Nutrient fluxes and net metabolism in Lobos coastal lagoon, México.

Abstract

Fluxes of nutrients and net metabolism were estimated in coastal lagoon Lobos, a semi-arid subtropical lagoon from Gulf of California, Mexico. Sampling runs were carried out during summer and winter, seawater samples for nutrients were collected in coastal lagoon, offshore and a channel waste-water, physico-chemical parameters were measured in situ. Fluxes of nutrients and net metabolism were estimated using LOICZ biogeochemical model. Flushing time was 5 days in summer and 12 days in winter. Lobos coastal lagoon was a sink of nitrogen in summer (?DIN = - 5645 mol day-1) and in winter (?DIN = - 136,575 mol day-1 ), and it was a source of phosphorus in summer (?DIP = + 360 mol day- 1 ) and sink in winter (?DIP = 15,809 mol day-1). During summer, Net Ecosystem Metabolism (NEM) of Lobos lagoon was heterotrophic (- 0.38 mmol m-2 d-1) and denitrification process was observed ( - 0.1 mmol m-2 d-1); during winter the NEM was autotrofic (+ 16.49 mmol m-2 d-1) and nitrogen fixation process was observed ( + 1.1 mmol m-2 d-1). These results suggest the hypothesis that coastal lagoons semi-arids subtropicals from Eastern coast on Gulf of Califonia have seasonal changes, dominant processes of denitrification and net metabolism hetrotrophic during summer, while dominant processes of nitrogen fixation and net metabolism autotrophic during winter.