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The degradation of stranded carrion on a Baltic Sea sandy beach

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Jędrzejczak M. F.

tom Vol. 28, No. 3-4

109-141

Litterbags of two mesh sizes (0.5 mm and 0.02 mm) were employed to assess the role of faunal and physical components in carrion breakdown on sandy beaches. Field experiments were undertaken on two sandy beaches in Poland. The tissue of Gadus morrhua L. and the white of a hen's egg were used as substrata to be decomposed in the litterbags. The bags, together with control bags, were distributed in three trials in different beach locations (medium water-mark, strandline, backshore, and dune) and at appropriate depths (5, 20 and 50 cm deep). Each trial was run for 20 days and was set up on the beach profile. The litterbags were retrieved after 3, 6,10, 15 and 20 days. The remaining material was then dried and weighed, and analysed using a C11N Analyser. Organic material was rapidly lust from the litterbags. From 4 to 56 % of the original dry mass remained after 20 days in the field in the coarse-mesh bags. However, between llic low and higW-beach stations there were some differences in the decay process. At the former, degradation proceeded rapidly in the initial stages and then stabilised, at the latter it did so linearly throughout the study period. The fact that fauna were excluded from the carrion by the use of finer mesh litterbags had an appreciable effect on the rate of dry matter loss. Microbial decay, abiotic leaching and fragmentation were thought to be major causes of carrion weight loss from the litterbags. The rate of dry mass loss, expressed as loss of organic material, ranged from 1 to 14% per day. At the same time, the C/N ratio increased, which was evidence of the earlier use of nitrogen as an energy source. These results suggest that differences in organic matter degradation in high and low-beach areas can be explained by differences in moisture regime and nutrient status and not by differences in the decay processes themselves.

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

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Jędrzejczak M. F.

tom 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.