Composition and sedimentation of aquatic pigments associated with deep plankton in lakes
High Performance Liquid Chromatography (HPLC) pigment techniques were applied to study planktonic pigment composition and sedimentation in four Wisconsin (USA) lakes. In each lake, deep blooms of phytoplankton overlaid phototrophic sulfur bacteria in the region of the oxic-anoxic interface. Chlorophyll a and bacteriochtorophyll (a, d, and e) were observed as indicators of phytoplankton and phototrophic sulfur bacteria, respectively. Major taxonomic classes of phytoplankton were further resolved based on carotenoid signatures. In contrast to three oligo-mesotrophic Wisconsin lakes in which deep phytoplankton were comprised of dinoflagellates (indicated by the carotenoids peridinin, diadinoxanthin), cryptophytes (alloxanthin), and chrysophytes (fucoxanthin), the deep phytoplankton community in mesotrophic Mirror Lake was dominated by blue-green algae (oscillaxanthin, myxoxanthophyll, zeaxanthin, and echinenone). Deep planktonic production strongly influenced sedimentation of algal pigments and obscured the relationship between apparent water quality and sedimentary pigment deposition.