Journal of Geophysical Research: Biogeosciences最新文献

Shallow coastal lagoons with restricted connection to the ocean are often productive but can also be sensitive to nutrient enrichment and hydrologic changes. Resolving nutrient dynamics is important for their sustainable management, yet being able to accurately resolve nutrient budgets has remained a challenge due to their complex hydrological regimes and habitat heterogeneity. In this study, we undertake a systematic nutrient budget of a large shallow hypersaline lagoon (Coorong, South Australia), with assistance of a high-resolution coupled hydrodynamic-biogeochemical model, to demonstrate the conditions that lead to nutrient retention. Under current conditions, high rates of evapo-concentration and limited water connectivity have led to a persistent accumulation of nutrients and poor water quality in substantial areas of the lagoon. The interplay between hydrological drivers and biogeochemical processes was quantified using an adjusted Damköhler number, comparing the timescales of nutrient flushing versus processing. This showed a general transition from hydrologic control to biogeochemical control with increasing distance from the main ocean connection, modified by episodes of increased flows and external loads. Whilst water age was a useful indicator of the factors controlling rates of nutrient retention, interannual variability in retention between areas of the lagoon was explained based on river flows and changes in mean sea level. As the system has been affected by reduced flows over past decades, the results provide evidence that increasing river flow to the lagoon would reduce the nutrient retention, and we discuss the potential for net nutrient export to the ocean under sustained high flows.

Popular evapotranspiration (ET) partitioning methods make assumptions that might not be well-suited to dryland ecosystems, such as high sensitivity of plant water-use efficiency (WUE) to vapor pressure deficit (VPD). Our objectives were to (a) create an ET partitioning model that can produce fine-scale estimates of transpiration (T) in drylands, and (b) use this approach to evaluate how climate controls T and WUE across ecosystem types and timescales along a dryland aridity gradient. We developed a novel, semi-mechanistic ET partitioning method using a Bayesian approach that constrains abiotic evaporation using process-based models, and loosely constrains time-varying WUE within an autoregressive framework. We used this method to estimate daily T and weekly WUE across seven dryland ecosystem types and found that T dominates ET across the aridity gradient. Then, we applied cross-wavelet coherence analysis to evaluate the temporal coherence between focal response variables (WUE and T/ET) and environmental variables. At yearly scales, we found that WUE at less arid, higher elevation sites was primarily limited by atmospheric moisture demand, and WUE at more arid, lower elevation sites was primarily limited by moisture supply. At sub-yearly timescales, WUE and VPD were sporadically correlated. Hence, ecosystem-scale dryland WUE is not always sensitive to changes in VPD at short timescales, despite this being a common assumption in many ET partitioning models. This new ET partitioning method can be used in dryland ecosystems to better understand how climate influences physically and biologically driven water fluxes.

In the soils of vanadium (V) smelters, a diverse array of microorganisms relies on metabolic activities for survival amid stress. However, the characteristics and functions of soil microbiomes in V mining environments remain unexplored on a continental scale. This study thoroughly investigates the microbial diversity, community assembly, and functional potential of soil microbiome across 90 V smelters in China. Alpha diversity decreases significantly along the V gradient, with V emerging as the primary factor influencing community structure, followed by other environmental, climatic, and geographic factors. The null model reveals that V induces homogeneous selection, shaping co-occurrence patterns and leading to increased number of positive associations, particularly with keystone genera such as f_Gemmatimonadaceae, Nocardioides, Micromonospora, and Rubrobacter under higher V concentrations (>559.6 mg/kg). Moreover, a metagenomic analysis yields 67 metagenome-assembled genomes, unraveling the potential metabolic pathways of keystone taxa and their likely involvement in the V(V) reduction process. Nitrate and nitrite reductase (nirK, narG), and mtrABC are found to be taxonomically affiliated with Micromonospora. sp, FEN-1250. sp, Nocardioides. sp, etc. Additionally, the reverse citric acid cycle (rTCA) likely serves as the primary carbon fixation pathway, synthesizing alternative energy for putative V reducers, highlighting a potentially synergistic relationship between autotrophic and heterotrophic processes that supports microbial survival. Our findings comprehensively uncover the driving forces behind soil community variation under V stress, revealing robust strategies possibly employed by indigenous microorganisms to mitigate the impact of V. These insights hold potential for applications in bioremediation.

