Tidal effect on organic primary productivity in a coastal lagoon of Ballenas Channel, Gulf of Californla

Abstract

Phytoplankton organic primary productivity (POP) and nutrient time series were generated in a coastal lagoon of the Gulf of California from 6 to 12 August 1986 to estimate the influence of Ballenas Channel during spring and neap tides. Ocean water temperature and salinity varied from 26 to 30°C and from 35.54 to 35.63%0, respectively. Oxygen was unsaturated at 85% in more than 70% of the data collected. Values of supersaturated oxygen were obtained during daylight hours only, which increased during neap tides due to the conditioning of the phytoplankton, resulting in greater photosynthesis. It can be inferred from the marked unsaturation that this is an area of high oxygen consumption and CO₂ production. The nutrients (nitrate, phosphate and silicate), chlorophyll a and POP show high values, similar to coastal lagoons of the Pacific coast of Baja California in upwelling conditions. POP maximums were as high as 80 mgC·m^–3·h^–1 in neap tides. It is deduced from the calculated photosynthetic quotient (PQ) and POP that photosynthesis is supported mainly by nitrates. Based on the ¹⁴C method, the assimilation ratio varied from 10 to 25 mgC·mgCha^–1·h^–1. These values are close to the theoretical maximums reported; however, the assimilation ratio using the oxygen method and PQ = 1.25 varied from 1.6 to 35.6 mgC·mgCha^–1·h^–1 and, with the calculated PQ, it varied from 1.0 to 7.2 mgC·mgCha^–1·h^–1. It is also deduced that this coastal lagoon is greatly influenced by the nutrient concentrations (mainly nitrate and silicate) from Ballenas Channel during spring tides. There is also an important increment of POP during neap tides.