Drift-Seaweed Evaluation for Fertilizer Use in Galiza (Northwest Spain): Tissue Elemental Characterization and Site-Sampling Differences

ABSTRACT

With the aim of evaluating the suitability of drift-seaweed for use as organic fertilizer, samples were obtained from 16 beaches on the coast of Galicia (NW Spain), for determination of nutrient and heavy metal contents. Samples were distributed between two difference zones: differences in oceanographic characteristics and organic-heavy metal pollution level. Drift-seaweed is still used in this region for fertilization of potato crops (35% of our respondents), vineyards and horticultural crops (23% in each case) and cereal crops (19%). The most abundant and most frequent seaweed taxon was Laminaria spp. (75% of the total dry biomass of the 16 samples; present in 44% of the samples). Phaeophytes showed relatively high mean C and K contents, and relatively low mean B and Ni contents. Rhodophytes showed high N, P, Cu, Zn and Cd contents, and low Mg, Fe, Na, Mn, Al and Cr contents. Chlorophytes showed high Mg, Na, Fe and Pb contents, and low C, P and Zn contents. Taken together, seaweed drifts in this region can be considered as useful organic fertilizers, particularly for soils requiring K and some micronutrients (B, Cu, Mn, Zn). Heavy metal contents are acceptably low, except for Cd, which may require special attention. Na and Al tissue concentrations were higher in those zones with lower input of nutrients and heavy metal. None of the other tissue element concentrations showed differences between sampling sites.

KEYWORDS:

• Drift-seaweed
• Galiza
• heavy metal
• macroalgae
• nutrient
• organic fertilizer
• Spain