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Soil metabolomics is an emerging approach for profiling diverse small molecule metabolites, i.e., metabolomes, in the soil. Soil metabolites, including fatty acids, amino acids, lipids, organic acids, sugars, and volatile organic compounds, often contain essential nutrients such as nitrogen, phosphorus, and sulfur and are directly linked to soil biogeochemical cycles driven by soil microorganisms. This paper presents an overview of methods for analyzing soil metabolites and the state-of-the-art of soil metabolomics in relation to soil nutrient cycling. We describe important applications of metabolomics in studying soil carbon cycling and sequestration, and the response of soil organic pools to changing environmental conditions. This includes using metabolomics to provide new insights into the close relationships between soil microbiome and metabolome, as well as responses of soil metabolome to plant and environmental stresses such as soil contamination. We also highlight the advantage of using soil metabolomics to study the biogeochemical cycles of elements and suggest that future research needs to better understand factors driving soil function and health.

Drier and hotter conditions linked with anthropogenic climate change can increase wildfire frequency and severity, influencing terrestrial and aquatic carbon cycles at broad spatial and temporal scales. The impacts of wildfire are complex and dependent on several factors that may increase terrestrial deposition and the influx of dissolved organic matter (DOM) from plants into nearby aquatic systems, resulting in the darkening of water color. We tested the effects of plant biomass quantity and its interaction with fire (burned vs. unburned plant biomass) on dissolved organic carbon (DOC) concentration and degradation (biological vs. photochemical) and DOM composition in 400 L freshwater ponds using a gradient experimental design. DOC concentration increased nonlinearly with plant biomass loading in both treatments, with overall higher concentrations (>56 mg/L) in the unburned treatment shortly after plant addition. We also observed nonlinear trends in fluorescence and UV-visible absorbance spectroscopic indices as a function of fire treatment and plant biomass, such as greater humification and specific UV absorbance at 254 nm (a proxy for aromatic DOM) over time. DOM humification occurred gradually over time with less humification in the burned treatment compared to the unburned treatment. Both burned and unburned biomass released noncolored, low molecular weight carbon compounds that were rapidly consumed by microbes. DOC decomposition exhibited a unimodal relationship with plant biomass, with microbes contributing more to DOC loss than photodegradation at intermediate biomass levels (100-300 g). Our findings demonstrate that the quantity of plant biomass leads to nonlinear responses in the dynamics and composition of DOM in experimental ponds that are altered by fire, indicating how disturbances interactively affect DOM processing and its role in aquatic environments.

Marine dissolved organic matter (DOM) is one of the largest reservoirs of organic carbon and nitrogen in the world. Yet, despite its global importance, most DOM remains molecularly uncharacterized. Solid-state nuclear magnetic resonance (NMR) spectroscopy of isolated DOM fractions represents one of the most powerful techniques to understand overall structural composition. However, it is well known that standard cross polarization magic angle spinning (CP/MAS) NMR, the technique used for almost all past solid-state NMR studies of DOM, is at best "semi-quantitative," and underestimates fully substituted NMR active nuclei. Additionally, almost all past solid-state NMR work analyzed high molecular weight (HMW) material isolated by ultrafiltration, which is now understood to represent mostly 14C-young, "semi-labile" compounds. In contrast, there is far less information regarding the composition of older, low molecular weight (LMW) DOM, which represents the vast majority of the ocean's accumulated refractory DOM pool. Here, we applied 13C and 15N solid-state multiCP/MAS NMR, improved NMR methods optimized to more quantitatively resolve fully substituted NMR nuclei, to both HMW and LMW DOM isolated from the surface and deep North Pacific Subtropical Gyre. These methods confirm past work indicating most nitrogen containing HMW DOM as amide compounds, but also demonstrate a modest heterocyclic N component not previously identified. In contrast, we found that LMW DON is almost entirely aromatic heterocyclic N, consistent with the hypothesis that heterocyclic N structures may be largely responsible for the accumulation of the ocean's refractory DON pool. Surprisingly, however, we find DOC aromatic functionalities still represent only a very minor portion of either the HMW or the LMW refractory carbon pools, in marked contrast to refractory DON composition. Together, these more quantitative solid-state NMR techniques likely represent the most accurate picture of DON and DOC functional and compound-class makeup to date, and so have broad implications for our understanding of marine DOM structure and cycling. Specifically, our new data suggests that while chemical composition likely acts as a key control on DOM lability, the most refractory components of DOC and DON have very different compositions, sources, and cycling, supporting the idea that DOC and DON cycling in the ocean may be largely decoupled. [ABSTRACT FROM AUTHOR]

Adsorptive fractionation and oxidation of dissolved organic matter (DOM) on manganese (Mn) oxide surfaces alter the molecular composition and stability of DOM, but the impact of iron (Fe) oxides on the coupled adsorption-oxidation processes of DOM by Mn oxides is largely unknown. In this study, the underlying mechanisms of molecular transformation of DOM on birnessite (Bir) in the presence of ferrihydrite (Fh), with varying Fh/Bir mass ratios, were investigated at both molecular levels and microscopic scales with a suite of characterization techniques, including Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM). We found that higher Fh/Bir mass ratio impeded the adsorption of DOM by birnessite and the reductive dissolution of birnessite to release dissolved Mn, and the impediment on the reductive dissolution of birnessite was proportional to Fh/Bir mass ratio. Overall, during the interactions of DOM with ferrihydrite and birnessite, phenolic compounds were preferentially adsorbed by Fe and Mn minerals, and compounds with higher oxygen contents and polymeric substances were formed. FT-ICR-MS analysis further suggested that higher Fh/Bir mass ratio inhibited the occurrence of aromatic ring-opening and carboxylation of substituted groups on aromatic rings, but promoted polymerization of phenolic compounds. Cs-STEM analysis revealed that DOM distributions on ferrihydrite, birnessite, and their mixtures were regulated by their microscopic structures and reactivity. Compared with aromatic carbon (C), carboxylic and phenolic C were more likely to associate with birnessite. Our results highlighted the significance of organo-mineral associations with the mixed minerals in regulating the distribution and reactivity of organic C. This study has provided molecular evidences for molecular transformation of DOM mediated by both Mn and Fe oxides, which contributed to advancing our understanding on coupled reactions of organic C at the mineral–water interfaces in the environment. [ABSTRACT FROM AUTHOR]

Autochthonous dissolved organic matter (Auto-DOM) produced by a biological carbon pump using dissolved inorganic carbon (DIC) from carbonate weathering plays an important role in carbon cycling within inland waters. However, little is known regarding how environmental conditions impact the composition and fate of organic matter, especially in surface waters of the semi-arid Loess Plateau, which is enriched in DIC by significant carbonate weathering. To obtain novel insight, we combined hydrochemistry, isotopic composition (δ2H, δ18O, and δ13C DIC), Rayleigh fractionation model, optical spectroscopy (absorbance and fluorescence), and Fourier transform ion cyclotron resonance mass spectrometry measurements to elucidate how primary production and hydrology impact the composition of DOM and the stability of the resulting Auto-DOM throughout the river–reservoir–wetland aquatic continuum of the Bahe River in the carbonate-mineral-rich semi-arid Loess Plateau where carbonate weathering is significant. The Rayleigh fractionation model results indicated that watershed DIC is primarily consumed through aquatic primary production rather than CO 2 degassing. Further investigation revealed that primary production and evaporation co-occurred in this watershed. With the enrichment of the stable water isotope δ2H, the relative abundances of the allochthonous compounds decreased and the relative abundances of the autochthonous substances increased, suggesting that the terrestrial signal of riverine DOM decreased while autochthonous production increased along the flow pathway. In addition, associations between optical and molecular characteristics among DOM samples from different water bodies revealed that the stability ratio (Fmax(C2/(C2 + C4))) of Auto-DOM to the ratio of carboxylic-rich alicyclic molecules showed a consistent trend, suggesting that phytoplankton-derived and biomineralized C2 compounds are potentially recalcitrant DOM in inland waters. We conclude that hydrology and primary production affect the source, composition, and, potentially, the stability of DOM in DIC-enriched surface waters of the semi-arid Loess Plateau, which may lead to a more humic-like DOM composition in inland water and export this lower bioavailability DOC to the ocean in the long term. [ABSTRACT FROM AUTHOR]

