Distribution of hopanoids along a land to sea transect: Implications for microbial ecology and the use of hopanoids in environmental studies

Abstract

Bacteriohopanepolyols (BHPs) are lipid constituents of diverse bacteria and have great potential as taxonomically and environmentally diagnostic biomarkers. In order to examine their environmental behavior and potential for tracing biogeochemical processes, we analyzed BHPs and geohopanoids (the diagenetic products of BHPs) in soils and surface sediments from the middle Yangtze River catchment to the East China Sea (ECS) shelf. These data are compared to an up‐to‐date survey of BHP distributions in soils, including regions collectively covering the Arctic, temperate, subtropics, and tropics. Regional climatic differences, particularly temperature, likely exert an important control on BHP distributions in soils. In the aquatic (river–estuary–shelf) setting, BHP concentrations and structural diversity are substantially lower than in soils, suggesting that in aquatic environments either bacterial biodiversity is lower or there is not the same requirement for hopanoid synthesis. However, different aquatic regimes vary substantially: high BHP diversity and enhanced BHP production occur in the biogeochemically dynamic Yangtze estuary, whereas BHP distribution is uniform with much less structural diversity in the oligotrophic ECS open shelf. The Rsoil index, based on the relative abundances of soil‐marker BHPs against bacteriohopanetetrol, is suggested as a new approach to trace soil organic matter input into marine sediments. The Rsoil indices decrease from the river to the ECS, correlating strongly with branched and isoprenoid tetraether indices and moderately correlating with δ13C of organic carbon values and the concentrations of higher plant biomarkers, demonstrating their ability to trace soil organic matter inputs at least to the ECS.