61. 题目: Spatial and temporal occurrence of preformed nitrate anomalies in the subtropical North Pacific and North Atlantic oceans
Preformed nitrate (PreNO3) was formulated to act as a conservative tracer of ocean circulation after accounting for the stoichiometry of marine biochemical reactions involving oxygen and nitrate. However, PreNO3 anomalies (e.g. negative values) have been identified within the shallow subsurface of the subtropical ocean which still have yet to be fully explained. The mechanisms proposed to drive the formation of PreNO3 anomalies include: vertical export and remineralization of N-poor dissolved organic matter (DOM) or transparent exopolymer particles (TEP), and the actions of vertically migrating phytoplankton. In this study we use observations from the subtropical Pacific and Atlantic Oceans taken by twenty Biogeochemical Argo profiling floats to assess the spatiotemporal variability of negative subsurface and positive euphotic zone PreNO3 anomalies and their formation rates. After explicitly accounting for the magnitude of DOM cycling, residual euphotic zone positive PreNO3 anomalies and subsurface negative PreNO3 anomalies are consistently observed between 40°S and 40°N. The seasonal timing of euphotic zone positive residual PreNO3 anomaly formation in relation to subsurface negative residual PreNO3 anomalies suggests that both vertically migrating phytoplankton and the remineralization of N-deficient TEP likely contribute to the formation of residual PreNO3 anomalies, but with regional variance suggesting a potentially larger role for migrating phytoplankton in the North Pacific and TEP processes in the North Atlantic. Since migrators include large diatoms that produce ballasted organic matter while TEP may only sink shallowly before remineralization, further investigation into the mechanisms generating PreNO3 anomalies and their quantitative significance is needed to assess the future trajectory of the biological carbon pump in an expanding subtropical ocean ecosystem.
62. 题目: Microbial fuel cells in coral reef sediments as indicator tools for organic carbon eutrophication
Eutrophication with organic carbon (OC) can be harmful for corals and their reefs due to its stimulating effects on associated and sedimentary microbes, leading to oxygen deficits. Mitigation measures require real-time monitoring of wastewater pulses close to coral reefs, where biogenic carbonate sands act as biocatalytic filters for OC. Microbial fuel cells (MFCs) where the anode is deployed in sediments and the cathode is in contact with the overlying water can directly generate electricity from the microbial degradation of OC in sediments, but their application in coral reefs has not yet been tested. During a laboratory experiment, we thus investigated if MFCs, vertically deployed in coral reef sands, can be used as indicator tools for eutrophication with artificial wastewater (AW, prepared from organic compounds and chemicals) at OC concentrations of 20, 40, or 52 mg C L-1 higher than controls. AW pulses were repeated three times at every concentration, with five weeks between the first and second pulse, and six months between the second and third pulse. Results revealed significant increases in current densities in all AW treatments (means up to 11, 36, and 39 mA m−2, respectively), while controls remained stable and low (-1 to 3 mA m−2). Current densities and OC concentrations correlated significantly (rrm = 0.64), and the slope of the correlation increased with each consecutive AW pulse. This highlights the functionality of the MFC as a qualitative indicator tool for OC pulses even months after deployment. The response time of the MFCs was fast (<1 day) compared to other indicators for water quality (e.g., coral colony- or community measures that take weeks to years to respond), and they successfully detected OC concentrations expected for wastewater effluents. Measurements can be automated for continuous monitoring, and no laboratory facilities are required (as for OC analysis), making MFC sensors a suitable tool for remote locations. Overall, these findings emphasize the high potential of these low-cost (<20 € per MFC) MFCs as indicator tools for OC pulses in coral reef environments.
