Ecological Indicators (Mar 2023)
Driving forces underlying changes in carbon molecular component deposition in a river-lake ecotone
Abstract
Carbon molecular deposition in sediments removes organic carbon (OC) from the biosphere-atmosphere carbon cycle and therefore limits the emission of greenhouse gases (i.e. CH4 and CO2) from natural water systems. At present, the occurrence characteristics, deposition fluxes, and driving force of OC components in the river-lake ecotone are unclear. Here, the tempo-spatial distribution of polycyclic aromatic hydrocarbons (PAHs) and Σn-alkanes (nC13–nC32) related to organic nitrogen (ON) and OC in the estuarine sediments from Poyang Lake and their sources and effects were investigated. The ON and OC contents in the sediment cores ranged from 0.35−0.64 % and 1.9–4.24 %, respectively, and the PAH fluxes varied between 672.19 and 24703.97 ng cm−2 a-1, showing an upward risk to the water bodies and human health. In particular, it is worth noting that the 5–6 ring monomers were dominant, accounting for 66.48 % of the ΣPAHs in the sediment profile. The sources were mainly derived from biomass combustion and automobile exhaust emissions, while the latter proportion has increased in recent decades. In the sediment profile, the n-alkane abundance peak was found at nC31 with a marked odd-even predominance. The deposition flux for Σn-alkanes ranged between 10.92 and 73.46 μg cm−2 a-1. In addition, long-chain monomers dominated the Σn-alkanes and were found to be herbaceous in origin. An analysis of the environmental indicators in the sediment layers showed that forest restoration and the eutrophication of water bodies caused by anthropogenic stress and climate change were mainly responsible for the relatively large contribution made by vascular plants and autochthonous organisms.
