The objective of this research was to assess the phytoplankton diversity of San Pablo Lake and, based on its composition, determine its current trophic status. Samples were collected from May to August 2023 to account for seasonal variations. Taxonomic identification and photographic records were obtained using an inverted microscope equipped with a camera. A total of 77 species of microalgae and cyanobacteria, belonging to eight phyla, were identified. The most representative groups were Heterokontophyta (31 % of total species), followed by Chlorophyta (25%) and Charophyta (17 %). Cell density peaked in May, reaching 75,535 org/mL, coinciding with the highest rainfall levels. Microcystis aeruginosa, a potentially toxic cyanobacterium, was detected. Nitrogen and total phosphorus levels were elevated compared to other lentic ecosystems in the region. The saprobic index and organic pollution index confirm significant contamination and high organic pollution in San Pablo Lake, classifying it as eutrophic.

Nostoc sp. is a cyanobacterium identified in several localities of Ecuador, and it exhibits significant potential in the pharmaceutical, food, and environmental sectors, which urges the exploration of its possible applications in the country. Macrocolonies of Nostoc sp. were collected at different seasons, and the content of metals, sulfur, and biochemical composition was analyzed according to altitude and geographic position. The results showed that the average carbohydrate content corresponds to 30.34% dry biomass, 27.38% ash, 25.33% protein, 7.66% crude fiber, and 0.71% fat. Regarding the content of metals and elements, it was found that Aluminum presented the highest value of 2049.23 mg/kg, followed by 1786.74 mg/kg, 1364.08 mg/kg, and 443.12 mg/kg of Fe, Mg, and S, respectively, and with the lowest for Cu, Ni, Pb, and Cd of 7.34 mg/kg, 5.62 mg/kg, 3.99 mg/kg and 0.74 mg/kg; respectively; with the following descending order: Al>Fe>Mg>S>Cu>Ni>Pb>Cd at all sites sampled and regardless of altitude and period of rain or drought. Consequently, its potential to adsorb these elements from the environment is preliminarily demonstrated, showing that it could be used in applications for bioremediation of contaminated soils and waters or be an essential bioindicator of environmental pollution.

Phytoplankton are key indicators of water quality and low-cost tools for freshwater monitoring, yet their diversity and ecological drivers remain poorly documented in the Tropical Andes. This study provides the first national-scale, multi-ecosystem assessment of net phytoplanktonic communities (including microalgae and cyanobacteria), across Ecuador, integrating physicochemical, multivariate, and geospatial analyses. Eighteen lakes and rivers from three biogeographic regions and a wide altitudinal gradient were surveyed, yielding 129 taxa, 77 identified at species level, the most comprehensive checklist reported to date for Ecuador. Community structure showed a clear lentic–lotic differentiation driven by hydrodynamic contrasts, while the absence of distance–decay patterns indicated high dispersal and environmental filtering pattern rather than spatial structuring. Anthropogenic pressure acted as a secondary gradient: pristine high-Andean lakes were dominated by desmids and diatoms, whereas agricultural and urban basins showed chlorophyte and potentially toxic cyanobacterial assemblages. Palmer’s Index detected organic pollution but underestimated eutrophication in endorheic, geochemically enriched lakes. Land-use effects presented strong basin-scale signals in lakes but weak correlations in rivers due to overriding hydromorphological constraints. These findings establish a robust spatial baseline for freshwater bioassessment in the Andes, demonstrating the value of phytoplankton as effective, low-cost indicators readily applicable to national water-quality assessment programs.

Microplastics (MPs) are emerging contaminants in freshwater systems, yet their sources and transport pathways in tropical high-altitude lakes remain poorly understood. This study quantified and characterized MPs in two Andean lakes in Ecuador with contrasting watershed conditions: San Pablo (2672 m a.s.l.), influenced by agricultural and urban land use, and Caricocha (3724 m a.s.l.), a protected high-Andean lake. Sixteen samples per lake were collected during four field campaigns. MPs were identified using visual and morphological criteria, and classified by shape, color, and size. MP concentrations were higher in San Pablo (238 ± 32 MP m⁻³, mean ± SD) than in Caricocha (32 ± 10 MP m⁻³). Fibers dominated (87.3%), followed by fragments, while microspheres were detected only in Caricocha. MP concentrations showed positive correlations with urban-agricultural land use (ρ = 0.87, p < 0.0001) and negative correlations with natural vegetation cover (ρ = −0.87, p < 0.0001). Principal Component Analysis linked fiber abundance and small size classes (<500 µm) and anthropogenic land use, consistent with surface runoff and wastewater-associated pathways. In contrast, MPs in the protected lake may originate from long-range atmospheric deposition. These results indicate that watershed configuration and protection status shape MP inputs in high-Andean lakes.

Se investigó la diversidad de los géneros Monactinus, Pediastrum, Pseudopediastrum y Stauridium en dos lagos eutróficos de alta montaña en los Andes ecuatorianos: San Pablo y Yahuarcocha, a fin de aportar al conocimiento de la ficoflora local. Estas algas verdes, pertenecientes a la familia Hydrodictyaceae, presentan variedad en cuanto a forma y tamaño; además pueden ser utilizadas como bioindicadores de la calidad del agua y revelar variaciones de temperatura. Las muestras se recolectaron entre noviembre de 2023 y enero de 2024, mediante arrastres con red de plancton de 24 µm de abertura de poro en la zona limnética y raspado de raíces de plantas acuáticas en zonas litorales. Las muestras fueron preservadas con solución de Transeau. Se identificaron once especies, de los cuales cinco fueron exclusivas de la Laguna de Yahuarcocha, cuatro del Lago San Pablo y dos se encontraron en ambos cuerpos de agua. Este estudio amplía el conocimiento de la ficoflora andina ecuatoriana, superando registros previos en el país. Se reportan siete nuevos registros: Monactinus simplex var. duodenarium, M. simplex var. echinulatum, M. simplex var. sturmii, Pseudopediastrum boryanum var. longicorne, Ps. brevicorne, Stauridium tetras var. apiculatum y S. tetras var. excisum. Esta contribución resalta la importancia de continuar y ampliar los estudios taxonómicos de la ficoflora del Ecuador.