Biogeochemistry最新文献

Turbid coastal waters are dynamic systems where fine-grained sediments interact with organic matter, significantly influencing the fate of both the components. We investigated the seasonal dynamics of particulate (POC) and dissolved (DOC) organic carbon pools along a suspended particulate matter (SPM) gradient from nearshore to offshore waters in a mid-latitude coastal zone. To assess temporal and spatial variations in POC composition, we quantified the relative contributions of phytoplankton (POC_phyto), heterotrophs (POC_het), detritus (POC_det), and mineral-associated organic matter (POC_mineral) to the bulk POC pool. In nearshore waters, frequent tidal resuspension and high SPM concentrations led to elevated POC_det and POC_mineral fractions, masking the increase in POC_phyto, despite the higher primary productivity during the spring bloom. In contrast, offshore waters exhibited a greater relative contribution of POC_phyto, with seasonal POC increases corresponding to elevated chlorophyll a (Chla) levels in spring and summer, similar to the open-ocean dynamics. These trends were further reflected in particulate organic carbon to nitrogen (POC:PON) ratios and POC:Chla ratios, commonly used to assess sources and quality of organic matter. The cross-shore gradient in organic matter partitioning, with dominance of POC nearshore and DOC offshore, highlights the role of particle resuspension and phytoplankton production in controlling organic carbon distribution between the two pools. Overall, our findings underscore the complex interplay between biological production, nutrient cycling, hydrodynamic forces, and SPM in shaping the composition and fate of organic carbon in turbid coastal systems.

Dissolved organic matter (DOM) consists of dissolved molecules, biopolymers, and aggregates with a broad range of molecular sizes. In freshwater and seawater environments, spontaneous self-assembly of DOM forms hydrated particulate organic matter (POM) networks. This conversion from DOM to POM affects carbon transfer through microbial and particle food webs and export to sediments. Particle food webs are based on the direct POM ingestion by zooplankton species. This DOM assembly occurs when the inter-polymer or inter-colloid distances allow chemical (covalent) or physical (e.g., electrostatic, hydrogen) bonds. Here we explore the underlying mechanisms of self-assembly using lake waters with different concentrations of polyanionic DOM with humic content and calcium (Ca) and iron (Fe) crosslinking. We experimentally adjusted the cations by chelating and/or increasing the concentration of calcium or iron. To monitor the self-assembly of DOM, we employed homodynamic laser scattering. Results indicate that DOM self-assembly and physical gel-particle formation result from low-energy Ca⁺² and Fe⁺³ counterion bonding. It can be readily reversed by Ca and Fe chelators, resulting in the disassembly of the network and dispersion of DOM polymers. Calcium cations appear to promote a higher level of self-assembly, reaching larger hydrodynamic sizes during stabilization, compared to iron cations. Our results indicate that the chemical environmental context critically affects the formation of POM from DOM, influencing ecosystem processes such as carbon sedimentation and storage, and providing alternative pathways for heterotrophic consumers (i.e., food webs based on particles).

The 11 BIOGEOMON (International Symposium on Ecosystem Behavior) conferences span 37 years of research in ecosystem science. Here we discuss the history of BIOGEOMON in two parts. In Part 1 we focus on the structure of the conference over the years: its inception, the demographics of attendees, the major biomes and ecosystems studied, and the evolution of dominant topics and themes. We argue that the fundamental goal of understanding the response of ecosystems to perturbations has remained the same over the meetings, but the drivers of change focused upon have evolved over time, reflecting the emergence of new issues and the development of scientific understanding. Each conference is therefore partly a snapshot of the important topics of the day, and partly the core themes that define BIOGEOMON: the cycling and transformations of the major biogeochemical elements on land, and the investigative techniques of monitoring, modelling, and catchment manipulation. We conclude with some reflections on the conference from BIOGEOMON attendees over the years.

The 11 BIOGEOMON (International Symposium on Ecosystem Behaviour) conferences span 37 years of research in ecosystem science.  In this set of papers, we discuss the history of BIOGEOMON in two parts.  In Part 2 we consider the development in understanding of three topics over successive conferences:  acid deposition, peatland biogeochemistry, and isotope geochemistry. Using these three topics as examples, we show how the BIOGEOMON conferences both reflect, and lead, advances in biogeochemistry research.  Using published papers from conference special issues, conference proceedings, and other publications from BIOGEOMON delegates, we highlight the changing importance of these research strands over the years, and consider the questions, insights, and surprises, played out in the meetings.

