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

Nutrients (NO3 + NO2, PO4) and total organic carbon (TOC) from Estero de Pu nta Banda, a coastal lagoon of Baja California(Mexico), were studied during the 1992-93 El Nino. Samples were collected at four sites distributed alon g the main channel of the lagoon, during four different tidal stages. Accor ding to reports in the literature, this coastal Lagoon behaves as an anties tuary most of the time, with salinity increasing significantly from the mou th inwards. Greater input of fresh water due to a larger rainfall, well abo ve 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 mu M, and those of TOC between 2.3 a nd 9.8 mg L-1, with a clear tendency to increase from the entrance to the i nterior of the lagoon. NO3 values fluctuated between 0.2 and 2.3 mu M in Se ptember 1992, and between 1.4 and 6.8 mu M 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 1 993. The change of this lagoon from antiestuary to estuary for long periods , of almost up to one year, is related to meteorological phenomena influenc ed by large scale events like El Nino.