Reconstructing eutrophication trends of a shallow lake environment using biomarker dynamics and sedimentary sterols

Abstract

Major extractable lipid biomarkers (hydrocarbons, sterols and fatty acids) were assessed in Lake Seeburg, a shallow eutrophic lake that has increasingly been suffering from cyanobacterial blooms due to continued anthropogenic nutrient inputs over the last decades. Over the course of one year (2018/19), the distributions of these compounds were analyzed in the inflow, the lake water, and the topmost sediments (0–2 cm) to assess their origin and transfer into the lake deposits. Principal component analysis (PCA) was used to cluster the studied biomarkers into 5 groups with similar characteristics. These groups were comprised of (i) compounds delivered from external sources via the inflow, (ii) autochthonous compounds formed in the lake by eukaryotes or (iii) bacteria, (iv) compounds accumulating in the surface sediment, and (v) C27 to C29 stenols together with their degradation products, C27 to C29 5α(H)-stanols. Their seasonal partition clearly revealed that C27 stenols mainly derived from autochthonous sources within the lake, whereas C29 stenols largely reflect allochthonous material reaching the lake via the inflow. Analysis of stenol plus stanol concentrations with depth in two lake sediment cores (≈30 and 50 cm) found highest C27 to C29 ratios in surface sediments with lowest ratios at depth. These signals are interpreted to reflect the increasing trend of eutrophication of Lake Seeburg and, thus, enhanced autochthonous organic matter production in the lake over the last decades. The abundances of C27 vs. C29 stenols, summed with their respective degradation products, 5α(H)-stanols, are considered as suitable molecular indicators to qualitatively reconstruct historical eutrophication trends.