Spatio-temporal variability of nutrients and seston in the coastal lagoon La Cruz, Sonora

Abstract

Monthly (May 1987 to July 1988) samples were taken in triplicate of surface water at eight stations in the coastal lagoon La Cruz, Sonora, in order to determine the concentrations of nitrates, nitrites, phosphates and seston. In addition, surface salinity and temperature work measured at these stations. The temperature showed a marked seasonal trend with values between 32ºC (September) and 16ºC (January). The monthly salinity fluctuated between values of 3.5 and 40‰ The mean monthly concentration of phosphates had values of 0.21 to 3.6 µM. The nitrates had values of 0.42 to 3.8 PM, whereas the nitrites had concentrations from undetectable values to 0.38 µM. The total, inorganic and organic seston had minimum values of 10.2, 7.0 and 3.0 g/m³ and maximum values of 62.0, 35.2 and 6.9 g/n³, respectively. Temporally, the maxima and minima of the variables only partially coincided. The spatial distribution of the concentrations of each variable showed homogeneity on several occasions and, during the months when this did not occur, there was no defined pattern. The strong tidal exchange could be responsible for the high variability of the system.