Ocean acidification due to anthropogenic carbon dioxide (CO₂) uptake threatens marine ecosystems, but coastal waters have complex and highly variable carbonate system dynamics. More coastal time series are therefore needed to better constrain coastal pH dynamics, but especially in the tropics such time series are rare. Southeast Asia’s Sunda Shelf Sea has exceptionally high marine biodiversity and rapidly increasing anthropogenic pressures, but we have little knowledge of coastal carbonate system dynamics in the region. We analyzed 7-years of monthly carbonate system data from the Singapore Strait in the central Sunda Shelf. Our results show consistently low seawater pH (total scale; pH_T; < 8.0) and aragonite saturation state (Ω_Ar, usually < 3.0), but with a clear seasonal pH_T variation by 0.11–0.19 units. The observed seasonality reflects the monsoon-driven advection of water masses that have been shaped by different biogeochemical processes. Specifically, during the southwest monsoon, remineralization of terrestrial dissolved organic carbon originating from regional peatlands lowers pH_T, while calcium carbonate (CaCO₃) formation and dissolution are more important during other seasons. Comparing our data to predicted values for purely conservative mixing of river water and seawater shows that these non-conservative biogeochemical processes are dominant drivers. Our time series shows a significant decreasing trend in pH_T of –0.043 units per decade, exceeding the theoretical trend detection time (TDT) of 5.0 ± 1.3 years. However, the seasonal pH_T variability itself shows interannual variability, and pH_T is also correlated with the El Niño Southern Oscillation. This longer-term climatic control may complicate trend quantification. Our study highlights how terrestrial dissolved organic carbon remineralization may enhance future ocean acidification in Sunda Shelf region, emphasizing the importance of continuing the time series to better quantify climatic drivers and long-term trends.

Biogenic methane, the largest contributor to atmospheric methane, is produced via different microbial methanogenic pathways, depending on the substrates and type of methanogens. Stable carbon and hydrogen isotope measurements (δ¹³C and δD) and the clumped isotopologues (Δ¹³CH₃D and Δ¹²CH₂D₂) of methane have emerged as important diagnostic tools, providing insights into methane sources and reaction pathways. Here, we investigate the pathway-specific bulk and clumped isotopic signatures of methane produced by microbial communities in sediments from a marine coastal system (lake Grevelingen, the Netherlands). Sediment batches were incubated with different substrates (acetate, carbon dioxide + hydrogen, methanol, and methanol + hydrogen) to promote the different methanogenic pathways. Our results show that the methanogenic pathways studied produce isotopically distinct methane. Analysis of the 16S rRNA gene from the sediment reveals a metabolically diverse methanogenic community capable of sustaining hydrogenotrophic, acetoclastic, and methylotrophic pathways, consistent with the isotopic variability observed in methane produced during incubations. The methylotrophic and acetoclastic pathways yield methane with significantly lower Δ¹²CH₂D₂ than the hydrogenotrophic pathway due to the combinatorial anti-clumping effect. The methane produced in situ in the sediments predominantly originates from the hydrogenotrophic pathway, with Δ¹³CH₃D and Δ¹²CH₂D₂ values closely matching incubations with carbon dioxide and hydrogen. Overall, the incubation results using lake sediments align well with previous pure culture studies, highlighting the potential of clumped isotope analysis to differentiate methane production pathways in natural environments.

Alien invasive species impact native plant communities, not only through direct negative effects on native species but also by altering nutrient cycling and availability. However, the mechanisms driving these changes—such as differences in litter decomposition rates and litter quality, or increased overall decomposition rates within invaded stands—remain unclear. This study examines how Solidago gigantea, an invasive species in Europe and Asia, affects decomposition. A climate chamber experiment tested whether S. gigantea litter decomposes faster than litter from co-occurring native species. The study examined whether differences in decomposition rates could be attributed to litter quality (using C/N ratio as a proxy) or to variations in soil microbiota (via inoculum from invaded vs. non-invaded plots). A field experiment measured overall decomposition rates in invaded and non-invaded plots using tea bags and wooden spatulas buried for 2–16 weeks. Soil moisture, carbon, and soil fauna activity were also assessed for their influence on decomposition. S. gigantea litter decomposed significantly faster than native graminoid species (decomposition rates of 0.91 and 0.33 g g⁻¹ day⁻¹ resp.), despite its higher C/N ratio (39.6 and 27.9 resp.). Invaded stands consistently had higher decomposition rates, which was attributed to abiotic changes, including reduced soil moisture and increased soil carbon, rather than to biotic changes in soil fauna or microbiota activity. These findings highlight S. gigantea’s substantial impact on nutrient cycling in invaded ecosystems. However, the extent—and potentially the direction—of these effects likely depends on the invaded plant community. Grass-dominated and wetter communities may experience the greatest increases in nutrient cycling, potentially enhancing primary productivity.