The degradation of vegetation in the watershed and associated release of dissolved organic matter (DOM) and particulate organic matter (POM) can influence the water quality of new reservoirs. This study aimed to evaluate whether water velocity influences the degradation of twigs of different diameters that remain in the watershed of new reservoirs. The results of twigs degradation under flowing and stagnant water over time were fitted to a double exponential decay kinetic model, which presents the detritus as labile/soluble and refractory compounds. The model parameterization showed that labile fractions presented higher decomposition rates (KT) in flowing than, but there was not a clear trend in the comparison between the diameters in each water condition. On the contrary, the refractory fraction decomposition rates (kR) showed a clear pattern in all comparisons, showing higher values in flowing water and for thin twigs. These results showed that thinner twigs decompose more rapidly, due to the greater A:V ratio, and that the abrasive effect of water velocity promotes faster decomposition. In general, we observed that there was a pattern of increasing decomposition rates as the twigs decrease in diameter (9–10 mm < 5–6 mm < 2–3 mm) and from stagnant water to flowing water. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) released from submerged leaf litter is an important allochthonous carbon source for heterotrophic bacteria that enhances the detrital food chain in freshwater ecosystems. In contrast, nitrogen (N), phosphorus (P) and micronutrients released during the leaching process support primary production and enhance the grazing food chain in these ecosystems.This study investigated how DOC and dissolved N and P from the leaf litter of two temperate broadleaf and two coniferous tree species affect heterotrophic and autotrophic biomass by incubating the freshwater microbial community in the culture media prepared from the leaf litter leachate.The results showed that heterotrophic biomass, including bacteria, heterotrophic‐flagellated protists and fungal zoospores, was the highest in the leaf litter leachate, which contained the highest DOC concentration relative to dissolved N and P (Japanese hemlock). In contrast, autotrophic biomass, including small algae, autotrophic flagellated protists and cyanobacteria, was associated with concentrations of dissolved N and P in the leaf litter leachates.Amendment of basal nutrients other than N and P, including micronutrients, trace elements and vitamins, increased autotrophic biomass in two leaf litter leachates (oak, Siebold's beech), suggesting that some elements other than N and P were deficient relative to the requirements of autotrophic organisms.These results indicated that the elemental composition of leaf litter leachates influences microbial community structure and heterotrophic versus autotrophic biomass in freshwater ecosystems. More importantly, the present results suggest that changes in forest vegetation surrounding freshwater ecosystems alter detritus‐based heterotrophic production relative to autotrophic production through the changes in the elemental composition (i.e. stoichiometry) of leaf litter inputs. [ABSTRACT FROM AUTHOR]

Rationale: High‐resolution mass spectrometry (HRMS) combined with electrospray ionization (ESI) has been the most useful technique for molecular characterization of dissolved organic matter (DOM) derived from diverse sources. However, the comprehensive detection of DOM composition was hindered by ionization suppression observed in ESI sources. HRMS coupled with liquid chromatography (LC) is a potential tool for comprehensive molecular characterization of DOM. Methods: The Suwannee River fulvic acids (SRFAs) and two DOM samples from seawater and refinery wastewater extracted by solid phase extraction (SPE) were analyzed by LC‐Orbitrap MS coupled with ESI. The mobile phases, solvent composition, and gradient in the LC‐Orbitrap MS analysis were optimized. Results: The number of detected molecular formulae of SRFAs by online LC‐Orbitrap MS was significantly increased by approximately 40% compared to direct injection. These additional detected compounds are mainly protein and lignin‐like compounds, with a low O/C ratio and high H/C ratio. For the SRFAs, the relative standard deviations (%) of reproducibility are 5.51, 2.33, 7.97, and 1.80 for average O/C, H/C, double bond equivalent, and modified aromaticity index, respectively. Conclusions: This study proposed a simple and rapid method based on LC‐Orbitrap MS for an in‐depth analysis of the molecular composition of DOM, achieving a remarkable analysis time of only 5 min per sample. The rapid method provides a dependable and efficient approach for the molecular characterization of DOM, thereby advancing our comprehension and investigation of DOM across diverse ecosystems. [ABSTRACT FROM AUTHOR]

The article in the journal "Frontiers in Earth Science" explores contemporary studies on cold seeps, hydrothermal vents, mud volcanoes, and related seafloor features. These features provide insights into deep processes that are typically inaccessible to scientists. The research emphasizes multidisciplinary approaches to studying seafloor fluid emissions, highlighting the importance of geologic, physical, chemical, and biological processes in these environments. The studies cover a wide range of topics, including microbial processes, fluid dynamics, mineralization, and the role of seafloor emissions in global biogeochemical cycles. [Extracted from the article]

Despite the rising interest in understanding how climate change could affect the emissions of greenhouse gases (GHGs) from river systems, including floodplains, we still lack a mechanistic understanding of how changing environmental conditions, such as moisture and nutrient availability, limit the temperature responses of GHG production in floodplain sediments. To examine the environmental co-limitations on the temperature responses of three major GHGs (CO2, CH4, and N2O) produced in floodplain sediments, sediments from a constructed wetland on the floodplain of the lower Han River were incubated for 24 d at four temperatures spanning 4–28 ℃, under three conditions (closed, open/wetting, and open/drying). The net production of all three GHGs exhibited nonlinear temperature responses with gas-specific patterns and magnitudes of response varying over the incubation period. During the later incubation phase, positive temperature responses were weakened for the net production of CO2 and CH4 in the dried treatments, whereas a similar weakening occurred for N2O production in the wet treatments. This, combined with incubation-induced changes in dissolved organic carbon and its fluorescence components, indicated the lack or excess of moisture and associated changes in O2 and organic carbon availability as critical co-limiting factors for the temperature responses of GHG production. Warming decreased δ13C in the CH4 emitted from wet and hypoxic sediments, implying a stronger warming effect on CH4 production over oxidation. Unlike many studies assuming a consistent relationship between temperature and GHG production in sediments irrespective of other environmental conditions, our results suggest that warming effects on the GHG emissions from floodplain sediments would depend on the balance between gas production and consumption under the prevailing constraints of moisture, O2, and labile carbon availability. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is a significant component of the global carbon cycle both in terrestrial and aquatic systems. Dissolved black carbon (DBC) is a significant portion of the total dissolved organic carbon (DOC) pool and represents a major flux of recalcitrant carbon to the coastal and deep oceans. Dissolved black carbon can originate from multiple sources related to its relative biogeochemical reactivity with the dynamics of highly recalcitrant DBC integral to long-term sequestration. Thus, understanding how the more recalcitrant fractions of DBC varies in diverse catchments is critical and currently underexplored. We used hydrogen pyrolysis to isolate the fraction of DBC with aromatic clusters above 7 rings, representing the more stable components. Here we report the dynamics of DBCHyPy over a hydrological year in a temperate catchment, with a long history of coal mining extraction. Quarterly measurements of DBC were undertaken from two main channel and four tributary sites. Hydrogen pyrolysis derived DBC comprised a significant percentage of the total DOC flux (3.2% to 28.3%) and included significant spatial variability. Unlike other studies examining more reactive DBC fractions, bulk DOC concentrations and DBCHyPy were poorly correlated when considered over an annual scale. Rather, DBCHyPy was correlated with indicators of groundwater such as dissolved inorganic carbon and conductivity. Data suggest a consistent source of DBCHyPy not subject to the same mobilisation drivers as DOC, which shows substantial seasonality. Rather, our data shows a potentially consistent supply of stable DBC originating from the coal mining-influenced groundwater. Petrogenic sources of DBC have been poorly constrained to date, the data presented here suggests in some catchments it may be significant and yield catchment scale DOC-DBC decoupling. The dynamics of DBC have implications for carbon fluxes, pollution transport and water quality/treatment requirements. These preliminary findings suggest potentially complex drivers in spatially heterogeneous catchments, contrasting with previous work finding tight DOC-DBC mobilisation dynamics. [ABSTRACT FROM AUTHOR]

Quantifying the relative influence of factors and processes controlling riverine ecosystem function is essential to predicting future conditions under global change. Dissolved organic matter (DOM) is a fundamental component of riverine ecosystems that fuels microbial food webs, influences nutrient and light availability, and represents a significant carbon flux globally. The heterogeneous nature of DOM molecular composition and its propensity for interaction (i.e., functional diversity) can characterize riverine ecosystem function across spatiotemporal scales. To investigate fundamental drivers of DOM diversity, we collected seasonal water samples from 42 nested locations within five watersheds spanning multiple watershed sizes (~ 5 to 30,000 km2) across the United States. Patterns in DOM molecular richness, aromaticity, relative abundance of N-containing formulas, and putative biochemical transformations derived from high-resolution mass spectrometry were assessed across gradients of explanatory variables associated with watershed characteristics (e.g., watershed area, water residence time, land cover). We found that putative biochemical transformations were more strongly related to explanatory variables across watersheds than common bulk DOM parameters and that watershed area, surface water residence time and derived Damköhler numbers representing DOM reactivity timescales were strong predictors of DOM diversity. The data also indicate that catchment-specific land cover factors can significantly influence DOM diversity in diverging directions. Overall, the results highlight the importance of considering water residence time and land cover when interpreting longitudinal patterns in DOM chemistry and the continued challenge of identifying generalizable drivers that are transferable across watershed and regional scales for application in Earth system models. This work also introduces a Findable Accessible Interoperable Reusable (FAIR) dataset (> 300 samples) to the community for future syntheses. [ABSTRACT FROM AUTHOR]

