Effects of sediment mixing and benthic algal production on fossil pigment stratigraphies

Abstract

Effects of sediment mixing and benthic algal production on fossil pigment profiles were quantified by fine-interval analysis of cores in a transect across the basin of Paul Lake, MI. Annually resolved profiles of carotenoids and chlorophyll a from varved sediments at deepwater (15 m) sites were compared to fine-interval (2.5-3.5 mm) stratigraphies from sites with increasing sediment mixing and benthic algal production (4 m > 7 m > 9 m). The degree of sediment mixing was also modelled using running means of pigment concentrations in varved sediments and compared to disturbed profiles. Effects of sediment mixing included reduction of peak pigment concentrations, broadening of peaks and migration of maxima deeper into deposits. Sedimentary signal strength was defined as the ratio of peak concentrations to baseline levels. Short-rived or weak signals (~ 1.5 x baseline) were resolved only in the least disturbed deposits, while strong signals (5 x baseline) withstood sediment homogenization to depths greater than 1 cm (> 5 year accumulation). Comparison of core-wide mean pigment concentrations suggested that cores recovered from within the photic zone are influenced by benthic algal production and will not represent either historical or current ecological dynamics in the water column. We conclude that: moderate levels of mixing do not destroy fossil pigment profiles; disturbed stratigraphies can remain ecologically interpretable; and fine-interval analyses are warranted in lakes with undisturbed a3VCs profiles and where sediment porosity < 90 ~o.

Comparison of Fossil Pigments with 20 Years of Phytoplankton Data from Eutrophic Lake 227, Experimental Lakes Area, Ontario

“…15-yr intervals. Samples were relyophilized for 2 h and stored under an N2 atmosphere, in the dark, at -20°C for 24 h before further analysis (Leavitt et al 1989).…”

“…Sedimentary pigments were extracted, filtered, and dried under N, gas following the procedures of Leavitt et al (1989). Carotenoid, Chl, and pigment-derivative concentrations were quantified using a Waters MPLC system following the reversed-phase procedure of Mantoura and LHewellyn (1983), as modified by Leavitt et al (1989).…”

“…Carotenoid, Chl, and pigment-derivative concentrations were quantified using a Waters MPLC system following the reversed-phase procedure of Mantoura and LHewellyn (1983), as modified by Leavitt et al (1989). An internal reference standard (3.2 mg -L -I ) of Sudm I1 (Sigma Chemical COT., St. Louis, Mo.)…”

“…zooplankton microfossil analyses, paleolimnologists can reconstruct predator-prey interactions in whole-lake food-web manipulations (Leavitt et al 1989(Leavitt et al , 1993. However, massbalance budgets show that sediments are also biased towards pigments that are incorporated into rapidly sinking material (herbivore feces, large colonies, consolidated detritus) (WeHschmeyer and Lorenzen 2985a, 1985b: Carpenter et al 1986.…”

Dynamics of phytoplankton pigments in water and surface sediments of a large shallow lake

“…(Leavitt & Carpenter 1990a, 1990bLeavitt 1993;Descy et al 1999;Patoine & Leavitt 2006). In shallow lakes resuspension and aerobic conditions in surface sediments enhance the transformation processes of organic matter, including PhPs, which strongly complicates the interpretation of palaeolimnological information stored in sediments (Leavitt & Carpenter 1989). However, as most of the World's lakes are shallow (Scheffer 1998), the evaluation of the possibilities of tracking historical changes in shallow lakes by using fossil sediment records is highly needed.…”