Biogeochemistry最新文献

Bransfield Strait has been identified as a climate hotspot for understanding regional environmental changes with global impact. This study focuses on enhancing the understanding of carbon cycle dynamics and its interactions with hydrographic variables in Bransfield Strait, located on the northern Antarctic Peninsula. The stable carbon isotopes of dissolved inorganic carbon (δ¹³C_DIC) were investigated in the study region during comprehensive sampling in 2023 along the major ocean basins. Bransfield Strait is influenced by two main source water masses: the Circumpolar Deep Water (CDW), which intrudes into the region from the Antarctic Circumpolar Current meander, and Dense Shelf Water (DSW), which is advected by coastal currents from the Weddell Sea continental shelf. The study reveals CDW’s dominant role in 2023, accounting for ~60% of the water mass mixture in the region and limiting the highest contribution of DSW to the deep layer of the central basin. The spatial variation of δ¹³C_DIC signatures showed that biogeochemical processes predominantly shape the δ¹³C_DIC distribution along the water column. Photosynthesis enriched the surface waters with the heavier carbon isotope, with signatures ranging from 2 to 1.5‰, while organic matter remineralization depleted it below the mixed layer (ranging from 0 to − 2‰). Horizontally, δ¹³C_DIC distribution was influenced by the higher contribution of each source water mass. Thermodynamic fractionation contributed to the enrichment of δ¹³C_DIC (~ 1 to 1.5‰) in the CDW layer in Bransfield Strait. Conversely, the predominance of younger and colder DSW exhibited a depletion of δ¹³C_DIC (− 1 to − 2‰). Therefore, δ¹³C_DIC is identified as an additional tracer to provide new insights into the biogeochemical and hydrodynamic processes of Bransfield Strait.

Polyphosphate is formed by polyphosphate-accumulating organisms occurring in various terrestrial, freshwater, and marine ecosystems as well as industrial environments. Although polyphosphate-accumulating organisms and polyphosphate have been well studied in enhanced biological phosphorus (P) removal from wastewater treatment plants, their role in the internal P cycle of natural lakes remains unclear. Several studies have shown that polyphosphate storage is widespread in lake sediments. In this study, ³¹P nuclear magnetic resonance spectroscopy was used to analyse the seasonal dynamics of polyphosphate and its drivers at the sediment surface of three stratified German lakes with strong seasonality of hypolimnetic oxygen concentrations. Similar seasonal patterns of polyphosphate were observed in all three lakes. Polyphosphate content increased by a factor of three to five at the beginning of summer stratification, with the maximum content observed in May when oxygen was already very low. During this period, strong redox gradients prevailed within the topmost sediment layer, and highly soluble reactive P concentrations were present in the pore water due to the reductive release of P bound to iron(III)oxides and oxide-hydroxides. Polyphosphate acted as a temporary P storage and was released after a delay, which may mitigate sedimentary P release into the water body during the (early) summer stratification. The observed seasonal dynamics of polyphosphate at the sediment surface offer a novel insight into the link between the P and iron cycles in lakes.

Ponds can store large amounts of organic matter (OM) in their sediments, often accumulated over long periods of time. Sediment OM is largely protected from aerobic mineralization under water saturated conditions but are vulnerable when exposed to oxygen during periods of drought. As climate change progresses, drought periods are likely to occur more frequently and may affect OM mineralization, and thus the release of greenhouse gases (GHGs) such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from pond ecosystems. Therefore, we aimed to test how GHG emissions and concentrations in the sediment respond to drought by gradually decreasing water levels to below the sediment surface. To this end, undisturbed sediment cores from two small ponds with distinct watershed and water chemistry characteristics were incubated in mesocosms for 118 days at 20 °C. Water levels were sequentially tested at 3 cm above the sediment surface (Phase I) and at the level of the sediment surface (Phase II). In Phase III, water levels were continuously lowered either by evaporation or by active drainage including evaporation. Mean CH₄ fluxes of both ponds were high (21 and 87 mmol m⁻² d⁻¹), contributing 90 and 96% to the GHG budget over the three phases. The highest CH₄ fluxes occurred in Phase II, while active drainage strongly reduced CH₄ fluxes in Phase III. A multivariate analysis suggests that dissolved organic carbon and sulphate were important drivers of CH₄ fluxes in Phase III. CO₂ and N₂O fluxes also responded to declining water levels, but their contribution to the GHG budget was rather small. Both gases were primarily produced in the upper sediment layer as indicated by highest concentrations at 5 cm sediment depth. Compaction of sediment cores by water level lowering increased bulk density and maintained high water contents. This side effect, retarding the drying of the sediment surface, was possibly relevant for the GHG net emission of the sediments in Phase II and III. Overall, GHG fluxes from the sediments exhibited high sensitivity to falling water levels. This study suggests that drying pond sediments have great potential to emit large amounts of GHGs to the atmosphere in the event of drought, representing hot spots of GHGs in the landscape.

