Using in situ hydro-chemical data and MODIS-SeaWiFS ocean color images as a proxy of river plumes and phytoplankton biomass from 2000 to 2014, this study documents the temporal co-variability of river discharge, plume area, nitrate and phosphate export and phytoplankton biomass in the coastal waters off Central Chile (33 •-37 • S). Five major rivers (Maipo, Mataquito, Maule, Itata, and Biobío) drain into this region with annual mean discharge ranging from 120 to 1000 m 3 s −1. River discharge and coastal plume area present a marked seasonal cycle, reaching maximum values during the winter rainy season (June-September). Export of riverine nutrients also peaks in winter, leading to an increase in phytoplankton biomass within the plumes that can be twice larger than the background values in coastal areas away from the river mouths. Wintertime river discharge, plume area and nutrient export are also correlated at interannual time scales. During a recent extended dry period (2010-2014), river discharges, plume areas and nutrient export clearly decreased by about 50% compared to historical values, reducing significantly the size of the chlorophyll pool within plumes off Central Chile during winter. The potential impacts of droughts are discussed in terms of coastal ecology and primary production, a highly relevant issue considering the projections of a dry climate over Central Chile in the future. Systematic evidence of mega-drought effects upon coastal productivity still does not exist, but it remains a priority to further investigate and quantify these impacts.

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Fjords and estuaries exchange large amounts of solutes, gases, and particulates between fluvial and marine systems. These exchanges and their relative distributions of compounds/particles are partially controlled by stratification and water circulation. The spatial and vertical distributions of N 2 O, an important greenhouse gas, along with other oceanographic variables, are analyzed from the Reloncaví estuary (RE) (~41°30′ S) to the gulf of Corcovado in the interior sea of Chiloé (43°45′ S) during the austral winter. Freshwater runoff into the estuary regulated salinity and stratification of the water column, clearly demarking the surface (<5 m depth) and subsurface layer (>5 m depth) and also separating estuarine and marine influenced areas. N 2 O levels varied between 8.3 and 21 nM (corresponding to 80 and 170 % saturation, respectively), being significantly lower (11.8 ± 1.70) at the surface than in subsurface waters in the Reloncaví estuary (14.5 ± 1.73). Low salinity and NO 3 − , NO 2 − , and PO 4 3− levels, as well as high Si(OH) 4 values were associated with low surface N 2 O levels. Remarkably, an accumulation of N 2 O was observed in the subsurface waters of the Reloncaví sound, associated with a relatively high consumption of O 2 . The sound is exposed to increasing anthropogenic impacts from aquaculture and urban discharge, occurring simultaneously with an internal recirculation, which leads to potential signals of early eutrophication. In contrast, within the interior sea of Chiloé (ISC), most of water column was quasi homohaline and occupied by modified subantarctic water (MSAAW), which was relatively rich in N 2 O (12.6 ± 2.36 nM) and NO 3 − (18.3 ± 1.63 μM). The relationship between salinity, nutrients, and N 2 O revealed that water from the open ocean, entering into ISC (the Gulf of Corcovado) through the Guafo mouth, was the main source of N 2 O (up to 21 nM), as it gradually mixed with estuarine water. In addition, significant relationships between N 2 O excess vs. AOU and N 2 O excess vs. NO 3 − suggest that part of N 2 O is also produced by nitrification. Our results show that the estuarine and marine waters can act as light source or sink of N 2 O to the atmosphere (air-sea N 2 O fluxes ranged from −1.57 to 5.75 μmol m −2 day −1 ), respectively; influxes seem to be associated to brackish water depleted in N 2 O that also caused a strong stratification, creating a barrier to gas exchange.