The effect of zostera noltii, spartina maritima and scirpus maritimus on sediment pore-water profiles in a temperate intertidal estuary

Abstract

The objective of the present work was to study the effect of plants common in temperate latitudes (Zostera noltii, Spartina maritima and Scirpus maritimus) on sediment nutrient profiles, and to compare it to sandand mud-flats without vegetation. The study focused on the organic matter contents, the concentration of dissolved inorganic nutrients (PO4–P, NH3–N, NO3–N), an on the estimation of the total amount of these nutrients during day and night conditions and their potential net-fluxes. It was also hypothesised that in an estuarine system, different plants may have specific effects, and consequently different contributions to the system nutrient dynamics as a whole. Sediment profiles of loss on ignition (LOI) showed an increase of the organic matter contents from sand-flat, to Zostera, Spartina, mud-flat and Scirpus. Statistically, there were significant differences between sediment profiles of phosphate, ammonia and nitrate (Mann-Whitney test, p<0.05), during day and night periods. These results suggest that there is an intense mobility of nutrients in the sediment, showing a day-night variation of nutrient concentrations in the pore-water. In the plants’ rhizosphere, the day-night variation of nutrients seemed dependent on plant biomass and penetration of the roots. Additionally, coupling between plant and sediment seems to be a species-specific process. In spring, Scirpus salt marsh reaches the maximum density and biomass, and despite the higher organic matter contents in the plant covered sediment, Scirpus acts as a sink of nutrients. In contrast, the top 10 cm of the sediment in the Spartina salt marsh and in the Zostera beds may contribute to the efflux of nutrients during the night period, especially phosphate.