This work presents a spatial and temporal distribution of tributyltin (TBT) and TBT pollution assessment of the Croatian Adriatic coast in the period 2016 - 2023. The monitoring of TBT pollution was carried out within the Water Framework Directive (2000/60/EC) and the Marine Strategy Framework Directive (2008/56/EC). TBT concentrations were measured at 63 sites in coastal and transitional waters in three compartments - water, sediments and mussels. The ranges of TBT concentrations were <0.06 - 6.40 ng(TBT)/L in the water column, <1 - 2546 ng (TBT)/g(d.w.) in sediments, and <1 - 655 ng(TBT)/g(d.w.) in mussels, while transitional waters were in general more polluted than coastal waters. Monitoring of TBT concentrations in water showed that 30% of monitored sites were continuously polluted with TBT with average annual concentrations exceeding AA-EQS [0.2 ng (TBT)/L], while 20% of the sites had concentrations in sediments above the proposed EQS for sediments [1.6 ng(TBT)/g(d.w.)]. In mussels, TBT was detected at 70% of the sites with more than 60% of the sites exceeding the OSPAR criteria [12.6 ng(TBT)/g (d.w.)], indicating that the occurrence of imposex in gastropods at these sites is very likely. Only a slight decrease in TBT levels was observed over the investigated period, but concentrations at most contaminated sites did not fall below the EQS. This study shows that, despite the ban of TBT-based antifouling paints more than 15 years ago (except for public and military vessels), contamination of the Croatian Adriatic coast with TBT still exists and regular monitoring is essential. The TBT distribution was primarily determined by the vicinity of the pollution source, i.e. shipping traffic, but the role of physicochemical parameters, such as dissolved organic carbon (DOC) and transparency of the water column, should not be disregarded as well as the influence of hydrodynamics in the transitional waters. Although monitoring of TBT concentrations in water is an established approach to assess recent pollution, this long-term study has shown that mussels can be the most reliable indicator of pollution in a given area over the last several months. [ABSTRACT FROM AUTHOR]

The release of dissolved organic matter (DOM) from sediments serves as an important part of the carbon cycle. Here, we address pore water DOM quality and its release from shallow sediments (0-10 cm) of the central and southern Baltic Sea - Gdansk, Bornholm, and Eastern Gotland Basins - using excitation-emission matrix spectroscopy and size-exclusion chromatography. DOM release from sediments displayed spatial variability, with diffusive DOC fluxes ranging from 0.02 to 1.06 mmol m-2 d-1, and basin-averaged fluxes increased in the order Gotland < Bornholm < Gdansk. DOM qualitative characteristics also varied among investigated basins. In the oxygen-limited study sites from the Gdansk Basin, we observed elevated abundances of low apparent molecular weight DOM fraction and proteinaceous-like fluorescent DOM, while in the Bornholm Basin, pore water DOM was generally more humic-like and of higher apparent molecular weight. Pore waters from the deepest study sites in the Gotland Basin were qualitatively very similar to those of the pore waters from the upper sediment layers (0-4 cm) from all other investigated sites, suggesting little organic matter reworking at depth at those stations. Our results suggest that the spatial variability in the magnitude of DOM release may be linked to the qualitative differences of DOM in sediments. [ABSTRACT FROM AUTHOR]

Biochar is widely recognized as an amendment that enhances soil properties and sequesters carbon, particularly in degraded soils. However, biochar applied solely to soil may also hinder plant development due to toxic by-products generated during pyrolysis or nutrient retention. To mitigate these adverse effects, it has been suggested to either mix biochar with compost or to process it by composting with fresh organic materials. To date, there is a lack of comparative studies evaluating the performance of these two approaches. In this study, three types of biochar, differing in their initial feedstocks (beech wood, hornbeam/beech/oak mixture, and digestate/cereal straw mixture), were investigated. These biochars were applied solely, mixed with green waste compost, or processed as composted biochar in two soils of different fertility (a Luvisol and a gleyic Fluvisol). A pot experiment was conducted under controlled conditions where lettuce was grown for three months. After harvesting, plant biomass, and soil microbial and physicochemical properties were measured. Composted biochar and compost additives maintained a neutral soil pH, contrary to biochar applied solely or mixed with compost. The dissolved organic carbon and total nitrogen were higher in composted biochar treatments, leading to a higher proportion of humified material with a high degree of condensed aromatic groups compared to other treatments. Microbial activities were higher in the composted biochar treatments compared to those in the compost with biochar, and more specifically in the less fertile Luvisol. Finally, composted biochar increased plant growth by almost six times compared to the control without amendments, whereas the mix of biochar and compost increased it by only three times. Solely applied biochars did not affect lettuce growth. This study demonstrates that biochar composting is more beneficial than mixing biochar with compost in terms of improving soil fertility and mitigating the negative effects associated with pure biochar application. Highlights: The positive effects of composted biochar application on soil properties and plant growth are higher than biochar and compost co-application. The composting process lessened the initial properties' differences among biochars differing in initial feedstock and physicochemical qualities. The beneficial effects of composted biochar on soil properties were more pronounced when applied to less fertile soils. [ABSTRACT FROM AUTHOR]

Aquatic species found in habitats with limited shade and little dissolved organic carbon (DOC) have increased vulnerability to ultraviolet radiation (UVR) damage. Pigmentation is a common mechanism used by animals for protection from UVR. A pigmented bdelloid rotifer, Philodina, occurs in high densities in shallow rock pools in El Paso Co., TX, and is subject to repeated desiccation and high UVR. To understand the roles of DOC, pigmentation, and dormancy in reducing the effects of UVR exposure in these rotifers: (1) DOC levels in rock pools were measured before and after the summer monsoon season and (2) hydrated or dormant bdelloids (desiccated for 0, 1, 7, or 32 d) that differed in degree of pigmentation (highly, moderately, lightly, and none) were exposed to three intensities of UVB radiation (low, mid, or high) and monitored for survival after 48 h. Pigmented bdelloids were found in rock pools with lower DOC concentrations. Logistic regression analysis indicated that pigmentation level, desiccation time, and UVB intensity all affected survival. Bdelloids in the dormant form for 1 d were more resistant to UVB exposure at all pigmentation levels. However, as desiccation time increased, the odds of surviving decreased. Hydrated highly pigmented bdelloids were three times more likely to survive desiccation, UVB radiation, and their combined effects. Prolonged periods of drought due to the changing climate will alter DOC concentrations, causing photoprotection to become an increasingly important survival strategy for aquatic invertebrates, especially those inhabiting shallow waters. [ABSTRACT FROM AUTHOR]

Viruses constitute the most diverse and abundant biological entities on Earth. However, our understanding of this tiniest life form in complex ecosystems remains limited. Here, we recover 20,102 viral OTUs from twelve intertidal zones along the Chinese coasts. Our analysis demonstrates high viral diversity and functional potential in intertidal zones, encoding important functional genes that can be potentially transferred to microbial hosts and mediate elemental biogeochemical cycles, especially carbon, phosphate and sulfur. Virus-host abundance dynamics vary among different microbial lineages. Viral community composition is closely associated with environmental conditions, including dissolved organic matter. Concordant biogeographic patterns are observed for viruses and microbes. Viral communities are generally habitat specific with low overlaps between intertidal and other habitats. Environmental factors and geographic distance dominate the compositional variation of intertidal viromes. Overall, these findings expand our understanding of intertidal viromes within an ecological framework, providing insights into the virus-host coevolutionary arms race. The dynamic intertides, located between marine and terrestrial ecosystems, serve as a favorable habitat for exploring virus-host relationships. Here, the authors recover 20,102 viral OTUs from twelve intertidal zones along the Chinese coasts, with further analyses expanding our understanding of intertidal viromes within an ecological framework. [ABSTRACT FROM AUTHOR]

This study uses dual‐labeled (13C and 15N) stable isotope applications to examine microbial uptake and short‐term processing of carbon (C) and nitrogen (N) from organic and inorganic compounds in subtropical intertidal sediment. Four treatment applications were applied: (1) algal dissolved organic matter (DOM), (2) amino acid mixture, (3) glucose and NH4+, and (4) NaHCO3 and NH4+ to assess bioavailability effects on processing (1 vs. 2) and short‐term processing for OM fixed via microphytobenthos only (pennate diatom dominated) (4) vs. material taken up by the entire microbial community (3) across 24 h. 13C from algal‐DOM was preferentially used by the microbial community vs. 15N. At 24 h more 13C from algal‐DOM remained in microbial biomass indicating use of labeled precursor molecules to form biomass. Conversely, 13C from the amino acid treatment was not incorporated into biomass and was either rapidly respired to DIC or discarded as the in situ microbial community preferentially used and retained 15N from amino acids. Short‐term export of 13C as CO2 from glucose was lower than from microphytobenthos‐C, while retention of 15N from NH4+ was similar between treatments (3 and 4) despite doubling the application N concentration, suggesting potentially higher glucose‐stimulated 15N export via nitrification–denitrification that was not confirmed via flux measurements in this study. Despite careful site selection for similar tidal exposure and sediment types among the three estuaries, the uptake and processing of labeled substrate varied substantially between replicates and sites which challenged traditional statistical analysis. Disproportionate processing of substrates occurring in sediment hotspots of microbial activity can cause variability spanning orders of magnitude which was found to be widespread through comparison of our results against 19 previous studies in intertidal settings. Development of robust analytical techniques to handle variability from abiotic and biotic factors will allow greater clarity surrounding in situ biogeochemical processing in intertidal environments. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) released by macroalgae supports coastal ocean carbon cycling and contributes to the total oceanic DOC pool. Salinity fluctuates substantially in coastal marine environments due to natural and anthropogenic factors, yet there is limited research on how salinity affects DOC release by ecologically important macroalgae. Here we determined the effect of short‐term salinity changes on rates of DOC release by the habitat‐forming fucalean seaweed Sargassum fallax (Ochrophyta). Lateral branches (~4 g) cut at the axes of mature individuals were incubated across a salinity gradient (4–46) for 24 h under a 12:12 light:dark cycle, and seawater was sampled for DOC at 0, 12, and 24 h. Physiological assays (tissue water content, net photosynthesis, respiration, tissue carbon, and nitrogen content) were undertaken at the end of the 24‐h experiment. Dissolved organic carbon release increased with decreasing salinity while net photosynthesis decreased. Dissolved organic carbon release rates at the lowest salinity tested (4) were ~3.3 times greater in the light than in the dark, indicating two potential DOC release mechanisms: light‐mediated active exudation and passive release linked to osmotic stress. Tissue water content decreased with increasing salinity. These results demonstrate that hyposalinity stress alters the osmotic status of S. fallax, reducing photosynthesis and increasing DOC release. This has important implications for understanding how salinity conditions encountered by macroalgae may affect their contribution to the coastal ocean carbon cycle. [ABSTRACT FROM AUTHOR]

