Spatial and temporal variability of water quality and zooplankton in an artisanal salina

Conditions in artisanal salterns, or salinas, vary depending on their physical structure, seasonal effects, and the two periods of the salt production cycle. They therefore constitute unique wetland habitats, with particular communities that are still poorly studied. Water quality and zooplankton of a working artisanal salina were studied to evaluate spatial variability between sections and temporal variability between the salt production and flooded periods and between seasons. Zooplankton communities were related to environmental conditions. Sampling took place every second week, during almost two years, at six sites of the Tanoerias salina in Aveiro, Portugal: at the beginning and centre of the salina inlet channel, in a supply pond, in two evaporator and one crystalliser ponds. Since salt production occurs in the warm season only, seasonal effects concur with those caused by the salt production cycle. Results showed significant differences in temperature, dissolved oxygen (DO) and biochemical oxygen demand (BOD5) between salt production and flooded periods, i.e. summer and spring/winter seasons. Salinity and alkalinity were linked to salt production with extreme values in the salt-producing crystalliser pond. Zooplankton communities varied between seasons, but also with the salina section and the salt production cycle. Zooplankton densities and diversity tended to be lower during salt production, particularly under the extreme living conditions in the salina crystalliser pond. Variation in zooplankton communities between samples was mainly influenced by temperature, i.e. season, at the salina inlet, by BOD5 or DO, also related to temperature and season, in the first ponds and by nutrients throughout the system.