Comunidad planctónica de un embalse con alta tensión ambiental: La Playa, cuenca alta del río Chicamocha (Tuta, Boyacá), Colombia

The water reservoir La Playa (upper basin of the Chicamocha River) is a receptor system of residual water and works as a flow regulator to optimize an irrigation district. Although, it is a strategic system, there is no information about water quality. The plankton structure and relationship with physical and chemical variables was evaluated for two contrasting hydro-climatic periods (October 2011 and February 2012) and three stations (lacustrine, transition and riverine). According to principal component analysis during high rainfall oxygen concentration increased and lower transparency was recorded; during the dry season, conductivity was higher but phosphorus concentration was lower. Twenty-one species of planktonic algae and ten species of zooplankton were identified. The highest abundance was for Coelastrum microporum (74 %), Euglena sp. (21 %), Keratella tropica (79 %) and Metacyclops mendocinus (32 %). On the temporal scalel, no replacement of dominant species was found. This is considered indicative of their high trophic level and tolerance to variations in dissolved oxygen, pH and electrical conductivity. Despite the observed high environmental stress (physical and chemical fluctuations and concentration of organic load), these species are able to adapt to these changes