This study identifies the characteristics of water regions with negative normalized water-leaving radiance ( n L w (λ) ) values in the satellite observations of the Second-generation Global Imager (SGLI) sensor aboard the Global Change Observation Mission–Climate (GCOM-C) satellite. SGLI Level-2 data, along with atmospheric and in-water optical properties measured by the sun photometers in the AErosol RObotic NETwork-Ocean Color (AERONET-OC) from 26 sites globally, are utilized in this study. The focus is particularly on Tokyo Bay and the Ariake Sea, semi-enclosed water regions in Japan where previous research has pointed out the occurrence of negative n L w (λ) values due to atmospheric correction with SGLI. The study examines the temporal changes in atmospheric and in-water optical properties in these two regions, and identifies the characteristics of regions prone to negative n L w (λ) values due to atmospheric correction by comparing the optical properties of these regions with those of 24 other AERONET-OC sites. The time series results of n L w (λ) and the single-scattering albedo ( ω (λ) ) obtained by the sun photometers at the two sites in Tokyo Bay and Ariake Sea, along with SGLI n L w (λ) , indicate the occurrence of negative values in SGLI n L w (λ) in blue band regions, which are mainly attributed to the inflow of absorptive aerosols. However, these negative values are not entirely explained by ω (λ) at 443 nm alone. Additionally, a comparison of in situ n L w (λ) measurements in Tokyo Bay and the Ariake Sea with n L w (λ) values obtained from 24 other AERONET-OC sites, as well as the inherent optical properties (IOPs) estimated through the Quasi-Analytical Algorithm version 5 (QAA_v5), identified five sites—Gulf of Riga, Long Island Sound, Lake Vanern, the Tokyo Bay, and Ariake Sea—as regions where negative n L w (λ) values are more likely to occur. These regions also tend to have lower n L w (λ)   values at shorter wavelengths. Furthermore, relatively high light absorption by phytoplankton and colored dissolved organic matter, plus non-algal particles, was confirmed in these regions. This occurs because atmospheric correction processing excessively subtracts aerosol light scattering due to the influence of aerosol absorption, increasing the probability of the occurrence of negative n L w (λ) values. Based on the analysis of atmospheric and in-water optical measurements derived from AERONET-OC in this study, it was found that negative n L w (λ)   values due to atmospheric correction are more likely to occur in water regions characterized by both the presence of absorptive aerosols in the atmosphere and high light absorption by in-water substances. [ABSTRACT FROM AUTHOR]

ABSTRACT Aquatic macrophyte leachate is one of the autochthonous sources of carbon and nitrogen in aquatic systems, and microbial communities easily mineralize these elements. Understanding the effects of climate change on the consumption of dissolved oxygen (DO) due to the mineralization of leachate from aquatic macrophytes is fundamental for accurately establishing the oxygen balance in aquatic systems and forecasting element cycling rates. Bioassays were developed to determine the consumption of DO owing to the mineralization of carbon and nitrogen of the aquatic macrophytes leachates (Myriophyllum aquaticum, Hedychium coronarium, Salvinia auriculata, and Chara sp.) when exposed to a temperature increase of 4°C (from 21°C to 25°C). The results concerning accumulated DO were fitted to a first‐order kinetic model. At 25°C, oxygen consumption due to mineralization increased by 9.6%, whereas the chemical composition of the leachate changed oxygen consumption between 7.2 (21°C) and 9.2% (25°C). The O/C stoichiometry (oxygen consumed by oxidized carbon) indicated the compositions of the leachate, and temperatures determined the pattern of oxygen consumption. Due to the chemical composition of the leachate, the values varied by approximately 17% and were higher at 25°C (about 30%). Regardless, the increase in temperature improved the oxygen consumption of leachate mineralization. After 90 days at 25°C, the highest concentrations of remaining dissolved organic carbon occurred, suggesting the selection of microorganisms and the catabolic routes that favored the production of refractory organic compounds to the detriment of mineralization. The results indicate that knowledge of the effects of climate variations on aquatic systems is crucial for an accurate understanding of the biogeochemical cycles in these environments. [ABSTRACT FROM AUTHOR]

Elevated concentrations of toxic cationic aluminum (Ali) are symptomatic of terrestrial and freshwater acidification and are particularly toxic to salmonid fish species such as Atlantic salmon (Salmo salar). Speciated metal samples are rarely included in standard water monitoring protocols, and therefore the processes affecting Ali dynamics in freshwater remain poorly understood. Previous analysis of Ali concentrations in Nova Scotia (Canada) rivers found that the majority of study rivers had concentrations exceeding the threshold for aquatic health, but a wide‐scale survey of Ali in Nova Scotia has not taken place since 2006 (Dennis, I. F., & Clair, T. A., 2012, Canadian Journal of Fisheries and Aquatic Sciences, 69(7), 1174–1183). The observed levels of dissolved aluminum in Atlantic salmon (Salmo salar) rivers of Atlantic Canada have potential serious and harmful effects for aquatic populations. We present the findings of the first large‐scale assessment of the Ali status of Nova Scotia rivers in 17 years; we measured Ali concentrations and other water chemistry parameters at 150 sites throughout the Southern Uplands region of Nova Scotia from 2015 to 2022. We found that Ali concentrations exceeded toxic thresholds at least once during the study period at 80% of the study sites and that Ali concentrations increased during the study period at all four large‐sample study sites. Modeling of relationships between Ali concentrations and other water chemistry parameters showed that the most important predictors of Ali are concentrations of the dissolved fractions of Al, iron, titanium, and calcium, as well as dissolved organic carbon and fluoride. We developed a fully Bayesian linear mixed model to predict Ali concentrations from a test data set within 15 μg/L. This model may be a valuable tool to predict Ali concentrations in rivers and to prioritize areas where Ali should be monitored. Environ Toxicol Chem 2024;00:1–12. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The exchange and transformation of dissolved organic matter (DOM) at the sediment–water interface are crucial factors in regulating watershed biogeochemistry, with the molecular composition of DOM serving as a pivotal determinant in elucidating this process. High-resolution mass spectrometry (HRMS) is an effective tool for resolving the composition of DOM. By analyzing the compositional characteristics of DOM at the sediment–water interface under three different salinities at the same latitude region in northern China, the findings indicate certain variations in component characteristics of DOM between low-salinity inland waters and high-salinity seawaters, with the former exhibiting greater molecular diversity and higher molecular weights, whereas the latter displayed a higher saturation and bioavailability. Notably, the presence of more CHOS substances in the low-salinity inland waters underscores the transformation of the DOM influenced by terrestrial inputs and anthropogenic activities. Conversely, the presence of more CHO and CHNO substances in high-salinity seawater underscores the microbial effects. The chemical transformation process from overlying water to pore water to sediments was characterized by methylation, hydrogenation, decarboxylation, and reduction, as determined by calculating the relations between the H/C and O/C ratios of different compound types. These findings indicate that HRMS can yield more refined results in revealing the process of DOM at the sediment–water interface under different environments, which provides a more reliable basis for a deeper understanding of the source–sink mechanism of sediment organic matter. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metals in MSW IBA begin to be mobilised to aqueous solution at below neutral pH. • MSW IBA has a high pH buffering capacity. • Reaching below neutral pH with rainwater infiltration is extremely unlikely. • DOC causes enhanced metal mobilization only at unrealistically high concentrations. • Persistent organic pollutants in the MSW IBA are well below regulatory limits. Increasing municipal solid waste (MSW) production poses challenges for sustainable urban development. Modern energy-from-waste (EfW) facilities incinerate MSW, reducing mass and recovering energy. In the UK, MSW incineration bottom ash (MSW IBA) is primarily reused in civil engineering applications. This study characterizes UK-produced MSW IBA, examining its pH-dependent leaching behaviour and response to environmental lixiviants. Results show predominant components include a melt phase, primary glass and fine ash aggregations, and a chemical composition dominated by SiO 2 (30–50 %), CaO (∼15 %), Fe 2 O 3 (∼10 %), and Al 2 O 3 (∼8%). X-ray absorption near edge structure (XANES) analysis shows that Zn and Cu are most likely oxygen-bound (adsorbed to oxy-hydroxides and as oxides) with some sulphur bound. Polychlorinated biphenyls (PCBs) and polychlorinated dibenzodioxins/furans (PCDD/Fs) are well below regulatory limits, and polycyclic aromatic hydrocarbons (PAHs) were undetectable. Leaching tests indicate trace elements mobilize at pHs ≤ 6. With a natural pH of 11.3 and high buffering capacity, significant acid inputs to the MSW IBA are required to reach this pH, which are improbable in the environment. Wood chip additions increase leachate's dissolved organic carbon (DOC) and reduce pH, but had minimal impact on metal-leaching behaviour. Synthetic plant exudate solutions minimally affect metal leaching at realistic concentrations, only enhancing leaching at ≥ 1500 mg l−1 DOC. This work supports MSW IBA's low-risk in specified civil engineering applications. [ABSTRACT FROM AUTHOR]