Black carbon has been shown to suppress microbial methane production by promoting anaerobic oxidation of organic carbon, diverting electrons from methanogenesis. This finding represents a new process through which black carbon, such as wildfire char and biochar, can impact the climate. However, the mechanism and capacity of black carbon to support metabolism remained unclear. We hypothesized black carbon could support microbial growth exclusively through its electron storage capacity (ESC). The electron contents of a wood biochar was quantified through redox titration with titanium(III) citrate before and after Geobacter metallireducens growth, with acetate as an electron donor and air-oxidized biochar as an electron acceptor. Cell number increased 42-fold, from 2.8(± 0.6) × 10⁸ to 1.17(± 0.14) × 10¹⁰, in 8 days based on fluorescent cell counting and the result was confirmed by qPCR. The qPCR results also showed that most cells existed in suspension, whereas cell attachment to biochar was minimal. Graphite, which conducts but does not store electrons, did not support growth. Through electron balance and use of singly ¹³C-labeled acetate (¹³CH₃COO^–), we showed (1) G. metallireducens could use 0.86 mmol/g, or ~ 19%, of the biochar's ESC for growth, (2) 84% and 16% of the acetate was consumed for energy and biosynthesis, respectively, during biochar respiration and (3) ca. 80 billion electrons were deposited into biochar for each cell produced. This is the first study to establish electron balance for microbial respiration of black carbon and to quantitatively determine the mechanism and capacity of biochar-supported growth.

Graphical Abstract

The Caribbean region is experiencing seasonal inundation of the shoreline by large mats of pelagic Sargassum spp. (Sargassum) leading to novel impacts to ecological communities. Where Sargassum becomes trapped along the shoreline, leachates turn the water a brown color, coined Sargassum Brown Tide (Sbt). We conducted monthly sampling at six sites along the offshore mangrove keys of Jobos Bay, PR between April 2022 to July 2023 to collect temperature, pH, salinity, dissolved oxygen, total nitrogen (TN), total phosphorus (TP), chlorophyll a (chl a), total suspended solids (TSS), and volatile suspended solids (VSS) at nearshore, midshore, and offshore zones along transects running perpendicular to the shoreline. We also collected data on submerged aquatic vegetation (SAV) community dynamics along transects at each site. We found significantly higher chl a and lower dissolved oxygen concentrations within the nearshore zone during Sbt events but the differences did not extend out to the midshore and offshore zones. Total suspended solids were also higher at nearshore zones compared to offshore zones when a Sbt event occurred. In addition, sites that experienced Sbt had higher turbidity and lower pH. Total percent cover of SAV was different between sites impacted by Sbt and control sites depending on transect zone, with higher SAV percent cover for control sites within the 5 m zone and often within the 15 m zone. Our data suggest that Sbt has significant impacts to nearshore water quality, chl a, and SAV percent cover; however, most impacts are not seen beyond 45 m in well flushed systems.

Climate-related events and bark beetle outbreaks influenced hydrological dynamics and nitrogen cycling in three Central European forest catchments in the GEOMON network. Since 1994, distinct environmental phases were observed at studied catchments. Initially, nitrate (NO₃^⁻) concentrations declined at Anenský potok and Polomka due to reduced acid deposition, while remaining stable at Pluhův bor. From 2015 onwards, drought and extensive spruce dieback caused significant hydrological disruptions, including over a 200% increase in runoff at Anenský potok. In contrast, moderated hydrological impacts due to differences in the evapotranspiration-to-precipitation ratio was observed at Polomka. At Pluhův bor, gradual deforestation combined with climate change effects, such as rising temperatures and decreasing precipitation, resulted in stable runoff compared to the abrupt changes in the other two catchments. Despite these differences, disturbances across all catchments intensified nitrate leaching and disrupted nitrogen retention. This led to substantial dissolved inorganic nitrogen (DIN) export, particularly at Polomka, which is characterized by a low soil carbon-to-nitrogen ratio (C/N). These findings highlight the vulnerability of forest ecosystems to nitrogen loss under environmental stressors and underscore the importance of effective management strategies to mitigate nitrogen cycle disruptions in the context of ongoing climate change.

Soil microbial communities play a pivotal role in controlling soil carbon cycling and its climate feedback. Accurately predicting microbial respiration in soils has been challenged by the intricate resource heterogeneity of soil systems. This makes it difficult to formulate mathematical expressions for carbon fluxes at the soil bulk scale which are fundamental for soil carbon models. Recent advances in characterizing and modeling soil heterogeneity are promising. Yet they have been independent of soil structure characterizations, hence increasing the number of empirical parameters needed to model microbial processes. Soil structure, intended as the aggregate and pore size distributions, is, in fact, a key contributor to soil organization and heterogeneity and is related to the presence of microsites and associated environmental conditions in which microbial communities are active. In this study, we present a theoretical framework that accounts for the effects of microsites heterogeneity on microbial activity by explicitly linking heterogeneity to the distribution of aggregate sizes and their resources. From the soil aggregate size distribution, we derive a mathematical expression for heterotrophic respiration that accounts for soil biogeochemical heterogeneity through measurable biophysical parameters. The expression readily illustrates how various soil heterogeneity scenarios impact respiration rates. In particular, we compare heterogeneous with homogeneous scenarios for the same total carbon substrate and microbial biomass and identify the conditions under which respiration in heterogeneous soils (soils having non-uniform distribution of carbon substrate and microbial biomass carbon across different aggregate size classes) differs from homogeneous soils (soils having uniform distribution of carbon substrate and microbial biomass carbon across different aggregate size classes). The proposed framework may allow a simplified representation of dynamic microbial processes in soil carbon models across different land uses and land covers, key factors affecting soil structure.