Limnological responses to active management of the invasive aquatic fern Salvinia molesta in Las Curias Reservoir, San Juan, Puerto Rico.

In the Anthropocene, human action and globalization are closely linked to the deterioration of natural habitats and water resources. Invasive aquatic weeds have been recognized as a major problem in watersheds worldwide due to their environmental impacts. This study focuses on the management of the Las Curias Reservoir in Cupey Puerto Rico in the Río Piedras watershed since the arrival of Salvinia molesta after Hurricane María in 2017.
Aquatic weed control consists of three methods: biological, mechanical, and chemical. Since December 2019, with the help of federal and local agencies, the University of Puerto Rico in Rio Piedras and a community-driven initiative led to the introduction of the Cyrtobagous salviniae in Las Curias Reservoir.  This insect is considered an effective biological control agent for S.  molesta.  Simultaneously, community members initiated a mechanical removal campaign using an aquatic harvester. Monthly sampling was conducted to measure physicochemical, biochemical, and biophysical variables in the reservoir in response to the reduction of S. molesta cover. In addition, monthly drone flights were conducted to create orthomosaic maps of the plant coverage over the water surface, as part of the monitoring of the ecosystem health and characterization. Probably the propagation of S. molesta occurred due to eutrophication after an increase in nutrient-rich sewage discharges from septic tanks and faulty sewage pump stations affected by power outages after Hurricane Maria. By 2019, the reservoir was completely covered with S. molesta. It is not until August 2020 that we noticed considerable changes in the reduction of plant density. Upon the reduction of S. molesta coverage, we found increases in the mean of water temperature (+3 Cِ°), dissolved oxygen (+1.4 mg/L), pH (+0.5) specific conductance (+118.3 µS/cm) and in light penetration (+255.6 μmo/m^²/s).  The water stored in Las Curias could become an invaluable source of raw water for public supply during future droughts, especially in the densely populated San Juan Metropolitan Area, where Las Curias is located. Therefore, its restoration is socially relevant and justifiable.