• Freeze process significantly promoted the oxidation of iodide. • Freeze-induced DOM iodination produced a large number of organoiodine compounds. • Effects of pH, I– and O 2 content on I– oxidation and DOM iodization in frozen solutions were revealed. • DOM iodination products were mainly composed of aromatic structures. • DOM iodination process was primarily via substitution and addition reactions. Freeze-induced acceleration of I– oxidation and the consequent iodination of dissolved organic matter (DOM) contribute to the formation of organoiodine compounds (OICs) in cold regions. The formed OICs may be a potentially important source of risk and are very closely with the environment and human health. Herein, we investigated the acceleration effects of the freeze process on I– oxidation and the formation of OICs. In comparison to reactive iodine species (RIS) formed in aqueous solutions, I– oxidation and RIS formation were greatly enhanced in frozen solution and were affected by pH, and the content of I– and O 2. Freeze-thaw process further promoted I– oxidation and the concentration of RIS reached 45.7 µmol/L after 6 freeze-thaw cycles. The consequent products of DOM iodination were greatly promoted in terms of both concentration and number. The total content of OICs ranged from 0.02 to 2.83 µmol/L under various conditions. About 183–1197 OICs were detected by Fourier transform ion cyclotron resonance mass spectrometry, and more than 96.2% contained one or two iodine atoms. Most OICs had aromatic structures and were formed via substitution and addition reactions. Our findings reveal an important formation pathway for OICs and shed light on the biogeochemical cycling of iodine in the natural aquatic environment. [Display omitted] [ABSTRACT FROM AUTHOR]

• Algal DOM (ADOM) showed stronger adsorption on FeOx than humic acid (HA). • ADOM had a stronger inhibition on phosphate sink than HA, promoting eutrophication. • Carboxylic-rich alicyclic molecules in ADOM contributed to strong adsorption. • Adsorption reduced source-specific compounds: aromatics in HA and proteins in ADOM. Dissolved organic matter (DOM) is a heterogeneous pool of compounds and exhibits diverse adsorption characteristics with or without phosphorous (P) competition. The impacts of these factors on the burial and mobilization of organic carbon and P in aquatic ecosystems remain uncertain. In this study, an algae-derived DOM (ADOM) and a commercially available humic acid (HA) with distinct compositions were assessed for their adsorption behaviors onto iron (oxy)hydroxides (FeO x), both in the absence and presence of phosphate. ADOM contained less aromatics but more protein-like and highly unsaturated structures with oxygen compounds (HUSO) than HA. The adsorption capacity of FeOx was significantly greater for ADOM than for HA. Protein-like and HUSO compounds in ADOM and humic-like compounds and macromolecular aromatics in HA were preferentially adsorbed by FeOx. Moreover, ADOM demonstrated a stronger inhibitory effect on phosphate adsorption than HA. This observation suggests that the substantial release of autochthonous ADOM by algae could elevate internal P loading and pose challenges for the restoration of restore eutrophic lakes. The presence of phosphate suppressed the adsorption of protein-like compounds in ADOM onto FeOx, resulting in an increase in the relative abundance of protein-like compounds and a decrease in the relative abundance of humic-like compounds in post-adsorption ADOM. In contrast, phosphate exhibited no discernible impact on the compositional fractionation of HA. Collectively, our results show the source-composition characters of DOM influence the immobilization of both DOM and P in aquatic ecosystems through adsorption processes. The preferential adsorption of proteinaceous compounds within ADOM and aromatics within HA highlights the potential for the attachment with FeO x to diminish the original source-specific signatures of DOM, thereby contributing to the shared DOM characteristics observed across diverse aquatic environments. This is special type of abstract that is so short and could be inserted after main abstract of article, as a blurb or inserted as annotations into a Table of contents [Display omitted] [ABSTRACT FROM AUTHOR]

The vegetation surrounding aquatic ecosystems contributes allochthonous sources of organic matter to the water bodies. In Andean-Patagonian catchments, several non-native species grow among native ones. Different sources of dissolved organic matter (DOM) may vary in their contribution, potentially affecting aquatic functioning. This study evaluates differences in DOM contributions from native and non-native plants, analyzing DOM reactivity through its optical properties. An outdoor experiment was conducted with DOM leaf leachates from two native (Maytenus boaria and Nothofagus dombeyi) and two invasive trees (Salix fragilis and Pinus contorta). We characterized DOM concentration and quality optically by UV–Visible and fluorescence spectroscopy and found differences in both quantity and quality between the different leaf leachates. The exotic S. fragilis presented up to 7 times higher dissolved organic carbon (DOC) values than the other species. We found that leachates response to light exposure depended on its DOM composition. Decreasing patterns of DOC absorbance and fluorescence were observed in all leachates over time. We detected a gradient in leaf leachate photoreactivity due to solar exposure: (S. fragilis > P. contorta > M. boaria = N. dombeyi). Overall, our work shows that the invasive plants studied produce larger amounts of degradable DOM than some local native species. [ABSTRACT FROM AUTHOR]

Defoliation by eastern spruce budworm is one of the most important natural disturbances in Canadian boreal and hemi‐boreal forests with annual area affected surpassing that of fire and harvest combined, and its impacts are projected to increase in frequency, severity, and range under future climate scenarios. Deciding on an active management strategy to control outbreaks and minimize broader economic, ecological, and social impacts is becoming increasingly important. These strategies differ in the degree to which defoliation is suppressed, but little is known about the downstream consequences of defoliation and, thus, the implications of management. Given the disproportionate role of headwater streams and their microbiomes on net riverine productivity across forested landscapes, we investigated the effects of defoliation by spruce budworm on headwater stream habitat and microbiome structure and function to inform management decisions. We experimentally manipulated a gradient of defoliation among 12 watersheds during a spruce budworm outbreak in the Gaspésie Peninsula, Québec, Canada. From May through October of 2019–2021, stream habitat (flow rates, dissolved organic matter [DOM], water chemistry, and nutrients), algal biomass, and water temperatures were assessed. Bacterial and fungal biofilm communities were examined by incubating six leaf packs for five weeks (mid‐August to late September) in one stream reach per watershed. Microbiome community structure was determined using metabarcoding of 16S and ITS rRNA genes, and community functions were examined using extracellular enzyme assays, leaf litter decomposition rates, and taxonomic functional assignments. We found that cumulative defoliation was correlated with increased streamflow rates and temperatures, and more aromatic DOM (measured as specific ultraviolet absorbance at 254 nm), but was not correlated to nutrient concentrations. Cumulative defoliation was also associated with altered microbial community composition, an increase in carbohydrate biosynthesis, and a reduction in aromatic compound degradation, suggesting that microbes are shifting to the preferential use of simple carbohydrates rather than more complex aromatic compounds. These results demonstrate that high levels of defoliation can affect headwater stream microbiomes to the point of altering stream ecosystem productivity and carbon cycling potential, highlighting the importance of incorporating broader ecological processes into spruce budworm management decisions. [ABSTRACT FROM AUTHOR]

