Modelos conceptuales de abundancia de fitoplancton asociados a la heterogeneidad espacial en el Embalse Rapel (Chile central)

Abstract

Heterogeneous morphology generates abundance patterns and a differential response of the planktonic assemblages in regulated aquatic systems. This is the case at the Rapel reservoir (34°10′ S, 71°29′ W). A longitudinal morphoedaphic gradient and localized hydrodynamic conditions produce spatial complexity in this type-dendritic basin, that has been proposed as probable causal mechanism of the main diferences in phytoplankton abundance among areas inside of the reservoir. In this study, mechanisms and conceptual models of phytoplankton abundance are proposed, describing algae distribution patterns in three reservoir areas: Las Balsas, Alhué and El Muro. Also, the main predictive variables were identified which lead to propose a specific functioning model in each reservoir area. A data base published was used in order to obtain phytoplankton total abundance and physical and chemical variables from each station sampling that represent the reservoir areas, including the Confluencia area localized between Las Balsas and El Muro areas. Cluster and principal components analysis were applied in order to describe the spatial pattern and a multiple linear regression analysis was utilized to identify predictive variables in each sampling station. Results showed two significant groups: 1 = Las Balsas-El Muro, and 2 = Alhué-Confluencia. Physical and chemical variables also were segregated in the space, according to the sampling stations. Different groups of predictive variables among the stations were found. At the Las Balsas station, variables associated to phytoplankton abundance were temperature, soluble reactive phosphorous concentration and specific conductivity. On the contrary, at the Alhué and El Muro stations, the greater variability was explained by the nitrogen compounds concentration, and nitrate specially important at the Alhué station and ammonia at the El Muro station. These results suggest a differential control of the phytoplankton abundance associated to each reservoir areas. While in Las Balsas station an external control generated by discharge of tributaries would prevail, in the El Muro station an internal control is proposed, that emerges from the ammonia in situ generation. At the Alhué station, the significant association to nitrate and organic nitrogenous would reveal a double control in the generation of the phytoplanktonic pattern.