Nutrient and plankton dynamics in a Mediterranean salt marsh dominated by incidents of flooding. Part 1: Differential confinement of nutrients

Abstract

Variations in the physical and chemical characteristics of the water in a series of depressions in some Mediterranean salt marshes were studied. The quantity of water entering the system, and the associated energy, seems to be the determining factor in the physical and chemical characterization of the water. The first four axes of the principal components analysis (65.1% of the variance) indicate, with varying time delays, this entry of energy. There is a high degree of subterranean circulation and its importance becomes clear in the level of nutrient accumulation which depends on the capacity of the nutrients to circulate through the aquifer. These basins tend to accumulate phosphorus, which is not able to pass through the sediment and, at the same time, tend to lose nitrogen, whose inorganic forms circulate through the aquifer more freely. This factor, which we have called 'differential confinement', together with denitrification, results in especially low nitrogen/phosphorus ratios. The amount of phosphorus accumulated conditions the degree of eutrophy of the basins. On the other hand, production is related to the external supply of nitrogen which circulates or the ease with which it is lost (by infiltration and denitrification). The alteration of the nitrogen/phosphorus ratio is the main cause of the tendency to eutrophication in these environments when water inputs are regulated.