Scales of variability in the sediment chlorophyll content of the shallow Palmones River Estuary, Spain

A study on the spatial distribution of chlorophyll pigments (CP) at different scales in the sediments of the Palmones River Estuary was carried out. Intertidal and subtidal sediments were sampled across a range of spatial scales: centimetres (depth and replicate samples), meters (left and right banks, middle of the estuary) and kilometres (mouth to upper part of the estuary). CP concentration was in the same order of magnitude as in the other estuarine areas, and followed a similar distribution. Important spatial variation occurred at a broad scale (between stations, km), while, the scale in the order of centimetres was comparatively less important. Because the variability in the CP distribution was dependent upon scale, a ratio between the CP variation at different scales is proposed. This ratio showed that the changes that occurred in depth were much more important than those occurring in the longitudinal axis of the estuary. This was due to the strong gradient found for chlorophyll in depth. Different biotic and abiotic factors determine the spatial distribution. Differences between the stations are mainly related to hydrodynamic forces (waves, winds and tides). Light penetration through the water column and into the sediment surface can explain differences in depth, and between subtidal and intertidal sediments.