Variaciones temporales del fitoplancton de los ríos tributarios y emisario del embalse C. Gelsi (Tucumán, Argentina)

Temporal variations of the phytoplankton of the tributaries and effluent from the C. Gelsi reservoir (Tucumán, Argentina). In this paper we analyzed the phytoplankton variation in the tributaries (Salí, Tapia, and Vipos rivers) and effluent (Salí River) from the C. Gelsi reservoir according to a seasonal gradient. The minimum algal abundance took place in summer with a biomass of 0.19-0.58 µg Cl-a L-1, while the maximum occurred in winter or in spring, with a biomass of 5.43-6.79 µg Cl-a L-1. In the tributaries pennate diatoms prevailed, Diatoma vulgare and Cymbella affinis were most abundant, while in the Salí river (Gelsi effluent) centric diatoms were dominant, particularly Aulacoseira granulata and Cyclotella meneghiniana. Chlorophyta were ranked second in the Salí River, Cyanobacteria codominated in the Vipos and Tapia rivers in March 1998, and Dinophyta could only be seen in the Salí River (Gelsi effluent). The specific diversity index ranged from 0.2 to 4.2 and the saprobic index characterized waters as “non-polluted” or “slightly polluted” in winter, and as “moderately polluted” in summer. The NMDS arranged temporarily the samples according to the abundance of the algal species considered. The RDA showed that the two first axes separated the samples according to gradients of temperature, pH, conductivity, BOD5 and nitrate, and also abundance of Aulacoseira granulata, Cyclotella meneghiniana, Ulnaria ulna, Cymbella affinis and Leptolyngbya foveolarum.