Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Abstract

Molybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea‐salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in diameter) to be 23 Gg Mo yr−1, with 40%–75% from anthropogenic sources. We approximated that for the top meter of soil, Mo turnover times range between 1,000 and 1,000,000 years. In some industrialized regions, anthropogenic inputs have enhanced Mo deposition 100‐fold, lowering the soil Mo turnover time considerably. Our synthesis of global observational data, modeling, and a mass balance comparison with riverine Mo exports suggest that anthropogenic activity has greatly accelerated the Mo cycle, with potential to influence N‐limited ecosystems.

New insights into the drivers of moss‐associated nitrogen fixation and cyanobacterial biomass in the eastern Canadian boreal forest

“…This shows that Mo depositions are generally low in pristine high‐latitude boreal forests and that Mo limitation of N 2 ‐fixation is likely widespread in boreal feather mosses. Mo deposition is expected to increase globally with human activities (Wong et al, 2021), which could possibly alleviate the Mo limitation and promote moss N 2 ‐fixation. Ma et al (2019) found that Mo addition increased cyanobacteria relative abundance in paddy soils, and Rousk, Degboe, et al (2017) observed higher cyanobacteria colonization of moss that had been supplemented with Mo.…”

“…Modification of the atmospheric deposition regime that is linked to the development of human activity is likely to affect nutrient inputs affecting both N 2 ‐fixation and cyanobacterial growth. For instance, atmospheric deposition of iron (Fe), molybdenum (Mo) and vanadium (V), the metal cofactors of the nitrogenase enzyme catalysing the N 2 ‐fixation reaction (Bishop et al, 1980), have substantially increased since the beginning of the Industrial Revolution and are expected to continue to rise (Hamilton et al, 2020; Schlesinger et al, 2017; Wong et al, 2021).…”

“…This shows that Mo depositions are generally low in pristine high-latitude boreal forests and that Mo limitation of N 2 -fixation is likely widespread in boreal feather mosses. Mo deposition is expected to increase globally with human activities(Wong et al, 2021), which could possibly alleviate the Mo limitation and promote moss N 2 -fixation Ma et al (2019).…”

Atmospheric Wet Iron, Molybdenum, and Vanadium Deposition in Chinese Terrestrial Ecosystems

“…Anthropogenic activities have markedly changed trace metal contents [i.e., iron (Fe), molybdenum (Mo), and vanadium (V)] in the atmosphere, which, in turn, have affected trace metal deposition. − A recent study reported that atmospheric Mo deposition might increase by 100 times or more in some industrialized regions owing to coal combustion and smelting operations . Schlesinger et al revealed that global wet V deposition had increased by 2.7 times from that in the preindustrial period (15 Gg V a –1 ).…”

“…Schlesinger et al revealed that global wet V deposition had increased by 2.7 times from that in the preindustrial period (15 Gg V a –1 ). In general, natural sources of trace metals in the atmosphere include dust, sea spray aerosols, volcanic activity, soil, and wildfire, among others, − and anthropogenic sources are mainly derived from the exploitation and combustion of fossil fuels (i.e., coal and oil) as well as biomass combustion, mineral mining, and traffic emissions. − ,− …”