Nutrient concentrations in pore waters of intertidal sediments in a coastal lagoon: Patchiness and temporal variations

Abstract

We generated ∼ 6 h time series data by means of in-situ samplings to study the variations in the properties of pore waters in a low salt marsh with tall Spartina foliosa. The location was a coastal lagoon on the northwestern coast of Baja California, Mexico. Salinity (S‰), reactive phosphate (PO 4), and ammonia (NH 3) displayed great temporal and spatial variation and irregular variations with depth. The most marked variation in salinity, from 32.5 to 44‰ in 3 h, was at 10 cm depth. Low salinity values were attributed to underground freshwater input, and high values to excess evaporation from the surface. Within a line ∼ 8 m parallel to the water front, at 30 cm depth, we obtained PO 4 variation with time from as low as 20–29 μM to as high as 103 μM at two locations, and NH 3 from 19–55 μM to 220–1970 μM. In some cases, with samplers only 7 cm apart, for the same depth and sampling time, salinity differed by as much as 6‰; PO 4 concentrations differed by a factor of five. Patchiness, mostly created by biota, and percolation with tides, enhanced by movements through plants' roots and animals' burrows, are mainly responsible for these changes in the properties of pore waters.