Journal
BIOGEOCHEMISTRY
Volume 146, Issue 2, Pages 105-123Publisher
SPRINGER
DOI: 10.1007/s10533-019-00621-1
Keywords
Terrigenous dissolved organic matter; Land ocean aquatic continuum (LOAC); Biogeochemical model; Biogeochemistry; Photooxidation
Funding
- Natural Environment Research Council, UK, as part of the Land Ocean Carbon Transfer (LOCATE) project [NE/N018087/1]
- U.S. NSF [OCE-1436748]
- NERC [NE/J011967/1]
- MWK-BIME [ZN 3184]
- NERC [NE/R012814/1, pml010010, bgs05007, NE/J011967/1, NE/N018087/1] Funding Source: UKRI
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The transport of dissolved organic matter (DOM) across the land-ocean-aquatic-continuum (LOAC), from freshwater to the ocean, is an important yet poorly understood component of the global carbon budget. Exploring and quantifying this flux is a significant challenge given the complexities of DOM cycling across these contrasting environments. We developed a new model, UniDOM, that unifies concepts, state variables and parameterisations of DOM turnover across the LOAC. Terrigenous DOM is divided into two pools, T-1 (strongly-UV-absorbing) and T-2 (non- or weakly-UV-absorbing), that exhibit contrasting responses to microbial consumption, photooxidation and flocculation. Data are presented to show that these pools are amenable to routine measurement based on specific UV absorbance (SUVA). In addition, an autochtonous DOM pool is defined to account for aquatic DOM production. A novel aspect of UniDOM is that rates of photooxidation and microbial turnover are parameterised as an inverse function of DOM age. Model results, which indicate that similar to 5% of the DOM originating in streams may penetrate into the open ocean, are sensitive to this parameterisation, as well as rates assigned to turnover of freshly-produced DOM. The predicted contribution of flocculation to DOM turnover is remarkably low, although a mechanistic representation of this process in UniDOM was considered unachievable because of the complexities involved. Our work highlights the need for ongoing research into the mechanistic understanding and rates of photooxidation, microbial consumption and flocculation of DOM across the different environments of the LOAC, along with the development of models based on unified concepts and parameterisations.
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