Evaluation of the Trophic State of Lagoons and Reservoirs in the High Andean Southern Peru

Introduction: High Andean lagoons in southern Peru have critical hydrological and ecological functions; however, long-term time series integrating trophic, integral quality, and metal contamination metrics to support adaptive management are lacking. Methods: A total of 1,846 records (2015–2024) from four systems (3,100–4,600 m asl) were analyzed using seven indices (CTSI, TRIX, OWQI, WQIHA, CCME-WQI, HPI, and CD). Temporal trends were assessed by using Mann–Kendall and Theil–Sen slope; spatial heterogeneity using Kruskal–Wallis and Dunn–Bonferroni comparisons; controlling factors using distance-based redundancy analysis (999 permutations); and functional typology using Ward's hierarchical clustering on Z-standardized data. Results: 97% of the series lacked monotonic trends, demonstrating high interannual stability; spatial variance was marked (ε² = 0.73 in CCME-WQI). db-RDA explained 24.6% of the total variability by lake identity, year, and wet-dry period. Four functional archetypes emerged, including a metal-eutrophic hotspot (HPI ≈ 213; CD ≈ 25 µg L⁻¹) and recovering reservoirs with CCME-WQI ≈ 63. CTSI thresholds ≥ 60 combined with HPI ≥ 100 signaled the transition to cyanobacterial dominance. Conclusions: Systems show temporal resilience but strong spatial divergence induced by local pressures; The proposed typology and thresholds provide an operational basis for early warnings and prioritization of remediation actions in high-mountain ecosystems subject to increasing anthropogenic stress.