Permeable sediments, which make up almost half of the continental shelf worldwide, are potential sources of the important greenhouse gas N₂O from coastal regions. Yet, the extent to which interactions between these sediments and anthropogenic pollution produce N₂O is still unknown. Here we use laboratory experiments and modeling to explore the factors controlling N₂O production at a eutrophic site in a temperate shallow marine embayment (Port Phillip Bay, Australia). Our results show that denitrification is the main source of N₂O production within permeable sediments, but the extent to which N₂O is actually released is determined by the rate of seawater exchange with the sediment bed (which governs solute residence time within the bed). In wave-dominated coastal areas, shallower water with more intense waves (wave height > 1 m) release the most N₂O, with up to 0.5% of dissolved inorganic nitrogen pumped into biologically active eutrophic sediment being released as N₂O. Our results suggest rates of N₂O production in coastal permeable sediments are generally low compared to other environments.

Ecosystem structure and its heterogeneity shape ecosystem processes. Ecosystem heterogeneity has been characterized in smaller stream ecosystems dominated by benthic processes. However, in larger river ecosystems structured by water column characteristics including suspended sediment and phytoplankton, ecosystem heterogeneity has not been directly observed. We assessed flow-dependent ecosystem structure along 230 km of a large, highly managed Great Plains river (The Kansas River) by analyzing 1-dimensional, downstream color profiles across flow conditions derived from satellite imagery. River color is a robust metric that reflects the combined state of several important large-river habitat features, specifically suspended sediment, chromophoric dissolved organic matter, and phytoplankton. We found that at flows above a flow threshold that we call Q_patch (240 m³ s⁻¹), the entire river was uniformly yellow. At flows below Q_patch, the river was generally greener and often had patches of very green water that occurred upstream of run-of-river dams. Comparing color with in situ data showed the color patches were likely areas of elevated chlorophyll-a concentrations from phytoplankton accumulation, indicating that the patches reflected biological processes. Flows were below Q_patch on 77% of days during the period of record (1985–present), indicating that the ecosystem spends significant time in a patchy state. Our findings uniquely demonstrate that the water column characteristics structuring temperate, large-river ecosystems can be patchy.

Temperate reservoirs and lakes worldwide are experiencing decreases in ice cover, which will likely alter the net balance of gross primary production (GPP) and respiration (R) in these ecosystems. However, most metabolism studies to date have focused on summer dynamics, thereby excluding winter dynamics from annual metabolism budgets. To address this gap, we analyzed 6 years of year-round high-frequency dissolved oxygen data to estimate daily rates of net ecosystem production (NEP), GPP, and R in a eutrophic, dimictic reservoir that has intermittent ice cover. Over 6 years, the reservoir exhibited slight heterotrophy during both summer and winter. We found winter and summer metabolism rates to be similar: summer NEP had a median rate of −0.06 mg O₂ L⁻¹ day⁻¹ (range: −15.86 to 3.20 mg O₂ L⁻¹ day⁻¹), while median winter NEP was −0.02 mg O₂ L⁻¹ day⁻¹ (range: −8.19 to 0.53 mg O₂ L⁻¹ day⁻¹). Despite large differences in the duration of ice cover among years, there were minimal differences in NEP among winters. Overall, the inclusion of winter data had a limited effect on annual metabolism estimates in a eutrophic reservoir, likely due to short winter periods in this reservoir (ice durations 0–35 days), relative to higher-latitude lakes. Our work reveals a smaller difference between winter and summer NEP than in lakes with continuous ice cover. Ultimately, our work underscores the importance of studying full-year metabolism dynamics in a range of aquatic ecosystems to help anticipate the effects of declining ice cover across lakes worldwide.

Pelagic larval stages play a critical role in the dynamics of marine populations since they are the main way of dispersal and habitat colonization. Here, we examined the larval dispersal pathways of two common stomatopod species in the western Atlantic: Squilla empusa and Lysiosquilla scabricauda. To complement this goal, we also analyzed the haline tolerance of the stomatopod larvae collected in an estuary from the southern Gulf of Mexico. Larval dispersal was simulated using a Lagrangian particle-tracking module coupled to the Global HYCOM model and consisted of releasing 100 passive particles from each starting site. Results indicated a high level of larval retention in the west Florida shelf and over the narrow western shelf of the Gulf of Mexico. In the South Atlantic Bight, Central America, and northern South America the larval transport was almost unidirectional following the pattern of currents. Generally, connections were among nearby sites, but long-distance transport can also occur when larvae are trapped by great high-speed currents. Retention of larvae and connection with neighboring sites were due to local atmospheric and hydrological conditions. During fieldwork, we found two kinds of larvae: antizoea and alima. Morphological characteristics of the antizoea correspond to the superfamily Lysiosquilloidea, and those of the alima, with the superfamily Squilloidea. The antizoea larvae were found in salinity values as low as 21.9 psu, while the alima were at 23.2 psu. Salinity tolerances and dispersal potential of larvae indicate a high level of colonization of new habitats and a broad intrusion into the estuaries.