63. 题目: Organic carbon preservation in wetlands: Iron oxide protection vs. thermodynamic limitation
The sequestration of organic carbon (OC) in wetland sediments is influenced by the presence of oxygen or lack thereof. The mechanisms of OC sequestration under redox fluctuations, particularly by the co-mediation of reactive iron (Fe) protection and thermodynamic limitation by the energetics of the OC itself, remain unclear. Over the past 26 years, a combination of field surveys and remote sensing images had revealed a strong decline in both natural and constructed wetland areas in Tianjin. This decline could be attributed to anthropogenic landfill practices and agricultural reclamation efforts, which may have significant impacts on the oxidation-reduction conditions for sedimentary OC. The Fe-bound OC (CBD extraction) decreased by 2 to 10-fold (from 8.3–10% to 0.7–4.5%) with increasing sediment depth at three sites with varying water depths (WD). The high-resolution spectro-microscopy analysis demonstrated that Fe (oxyhydr)oxides were colocalized with sedimentary OC. Corresponding to lower redox potential, the nominal oxidation state of C (NOSC), which corresponds to the energy content in OC, became more negative (energy content increased) with increasing sediment depth. Taken together, the preservation of sedimentary OC is contingent on the prevailing redox conditions: In environments where oxygen availability is high, reactive Fe provides protection for OC, while in anoxic environments, thermodynamic constraints (i.e., energetic constraints) limit the oxidation of OC.
64. 题目: Possibility of exogenous organic carbon input to increase global soil nitrogen supply potential: A meta-analysis
Soil nitrogen (N) mineralization is regulated by the input of exogenous organic carbon (C, ExoC) substrate via changing C availability. Although ExoC input occurs widely among global terrestrial ecosystems, it is still not clear how ExoC input affects soil gross N mineralization (GNM). Here, 265 observations from 63 peer-reviewed publications were collected for a global meta-analysis to investigate the effect and the drivers of ExoC input upon soil GNM. The results showed that ExoC input significantly increased GNM by 40.8%, and the influence depended on the types of ExoC substrate. The input of complex ExoC substrate (straw, animal manure, cellulose, etc.) increased soil GNM by 44.8%, while simple ExoC substrate (glucose, amino acids, oxalic, etc.) had no significant effect on GNM. Only in cropland the ExoC input promote the rate of soil GNM, with no significant effect found in either forest or grassland. Furthermore, the results revealed that the application rate of ExoC was the paramount factor affecting soil GNM, given their significant positive correlations. This study also emphasized that initial soil pH (i.e. soil pH before ExoC input) and pH of ExoC, rather than the change of bulk soil pH, played an important role in regulating soil GNM after the ExoC input, and both were significantly negatively correlated with GNM. In addition, soil GNM was also negatively correlated with mean annual temperature but positively related with soil total N and mean annual precipitation. The findings of this meta-analysis contribute to a comprehensive understanding of how soil N availability and cycling respond to ExoC input on a global scale. That means the factors related to rate of ExoC, soil total N, initial soil pH, the pH of ExoC, and climate factors and the interaction among above factors may affect global soil N supplying potential.
65. 题目: Detection of Early-Middle Devonian biotic crises in East Gondwana, Paraná Basin, Brazil: an organic geochemical approach
Changes detected in physicochemical conditions of Ponta Grossa Formation’s depositional paleoenvironment (Early-Middle Devonian), East Gondwana, were correlated with significant biotic crises that preceded the great Devonian extinction event (Frasnian-Famennian), culminating in the extinction of the Malvinokaffric fauna. The present study identified Zilchov, Daleje, Choteč, and Kačák biotic crisis events through geochemical analyses. Fifteen outcrop shale samples were analysed by well-established geochemical parameters, such as saturated and aromatic biomarkers and polycyclic aromatic hydrocarbons. Parameter results were correlated to polar compounds distribution using atmospheric pressure photoionisation (APPI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in positive ionisation mode. A decrease in the summation of n-alkanes, αβC30 hopane, and gammacerane concentrations was observed at the Pragian-Emsian interval, related to the Zilchov event and the first decline of the Malvinokaffric fauna. At the Late Emsian, a severe change in paleoenvironment depositional conditions was detected by the increase in αβ C30 hopane, tetrahydrophenanthrene and gammacerane concentration values, suggesting water column stratification. Moreover, Tricyclic Index values indicated a change to a more freshwater lacustrine environment, which was confirmed by n-alkyl cyclohexanes series occurrence. In addition, high percentages of O1 and N1 class compounds indicated that this interval was probably composed of a mixture of bacterial and terrigenous organic matter. These results indicated a large inflow of fresh and continental waters due to a regression related to the Daleje event and the second decline of the Malvinokaffric fauna. A significant decrease of Pristane/Phytane, summation of n-alkanes, αβ C30 hopane and gammacerane concentration values was observed, along with the absence of N1 compounds at the Emsian-Eifelian interval, representing a rapid transgression, corresponding to the Choteč event. At the Eifelian-Givetian interval, the detection of n-alkanes and biomarkers low concentration values, low Pristane/Phytane values (anoxia), as well as the non-detection of N1 class compounds, indicated a great transgression related to the Kačák event and the disappearance of the Malvinokaffric fauna.
