Microbial dispersal from a hyperactive sandsheet in the Icelandic Highland.

From Stockholm to Minamata and beyond: Governing mercury pollution for a more sustainable future

Most research on the global Si cycle has focused nearly exclusively on weathering or the oceanic Si cycle and has not explored the complexity of the terrestrial biogeochemical cycle. The global biogeochemical Si cycle is of great interest because of its impact on global CO2 concentrations through the combined processes of weathering of silicate minerals and transfer of CO2 from the atmosphere to the lithosphere. A sizable pool of Si is contained as accumulations of amorphous silica, or biogenic silica (BSi), in living tissues of growing plants, known as phytoliths, and, after decomposition of organic material, as remains in the soil. The annual fixation of phytolith silica ranges from 60–200 Tmol yr−1 and rivals that fixed in the oceanic biogeochemical cycle (240 Tmol yr−1). Internal recycling of the phytolith pool is intense with riverine fluxes of dissolved silicate to the oceans buffered by the terrestrial biogeochemical Si cycle, challenging the ability of weathering models to predict rates of weathering and consequently, changes in global climate. Consideration must be given to the influence of the terrestrial BSi pool on variations in the global biogeochemical Si cycle over geologic time and the influence man has had on modifying both the terrestrial and aquatic biogeochemical cycles.

Mercury (Hg) retention in forest ecosystem plays a key role in global biogeochemical cycling. We present a comprehensive review of the research status of forest Hg in China to characterize the Hg budgets and pools. Averaged total Hg (THg) inputs at remote forests and rural and suburban forests in China are about 2–4-fold and 2.5–5-fold higher than the observed values in Europe and North America, respectively. The highly elevated THg inputs are mainly derived from the elevated atmospheric Hg concentrations and litterfall biomass. THg outputs from the forest ecosystems are much lower than the atmospheric depositions. The annual THg retentions range from 26.1 to 60.4 µg m−2 at subtropical forests and from 12.4 to 26.2 µg m−2 at temperate forests. Given the large areal coverage, THg retention in forest is ∼69 t year−1 in China and is much high than that in global scale estimated by models. The much higher THg retention has elevated the THg pools in Chinese subtropical forests. This study has implication for the role of China forests in the global Hg biogeochemical cycle and the optimization of atmospheric Hg transport and deposition models.

Influence of measurement uncertainties on fractional solubility of iron in mineral aerosols over the oceans

Global population growth and economic growth lead to increasing energy demand. This propels the construction of river dams and artificial reservoirs to produce hydropower. Ecological effects of water impoundments, such as the fragmentation of free-flowing rivers, habitat changes, loss of habitats and biodiversity, and changes in biogeochemical cycles have been addressed by researchers for several decades. Also, the influence of flooding on the soils within reservoirs and shore erosion have been studied in a variety of environments and soil types. The development of soil carbon stocks in the submerged soils and soil carbon mineralization upon flooding are of particular interest. Some studies observe a significant decrease of carbon stocks in submerged soil, whereas others report the opposite. Here, we present a study on the influence of 24 years of water impoundment on properties of organic and mineral constituents in submerged Andosols of the Blöndulón hydro-electric reservoir in the Icelandic highlands. Drowned soils are relatively enriched in carbon content, carbon densities and carbon stocks compared to the reference soils, while they are depleted in pedogenic minerals ferrihydrite and allophane. Depth patterns of carbon are rather uniform in the drowned soils in contrast to declining trends in the reference soils. Likely, movement of organic material from upper to lower horizons, and carbon additions from decaying vegetation in the years after the reservoir impoundment explain the carbon enrichment and altered depth distribution. While the drowned soils are enriched in carbon after a comparatively short inundation time of less than three decades, the stability of the soils carbon is uncertain. The apparent loss of mineral soil colloids will likely render the carbon more sensitive to oxidation in the coming decades, particularly during times of exposure of the inundated soils. Assessments of the consequences of water level fluctuations or potential future dam removal need to take the vulnerability of the exposed soils into account.

Biosilicification—the formation of biological structures composed of silica—has a wide distribution among eukaryotes; it plays a major role in global biogeochemical cycles, and has driven the decline of dissolved silicon in the oceans through geological time. While it has long been thought that eukaryotes are the only organisms appreciably affecting the biogeochemical cycling of Si, the recent discoveries of silica transporter genes and marked silicon accumulation in bacteria suggest that prokaryotes may play an underappreciated role in the Si cycle, particularly in ancient times. Here, we report a previously unidentified magnetotactic bacterium that forms intracellular, amorphous silica globules. This bacterium, phylogenetically affiliated with the phylum Nitrospirota, belongs to a deep-branching group of magnetotactic bacteria that also forms intracellular magnetite magnetosomes and sulfur inclusions. This contribution reveals intracellularly controlled silicification within prokaryotes and suggests a previously unrecognized influence on the biogeochemical Si cycle that was operational during early Earth history.

