Characterization and comparison of microphytoplankton biomass in the lower reaches of the Biobío River and the adjacent coastal area off Central Chile during autumn winter conditions

Abstract

ABSTRACT. The Biobío River in central Chile is the third largest watershed and second largest river in Chile in terms of discharge volume. Three sampling campaigns were made in the lower reaches of the river and the adjacent coastal ocean to evaluate the influence of the river plume on the physical/chemical conditions and the abundance/biomass of microphytoplankton during autumn-winter conditions. In addition, a preliminary quantification of riverine nutrients, dissolved silica, and phytoplankton carbon flux to the adjacent ocean was also conducted. High nitrate (NO 3 -) and silicic acid (Si(OH) 4 ) concentration (>18 and 50 µM, respectively) was observed in the lower reaches of the river during all field campaigns. Si(OH) 4 was even high in surface river plume waters. Hydrographic conditions indicate that river plume waters were piled coastward, and they could drove to the south at the Arauco Gulf. In all sampling, highest microphytoplankton biomass (>5000 μgC m -3 ) was associated to the lower reaches of the river and river plume waters as they were moving southward. During autumn-winter conditions a significant flux of phytoplankton carbon and nutrients to the adjacent coastal ocean also played an important role in the high biological productivity of this coastal upwelling area. These preliminary results evidence the need to conduct large-term studies, which should consider the importance of these allochthonous carbon sources in global carbon budgets and coastal food-web models. Keywords: phytoplankton carbon, river plume, nutrient fluxes, silicic acid, coastal food webs, Chile.Caracterización y comparación de la biomasa microfitoplanctónica en el curso inferior del río Biobío y la zona costera adyacente frente a Chile Central durante condiciones de otoño-invierno RESUMEN. El río Biobío, en la zona central de Chile es la tercera cuenca más grande y segundo río más grande de Chile en términos de volumen de descarga de agua dulce. Se realizaron tres campañas de muestreo en el curso inferior del río y la zona costera adyacente para evaluar la influencia de la pluma del río Biobío, en las condiciones físicas/químicas relacionadas con la abundancia/biomasa del microfitoplancton en condiciones de otoño-invierno. Además, se realizó una cuantificación preliminar de los flujos de nutrientes fluviales, sílice disuelta, y el flujo de carbono fitoplanctónico al océano adyacente. Se observó alta concentración de nitrato (NO 3 -) y ácido silícico (Si(OH) 4 ) (>18 y 50 μM, respectivamente) en el curso inferior del río en todas las campañas de terreno. La concentración de Si(OH) 4 fue también alta en las aguas superficiales de la pluma del río. Las condiciones hidrográficas revelaron que las aguas de la pluma del río se apilaron hacia la costa y al sur, en el golfo de Arauco. En todas las muestras, la más alta biomasa microfitoplanctónica (>5000 μgC m -3 ) estuvo asociada a la porción baja del río y las aguas de la pluma que se estaban moviendo hacia el sur. Durante las condiciones de muestreo en otoño-invierno el significat...

Influence of coastal upwelling on micro-phytoplankton variability at Valparaíso Bay (~33ºS), Central Chile

“…Therefore, recent studies have suggested changes in the upwelling versus nonupwelling cycle at Concepcion Bay (~36.5ºS) due to the key role of river discharge in coastal systems (Testa et al 2018). In this bay high nutrient concentrations have been described along the year associated to Itata river input and coastal upwelling activity with peaks in winter and spring, respectively (Léniz et al 2012, Anabalón et al 2016.…”

“…These changes are not related to river discharge as seen in other coastal upwelling systems, (e.g., California/Oregon, NW Iberian-Portugal coasts), or even in central-south Humboldt area. In those areas, freshwater input leads to changes in phytoplankton structure, biomass (Chl-a) and PP (Warrick et al 2005, Silva et al 2009, Iriarte et al 2012, Léniz et al 2012, Testa et al 2018, Aparicio-Rizzo & Masotti 2019.…”

“…However, nutrients from rivers in Central Chile can also impact the phytoplankton (Iriarte et al 2012, Anabalón et al 2016, Aparicio-Rizzo & Masotti 2019. Seasonal freshwater discharge can impact coastal systems during weak upwelling activity periods when nutrient input from rivers can help maintain basal phytoplankton biomass (Chl-a) and PP (Léniz et al 2012, Testa et al 2018. In these areas, with quasi-constant high nutrient concentrations year-round, changes in phytoplankton are not just linked to nutrients availability but also other factors (temperature, salinity, stratification/mixing conditions, or solar radiation).…”

Inter-annual variability of oceanographic conditions and phytoplankton in Valparaíso Bay (~33°S), central Chile

“…In upwelling areas of the Chilean coast, river discharges can also modify oceanographic conditions and nutrient export (Léniz et al 2012, Pérez et al 2015, Masotti et al 2018. Thus, previous studies have shown that an increase in river flow changes salinity and the exportation of nutrients (Pérez et al 2015, Masotti et al 2018.…”

The Influence of River Discharge on Nutrient Export and Phytoplankton Biomass Off the Central Chile Coast (33°–37°S): Seasonal Cycle and Interannual Variability

“…In this region, recent studies have shown evidences of the impact of the nutrient export in these river plumes on the carbon biogeochemistry and phytoplankton community of coastal waters off Central Chile in winter (Iriarte et al, 2012;Léniz et al, 2012;Pérez et al, 2015;Yevenes et al, 2016) and its possible contribution in maintaining high primary productivity rates in coastal waters (Testa et al, 2018). Nonetheless, there is a lack of a systematic analysis into the regional scale influence of the river discharges variability on nutrient loading and phytoplankton biomass in coastal waters.…”