| Popis: |
Terrestrial plant wax compounds preserved in lake sediments are important archives of paleoclimate data. Of these compounds, the hydrogen isotopic composition of n-alkanes (δD) is commonly used to track changes in hydrology over different spatial and temporal scales. Despite the existing utility of n-alkane δD, questions remain about the integration of n-alkanes into lake sediments and how their transport from source to sediment may affect the plant wax δD signal. Our understanding of the relative sourcing and contribution of sedimentary n-alkanes is improving. However, existing studies investigating the integration and spatial distribution of n-alkanes into lake sediments has been restricted to a single lake basin or limited sampling from lake basins over a broad geographic area. This study evaluated the spatial variability of sedimentary n-alkanes and their hydrogen isotopic compositions between and within three lake basins over a small geographic area in the Adirondack Mountains to compare n-alkane deposition, sourcing, and distribution in modern lake sediments.Concentrations for n-alkane homologous varied considerably between and within lake basins reflecting differences in basin-specific properties such as vegetation composition, trophic state, size, and hydrologic configuration. The highest long-chain n-alkane concentrations were measured from samples collected near stream input highlighting important implications for terrestrially-sourced n-alkane transport. Also, the predominant source of long-chain n-alkanes between basins was determined to be controlled by the local vegetation as evidenced by differences in compound-specific carbon isotopes and concentrations coincident with differences in the abundance of conifer species which provides important insight for the integration of terrestrial n-alkanes in temperate forest settings. Despite the variability of n-alkane concentrations, the hydrogen isotopic compositions of long-chain n-alkanes were indistinguishable between and within lake basins. Mean δD values for the n-C29 (-184.5, -184.2, and -183.0 ‰) and n-C31 (-174.0, -172.4, and -171.2 ‰) alkanes fell within the analytical uncertainty of 4.2 ‰.The broader implications of this study are outlined in concurrent calibration research aimed at better understanding how the regional sediment-level δD signal from Adirondack mid-latitude temperate forests compare to the sediment-level δD signal observed in other biomes as a guide for future site selection. The homogeneity of the long-chain n-alkane δD signal in our lakes helps to reconcile and improve paleorecords by applying quantitative constraints on their interpretation. |
