Effects of soot deposition on particle dynamics and microbial processes in marine surface waters

Abstract

Large amounts of soot are continuously deposited on the global ocean. Even though significant concentrations of soot particles are found in marine waters, the effects of these aerosols on ocean ecosystems are currently unknown. Using a combination of in situ and experimental data, and results from an atmospheric transport model, we show that the deposition of soot particles from an oil-fired power plant impacted biogeochemical properties and the functioning of the pelagic ecosystem in tropical oligotrophic oceanic waters off New Caledonia. Deposition was followed by a major increase in the volume concentration of suspended particles, a change in the particle size spectra that resulted from a stimulation of aggregation processes, a 5% decrease in the concentration of dissolved organic carbon (DOC), a decreases of 33 and 23% in viral and free bacterial abundances, respectively, and a factor~2 increase in the activity of particle-attached bacteria suggesting that soot introduced in the system favored bacterial growth. These patterns were confirmed by experiments with natural seawater conducted with both soot aerosols collected in the study area and standard diesel soot. The data suggest a strong impact of soot deposition on ocean surface particles, DOC, and microbial processes, at least near emission hot spots.

Bacterial-viral interactions in the sea surface microlayer of a black carbon-dominated tropical coastal ecosystem (Halong Bay, Vietnam)

“…Bacterial cells may be trapped within BC particles, which could result in the hiding of bacterial receptors thereby lowering the chances of viral infection. In our study, the percent BP associated with the particulate fraction >3 µm was low, in contrast to a previous study reporting high BP on aggregates, as well as a high percentage of microbes attached to soot particles and low viral infection rates (Mari et al, 2014). Stimulation of bacterial activity in the SML by DOC and the dissolved fraction of BC, as reflected by high BP in this study, could have led to high lytic infection and eventually viral production.…”

“…Ultimately, by impacting the physiological state of bacteria and their overall community metabolism, the bacterial utilization of black carbon becomes a potential factor influencing viral life strategies in aquatic systems (Maurice et al, 2013;Palesse et al, 2014). Previous reports have suggested that virally mediated bacterial mortality decreases with an increase in BC concentration (Mari et al, 2014;Malits et al, 2015). Bacterial cells may be trapped within BC particles, which could result in the hiding of bacterial receptors thereby lowering the chances of viral infection.…”

“…Owing to their high specific area-to-mass ratio and high surface-active properties (Koelmans et al, 2006), and by virtue of their own composition which may contain substances that could inhibit microbial activities (Grahame et al, 2014), BC particles can strongly affect the functioning and structure of aquatic microbial food web (Cattaneo et al, 2010;Weinbauer et al, 2012;Mari et al, 2014). It has been established that processes mediated by heterotrophic bacteria and archaea (or prokaryotes, hereinafter referred to as "bacteria") are crucial for biogeochemical cycles and the functioning of aquatic ecosystems (Azam and Malfatti, 2007), with most metabolic pathways performed exclusively by these microorganisms.…”

“…Previous reports have shown that bacteria and viruses were efficiently adsorbed onto BC particles (Mari et al, 2014;Malits et al, 2015). Such phenomenon can be expected to impact bacterial production (BP) and viral lysis, and hence biogeochemical cycles.…”

Seasonal dynamics of atmospheric and river inputs of black carbon, and impacts on biogeochemical cycles in Halong Bay, Vietnam

“…This exercise suggests that PBC may be three times less involved than non-pyrogenic POC in marine processes. As particulate matter can be involved in physical (e.g., sedimentation) and biological processes (e.g., remineralization), and PBC and nonpyrogenic POC are probably involved in the same physical processes as they combine into marine aggregates (Mari et al, 2014), this discrepancy suggests that PBC is less subjected to bacterial degradation and is mostly removed by sedimentation. In addition, this exercise shows that DIN and non-pyrogenic DOC concentrations decrease, respectively, 7.0 and 4.3 times faster than explained by dilution, and hence are rapidly processed in Halong Bay.…”