Reconstructing long-term records of air pollution and comparing present-day air quality with that of the pre-Industrial Revolution era are crucial for predicting the trajectory of recovery from sulfur-based air pollution. The annual rings of trees contain sulfur compounds that have accumulated over time, and the sulfur stable isotope ratio (δ³⁴S) reflects the past δ³⁴S values in the atmosphere. Although δ³⁴S in tree rings has been analyzed in the past, there are no δ³⁴S data in tree rings from before the Industrial Revolution (1760), when humans began to emit large amounts of sulfur compounds to the atmosphere. Therefore, we analyzed long-term variations in δ³⁴S in the annual rings of two giant Japanese cedars (Cryptomeria japonica) from the Okute-Shinmei Shrine and Ise Jingu in central Japan, spanning over 350 years. The fluctuation trend of δ³⁴S values was statistically divided into periods before and after industrialization. Before industrialization, δ³⁴S values were stable and high, averaging + 6.0 ± 0.6‰ in Okute and + 10.5 ± 0.9‰ in Ise. The values closely match previously reported adjusted δ³⁴S values from Greenland ice cores. After industrialization, values declined sharply owing to fossil fuel use. This decline stabilized around the 1990s, and values increased slightly. Despite these reductions in sulfur emissions, δ³⁴S values remain significantly lower than pre-industrial levels, implying that air quality has not yet returned to pre-industrial conditions.

Understanding mercury (Hg) accumulation and distribution patterns in alpine timberline forests is essential for understanding the biogeochemical cycling of Hg in these ecosystems. To this end, we systematically analyzed Hg concentrations and isotopic compositions in the soil–plant system to elucidate the spatial distribution and source contributions of Hg in the timberline ecotone. The transition from coniferous forests to shrubbery resulted in a distinct decrease in Hg pool size—67% in vegetation and 19% in soil, respectively. The Hg isotopic mixing model further demonstrated that vegetation-induced atmospheric Hg⁰ deposition, with an average contribution of 74 ± 10%, was the dominant source of soil Hg in the timberline ecotone. Hg concentration exhibited an increasing trend from Oi to Oe soil horizons, followed by a decline in the mineral layers. The rising Hg concentrations in organic soils resulted from accelerated organic carbon loss during decomposition, while the decreasing gradient in mineral soils was primarily driven by the combined effects of geological Hg sources and long-term Hg depletion during soil formation. Vegetation transition across the timberline ecotone significantly reduced Hg pool dynamics in the soil–plant system. The upward migration of fir forests driven by climate warming may enhance atmospheric Hg deposition, underscoring the need for a comprehensive assessment of Hg cycling in warming alpine ecosystems.

The abundant lakes in the boreal region are an active zone for cycling of organic carbon (OC), functioning as simultaneous sources and sinks of atmospheric carbon dioxide. While previous studies have documented increased OC loading and accelerated carbon accumulation to inland waters, the drivers of this increase remain ambiguous. In this study we investigate carbon accumulation rates in 208 boreal lakes in the context of land use. We show that modern sediment carbon accumulation rates in boreal lakes have increased to median of 24.5 g m⁻² y⁻¹, representing a roughly fivefold increase over Holocene record, mainly due to increased terrestrial organic carbon inputs. Land use has become the most significant predictor of modern lake sediment carbon accumulation with lake morphometrics primarily affecting the efficiency of carbon burial. Recalcitrant terrestrial carbon from forested and peatland areas is buried more effectively, whereas increased soil erosion and enhanced mineralization of labile OC from agricultural runoff reduces the relative burial of terrestrial OC.