The globally increasing reactive N richness affects even remote ecosystems such as the tropical montane forests in Ecuador. We tested whether the δ15N values of total dissolved N (TDN), measured directly in solution with a TOC‐IRMS, can be used to help elucidate N sources and sinks along the water path and thus might be suitable for ecosystem monitoring. From 2013 to 2016, the δ15N values of TDN in bulk deposition showed the most pronounced temporal variation of all ecosystem solutions (δ15N values: 1.9–5.9‰). In throughfall (TF), TDN was on average 15N‐depleted (−1.8 ± s.d. 0.4‰) relative to rainfall (3.4 ± 0.9‰), resulting from net retention of isotopically heavy N, mainly as NH4+. Simultaneously, N‐isotopically light NO3−‐N and dissolved organic nitrogen (DON) with a δ15N value between NO3−‐N and NH4+‐N were leached from the canopy (leaves: −3.5 ± 0.5‰). The increasing δ15N values in the order, TF < stemflow (SF, 0.1 ± 0.6‰)< litter leachate (LL, 1.3 ± 0.7‰) concurred with an increasing DON contribution to TDN reflecting the δ15N value of the organic layer (1.9 ± 0.9‰). The lower δ15N value of the mineral soil solution at the 0.15 m soil depth (SS15, −1.5 ± 0.3‰) than in LL can be explained by the retention of DON and NH4+ and the addition of NO3− from mineralization and nitrification. The increasing δ15N values in the order, SS15 < SS30 (−0.6 ± 0.2‰) < streamflow (ST, 0.5 ± 0.6‰) suggested gaseous N losses because of increasing denitrification. There was no seasonality of the δ15N values. Our results demonstrate that the δ15N values of TDN in ecosystem solutions help identify N sources and sinks in forest ecosystems. Plain Language Summary: Many ecosystems experience increasing nitrogen availability because of nitrogen deposition from the atmosphere caused by human activities. The deposited nitrogen can produce a growth boost or be leached into groundwater and surface water. The stable isotope ratios of nitrogen (δ15N values) provide a tool to investigate into the consequences of increasing nitrogen availability. Here, we applied a new direct measurement method of δ15N values in total dissolved nitrogen of ecosystem solutions to follow sources and sinks of nitrogen in a tropical montane rain forest in Ecuador. We found that the isotopically heavy nitrogen input via rainfall is enriched by isotopically lighter nitrogen from plants and nitrogen turnover during the water passage through the canopy. Once, the solutions reach the mineral soil, dissolved organic nitrogen, which is comparatively rich in the heavy nitrogen isotope, is retained rendering the remaining nitrogen isotopically lighter. This process is reversed deeper in the soil by conversion of the nitrate to nitrogen gasses, which are depleted in the heavy nitrogen isotope and leave the ecosystem to the atmosphere. The direct measurement of δ15N values provides a tool to monitor the changing nitrogen cycle in ecosystems. Key Points: Increasing δ15N values in total dissolved nitrogen from throughfall to litter leachate correlated with an increasing organic contributionThe retention of N‐isotopically heavy dissolved organic nitrogen in the mineral topsoil decreased the δ15N values in mineral soil solutionsIncreasing δ15N values from the topsoil solution via the subsoil to the streamflow suggested gaseous N losses because of denitrification [ABSTRACT FROM AUTHOR]

The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial organic carbon to the deep sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the submarine Congo Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ∼7 % of the dissolved and particulate organic carbon from the world's rivers. However, sediment and particulate organic carbon transport mechanisms that operate in the Congo Canyon and submarine canyons more globally are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps, and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the submarine Congo Canyon to the deep sea. We show that particulate organic carbon transport in the canyon axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 ms-1) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 ms-1) turbidity currents occur for 35 % of the time during monitoring periods and transport particulate organic carbon with mud and sand at an estimated transit flux that is more than 3 to 6 times the flux induced by tides. Organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo submarine fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally. [ABSTRACT FROM AUTHOR]

Understanding the evolution of hydrochemical characteristics in river systems is essential for environmental assessment and water resource management. This study explores the spatiotemporal distribution and the determinants of hydrochemical characteristics in the Hailar River basin, China, over an extensive period. Our results revealed that CODMn and CODCr were the primary concerns for long-term river management, with exceedance rates of 42.92% and 50.62%, respectively. These exceedances were predominantly driven by interactions between riparian soils and surface water, rather than anthropogenic pollution, as suggested by the strong correlations between dissolved organic carbon and soil water-extractable organic carbon, and the limited human footprint in this region. Piper trilinear and Gibbs diagram analysis further revealed that long-term rack weathering shaped the basin's hydrochemical characteristics, resulting in distinct HCO3−-Ca2+ and HCO3−-Ca2+-Na+ signatures. In addition, APCS-MLR analysis identified that elevated of CODMn and CODCr levels were mainly attributed to the interactions with adjacent soils, which are extensively covered by forests and grasslands. In contrast, leaching and migration processes contributed significantly on total dissolved solids and total phosphorus. The study also found that environmental self-purification processes played a key role in regulating Fe concentrations. This investigation provides a nuanced understanding of the environmental background's influence on hydrochemistry and dissolved organic matter (DOM) in the Hailar River basin, which offers valuable insights and methodologies for the rational assessment of water quality and aquatic ecosystem health in similar riverine systems. [ABSTRACT FROM AUTHOR]

Forests are critical source regions of high-quality drinking water but forest disturbances such as harvesting can alter stream dissolved organic carbon (DOC) concentrations and influence source water treatability. Most stream DOC-centric forest harvesting impact studies report on effects <10 years post-harvest; less is known about the legacy effects of forest harvesting on stream DOC. Here, inter- and intra-catchment variability in stream DOC concentration and export were evaluated in two northern hardwood-dominated headwater catchments (unharvested reference and 24 years post-clearcut). The relationship between stream DOC and the concentration, spatial distribution, and hydrologic connectivity of hillslope solute pool DOC was investigated. Stream DOC concentrations in the legacy clearcut catchment exceeded those in the reference catchment for all flow conditions. Inter-catchment differences in DOC export were inconsistent. Hillslope solute pool DOC concentrations decreased with soil depth but were not significantly different between catchments. Concentration–discharge regression analysis indicated that DOC was primarily transport-limited (flushing) in both catchments. Aqueous potassium silica molar ratio data indicate the influence of groundwater on stream chemistry and streamflow was similar in both catchments. Results suggest that while clearcut harvesting can have detectable decadal-scale effects on stream DOC concentrations in northern hardwood-dominated headwater catchments, the effects are limited and likely do not pose a reasonable threat to downstream drinking water treatment operations. [ABSTRACT FROM AUTHOR]

Access to safe water and sanitation is a critical global challenge, posing significant health risks worldwide due to waterborne diseases. This study investigates the efficacy of ultraviolet type C radiation as a disinfection method for improving water quality. The research elucidates UV-C's mechanism of action, highlighting its ability to disrupt DNA and RNA replication, thereby inactivating pathogens. Furthermore, the study analyses the influence of key factors on UV-C disinfection effectiveness, including water turbidity and the presence of dissolved organic matter, which can attenuate UV-C penetration and reduce treatment efficiency. The experimental results demonstrate a substantial reduction in microbial content following UV-C treatment. River water samples exhibited a 57.143% reduction in microbial load, while well water samples showed a 50% reduction. Notably, Escherichia coli (E. coli) concentrations decreased significantly, with an 83.33% reduction in well water and a 62.5% reduction in borehole water. This study makes a novel contribution to the understanding of UV-C disinfection by identifying the presence of resistant organisms, including Adenoviruses, Bacterial spores, and the Protozoan Acanthamoeba, in water samples. This finding expands the scope of UV-C research beyond easily culturable bacteria. To address this challenge, future investigations should explore synergistic disinfection strategies, such as combining UV-C treatment with advanced oxidation processes. Optimising UV-C system designs and developing robust, real-time monitoring systems capable of detecting and quantifying known and emerging UV-resistant pathogens are crucial for ensuring comprehensive water decontamination. [ABSTRACT FROM AUTHOR]

Membrane fouling caused by effluent organic matter (EfOM) limits its further application in wastewater reuse. In this study, the effect of UV/chlorine pretreatment on membrane fouling was investigated in treating secondary effluent by ultrafiltration (UF) process. The relation between organic matter changes and fouling alleviation after UV/chlorine pretreatment was also studied according to the molecular weight (MW) changes in various resin fractions derived from EfOM. Results showed that UV/chlorine pretreatment effectively alleviated irreversible fouling, whereas chlorine pre-oxidation primarily mitigated reversible fouling. UV/chlorine pre-oxidation reduced 18% of reversible membrane fouling and 38% of irreversible membrane fouling at a chlorine dosage of 8 mg/L, indicating better performance in membrane fouling mitigation than chlorine pre-oxidation. UV/chlorine pre-oxidation also decreased dissolved organic matter in the UF permeate. The hydrophobic acidic (HPO-A) fraction caused dominant membrane fouling, while the hydrophilic (HPI) fraction contained most of high MW organic matter. Pre-oxidation changed the polarity of organic matter in the HPO-A fraction and decomposed the organics of high MW in the HPI fraction, which alleviated membrane fouling. These results showed that UV/chlorine pre-oxidation was a prospective pretreatment process prior to UF in wastewater reclamation. [ABSTRACT FROM AUTHOR]

Both ibuprofen (IBP) and chlorophene (CP) are frequently detected contaminants in surface aqueous environment. Dissolved organic matter (DOM) is an important component in water with high photo-reactivity, playing an important role in the transformation processes of various organic pollutants. This study systematically studied the influence of DOM on the photochemical transformation of IBP and CP by using humic acid as model DOM. In addition, the effect of inorganic salts on this process is also considered due to the high salt content in the ocean. Further quenching experiments and reactive oxygen species (ROSs) detection were also conducted to explore the reactive species acting on the IBP and CP transformation. Based on the products analysis and theoretical calculation, we proposed the IBP and CP transformation mechanism. Overall, this study provides some new insights into the transformation of organic pollutants in natural surface water, which is significant for assessing the fate of pollutants. [ABSTRACT FROM AUTHOR]

