PLANT PIGMENT ANALYSIS

Carotenoids, chlorophylls and their derivatives extracted from algae, bacteria and higher plants are measured using highperformance liquid chromatography (HPLC). Plants synthesise a variety of pigments for use in photosynthesis. Sedimentary plant pigment analysis can be used to address changes in algal and bacterial community composition, trophic level, food-web interactions, lake acidification and anthropogenic impacts on aquatic ecosystems. Fossil pigment compositions can discriminate between most algal groups and are, therefore, useful environmental indicators in palaeoecology. Changes in phytoplankton composition, algal sedimentation and primary productivity can be determined by pigment analysis. Chlorophyll concentrations are frequently used to estimate phytoplankton biomass and productivity, while the products of decomposition are diagnostic indicators of physiological status, detrital content and grazing processes in natural populations of phytoplankton. When used in conjunction with microfossil analysis of zooplankton, plant pigments can help reconstruct predator-prey relationships in whole-lake food webs. Some benthic algae produce unique pigments when exposed to ultraviolet (UV) radiation and these pigments can be used to examine past changes in UV radiation. Sedimentary pigments have been proposed as a means of inferring past phosphorous concentrations in lakes. The preservation of fossil pigments varies with the water environment and is reduced under conditions of high light, oxygen, temperature and turbulence. Fossil pigments from siliceous algae are poorly preserved and, [Page 850]therefore, fossil pigment interpretations should only be based on historical changes in pigment concentration.

[See alsopigments: fossil]