Interesting properties and abundance of bacteriophages suggest their potential effect on precipitation of various minerals. Here we present an experimental study regarding the influence of two different bacteriophages (Escherichia phage P1 and Pseudomonas phage Φ6) on mineral precipitation. A wide range of instrumental techniques was implemented: epifluorescence microscopy (binding of phages to mineral particles); laser diffraction (size distribution); X-ray powder diffraction (mineral phases composition); ⁵⁷Fe Mössbauer spectroscopy (for better characterization of iron-bearing mineral phases); and transmission electron microscopy coupled with microcrystal-electron diffraction (for characterization of mineral particles precipitated with bacteriophages). We showed that bacteriophages can affect mineral precipitation, especially for carbonate and iron-bearing mineral phases. Bacteriophages can increase or reduce the average size of particles or agglomerates of particles depending on the type of mineral phase. It was clearly visible for carbonates, phosphates, and Fe-oxides. Importantly, changes in mineral composition of the studied mineral phases were also noted. It is therefore assumed that bacteriophages may have industrial but also environmental implications on precipitation of minerals.

Northern peatlands are a globally significant source of methane (CH₄), and emissions are projected to increase due to warming and permafrost loss. Understanding the microbial mechanisms behind patterns in CH₄ production in peatlands will be key to predicting annual emissions changes, with stable carbon isotopes (δ¹³C-CH₄) being a powerful tool for characterizing these drivers. Given that δ¹³C-CH₄ is used in top-down atmospheric inversion models to partition sources, our ability to model CH₄ production pathways and associated δ¹³C-CH₄ values is critical. We sought to characterize the role of environmental conditions, including hydrologic and vegetation patterns associated with permafrost thaw, on δ¹³C-CH₄ values from high-latitude peatlands. We measured porewater and emitted CH₄ stable isotopes, pH, and vegetation composition from five boreal-Arctic peatlands. Porewater δ¹³C-CH₄ was strongly associated with peatland type, with δ¹³C enriched values obtained from more minerotrophic fens (−61.2 ± 9.1‰) compared to permafrost-free bogs (−74.1 ± 9.4‰) and raised permafrost bogs (−81.6 ± 11.5‰). Variation in porewater δ¹³C-CH₄ was best explained by sedge cover, CH₄ concentration, and the interactive effect of peatland type and pH (r² = 0.50, p < 0.001). Emitted δ¹³C-CH₄ varied greatly but was positively correlated with porewater δ¹³C-CH₄. We calculated a mixed atmospheric δ¹³C-CH₄ value for northern peatlands of −65.3 ± 7‰ and show that this value is more sensitive to landscape drying than wetting under permafrost thaw scenarios. Our results suggest northern peatland δ¹³C-CH₄ values are likely to shift in the future which has important implications for source partitioning in atmospheric inversion models.

Leaf-level photosynthetic capacity exhibits vertical variations along the canopy profile. The dynamics of photosystem energy partitioning involved in dissipating absorbed light energy, namely photochemical yield (ΦP), fluorescence yield (ΦF), and the efficiency of non-photochemical quenching yield (ΦN) in dissipating excess light energy as heat, along the vertical canopy profile remain unclear. Here, vertical variations in photosystem energy partitioning and photosynthetic nitrogen allocation were measured at different canopy positions of rice using active fluorescence detection and photosynthetic gas exchange measurement in subtropical southern China. We observed the decline in leaf nitrogen per leaf mass (N_mass) from the top to the bottom of the canopy. ΦP significantly decreased from vegetative growth stage to ripening stage, while ΦN showed an opposite trend. The top and bottom leaves had consistent relationships between photosynthetic nitrogen allocation and photosystem energy partitioning. Our findings reveal the vertical variations in physiological traits of subtropical rice.