Protected land enhances the survival of native aquatic macrophytes and limits invasive species spread in the Panama Canal

This study examined whether protected land in a tropical reservoir's catchment can promote the survival of native aquatic plants (macrophytes) and limit the spread of invasive alien plant species (macrophyte IAS), which can threaten native wildlife and require expensive remediation. As the number of tropical river dams is expected to increase in the coming decades to meet societal demands, it is crucial to explore solutions for preserving aquatic biodiversity.The study used a before-after-control-intervention design, based on monitoring data and long-term sedimentological, climatic and ecological records from both lake and river zones adjacent to protected and unprotected lands around the 100-year-old Gatun Lake in the Panama Canal, Panama. The research examined the impact of impoundment and the invasion of Pontederia crassipes (water hyacinth) and Hydrilla verticillata (water thyme) on native macrophyte communities and environmental variables.Lake zones adjacent to protected lands had lower nutrient concentrations, greater variations in water depth profiles and reduced fluctuations in water chemistry than lake zones outside areas of land protection. In addition, the results showed that whereas zones adjacent to unprotected land became dominated by macrophyte IAS, lake zones adjacent to protected areas were more resilient to the spread of macrophyte IAS and were able to maintain viable populations of native pre-dam species for >100 years.This study indicates that protecting land adjacent to tropical reservoirs could be a cost-effective solution for preserving aquatic macrophyte biodiversity by retaining nutrients, stabilizing water chemistry, providing habitat heterogeneity and protecting native vegetation, while still supporting terrestrial conservation goals. These findings could aid in planning measures for the hundreds of proposed dam projects across lowland tropical areas and provide new insights into best practices for enhancing river ecosystem resilience.