Inorganic nutrients and phytoplankton production in a subtropical coastal lagoon of Mexico

Temporal variability of hydrographic data, nutrients, phytoplankton chlorophyll alpha, and rate of primary production for the Cuyutlan Lagoon (CL) were analyzed. Surface temperature had a seasonal pattern, lower in December and higher by July and October. Lowest salinity values were observed in October associated to the raining season, which created estuarine features inside the lagoon. Nutrient concentrations (NO3-+NO2-) increased in February and June as result of organic matter remineralization, with higher silicate concentrations by October because freshwater run-off influence into the lagoon. During the other months dissolved silicate increase due to biogenic silica dissolution. Using the Redfield ratio as a stoichiometric nutrient balance criterion, phosphate deficits were observed in CL due to phytoplankton nutrient uptake. Chlorophyll alpha increased above 2.0 mg m(-3) as result of rich-nutrient water, producing an elevated phytoplankton biomass. Average phytoplankton production was 1.26 g C m(-3) d(-1), indicating that Cuyutlan Lagoon is similar to 40% more productive related to other subtropical and temperate coastal lagoons. With chlorophyll alpha concentration as criteria to define trophic levels, CL could be described as a eutrophic ecosystem. Physical variables, dissolved inorganic nutrients, and chlorophyll alpha exhibited temporal variability in the lagoon without a relationship with tidal circulation, except for dissolved oxygen.