Chlorophyll-a and derivatives in recent sediments as indicators of productivity and depositional conditions

Chlorophyll-a and its derivatives in the recent sediments of nineteen sites from the southern coast of the Baltic, an eutrophic sea, were examined and compared to those of other regions of the world. This included the Venice Lagoon in Italy, Ardmucknish and Dunstaffnage Bays of Scotland and the southern coast of Florida (USA). High photoautotrophic production and high sedimentation rates were found to aid the development of hypoxic/anoxic conditions in sediments. Additionally, when physical mixing in water and/or sediments was slow or absent, anoxia resulted and enhanced the preservation of chloropigments-a. Alternately, low productivity, low sedimentation rates, and the turnover of water and/or mixing of sediments resulted in the maintenance of oxic conditions, and increased degradation of chloropigments-a and decomposition to colorless products. In this work, specific chlorophyll-a derivatives are becoming better identified as indicators for certain combinations of environmental processes, such as grazing by zooplankton and benthic biota, input of fresh microalgal material, oxygenation, anaerobic microbial activity and others. The distribution both of the sum of chloropigments-a (Σ Chlns-a, in nmoles/g-sediment, dry wt.) and the percentages specific derivatives in recent sediments are concluded as excellent, spatiotemporal averaged indicators of productivity and the physicochemical state/trends of various depositional environments. Conclusions drawn on the basis of past studies of Baltic Sea sediments, as well as those reported herein, appear extendable to other coastal areas.