Global estimates of the supply of dissolved and suspended materials to the ocean, in order to be relevant at either political or ecological scales, belie a finer-scale analysis necessary for understanding specific terrestrial-marine interactions. This is especially true for continental runoff to themarine critical zone of inland fjords and channels, where mechanisms, drivers, and predictions need to be elaborated in the context of changing land use and shifting climate forcing. In fjords in southwestern Patagonia, runoff from small coastal and large continental basins (~310 x103 km2), sourced from a diverse geography and wide climatic gradient (<150 - 6,000+ mm/year), correspond with a very low density of hydrological and water quality observations. Based on the recently developed regional runoff model (FLOW), we estimated the coastal freshwater discharges and characterized flowweighted sourcing (land use-cover type, climate, glaciers/geology, and soil province) for Pacific drainages from 41° to 56° south latitude. An estimated 692 km3/year (mean across 1979-2018), or 2% of worldwide total, is more than 85% of previous estimates for the much larger Pacific South American input. Based on limited water quality observations and inference from runoff sourcing, we predict general patterns of export for four groups of continental resources important for marine productivity, including: significant regional variation in flow seasonality, a N-S gradient in declining input of silicic acid and increased glacial input of sediment and iron, and potential shift in dissolved organic matter input sources from rainforest (potentially labile) to peatlands (refractory). Finally, we emphasize the temporal and spatial consequences of near-reference condition river runoff for marine ecosystem productivity and function in the Patagonian fjords, with specific recommendations for water quality standards and sustained monitoring for coupled river and marine ecosystems. [ABSTRACT FROM AUTHOR]

Methyl halides are crucial trace greenhouse gases in the atmosphere, playing a significant role in global climate change and the atmospheric environment. This study investigated the photochemical production of methyl halides in an artificial seawater system using guaiacol as a precursor through laboratory simulation experiments. The influences of various environmental factors, including illumination time, radiation wavebands, illumination intensity, concentrations of guaiacol and halide ions (X−), Fe3+, salinity, dissolved oxygen (DO), and pH value on the photochemical production of methyl halides were examined. We demonstrated that increased illumination intensity and duration promote the photochemical production of methyl halides, with a notable enhancement under UV-B radiation. Guaiacol and halide ions were identified as key precursors, and their high concentrations facilitated the formation of methyl halides. Additionally, different types of halide ions exhibited a competitive relationship in producing methyl halides. The study found that an increase in pH inhibited the photochemical formation of CH3I due to the reaction between OH− and ·CH3. Dissolved oxygen was found to inhibit the photochemical formation of CH3I while promoting the formation of CH3Cl. Conversely, an appropriate concentration of Fe3+ enhanced the photochemical production of methyl halides. Field observations indicated a high photochemical production of methyl halides in the natural waters near Qingdao's coastal area, likely due to the high concentration of dissolved organic matter (DOM), which supports photochemical reactions. Furthermore, the photochemical production of methyl halides in natural seawater was significantly higher than in dark conditions, underscoring the importance of illumination in promoting these photochemical processes in seawater. [ABSTRACT FROM AUTHOR]

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Urban beaver and stormwater ponds provide hydrologic retention in the landscape while collecting dissolved organic matter (DOM)-rich runoff that can promote primary productivity. Our objective was to determine how the quantity, source, and bioavailability of DOM changed across urban stormwater and beaver pond systems, then compare the two pond types to each other. We measured dissolved organic carbon (DOC) and specific ultraviolet absorbance at 254 nm (SUVA254) from upstream, within, and downstream of seven ponds in Atlanta, GA, USA, biweekly from March to December 2021. Additionally, we completed 28-day laboratory microcosm incubations of pond in- and out-flow during summer and autumn of 2021. We found higher concentrations of DOC in the pond and outflows of stormwater ponds, whereas beaver ponds did not cause any change. Effects of pond type (beaver vs. stormwater) were greater than other controls on concentration, including flow and season. In contrast, SUVA254 showed a shift toward more aromatic carbon below both systems without a clear difference between pond types. Beaver and stormwater pond outflows had similar ranges of DOM bioavailability in summer, but during autumn bioavailability at both sites declined to near zero. Overall, we found that stormwater ponds and beaver ponds had similar impacts on aromaticity and bioavailability, however stormwater ponds increased the quantity of DOC while beaver ponds did not. This suggests that in addition to increasing hydrologic residence times in urbanized systems, urban beaver ponds may limit the export of bioavailable carbon and reduce microbial processing downstream. [ABSTRACT FROM AUTHOR]

Freshwater from the Arctic participates in the globally important Atlantic Meridional Overturning Circulation (AMOC). We use high‐resolution, in situ observations of dissolved organic matter (DOM) fluorescence to trace the origins of freshwater and organic carbon in the densest component of the AMOC, namely Denmark Strait Overflow Water (DSOW). We find a distinct terrestrial DOM signal in DSOW and trace it upstream to the Siberian shelves in the Arctic Ocean. This implies a riverine origin of freshwater in DSOW. We estimate that the Siberian Shelf water contribution constitutes approximately 1% of DSOW. Ocean circulation modeling confirms the inferred pathway and highlights Denmark Strait as an important location for the entrainment of the riverine signal into DSOW. Our proposed method can be deployed on a range of observing systems to elucidate freshwater dispersion across the Arctic and subarctic, thereby contributing to the broader discussion on freshwater impacts and organic carbon sequestration in the AMOC. [ABSTRACT FROM AUTHOR]

The nitrate--nitrogen (NO3-N) concentration is a key variable affecting the ecosystem services supported by headwater streams. The availability of such data monitored continuously at a high frequency (in parallel to hydrometric and other water quality data) potentially permits a greater insight into the dynamics of this key variable. This study demonstrates how single-input single-output (SISO) system identification tools can make better use of these high-frequency data to identify a reduced number of numerical characteristics that support new explanatory hypotheses of rain-driven NO3-N dynamics. A second-order watershed managed for commercial forestry in upland Wales (United Kingdom) provided the illustrative data. Fifteen-minute rainfall time series were used to simulate NO3-N concentration dynamics and the potentially associated dynamics in dissolved organic carbon (DOC) and runoff, monitored at the same high resolution for two 30-day periods with a differing temperature regime. The approach identified robust, high-efficiency models needing few parameters. Comparison of only three derived dynamic response characteristics (DRCs) of δ, TC, and SSG for the three variables for the two different periods led to new hypotheses of rain-driven NO3-N dynamics for further exploratory field investigation. [ABSTRACT FROM AUTHOR]

Dissolved organic matter and nutrients released from leaf litter are important cross‐ecosystem resources supporting freshwater food webs. Dissolved organic matter supports heterotrophic organisms in freshwater communities. However, the role of nutrients released from leaf litter in the autochthonous production in aquatic ecosystems is not well understood. Therefore, we investigated how dissolved nutrients released from leaf litter affect algal growth, biomass production, and cellular elemental ratios. Specifically, we experimentally examined the response of green algae to nitrogen (N) and phosphorus (P) released from leaf litter of 11 temperate tree species and the degree of deficiency of nutrient elements other than N and P relative to algal demand in these litter leachates by supplementing these elements. We found that algal growth did not significantly increase with dissolved N or P in the leaf leachates. In contrast, algal biomass production increased with dissolved N concentration, regardless of amendment. Algal growth and production limitation by deficiency of elements other than N and P was found only in the leachate of Japanese hemlock, indicating that the concentrations or release efficiencies of these elements in this leaf litter were lower than those of N and P relative to algal requirements. More importantly, leaf litter leachates from different tree species altered algal cell quotas and C:N:P ratios, which would affect secondary production. These results suggest that variations in leaf litter leachate stoichiometry caused by vegetation change would affect the abundance and chemical composition of phytoplankton, and thus the trophic transfer efficiency between phytoplankton and herbivorous zooplankton. [ABSTRACT FROM AUTHOR]

The biological carbon pump (BCP) is the mechanism by which the ocean transports organic matter below the mixed layer, exporting or sequestering it for years to millennia. Physical transport of dissolved and particulate organic carbon, the sinking of particles, and the carbon transported by diel and seasonal vertical migrants are the three main mechanisms of the BCP. In the study of active flux, seasonality is almost unknown and changes in ocean productivity during the annual cycle could promote differences in this transport. Here, we show the results of a cruise performed during spring in the Canary Current System, where we studied zooplankton active flux in two transects from the coastal zone off Northwest Africa toward the ocean. We measured biomass and the enzymatic activity of the electron transfer system (ETS) as a proxy for respiration in the water column down to a depth of 900 m. Compared with a previous survey during fall, we found higher values of specific ETS activity in the mesopelagic zone, promoting a higher active flux. Our results showed that the seasonality of active flux is driven not only by differences in biomass but also by differences in respiration rates in the mesopelagic zone, mainly due to differences in zooplankton body size. A review of the zooplankton active flux values around the Canary Islands showed a fourfold increase during spring compared with other seasons. This small window of higher flux should be considered in models of active carbon export in the ocean. [ABSTRACT FROM AUTHOR]

