and the random chance of a passing animal walking into view. 

Ecology researchers have long recognized the short comings of traditional methods but lacked alternatives. Environmental DNA provides a viable alternative.  

It’s all in the water

Recent eDNA research done in Scotland and England focused on data collection at the scale of a watershed. Water and sediment samples from streams and rivers provided a rich set of raw material for eDNA analysis. The logic behind this approach is simple – gravity. A single watershed collects water from a defined area, and all of that water then passes through a single constriction point. This constriction point occurs along the river or stream at the mouth of the watershed.

By definition, a watershed funnels all water runoff to its geographically lowest point. Gravity also takes anything dissolved in the water to this low point at the base of the watershed. So, water samples taken there contain animal DNA from the entire watershed upslope of the sample. Even secretive or low-density species will then contribute DNA to the water runoff.  

The collection of eDNA now opens a new window into environmental conservation and the management of ecosystems. Hopefully, eDNA’s role in the detection of biodiversity then provides a more accurate picture of what species live within individual ecosystems. The method may also yield information on population size and density, thus allowing researchers to detect invasive species, declining species, and secretive animals. Good science depends on good data, and eDNA is improving the quality of our ecological databases.


Environmental DNA in rivers offers new tool for detecting wildlife communities (Source: University of Massachusetts Amherst; Science Daily) – Also:

Environmental DNA (eDNA) (Source: USGS)  – Also:

Feature Image: Mountain stream (By Eirian Evans) (Modified) –  –  This file is licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license. –

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.