EDITORIAL article Front. Microbiol., 14 March 2014Sec. Terrestrial Microbiology https://doi.org/10.3389/fmicb.2014.00103

The article considers possible anthropogenic carbon sources and migration ways that were not previously included in the global biogeochemical cycle. Complementing the carbon cycle model is important for clarifying the scenarios awaiting the Earth.

Abstract. Marine aggregates are the vector for biogenically bound carbon and nutrients from the euphotic zone to the interior of the oceans. To improve the representation of this biological carbon pump in the global biogeochemical HAMburg Ocean Carbon Cycle (HAMOCC) model, we implemented a novel Microstructure, Multiscale, Mechanistic, Marine Aggregates in the Global Ocean (M4AGO) sinking scheme. M4AGO explicitly represents the size, microstructure, heterogeneous composition, density and porosity of aggregates and ties ballasting mineral and particulate organic carbon (POC) fluxes together. Additionally, we incorporated temperature-dependent remineralization of POC. We compare M4AGO with the standard HAMOCC version, where POC fluxes follow a Martin curve approach with (i) linearly increasing sinking velocity with depth and (ii) temperature-independent remineralization. Minerals descend separately with a constant speed. In contrast to the standard HAMOCC, M4AGO reproduces the latitudinal pattern of POC transfer efficiency, as recently constrained by Weber et al. (2016). High latitudes show transfer efficiencies of ≈0.25±0.04, and the subtropical gyres show lower values of about 0.10±0.03. In addition to temperature as a driving factor for remineralization, diatom frustule size co-determines POC fluxes in silicifier-dominated ocean regions, while calcium carbonate enhances the aggregate excess density and thus sinking velocity in subtropical gyres. Prescribing rising carbon dioxide (CO2) concentrations in stand-alone runs (without climate feedback), M4AGO alters the regional ocean atmosphere CO2 fluxes compared to the standard model. M4AGO exhibits higher CO2 uptake in the Southern Ocean compared to the standard run, while in subtropical gyres, less CO2 is taken up. Overall, the global oceanic CO2 uptake remains the same. With the explicit representation of measurable aggregate properties, M4AGO can serve as a test bed for evaluating the impact of aggregate-associated processes on global biogeochemical cycles and, in particular, on the biological carbon pump.

Biogeochemical Cycles

The critical role of trace gases in global atmospheric change makes an improved understanding of these gases imperative. Measurements of the distributions of these gases in space and time provide important information, but the interpretation of this information often involves ill-conditioned model inversions. A variety of techniques have therefore been developed to analyze these problems. Inverse Problems in Atmospheric Constituent Transport is the first book to give comprehensive coverage of work on this topic. The trace gas inversion problem is presented in general terms and the various different approaches are unified by treating the inversion problem as one of statistical estimation. Later chapters demonstrate the application of these methods to studies of carbon dioxide, methane, halocarbons and other gases implicated in global climate change. This book is aimed at graduate students and researchers embarking upon studies of global atmospheric change, biogeochemical cycles and Earth systems science.

Cleavage of aliphatic organosulfonate carbon to sulfur (C-S) bonds, a critical link in the global biogeochemical sulfur cycle, has been identified in Escherichia coli K-12. Enormous quantities of inorganic sulfate are continuously converted (Scheme I) into methanesulfonic acid 1 and acylated 3-(6-sulfo-{alpha}-D-quinovopyranosyl)-L-glycerol 2. Biocatalytic desulfurization (Scheme I) of 1 and 2, which share the structural feature of an aliphatic carbon bonded to a sulfonic acid sulfur, completes the cycle, Discovery of this desulfurization in E. coli provides an invaluable paradigm for study of a biotic process which, via the biogeochemical cycle, significantly influences the atmospheric concentration of sulfur-containing molecules.

Applications of autotrophic ammonia oxidizers in bio-geochemical cycles

Cleavage of aliphatic organosulfonate carbon to sulfur (C-S) bonds, a critical link in the global biogeochemical sulfur cycle, has been identified in Escherichia coli K-12. Enormous quantities of inorganic sulfate are continuously converted (Scheme I) into methanesulfonic acid 1 and acylated 3-(6-sulfo-{alpha}-D-quinovopyranosyl)-L-glycerol 2. Biocatalytic desulfurization (Scheme I) of 1 and 2, which share the structural feature of an aliphatic carbon bonded to a sulfonic acid sulfur, completes the cycle, Discovery of this desulfurization in E. coli provides an invaluable paradigm for study of a biotic process which, via the biogeochemical cycle, significantly influences the atmospheric concentration of sulfur-containing molecules.

Mercury biogeochemistry: Paradigm shifts, outstanding issues and research needs