Anoxic and oxic degradation of ¹⁴C‐labeled chloropigments and a ¹⁴C‐labeled diatom in Long Island Sound sediments

Abstract

Anoxic and oxic degradation pathways of sedimentary chloropigments were examined by spiking marine sediment with 14C-labeled algal cells and purified chloropigments from the diatom Skeletonema costatum. These experiments suggest that Chl a degrades through multiple pathways. Under oxic conditions, most bulk sedimentary Chl a degraded to various colorless compounds and only a minor fraction degraded to pheophytin a; added 14C-labeled Chl a also degraded quickly, but 30-40% of this Chl a was converted to pheophytin a. Under anoxic conditions, only a small fraction of bulk Chl a degraded, but added 14C-labeled Chl a continuously degraded and -30-40% of it was converted to pheophytin a, Pheophytin a is relatively stable under anoxic conditions but degrades under oxic conditions, thus it is a potential end product of chloropigmcnt degradation in anoxic environments.Degradation pathways are likely dependent on the relative proportion of unassociated Chl a to chlorophyll complexes present in the sediment. Only unassociated Chl a appears to be available for anoxic decomposition. Under oxic conditions, some colorless products were further degraded and solubilized, none of the 14C label added as purified pigments was lost under anoxic conditions during the l-month incubation. About 80% of the acetone-extractable "C in labeled cells was lost in 1 month from sediments under oxic conditions and -30% under anoxic conditions.

Role of physical and biological processes in sediment dynamics of a tidal flat in Westerschelde Estuary, SW Netherlands

“…During the spring algal bloom period, high chlorophyll a levels at the surface decreased very rapidly with depth over the upper 5 to 10 mm. This indicated that the degradation of algal pigments, through processes such as senescence, photodegradation, bacterial degradation and herbivore grazing, was more rapid than the vertical mixing (physical and biological) of cohesive/silty sediments (Sun et al 1993, Lucas & Holligan 1999. Large amounts of phaeopigments were produced in the Molenplaat sediment, with the relative contribution changing from phaeophytins in March/April to phaeophorbides in September as the role of the herbivorous community in chlorophyll a cycling became more significant.…”

Preservation of organic matter in mound-forming coral skeletons

“…Some protection may be afforded by the ability of endolithic algae to bore into the skeleton and deposit Chl-a in the restricted space of the skeletal matrix. In anoxic sediment incubation experiments where solutes are not allowed to diffuse across the sediment water interface, Chl-a preservation is also extensive (Sun et al, 1993a(Sun et al, , 1993bIngalls, 2002). Restricted diffusion and anoxia within coral heads (Sansone et al, 1990) are likely to contribute to the preservation of non-intracrystalline organic matter.…”

“…Since Chl-a is lost quickly from most environments (within months), its presence in old corals illustrates the preservation potential of coral skeletons. In anoxic sediments, where organic matter preservation can be extensive, Chl-a degrades to phaeophytin, which can then remain undegraded for decades (Sun et al, 1993b). The 1945The , 1965The and several bands between 1970 of the Florida Keys coral contain Chl-a (Fig.…”

Black spots produced by buried macroalgae in intertidal sandy sediments of the Wadden Sea: Effects on the meiobenthos

“…In strongly reduced sediments pH values can drop to approximately 6 (Giere et aL, 1988) because of the production of carbon dioxide, organic acids and hydrogen sulphide (Foree & McCarty, 1970;Berner 1980). This acidic environment may favour the breaking up of chlorophyll into phaeopigments (Sun et aL, 1993) which has been considered an indication of chloropigment diagenesis (Sun et aL, 1991). Chl a of algae is degraded over a period of several weeks (Bianchi et aL, 1988), a process which results in the release of their molecular components into the interstitial milieu.…”