Pattern of chlorophyll in a gradient of nutrient concentration in sediment

Abstract

Relationships between the appearance of chlorophyll patches and a nitrogen concentration gradient were studied in the laboratory using sediment from an eutrophic mouth river environment (Guadalhorce, SE Spain). An agar-ammonium nitrate block was inserted at one of the sides of a tray filled with this sediment. The tray was placed in a chamber with light and temperature constant. Eight samples which were placed along a line ranging from 1.5 to 22.5 cm from the nutrient source were taken periodically. Nitrate concentration measures, as well as an estimation of the total chlorophyll a concentration, were made to obtain a space/time distribution of these variables. Spatial cross-correlation and autocorrelation analyses were carried out, helping to show the maintenance of a pattern consisting of regularly spaced patches of chlorophyll. The tendency for a nutrient concentration gradient to be established in an environment with low terms of phytobenthos diffusivity, as well as a possible interrelation between space and microsuccessional stages with a preferred direction of development of the photosynthetic populations on areas where the resources have not been recently utilized, could be responsible for the maintenance of the observed instabilities.