TITLE:
Wind-Driven Dynamics of Beach-Cast Wrack in a Tide-Free System
AUTHORS:
Sven Hammann, Martin Zimmer
KEYWORDS:
Decomposition; Drift Line; Spatial Subsidy; Zostera marina
JOURNAL NAME:
Open Journal of Marine Science,
Vol.4 No.2,
April
4,
2014
ABSTRACT: Whereas wrack dynamics on tidally influenced beaches have been studied to some detail, essentially nothing is known about how drift lines in tide-free coastal systems vary in space and time. We provide evidence for high spatial and temporal dynamics of beach-cast wrack on a sand beach in the Western Baltic Sea. Over the course of one year, the amount of weekly deposited macrophyte wrack fluctuated from zero to 3000 g·m-1 shoreline. Wrack mostly accumulated just above the waterline. Part of the beach-cast wrack is frequently re-suspended into coastal water upon extreme high water level events, or wrack patches are translocated landwards by wind-driven changes in water level or along the shoreline by winds. Consequently, the deposited wrack does accumulate, but a steady-state of ca 400 g·m-1 builds up within 2 - 3 weeks. Eelgrass wrack buried in sand decomposed almost twice as fast as on top of the sand or re-suspended in water. Fragmentation of leaves promoted decomposition only when wrack remained on the sand surface. The spatial and temporal distribution of this valuable source of organic matter is unpredictable and depends on wind and wind-driven waves.