66. 题目: Structural characteristics of the moss (bryophyte) layer and its underlying soil structure and water retention characteristics
The influence of the moss layer on soil structure and soil water retention is not well understood. Therefore, this study aims to investigate the changes in soil structure and soil water retention under moss layer and to reveal the influencing factors of these changes.
3D networks of moss layer and soil macropores were quantified using CT scanning and image analysis techniques, and soil water retention characteristics were explored through soil water retention curves (SWRCs) and VG model.
The length densities of the soil macropores under the thin moss and thick moss layers were approximately 2.7 and 1.6 times higher than that under no moss cover. The soil water retention under the thin and thick moss layers were greater than those under no moss cover, with the highest plant-available water capacity under the thin moss layer. The maximum water-holding capacity of the moss layer was significantly positively correlated with the field water-holding capacity of the soil and negatively correlated with the equivalent diameter of the macropores, while the storage capacity of the moss layer was significantly and negatively correlated with the maximum effective water content of the soil. The field capacity (FC) and permanent wilting point (PWP) were significantly and positively correlated with the soil organic matter.
The effect of the moss layer on water retention may be mainly realized by influencing the pore distribution and organic matter accumulation. The moss layer had a positive ecohydrological effect on soil water retention and even water conservation in forest soils.
67. 题目: Enhanced Direct Photolysis of Organic Micropollutants by Far-UVC Light at 222 nm from KrCl* Excilamps
68. 题目: Biochar amendment to cattle slurry reduces NH3 emissions during storage without risk of higher NH3 emissions after soil application of the solid fraction
Cattle slurry storage is a major source of gaseous N emissions. The aim of this study was to evaluate the effects of biochar, clinoptilolite and elemental sulfur (S°) on (1) NH3 and greenhouse gas emissions during storage of cattle slurry and (2) after soil application of the enriched solid fractions; and (3) on the agronomic quality of the solid and liquid fractions. In the first phase, biochar was added to the slurry (10 g L-1); subsequently in the second phase, clinoptilolite (50 g L-1), S° (1 g L-1) and 40 g L-1 extra biochar were added. Gaseous emissions were monitored by a semi-continuous multi-gas analyzer and the agronomic quality of solid and liquid fractions was assessed after separation. The enriched solid fractions were applied to soil to study the effects on gaseous emissions, N and C mineralization. Amendment of biochar reduced NH3 emissions during cattle slurry storage by 12% during the first 7 days. Extra amendment of biochar, clinoptilolite and S° in combination with biochar resulted in a decrease of NH3 emissions of approximately 20%. The N sorbed from the slurry by the biochar was not released as NH3 during soil application of the solid fractions and was not released as mineral N in the short term (within 28 days). A short-term positive priming effect of biochar on the C mineralization of manure and biochar-manure mixture applied to soil was observed. The biochar-enriched solid fractions contained more C, total and organic N and water-available P with a slow release.
