By Anne Bloksgaard Nielsen. Photo: Lars Horn

Denmark has an incredibly rich freshwater system with around 69,000 kilometres of streams. When utility companies treat wastewater and rainwater from the sewage systems, the treated wastewater is discharged into nearby streams.

However, extreme weather events caused by climate change have increased the risk of overflows from wastewater treatment plants, where untreated wastewater flowing into the streams may have detrimental effects on the flora and fauna of the streams.

Urgent need for new monitoring methods

Current environmental monitoring systems for streams function by analysing primarily sediment samples (and the invertebrates within) gathered from the streams. This method cannot be used to monitor the effects of such incidents effectively, though: The species used as the baseline are only present in the sediment of the streams at specific times of year, as later they will develop into flying insects and leave the water.

In addition, the traditional methods can be time consuming, which is problematic when a fast answer is needed.

Since extreme weather incidents – or accidental discharges from wastewater treatment plants – can occur all year around, new methods are needed that will enable the utility companies to monitor the streams continually, quickly and in detail.

The protocol for one such method is currently being developed by Assistant Professor at the Department of Chemistry and Bioscience Nadieh de Jonge, in collaboration with Professor Jeppe Lund Nielsen from the Environmental Biomonitoring research unit at the Department, the utility company SK Forsyning A/S in Slagelse, and the consulting engineer companies NIRAS A/S and DMR A/S.

In the project, eDNA (environmental DNA) will be used as the key to monitoring the biodiversity of streams all year round – in a method that aims to be so convenient to use that the utility companies will be able to do it themselves.

The project “Spildevands påvirkning af biodiversitet” (Impact of wastewater on biodiversity) is funded by the Environmental Technology Development and Demonstration Programme (MUDP).

"With this eDNA-based method, we can gather, sequence and identify DNA from all organisms in the water column – including, for instance, the organisms in the bottom of the stream, those who have swum by, and the bacteria present naturally in the water or released with the wastewater from the plants. This will allow us to offer a much more detailed baseline for the state of Danish streams through mapping out the various organisms present over the course of a couple of years", says Nadieh de Jonge.

Providing vital information for wastewater treatment plants

In addition to offering a more detailed and diverse view on the biodiversity of the streams, the project is working towards making the sampling process easier for the wastewater treatment plants, as they themselves will be able to gather samples and make eDNA analyses in their own laboratories.

As an example, project partner Dansk Miljørådgivning (DMR A/S) is looking into automatic sampling through developing small sample boxes that can be placed in the water. In case of overflow or accidental discharges, the utility company can trigger the sample boxes, which will gather water samples containing DNA that can be sequenced. This will provide both a status of the biodiversity in the stream at the point in time when the overflow started, and information on how the overflow incident has affected it – in the short as well as the long term.

“Our aim is to present a protocol for a standardised, scalable and economically viable system for sampling, sequencing and analysing that utility companies themselves can use. Today, we have DNA sequencing machines so small that the end-user can use them in their own laboratories – all they need is a powerful computer. They can then compare their results with the new, more detailed baseline list of species of the stream at that specific time of year and get a reliable picture of its current state,” she explains and finishes:

“By offering a system that can be easily installed at key locations, and where the utility companies can do the sample analysis in-house, it will be possible to monitor the nearby streams continually. This will enable them to both discover accidental discharges but also to see how overflows impact the stream, and whether a critical level of overflow discharge has been reached because the biodiversity has started to change. This lets them react more quickly in order to limit potential damage to the vulnerable streams – thereby offering even better protection for our valuable and vulnerable freshwater environment.”