Inorganic nutrients in the inundation channels of tidal marshes of a coastal lagoon of northwestern Baja California

Abstract

We generated temperature, salinity, nitrate plus nitrite (NO3 + NO2), ammonia (NH4), and phosphate (PO4) time series for the mouth of three inundation channels of salt marshes of estero de Punta Banda, a coastal lagoon of northwestern Baja California. The channels are located near the lagoon’s mouth (B), at the middle (M), and at the internal extreme (C). Each channel was sampled twice, in August 1988. In each case, surface samples were taken every hour during twelve hours. Also, the main channel of the estero was sampled twice, at ten locations from the mouth to the internal extreme, to compare with the secondary channels. In these latter cases time series were not generated. We found highest salinity and nutrient values at channel C, where maximum salinity was 39.2‰, and maximum nutrient concentrations were 10 µM, 27 µM, and 7 µM, for NO3 + NO2, NH4, and PO4, respectively. B and M had similar values for water properties. Maximum S‰ and nutrient values for B and M were 36.0‰, and 4.9 µM, 24 µM, and 3.2 µM, for NO3 + NO2, NH4, and PO4, respectively. Higher values at C were due to higher residence time of water at the internal extreme of the lagoon. Our data do not support the hypothesis that nutrient concentrations of water ebbing from these inundation channels are higher than those of the lagoon’s main channel. Accumulation of nutrients and salt in channels B and M is lower than at C due to the former being closer to the lagoon’s mouth. Large residence times in the internal extreme of the lagoon make it very vulnerable to the input of pollutants.