The concentration and distribution of nutrients (nitrate, nitrite, phosphate, silicate) in water, photosynthetic pigments (chlorophyll a and phaeopigments) in suspended particulate matter (SPM), and phytoplankton from Mar Chiquita Coastal Lagoon, in Argentina, was studied along six (6) sampling stations during a year in order to know their spatial and temporal variations. Internationally standardized analytical methods were applied in order to reach these objectives. The use of soils for farming and continental runoff of the adjacent terrestrial systems close to the coastal lagoon seemed to be a significant nutrient source for this water body, which is able to support its own dynamic of phytoplankton within this water body.

Results obtained regarding nutrient and pigment distribution allowed the identification of two different systems within the coastal lagoon: one under marine influence and the other under inland influence, with different ecological and environmental characteristics. Temporal trends of the corresponding phytoplankton development have been identified, and it has been observed that the biological production which occurred within the coastal lagoon along the whole year was higher than corresponding ones from other coastal environments in Argentina. Moreover, nutrient occurrence within the internal region favored the development of the highest biomass detected within the whole lagoon. The system seems to function as a transition zone, which profits from unusual nutrient inputs, together with other environmental conditions (salinity, temperature), bringing continuous nutrient availability for phytoplankton and consequently food supply for marine and estuarine organisms.