Biogeochemical properties and fate of dissolved organic matter in wet deposition: Insights from a mariculture area in North Yellow Sea

Abstract

To address the potential roles of atmospheric wet deposition in carbon cycling in coastal waters, a comprehensive study of the biogeochemical properties of dissolved organic matter (DOM) in precipitation and the resulting implication in a mariculture area in North Yellow Sea was conducted. The annual mean concentrations of dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were 1.52 ± 1.52 mg C L^-1, 0.36 ± 0.66 m^-1 and 0.38 ± 0.35 QSU, respectively. The concentrations of most DOM proxies exhibited significant negative correlations with the corresponding precipitation amount (R² = 0.15-0.40, P < 0.01), but the dilution effects became less significant when the precipitation amount exceeded 10.2, 10.7, 10.2 and 2.4 mm for DOC, CDOM, highly‑oxygenated and hypoxic structured humic-like substances, respectively. Seasonally, the dominant precipitation type in winter was snowfall, in which the DOM contained more high-molecular-weight compounds with higher aromaticity and humification degree, while the characteristics of DOM in intensive rainfall in summer were contrary to those in winter. The wet deposition flux of DOC to this region was estimated to be 6.31 × 10⁸ g C a^-1, which was 3.3 and 1.4 times that of the dry deposition and local riverine input, thereby contributing to 4.0 % of the DOC storage in the study area. In summer, the intensive input of DOC through wet deposition (0.43 g C m^-2) to surface seawater could enrich its bioavailable DOC by 10.7 μmol L^-1, the complete aerobic decomposition of which would cause an obvious dissolved oxygen depletion in the surface seawater by 21.4 μmol L^-1, demonstrating the influence of wet deposition on summer deoxygenation in coastal waters.

Keywords: Carbon cycle; Dilution effect; Dissolved organic matter; Rainfall and snowfall; Seawater deoxygenation.