69. 题目: High Voltage: The Molecular Properties of Redox-Active Dissolved Organic Matter in Northern High-Latitude Lakes
70. 题目: Positive effects of crop rotation on soil aggregation and associated organic carbon are mainly controlled by climate and initial soil carbon content: A meta-analysis
Understanding the global patterns and controls on soil aggregation and associated organic carbon (OC) is essential to improve soil carbon storage and mitigate climate warming. Crop rotation is an important feature of sustainable agricultural management and influences multiple soil properties. However, the effects of crop rotation on soil aggregation and associated OC remain poorly understood. We conducted a meta-analysis of 2199 paired observations from 53 studies to quantitatively analyze crop rotation-induced changes in soil aggregation and associated OC and elucidate optimal climatic, edaphic, and agronomic factors. Overall, crop rotation improved the proportions of macroaggregates (> 0.25 mm) by 7–14%, aggregate stability by 7–9%, and OC contents in all sizes of aggregates by 7–8% relative to continuous monoculture. Crop rotation increased soil aggregation and associated OC mainly in regions with mean annual temperature between 8 and 15℃, mean annual precipitation between 600 and 1000 mm, and also in topsoil (0–20 cm) with loamy textures and medium levels of initial soil OC (10–15 g kg−1), total nitrogen (0.75–1.50 g kg−1), and pH (6−8). Greater increases in soil aggregation and associated OC induced by crop rotation were associated with sub-soiling, no-till, straw retention, combined manure-inorganic fertilizers, and a lower nitrogen fertilization input rate with more rotation cycles and longer rotation length. Crop rotation effects were especially strong when the previously cultivated crop was soybean. The variance partitioning analysis revealed that variations in crop rotation-induced changes in soil aggregation and associated OC were mainly explained by climate (26–35%) and soil properties (17–34%). The random forest model indicated that climate (mean annual temperature and precipitation) and initial soil OC were the predominant controls on the effects of crop rotation. Overall, these findings suggest that the use of crop rotation can help sequester carbon by improving soil aggregation and associated OC, and highlight the importance of climate and initial soil OC in site-specific crop rotation systems to the sustainability of agroecosystems.
71. 题目: Algal organic matter accelerates the photodegradation of tetracycline: Mechanisms, degradation pathways and product toxicity
Algae are ubiquitous in eutrophic surface waters and they play important roles in the sunlight-driven transformation of environmental contaminants. The present study aims to investigate the role of algal organic matter (AOM) separated from Microcystis aeruginosa at different growth stages in tetracycline photodegradation along with the related photosensitive mechanisms. The results showed that AOM, both extracellular organic matter (EOM) and intracellular organic matter (IOM) at different growth phases all promote tetracycline photodegradation, but in different ways and performances. EOM exerts greater photolysis effectiveness than IOM with logarithmic phase (LP) organic matter more effective than that from the algae’s declining growth phase (DP). The promoting efficiencies of tetracycline photodegradation by four AOM types follow the order of LP-EOM > DP-EOM > LP-IOM > DP-IOM, accounting for 1.0420 h–1, 0.8281 h–1, 0.6527 h–1 and 0.4974 h–1, respectively. Such discrepant effectiveness is related to the different chemical constituents and structures of EOM and IOM. Scavenger experiments further demonstrated that triplet-state AOM (3AOM*) contributes the most to tetracycline degradation (30.01%∼48.51%), followed by •OH (1.68%∼10.66%) and 1O2 (1.34%∼10.08%). The steady-state concentrations of 3AOM*, •OH and 1O2 were measured with probe compounds in the range of 13.950∼155.234 L/mol, 2.494 × 10–17∼27.636 × 10–17 M and 1.410 × 10–14∼26.493 × 10–14 M, respectively. Interestingly, the photolytic intermediates show increasing toxicity to Photobacterium phosphoreum at first which then decreases with the extension of irradiation. These results provide comprehensive insight into the transport and environmental behavior of antibiotics in a eutrophic aqueous environment.
