The effect of El Niño on the nutrients and total organic cabon of a coastal lagoon of northwestern Baja California

Abstract

Nutrients (NO₃ + NO₂, PO₄) and total organic carbon (TOC) from Estero de Punta Banda, a coastal lagoon of Baja California (Mexico), were studied during the 1992–93 El Niño. Samples were collected at four sites distributed along the main channel of the lagoon, during four different tidal stages. According to reports in the literature, this coastal lagoon behaves as an antiestuary most of the time, with salinity increasing significantly from the mouth inwards. Greater input of fresh water due to a larger rainfall, well above the annual mean (393 mm), caused the Estero to behave as an estuary, with salinity values of <25 and with an increase of NO₃ + NO₂, PO₄ and TOC. PO₄ values fluctuated between 0.5 and 3.5 µM, and those of TOC between 2.3 and 9.8 mg L^–1, with a clear tendency to increase from the entrance to the interior of the lagoon. NO₃ values fluctuated between 0.2 and 2.3 µM in September 1992, and between 1.4 and 6.8 µM in March 1993, also with a clear tendency to increase towards the lagoon´ s interior in the latter case. PO₄ had a significant negative correlation (P < 0.05) with salinity in March 1993. The change of this lagoon from antiestuary to estuary for long periods, of almost up to one year, is related to meteorological phenomena influenced by large scale events like El Niño.