The effects of tritiated water on competitive outcomes of two Daphnia species in lakes: A reaction–diffusion tritium-taxis model

The discharge of nuclear-contaminated water, particularly tritiated water (HTO), poses a significant global environmental challenge due to its potential negative impacts on ecosystems. To examine how such discharges influence the competitive dynamics between two Daphnia species in lake environments, we develop a spatiotemporal competition model that incorporates a tritium-taxis term. Our findings indicate that a moderate HTO input rate, combined with varying radiosensitivity between the species, can reverse the competitive outcomes between the two species. Specifically, species with lower radiosensitivity to HTO may compensate for competitive disadvantages, potentially enhancing biodiversity, or conversely, gain a competitive edge, which could reduce biodiversity. Moreover, a low HTO removal rate can lead to bistability or tristability in the system, while strong tritium-taxis promotes the development of spatially heterogeneous patterns. This study underscores the importance of considering the indirect effects of moderate HTO input and species-specific radiosensitivity, which can result in counterintuitive ecological dynamics.