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Terrestrial plant biomarkers preserved in lake sediments are commonly used in paleoenvironmental reconstructions. Basin-specific transport pathways and distribution controls of plant biomarkers, however, are poorly understood. This study mapped the distribution of sedimentary n-alkanes sourced from vascular plant waxes to delineate possible transport pathways and quantified the contribution of terrestrial and aquatic input. We combine these data with existing leaf and pollen taphonomy literature and sediment focusing models to develop a better understanding of the controls on plant biomarker transport within lake basins. Here, we report the spatial distribution of sedimentary n-alkanes, the carbon isotope values and C:N ratios of bulk sediment, and percent organic matter from three lakes in the Adirondack Mountains, NY. Preliminary carbon isotope data and n-alkane concentrations within each lake suggests a large terrestrial input. Bulk sediment carbon isotope values ranged from - 26‰ to -32‰ consistent with carbon isotope values of modern terrestrial vegetation. The concentrations of long-chain n-alkanes (indicative of higher land plants), moreover, are much higher than short-chain n-alkanes (indicative of aquatic and microbial activity) by almost two times. By contrast, C:N ratios range from 11-14 indicating a mix of aquatic and terrestrial contribution to the lake’s total organic matter. We combined high-resolution sonar data with the sediment analyses to identify basin- specific controls on the distributions of n-alkanes and bulk sediment carbon isotopes. The statistical categorization of sediment zones based on relative hardness and roughness along the lake bottom delineates where organic material is concentrated. For the terrestrially sourced plant waxes, we measured low n-alkane concentrations in sandy littoral sediments relative to deeper sediments towards the main depo-center. Together, this information validates sediment focusing models and suggests that terrestrial carbon and n-alkanes are preferentially transported to the main depo-center of the lake. These observations highlight important relationships between basin-specific sediment properties and processes controlling the transport and deposition of n- alkanes.
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This content will become publicly available on January 1, 2026
Locally produced leaf wax biomarkers in the high-altitude Areguni Mountains outweigh downstream transport
Abstract. Sedimentary records of lipid biomarkers such as leaf wax n-alkanes are influenced by not only ecosystem turnover and physiological changes in plants but also earth surface processes integrating these signals into the sedimentary record, though the effect of these integration processes is not fully understood. To determine the depositional constraints on biomarker records in a high-altitude small catchment system, we collected both soil and stream sediments along a 1000 m altitude transect (1500–2500 m a.s.l.) in the Areguni Mountains, a subrange of the Lesser Caucasus Mountains in Armenia. We utilize a treeline at ∼ 2000 m a.s.l., which separates alpine meadow above from deciduous forest below, to assess the relative contribution of upstream biomarker transport to local vegetation input in the stream. We find that average chain length (ACL), hydrogen isotope (δD) and carbon isotope (δ13C) values of n-alkanes are significantly different in soils collected above and below the treeline. However, samples collected from the stream sediments do not integrate these signals quantitatively. As the stream drops below the treeline, the ACL, δD and δ13C values of n-alkanes preserved in streambed sediments reflect a bias toward n-alkanes sourced from trees. This suggests that either (1) there is minimal transportation of organic matter from the more open vegetation at higher elevations or (2) greater production of target biomarkers by trees and shrubs found at lower elevations results in overprinting of stream signals by local vegetation. Though these observations may preclude using n-alkanes to measure past treeline movement in these mountains, δD values of biomarkers in fluvial deposits in these settings are more likely to record local hydrological changes rather than reflect fractionation changes due to turnover in the upstream vegetation structure.
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- Award ID(s):
- 1752815
- PAR ID:
- 10616990
- Publisher / Repository:
- European Geophysican Union
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 22
- Issue:
- 4
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 831 to 840
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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