Abstract
Our understanding of the small-scale processes that drive global biogeochemical cycles and the Earth’s climate is dependent on accurate estimations of interfacial diffusive fluxes to and from biologically-active substrates in aquatic environments. In this study, we present a novel model approach for accurate calculations of diffusive fluxes of dissolved gases, nutrients, and solutes from concentration profiles measured across the substrate-water interfaces using microsensors. The model offers a robust computational scheme for automatized determination of the interface position and enables precise calculations of the interfacial diffusive fluxes simultaneously. In contrast to other methods, the new approach is not restricted to any particular substrate geometry, does not requirea prioridetermination of the interface position for the flux calculation, and, thus, reduces the uncertainties in calculated fluxes arising from partly subjective identification of the interface position. In addition, it is robust when applied to measured profiles containing scattered data points and insensitive to reasonable decreases of the spatial resolution of the data points. The latter feature allows for significantly reducing measurement time which is a crucial factor forin situexperiments.
Highlights
Biogeochemical functions and microbial respiration are key processes for our understanding of the aquatic element cycling (Jørgensen, 2000) and, to a large extent, related to the substratewater interfaces, e.g., aggregate-water and sediment-water interfaces
The diffusive boundary layer (DBL) is formed in a thin water layer surrounding all biologically active marine particles, including individual free-living microorganisms and phytoplankton cells, colonies of microorganisms, aggregates formed from detritus, or fecal pellets (Simon et al, 2002; Iversen et al, 2010, 2017; Belcher et al, 2016)
We applied the Derivative-Max model to calculate the flux and interface position for 14 oxygen concentration profiles measured through different types of sinking aggregates
Summary
Biogeochemical functions and microbial respiration are key processes for our understanding of the aquatic element cycling (Jørgensen, 2000) and, to a large extent, related to the substratewater interfaces, e.g., aggregate-water and sediment-water interfaces. The DBL is formed in a thin water layer surrounding all biologically active marine particles, including individual free-living microorganisms and phytoplankton cells, colonies of microorganisms, aggregates formed from detritus, or fecal pellets (Simon et al, 2002; Iversen et al, 2010, 2017; Belcher et al, 2016). It is formed above seafloor sediments (Glud, 2008) and around marine biofilms (Lewandowski, 2000; Flemming and Wuertz, 2019). Measured O2 concentration profiles have been extensively used to calculate O2 fluxes to and from marine substrates and subsequently to derive metabolic rates of, e.g., respiration and photosynthesis (Jørgensen and Revsbech, 1985; Paerl and Bebout, 1988; Ploug et al, 1997, 1999; Berg et al, 1998, 2003; Ploug and Grossart, 2000; Glud, 2008; Eichner et al, 2017)
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