Fluxes and transformations of aquatic pigments in Lake Mendota, Wisconsin

Abstract

Concentrations and fluxes of chlorophyll and carotenoid pigments were measured in suspended and settling particulate matter and in surface sediments in Lake Mendota. Flux comparisons were used to calculate the extent of alteration or degradation within the water column and at the sediment surface. Losses within the water column for specific time intervals ranged from almost negligible for diatoxanthin to 96% for peridinin. The extent of loss was influenced by pigment type and transport process.Surface sediment diagenesis in Lake Mendota resulted in differential degradation rates among chlorophyll and carotenoid constituents. Deposition of pheophorbide a-a grazing indicator-was most important during late spring, as zooplankton populations increased and chlorophyll levels in the water column dropped below 1 nmol liter-'. The ability to trace the magnitude of this annual event through the sedimentary record was obscured by selective degradation of pheophorbide relative to chlorophyll and pheophytin. Similarly, carotenoid composition was dramatically altered both within the water column and at the sediment surface. Fucoxanthin and peridinin, major watercolumn carotenoids, were degraded extensively before incorporation in the sediments.

Identification of bacteriochlorophylls in lakes via reverse‐phase HPLC

“…Reverse-phase HPLC has emerged as the preferred technique for rapid quantification of eucaryotic chlorophylls and carotenoids in lake and ocean water or in sediments (Mantoura and Llewellyn 1983;Bidigare et al 1985;Hurley and Armstrong 1990). Using reverse-phase HPLC with diode-array Notes absorbance detection, we extend this technique to bacteriochlorophylls and build on the work of Korthals and Steenbergen (1985) by demonstrating separation of five of six known bacteriochlorophylls.…”

Long‐term pigment dynamics and diatom survival in dark sediment

“…Several of these pigments are used as biomarkers for specific algal groups and are often assumed to be specific for living algae. However, photosynthetic pigments are in general not fully degraded in sediments (Hurley and Armstrong 1990;Sun et al 1993;Steenbergen et al 1994), and strong differences in degradability of individual pigments can occur (Hurley and Armstrong 1990;Steenbergen et al 1994). Like for other organic compounds, degradation of pigments is controlled by various factors (Burdige 2007).…”

Long‐term dynamics of algal and invertebrate communities in a small, fluctuating tropical soda lake

“…Normally, prolonged exposure to oxygen promotes selective loss of labile chlorophylls or their conversion to more chemically stable derivatives (Hurley and Armstrong 1990;Leavitt 1993). Because all reported carotenoids have similar chemical stabilities (Hurley and Armstrong 1990;Leavitt and Findlay 1994), compositional changes in the fossil pigment spectrum are more likely to have resulted from corresponding changes in the algal communities rather than selective pigment deposition and preservation. Consequently, the observed declines in ␤-carotene and myxoxanthophyll probably do record actual changes in algal abundance and community composition over the past half century.…”

“…Relatively low downcore variability in concentrations of the labile pigment Chl a (103 Ϯ 76 nmol [g OM] Ϫ1 ), consistently high Chl a : pheophytin a ratios (ϳ0.5), and the permanence of bottom anoxia implied by the preservation of sediment lamination throughout the core suggests that there have been no systematic changes in the preservation of algal pigments relative to that of bulk organic matter (Leavitt and Carpenter 1989;Leavitt 1993). Normally, prolonged exposure to oxygen promotes selective loss of labile chlorophylls or their conversion to more chemically stable derivatives (Hurley and Armstrong 1990;Leavitt 1993). Because all reported carotenoids have similar chemical stabilities (Hurley and Armstrong 1990;Leavitt and Findlay 1994), compositional changes in the fossil pigment spectrum are more likely to have resulted from corresponding changes in the algal communities rather than selective pigment deposition and preservation.…”