The Sources and Transformations of Dissolved Organic Matter in the Pearl River Estuary, China, as Revealed by Stable Isotopes
Open Access
- 24 September 2018
- journal article
- research article
- Published by American Geophysical Union (AGU) in Journal of Geophysical Research: Oceans
- Vol. 123 (9) , 6893-6908
Abstract
To investigate the sources and transformation processes of bulk marine dissolved organic matter (DOM), seasonally collected water samples from the Pearl River Estuary (PRE), south China, were analyzed for concentration and stable isotopic ratios (δ13C and δ15N) of DOM. The δ13C values clearly indicated a shift of dissolved organic carbon (DOC) sources from terrigenous material in the river to predominantly plankton in the lower estuary. The distribution of δ13C during the estuarine mixing, in combination with the notable deviation of DOC concentration, provided strong evidence for a substantial DOC removal in the salinity range of 5 to 22. In contrast to δ13C, the δ15N of DOM exhibits a strong seasonality, implying a clear decoupling of estuarine DOC and dissolved organic nitrogen (DON) dynamics. During dry periods with low river discharge, sewage‐derived DON contributed significantly to the riverine loading. While freshwater‐saltwater mixing is important in regulating the distribution of DON, the distribution of δ15N along the salinity gradient provided strong evidence for active sediment‐water interaction and adsorption/desorption processes at the middle to high salinities. During wet periods, severe soil loss and erosion, and/or in situ biological production, adsorption onto suspended particles dominate the riverine DON fluxes, whereas the DON dynamics might be governed by different biogeochemical processes between spring and summer, as reflected by distinct δ15DON patterns in the estuarine zone. In spring, highly degraded DON originating from soil experienced little further biological alternation during estuarine mixing, whereas there was a tight coupling of DON production and consumption in summer.Keywords
Funding Information
- Ministry of Science and Technology (MGK1811)
- National Natural Science Foundation of China (41325012)
- Guangzhou Science, Technology and Innovation Commission (201607010008)
- Ministry of Science and Technology (2016YFA0601204)
This publication has 79 references indexed in Scilit:
- Interbasin isotopic correspondence between upper-ocean bulk DON and subsurface nitrate and its implications for marine nitrogen cyclingGlobal Biogeochemical Cycles, 2011
- Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic SeaBiogeochemistry, 2011
- Bulk organic δ13C and C/N as indicators for sediment sources in the Pearl River delta and estuary, southern ChinaEstuarine, Coastal and Shelf Science, 2010
- Occurrence of nutrients in riverine runoff of the Pearl River Delta, South ChinaJournal of Hydrology, 2009
- Biogeochemical controls on distributions and fluxes of dissolved and particulate organic carbon in the Northern South China SeaDeep Sea Research Part II: Topical Studies in Oceanography, 2007
- Nitrification and Nitrifying Bacteria in the LowerSeine River and Estuary(France)Applied and Environmental Microbiology, 2003
- Source partitioning using stable isotopes: coping with too many sourcesOecologia, 2003
- Dissolved inorganic phosphorus, dissolved iron, and Trichodesmium in the oligotrophic South China SeaGlobal Biogeochemical Cycles, 2003
- Decomposition of dissolved organic matter from the continental marginDeep Sea Research Part II: Topical Studies in Oceanography, 2002
- Uncertainty in source partitioning using stable isotopesOecologia, 2001