Invasive species have long been a global ecological concern, causing a hazard for aquatic ecosystems. Among these invaders are submerged macrophytes like Elodea nuttallii.

Extreme flooding in rivers not only comes with the higher level and turbidity, but also resets almost all the biota by scouring. How the two negatives interact with each other in the fresh waters is very complex and remains controversial.

In order to figure out this question, researchers from Wuhan Botanical Garden conducted research in the Han River that used to be dominated by the invasive species E. nuttallii based on the three-year (2020-2023) field survey and controlled indoor experiments.

Results showed that the extreme flooding caused a critical change of turbidity and transparency, the water quality could return to the initial condition after seven months, and the peak of seasonal maximum biomass 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.

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

This study revealed that the extreme flooding can strongly suppress the invasive submerged macrophytes like E. nuttallii. By creating artificial regulation of water discharge from the upstream is a promising cost-effective method to solve the invasion of alien species E. nuttallii in Han River.

Results have been 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?”.