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Predrying of stranded wrack material as an aspect of the litterbag techniques in the sandy beach studies

Jędrzejczak M. F.

Oceanological and Hydrobiological Studies

2003

Vol. 32, No. 1

59-74

Methodological aspects of the arrangement of stranded wrack for the degradation rates within the litterbags were tested in a simple field experiment on temperate, fine/medium quartz sediment, sandy beach in Poland at the end of the Hel Peninsula (54°36’N, 18°49’E). Litterbags of the mesh size of 0.5 mm were used to construe and assess the role of the pre-drying of wrack before its placement into the bags. The field station was established on the backshore, 15 m in width seaward from the crest of a dune. Three methods of predrying were done: (1) air drying, (2) oven drying, (3) freeze drying, as well as (4) non-dried fresh material was used as reference. The stranded seagrass wrack (Zostera marina L.), obtained directly from the beach, and then prepared in accordance with the procedures described above, was used as the study material. Four trials were run with five repetitions of litterbags 7 cm long ´ 7 cm wide made from nylon mesh with 0.5 mm aperture widths. After exposition, bags were retrieved 5, 10, 50, 100, 150, 200 and 250 days post-placement. In the laboratory, samples of remaining material were dried by the same method as earlier, respectively, and then weighed, and analysed using a CHNS Analyser. It was shown that, under similar conditions of sediment composition, salinity and wave inundation, the method of predrying had little influence on the long-term process of decay. In the case of non-dried replicates, degradation rapidly proceeded in the initial stages and then stabilised to be linear, whereas, in dried samples it was done so linearly throughout the study period with only little differences. Such differences observed in the early part of the experiment were most likely the result of differences in material structure and the initial chemical composition of the plant material caused by a predrying-incurred disturbance in the chemical structure. Nevertheless, short-term environmentally driven sampling strategies fail to obtain conclusive results about degradation estimates of stranded wrack and should be avoided at least with the use of dried material.