Abstract

Coastal ecosystems depend on local marine productivity and the subsidized productivity of fluvial systems. Terrestrial subsidies in insular ecosystems represent a relevant source of nutrients for many coastal communities, so variations in these contributions can cause negative impacts. We evaluated the allochthonous contributions of suspended particulate material (SPM) and macronutrients from the Huenque River and their effect on microalgal assemblages in the coastal wetland of Chiloé Island and changes in the vegetation of the banks of the Huenque River using the Normalized Vegetation Index (NVDI) over 6 years. We recorded that progressive deforestation, mainly of the lower part of the Huenque River basin, and increases in insular rainfall during the study period contributed to temporary increases in suspended particulate matter (SPM), silicon (SiO2), and orthophosphate (PO4) to the Huenque River which were transported to the coastal wetland, causing temporary changes in the microalgal assemblages. The altered biomass and community composition are explained as responses to the variation of N:P. The highest abundance of microalgae (4.15 × 106 Cel/L) and (N:P 22:1) were observed in 2012. Anthropic disturbances, including deforestation of watersheds, are directly related to increases in macronutrient inputs to coastal ecosystems through rivers. © 2023, The Author(s), under exclusive licence to Coastal and Estuarine Research Federation.