In this blog post, Franziska Fiolka and colleagues discuss their study investigating flooding as a vector for organic pesticides, linking aquatic and terrestrial ecosystems. They assessed regularly and rarely flooded riparian plant contamination profiles in small streams around the Upper Rhine valley and found more and higher concentrations of organic pesticides in regularly flooded riparian soil and plants.
Our field study explored the transfer of contaminants from the aquatic ecosystem to the terrestrial ecosystem via flooding. We investigated the organic pesticide contamination of riparian plants and their root-zone soil at five streams in the Upper Rhine valley. All sampling locations included two paired sites differing in their flooding frequency, one rarely and one regularly flooded site per stream (example stream in Figure 1). We sampled five different plant species, stinging nettle, blackberry, ivy, ground ivy, and alder in October 2022 at each site and analyzed them using UHPLC-MS/MS to measure 98 pesticides and metabolites.
Nine pesticides, six fungicides and three herbicides, were classified as regularly occurring contaminants and used in the following analysis. We found that regularly soil contained about 10 times higher average pesticide concentrations than soil in rarely flooded sites (Figure 2). Plants in regularly flooded sites contained pesticide concentrations more than twice as high compared to plants in rarely flooded sites (Figure 2). Prosulfocarb, pendimethalin, cyflufenamid, and flufenacet occurred at higher concentrations in plants than in soil, while the opposite result was found for spiroxamine, metrafenone, and boscalid. We could also show that the pesticide concentrations vary between the five plant species, with alder displaying the highest pesticide concentrations.
The riparian soil serves as a contaminant sink in the riparian zone and consequently as a contamination source for riparian plant species. Our study provides evidence from the field that nontarget plant species typical for riparian stream sites receive considerable pesticide exposure via flooding events. These plant species, such as the stinging nettle, are known to be important host species to a variety of insects, such as butterfly larvae. Therefore, the pesticides found in riparian plants may also be taken up by herbivores feeding on them. In summary, our results provide a first insight from flooding events in small streams that flooding acts as a vector that links aquatic source with adjacent terrestrial recipient ecosystems.
The publication titled Flooding as a Vector for the Transport of Pesticides from Streams to Riparian Plants was authored by Franziska Fiolka, Alex Roodt, Alessandro Manfrin, and Ralf Schulz