Vibrio spp. is a group of heterotrophic bacteria that are ubiquitous in marine habitats, with various ecological and clinical importance. This study investigated the environmental factors that regulate Vibrio spp. dynamics in various tropical marine habitats, including nearshore (an estuary and a coastal beach) and offshore transects located northwest and southeast of Peninsular Malaysia, while focusing on the distribution of attached and free-living Vibrio spp., population growth, and community composition. The results showed that > 85% of the Vibrio spp. in nearshore waters occurred in attached form and correlated positively to total suspended solids (TSS) and Chlorophyll a (Chl a) concentrations. On the other hand, Vibrio spp. growth rates were positively correlated to dissolved organic carbon (DOC) concentrations, but negatively correlated to total bacterial counts, likely due to resource competition. In addition, high-throughput sequencing of 16S rRNA V3-V4 region showed that Vibrio spp. in these tropical waters contributed < 1 − 18% of the whole bacterioplankton community, and the six major Vibrio spp. taxa were V. alginolyticus group, V. brasiliensis, V. caribbeanicus, V. hepatarius group, V. splendidus group and V. thalassae. db-RDA (cumulative variance explicated = 93.53%) further revealed the influence of TSS, DOC, and dissolved organic nitrogen (DON) to the Vibrio spp. community profiles. The study highlighted the importance of suspended solids (TSS and Chl a) and dissolved organic nutrients (DOC and DON) towards Vibrio spp. dynamics in tropical marine waters. [ABSTRACT FROM AUTHOR]

Essential Climate Variables (ECVs) like ocean colour provide crucial information on the Optically Active Constituents (OACs) of seawater, such as phytoplankton, non-algal particles, and coloured dissolved organic matter (CDOM). The challenge in estimating these constituents through remote sensing is in accurately distinguishing and quantifying optical and biogeochemical properties, e.g., absorption coefficients and the concentration of chlorophyll a (Chla), especially in complex waters. This study evaluated the temporal and spatial variability of bio-optical properties in the coastal waters of the Western Iberian Coast (WIC), contributing to the assessment of satellite retrievals. In situ data from three oceanographic cruises conducted in 2019–2020 across different seasons were analyzed. Field-measured biogenic light absorption coefficients were compared to satellite estimates from Ocean-Colour Climate Change Initiative (OC-CCI) reflectance data using semi-analytical approaches (QAA, GSM, GIOP). Key findings indicate substantial variability in bio-optical properties across different seasons and regions. New bio-optical coefficients improved satellite data retrieval, reducing uncertainties and providing more reliable phytoplankton absorption estimates. These results highlight the need for region-specific algorithms to accurately capture the unique optical characteristics of coastal waters. Improved comprehension of bio-optical variability and retrieval techniques offers valuable insights for future research and coastal environment monitoring using satellite ocean colour data. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of plant-derived carbon (C) and nitrogen (N) transformation and stabilization in soil is fundamental for predicting soil capacity to mitigate climate change and support other soil functions. The decomposition of plant residues and particulate organic matter (POM) contributes to the formation of mineral-associated (on average more stable) organic matter (MAOM) in soil. MAOM is formed from the binding of dissolved organic matter (ex vivo pathway) or microbial necromass and bioproducts (in vivo pathway) to minerals and metal colloids. Which of these two soil organic matter (SOM) stabilization pathways is more important and under which conditions remains an open question. To address this question, we propose a novel diagnostic model to describe C and N dynamics in MAOM as a function of the dynamics of residues and POM decomposition. Focusing on relations among soil compartments (i.e., modeling in phase space) rather than time trajectories allows isolating the fundamental processes underlying stabilization. Using this diagnostic model in combination with a database of 36 studies in which residue C and N were tracked into POM and MAOM, we found that MAOM is predominantly fueled by necromass produced by microbes decomposing residues and POM. The relevance of this in vivo pathway is higher in clayey soils but lower in C-rich soils and with N-poor added residues. Overall, our novel modeling in phase space proved to be a sound diagnostic tool for the mechanistic investigation of soil C dynamics and supported the current understanding of the critical role of both microbial transformation and mineral capacity for the stabilization of C in mineral soils. [ABSTRACT FROM AUTHOR]

The components and sources of dissolved organic matter (DOM) in urban water bodies are extremely complicated due to multiple environmental and anthropogenic factors. The comprehensive analysis of the DOM molecular composition is crucial for deep understanding their reactivities, environmental behaviors, and fates in aquatic ecosystems, thereby improving our ability to monitor and protect aquatic systems. In this study, ultraviolet–visible spectroscopy (UV–Vis) and excitation-emission matrix fluorescence spectroscopy (EEM) were combined with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate the optical and molecular characteristics of DOM in the Yongding River (YDH) and Beiyun River (BYH), two typical urban rivers with distinct landscapes and anthropogenic influences in Beijing, China. Results showed that DOM in BYH was mainly composed of proteins from microbial and sewage sources with low aromaticity, molecular weight, and abundant saturated labile compounds, along with a significant presence of anthropogenic surfactants. Whereas the YDH was primarily composed of humic substances from plant- and soil-derived terrestrials, with higher aromaticity humification, unsaturation and refractory compounds. In addition, due to the accumulation of refractory compounds, the concentration of DOC and the degree of organic pollution increased from upstream to downstream of the rivers, manifested as an increase in humification and molecular weight at the molecular level. Our results confirmed that landscape urbanization broadly modified the structure of DOM to be more aliphatic and saturated. The findings of this study will provide important insights into the chemdiverse molecular composition of DOM undergoing different influences from human activities and provide significant guidance for water quality management in urban river ecosystems. Highlights: Distinct molecular composition was observed due to different landscapes and anthropogenic influences. The humification degree, molecular weight, and aromatics of DOM were higher in YDH than BYH. Terrestrial humic materials dominated in YDH, while sewage and microbial-derived proteins dominated in BYH. More anthropogenic surfactants were detected, especially in sewage influenced rivers. [ABSTRACT FROM AUTHOR]

Forests cover one-third of the global land and are important components of carbon and nitrogen cycling. Anthropogenic disturbances, such as forest road systems or skid trails for timber harvesting, can dramatically change the nutrient cycling in these ecosystems. Skid trails increase soil erosion and thus the displacement of soil organic carbon (SOC) and total nitrogen (Nt). Additionally, runoff transports high amounts of dissolved organic carbon (DOC), which can have a negative impact on aquatic ecosystems. One of the most important countermeasures against soil erosion is the quick recolonization of vegetation. To date, the extent to which natural vegetation succession influences the relocation of SOC and Nt, and in particular the role of mosses in this context, has not been well investigated. This study investigates the influence of natural vegetation succession and in particular of mosses on the displacement process of SOC and Nt as well as DOC caused by soil erosion. To this end, we combine the results of a field study using in-situ rainfall simulations with small-scale runoff plots in skid trails of the Schönbuch Nature Park in southwestern Germany with the results of ex-situ rainfall simulation experiments with infiltration boxes containing the substrate from the respective skid trails. The eroded sediments of skid trails were on average enriched in SOC by 16% and in Nt by 35% compared to the original soil, which lead to a decrease of the C/N ratio in sediments. As vegetation succession progressed, the displacement of SOC and Nt was reduced, confirmed by a negative correlation between the enrichment ratios of SOC (ERSOC), Nt and total vegetation cover. However, mosses tended to reduce ERSOC more than vascular plants. Additionally, mosses significantly decreased DOC concentration in surface runoff compared to bare soils, while no difference in DOC concentration in percolated water could be observed. Future research should explore the role of mosses in the storage of SOC and Nt in the soil and their impact on soil stability. Thus, utilizing mosses could potentially minimize environmental impacts from soil disturbances in forests. [ABSTRACT FROM AUTHOR]

Five decades of monitoring data (1974–2022) at the acidified forested catchment of Langtjern in southern Norway document strong chemical recovery and browning of surface water, related to changes in sulfur (S) deposition. Further recovery is likely to be impacted by future air quality and climate, through catchment processes sensitive to climate change, where the relative importance of these drivers of recovery is poorly known. Here, we explore the importance of the aforementioned drivers for recovery using the well‐established process‐oriented Model of Acidification of Groundwater In Catchments (MAGIC) with historical and projected deposition and climate from 1860 to 2100. New in MAGIC are (i) a solubility control of dissolved organic carbon (DOC) from S deposition, which allows inclusion of the role of organic acids in chemical recovery and (ii) climate‐dependency of weathering rates. MAGIC successfully described observed chemical recovery and browning, and the change toward organic acid dominated acidification status. Hindcasts of pH predicted lower preindustrial pH than previously modeled with MAGIC (simulated without S‐dependency of DOC solubility). Future deposition resulted in limited further recovery. Climate scenarios indicated a substantially wetter future, leading to increased base cation losses and slight surface water reacidification. A sensitivity analysis revealed that a 25%–50% increase of weathering rates was needed to reach preindustrial acid‐neutralizing capacity in 2100, provided S deposition is reduced to a minimum. We predict that the limited chemical recovery from reduced S deposition will be counteracted by climate‐driven reacidification from base cation losses, but that enhanced weathering rates could partly compensate these losses. [ABSTRACT FROM AUTHOR]