Burial and decomposition of plant pigments in surface sediments of the Baltic Sea: role of oxygen and benthic fauna

摘要

Degradation and burial of organic matter in sediments are important processes for oxygen dynamics and thus for the outcome of eutrophication. To assess the influences of bottom-water oxygen and macroinvertebrate fauna function on these processes, we investigated distributions of phytopigments as markers of phytoplankton detritus in surface sediments across the Baltic Sea. We compared pigment concentrations among sites with different oxygen levels and different values of a bioturbation potential index combining abundance, individual size and species-specific rankings of mobility and sediment reworking (BPI). BPI was positively influenced by oxygen availability, with a threshold at 45 to 90 umol I"1, below which it decreased rapidly to zero in anoxic sediments. There was significant co-variation between pigments and both oxygen and BPI after accounting for differences in pigment concentrations with sediment depth and among different sub-areas, which were largely attributed to different inputs of phytoplankton. Negative correlations between pigments and both BPI and oxygen in communities dominated by Macoma balth-ica and Scoloplos armiger, and between pigments and BPI in the upper sediment layers inhabited by Monoporeia affinis and Pontoporeia femorata, suggested increased degradation with increasing bioturbation. Positive correlations between pigments and BPI in communities dominated by Marenzelleria spp. suggested mainly burial, which also was supported by positive correlations between Marenzelleria abundance and both sediment water content and the freshness of buried organic material. It is hypothesised that a shift from sensitive resident species like Monoporeia or Scoloplos to the more hypoxia-tolerant Marenzelleria will slow down overall degradation rates, counteracting hypoxia formation in the bottom water.