Multiproxy probing of anthropogenic influences on the different components of dissolved organic matter in coastal rainwater

In an environment that is tightly linked to humankind, how anthropogenic activity affects the quality and quantity of dissolved organic matter (DOM) in atmospheric depositions is not well understood. In this study, dissolved organic carbon (DOC), UV-vis spectra combined with molecular markers, including formic acid (FA), acetic acid (AA) and dissolved black carbon (DBC), were applied to track the temporal variation and influential factors of rainwater DOM at a coastal site. The ranges of DOC, light absorption at 254 nm (a(254)), FA, AA and DBC were 23.2-471 mu mol L-1, 0.16-10.6 m(-1), 0.12-23.5 mu mol L-1, 0.44-37.8 mu mol L-1 and 0.02-4.8 mu mol L-1, respectively. The negative correlations between DOC, a(254), AA and precipitation amount revealed a dilution effect. The concentrations of all measured DOM components were statistically different among different seasons with the highest value in spring. Higher DOM concentrations also occurred in the rain with backward trajectories influenced by the land. Compared to the nearby riverine DOM, the DOC-specific UV absorbance (SUVA(254)) of rainwater was lower, suggesting lower aromaticity of rainwater DOM. Significant correlations among different DOM components suggest that they shared similar sources or were affected by the same processes, while the significant correlations with anions (SO42-, F- and NO3-) and the ratio of FA to AA all suggested that the direct emission and secondary production fromanthropogenic emissions (fossil fuel burning, biomass and biofuel burning) played important roles in regulating the level of DOM concentration in rainwater. Correlations with environmental variables (PM2.5, CO and NO2) further confirmed the input from anthropogenic activities. Furthermore, the monthly wet atmospheric deposition fluxes of DOM components (except DBC) can be successfully simulated by monthly precipitation and monthly average values of PM2.5 and NO2. Future studies should examine how atmospheric deposition affects the biogeochemical cycles in coastal regions.

Automated summary

In this study, the temporal variation and influential factors of rainwater dissolved organic matter (DOM) were tracked at a coastal site using dissolved organic carbon (DOC), UV-vis spectra, and molecular markers. The results showed negative correlations between DOC, light absorption, and precipitation amount, as well as higher DOM concentrations in spring and in rain influenced by the land. Human emissions and secondary production played important roles in regulating the level of DOM concentration, and environmental variables confirmed the input from anthropogenic activities. Future studies should focus on how atmospheric deposition affects biogeochemical cycles in coastal regions.