Seasonal changes in the concentrations of Ca, Fe, K, Mg, Mn and Na in eelgrass ( Zostera marina L.) in the Limfjord, Denmark

Abstract

The seasonal changes in concentrations of calcium, iron, potassium, magnesium, manganese and sodium in above- and below-ground parts of eelgrass ( Zostera marina L.) were studied at three locations in the Limfjord, Denmark. The concentrations of calcium, iron and manganese in eelgrass differed significantly at the three stations. Above-ground parts of eelgrass contained significantly higher concentrations of potassium and manganese than below-ground parts, whereas the concentrations of iron and sodium were highest in the below-ground parts. Calcium and mangnesium concentrations in the two fractions were not significantly different. Significant seasonal variations were observed in the concentrations of calcium, potassium, manganese and sodium in above-ground parts of eelgrass and in the concentrations of iron, magnesium and sodium in below-ground parts. Iron, potassium, manganese and, to an extent, sodium showed a similar seasonal pattern with maximum concentrations in the summer and minimum concentrations in the spring or fall, whereas calcium concentrations in the above-ground parts showed the opposite pattern. The observed seasonal variation patterns are discussed in relation to the respective metals and changes in environmental factors.