This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Can DNA traces in just two liters (0.5 gallons) of water reveal how a river's biodiversity changes over the course of a year? A study by the University of Duisburg-Essen using the River Lippe as an example shows how biodiversity in freshwater ecosystems can be monitored comprehensively, efficiently and at comparatively low cost.
The results have now been published in the journal Ecological Indicators. Till-Hendrik Macher and Robin Schütz, both doctoral researchers in biology at the University of Duisburg-Essen at the time of the study, visited the restored mouth of the River Lippe near Wesel every two weeks for a year, filtering two water samples on each occasion—26 sampling events and 52 samples in total. Across these samples, they detected a total of 1,072 species: 40 fish and lamprey species, 41 bird and 26 mammal species, 425 freshwater and 350 terrestrial invertebrate species, as well as 190 diatom species.
By comparison, the Global Biodiversity Information Facility (GBIF) lists a total of 1,029 species for the same location, based on records accumulated over more than 130 years. Conventional monitoring methods involve identifying individual organisms using nets, forceps, magnifying glasses and microscopes. DNA metabarcoding, by contrast, can identify species from the genetic information they leave behind in environmental samples.
"With two liters (0.5 gallons) of water per sampling event, we detected 1,072 species across the tree of life—from diatoms and mayflies to beavers," says Macher, first author of the study, who now conducts research at Trier University. "And we were able to show that our data actually reflect the biology of the River Lippe rather than merely DNA that happened to be washed into the river," adds Schütz, who now works as a scientist at the German Federal Agency for Nature Conservation. "Winter-spawning fish such as burbot and northern pike, for example, showed their eDNA peaks in winter, while the greater white-fronted goose peaked precisely during its wintering period." The study found that the seasonal patterns detected by eDNA largely reflected species-specific biological processes.
The approach is also economically attractive, as the demand for this kind of biodiversity data is growing. Both the Kunming-Montreal Global Biodiversity Framework (GBF) and national and European reporting requirements call for a spatial and temporal density of biodiversity data that is difficult to achieve using conventional methods alone. Using Macher and Schütz's approach, analyzing all 52 samples cost around €12,000.
A comparable conventional survey of the same groups of organisms over the course of a year would cost around €70,000—roughly six times as much. Overall, the study found eDNA monitoring to be highly cost-effective, providing substantially more biodiversity information than many conventional surveys at a fraction of the cost. Under the EU Water Framework Directive, an average of 1.71 of the four biological quality elements—fish, invertebrates, microalgae and aquatic plants—are currently assessed per river, while only a small proportion of water bodies are evaluated using all four.
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