TY - JOUR T1 - The impacts of global and local change on a tropical lake over forty years JF - bioRxiv DO - 10.1101/2020.10.21.347393 SP - 2020.10.21.347393 AU - Jemma M. Fadum AU - Ed K. Hall Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/10/22/2020.10.21.347393.abstract N2 - Lakes across the world are experiencing novel trophic states, declining water quality, and altered biogeochemical cycling due to the synergistic impacts of global change and local anthropogenic stressors. In the tropics these changes can be difficult to assess due to a lack of continuous monitoring or documented legacy conditions to serve as a reference for the contemporary lake. Over the last forty years, Lake Yojoa, located in west central Honduras, has shifted from an oligotrophic to mesotrophic ecosystem as evidenced by a loss of water clarity. To assess the changes that have occurred in Lake Yojoa as well as putative drivers for those changes, we compared secchi depth, dissolved inorganic nitrogen, and total phosphorus concentrations between 1979-1983 and today (2018-2020). While we found little change in total phosphorus between legacy and contemporary data, we found concurrent changes to seasonal trends in secchi depth and dissolved inorganic nitrogen (DIN). Seasonal peaks in DIN coincident with mixus suggest that accumulation of ammonium in the hypolimnion during stratification, and release to the epilimnion with mixus maintains algal productivity in what was previously a nutrient-limited, clear water phase, driving a change in the overall trophic state of Lake Yojoa. This impact of seasonal dynamics on the trophic state of the lake illustrates a key distinction in how physical structure and nutrients interact differently in tropical and temperate lake ecosystems and highlights the importance of warm anoxic hypolimnions to the biogeochemistry that governs the trophic state of tropical lake ecosystems.Competing Interest StatementThe authors have declared no competing interest. ER -