Invasive species have long been a global ecological problem, posing a threat to aquatic ecosystems. These invaders include submerged macrophytes such as Elodea nuttallii. Extreme rivers floods not only increase water levels and turbidity, but also scour out most of the biota. How the two negatives interact in freshwaters is very complex and remains controversial.

To find out, researchers from the Wuhan Botanical Garden of the Chinese Academy of Sciences conducted a three-year (2020-2023) field study and controlled indoor experiments on the Han River, which was previously dominated by the invasive species E. nuttallii.

The results showed that the extreme flooding caused a critical change in turbidity and transparency, the water quality could return to the initial condition after seven months, and the peak of the seasonal maximum biomass was delayed from July or August in 2020 and 2021 to October in 2022 after the extreme flooding. The biomass of E. nuttallii decreased significantly in 2022 after the flooding.

Meanwhile, the abundant propagule bank of native macrophytes showed a strong resilience to the extreme flooding, and their maximum total biomass in 2022 did not differ from that in the two years before the flooding, and short species were newly discovered in 2022.

This study shows that the extreme flooding can strongly suppress the invasive submerged macrophytes such as E. nuttallii. By artificial regulating water discharge from the upstream, it is a promising cost-effective method to solve the invasion of the alien species E. nuttallii in the Han River.

This work was published in Journal of Environmental Management entitled "Two negatives make an affirmative: can extreme flooding reduce the expansion of invasive submerged macrophyte in a large river?"