Seasonal dynamics in the inner Guayas Estuary, Ecuador

The Guayas estuary in Ecuador is the largest estuarine ecosystem on the Pacific coast of South America. This estuary provides nurseryand fisheries habitats, as well as filtering and detoxification services provided by suspension feeders, vegetation, and wetlands. Weused oceanographic and meteorological observations to understand the hydrodynamic variability of two areas in the inner part ofthe estuary, Manglares de Churute and Estero Salado, from February 2016 to February 2017. Churute has less anthropogenic impacts thanEstero Salado, which is currently uncoupled from river flow and highly influenced by Guayaquil, the second largest city in Ecuador, andadjacent shrimp pond effluents. The influences from the ocean and river on Churute include higher dissolved oxygen (DO) and lower salinity,temperature and phosphates than in Estero Salado, particularly during the wet season when the river is the dominant mode of forcing inthose warm and rainy first months of the year. Hypoxic levels (DO below 2 mg L-1) were found in Estero Salado in several stations duringthe hot, rainy season. These data suggest seasonal variability (dry/rainy season) influences the hydrographic conditions in the inner Guayasestuary mostly, adding variability to salinity, turbidity, nutrients and DO of the whole water column.