| Phytoplanktonic organisms significantly contribute to the productivity of coastal ecosystems. In estuarine waters, the variability in structure, function and distribution of phytoplankton communities is affected by seasonal changes in rainfall, which produce temporal differences in river discharge. The influence of these factors in the production of matter can be studied at sea through the Carbon-14 method and photosynthesis-light experiments. However, measurements of primary production through the 14C method in coastal waters are complicated by environmental conditions and technical errors, including inadequate sampling protocols. In this study, various experiments were carried out in an effort to develop an appropriate protocol for measurements of the photosynthetic parameters at estumine waters. Results show that the characteristics of the filter used during filtration of samples should be taken into consideration and GF/F, Whatmann 18 25 025 filters with pore size of 0.7μm gave the best outcome. Also, decontamination of inorganic carbon with HCl was measured. It was found that commercial HCl diluted to 50% or higher and exposing the filter to fumes result in less inorganic carbon retention. Finally, it was observed that when selecting an adequate value of ΣCO 2 for the calculation of P-E curves, the location of the study site and the season in which the sampling took place should be considered. Following these studies, productivity-irradiance experiments were performed to observe the variation of the photosynthetic parameters with changes in river discharge. Results presented an inverse relationship between discharge and Pmax and a direct relationship with alpha. This investigation provides corrections for an adequate use of the 14C method at estuarine waters and the basis for understanding variation in production with river discharge. |
