Chemical and physical characterization of calcified red algal deposits known as maerl

Maerl, comprised of shallow, subtidal deposits of calcareous red algae belonging to the family Corallinaceae, is used in agriculture, primarily to increase soil pH. Its use has been strongly criticised because of its high price compared to limestone. The chemical and physical characteristics of maerl and limestone are compared to determine whether these indicate if any benefit is to be gained with the use of the former. Analysis by inductively coupled plasma emission spectrophotometry shows that the proportion of magnesium in maerl is about ten times higher than that in the limestone samples tested. The levels of iron, boron and especially strontium are noticeably higher in the calcified seaweed than in the limestone, although the manganese contents are lower. Scanning electron microscopy shows that the surface characteristics of maerl and limestone are similar but, in section, maerl is considerably more porous because of its cellular structure. Atomic force microscopy revealed minor differences in fine structure between the two. The differences between maerl and limestone would not appear to compensate for the considerably higher costs involved with the utilization of the former material.