72. 题目: Rice husk biochar - A novel engineered bio-based material for transforming groundwater-mediated fluoride cycling in natural environments
Biochar, a promising carbon-rich and carbon-negative material, can control water pollution, harness the synergy of sustainable development goals, and achieve circular economy. This study examined the performance feasibility of treating fluoride-contaminated surface and groundwater using raw and modified biochar synthesized from agricultural waste rice husk as problem-fixing renewable carbon-neutral material. Physicochemical characterizations of raw/modified biochars were investigated using FESEM-EDAX, FTIR, XRD, BET, CHSN, VSM, pHpzc, Zeta potential, and particle size analysis were analyzed to identify the surface morphology, functional groups, structural, and electrokinetic behavior. In fluoride (Fˉ) cycling, performance feasibility was tested at various governing factors, contact time (0–120 min), initial Fˉ levels (10–50 mg L−1), biochar dose (0.1–0.5 g L−1), pH (2–9), salt strengths (0–50 mM), temperatures (301–328 K), and various co-occurring ions. Results revealed that activated magnetic biochar (AMB) possessed higher adsorption capacity than raw biochar (RB) and activated biochar (AB) at pH 7. The results indicated that maximum Fˉ removal (98.13%) was achieved using AMB at pH 7 for 10 mg L−1. Electrostatic attraction, ion exchange, pore fillings, and surface complexation govern Fˉ removal mechanisms. Pseudo-second-order and Freundlich were the best fit kinetic and isotherm for Fˉ sorption, respectively. Increased biochar dose drives an increase in active sites due to Fˉ level gradient and mass transfer between biochar-fluoride interactions, which reported maximum mass transfer for AMB than RB and AB. Fluoride adsorption using AMB could be described through chemisorption processes at room temperature (301 K), though endothermic sorption follows the physisorption process. Fluoride removal efficiency reduced, from 67.70% to 53.23%, with increased salt concentrations from 0 to 50 mM NaCl solutions, respectively, due to increased hydrodynamic diameter. Biochar was used to treat natural fluoride-contaminated surface and groundwater in real-world problem-solving measures, showed removal efficiency of 91.20% and 95.61%, respectively, for 10 mg L−1 Fˉ contamination, and has been performed multiple times after systematic adsorption-desorption experiments. Lastly, techno-economic analysis was analyzed for biochar synthesis and Fˉ treatment performance costs. Overall, our results revealed worth output and concluded with recommendations for future research on Fˉ adsorption using biochar.
73. 题目: Reactions of Monobromamine and Dibromamine with Phenolic Compounds and Organic Matter: Kinetics and Formation of Bromophenols and Bromoform
74. 题目: Chitin and crawfish shell biochar composite decreased heavy metal bioavailability and shifted rhizosphere bacterial community in an arsenic/lead co-contaminated soil
Sustainable management of ever-increasing organic biowaste and arable soil contamination by potentially toxic elements are of concern from both environmental and agricultural perspectives. To tackle the waste issue of crawfish shells and simultaneously minimize the threat of arsenic (As) and lead (Pb) to human health, a pot trial was conducted using chitin (CT), crawfish shell biochar (CSB), crawfish shell powder (CSP), and CT–CSB composite to compare their remediation efficiencies in As/Pb co-contaminated soil. Results demonstrated that addition of all amendments decreased Pb bioavailability, with the greatest effect observed for the CT–CSB treatment. Application of CSP and CSB increased the soil available As concentration, while significant decreases were observed in the CT and CT–CSB treatments. Meanwhile, CT addition was the most effective in enhancing the soil enzyme activities including acid phosphatase, α-glucosidase, N-acetyl-β-glucosaminidase, and cellobiohydrolase, whereas CSB-containing treatments suppressed the activities of most enzymes. The amendments altered the bacterial abundance and composition in soil. For instance, compared to the control, all treatments increased Chitinophagaceae abundance by 2.6-4.7%. The relative abundance of Comamonadaceae decreased by 1.6% in the CSB treatment, while 2.1% increase of Comamonadaceae was noted in the CT–CSB treatment. Redundancy and correlation analyses (at the family level) indicated that the changes in bacterial community structure were linked to bulk density, water content, and As/Pb availability of soils. Partial least squares path modeling (PLS-PM) further indicated that soil chemical property (i.e., pH, dissolved organic carbon, and cation exchange capacity) was the strongest predictor of As/Pb availability in soils following amendment application. Overall, CT–CSB could be a potentially effective amendment for simultaneously immobilizing As and Pb and restoring soil ecological functions in contaminated arable soils.
75. 题目: Adsorption of diuron in black soil amended with biochar can predict its bioavailability to crops and earthworms
In this study, the adsorption behavior of diuron in a typical black soil and its bioavailability to crops and earthworms were investigated by adsorption and incubation experiments, combined with biochar amendment and aging time.
In this study, the adsorption of diuron, and its uptake by corn and earthworms were investigated in black soil with 0.1–5% (w/w) bamboo charcoal.
Uptake of diuron by corns was reduced by 45% in black soil aged for 0 day in 0.1–5% biochar-amended soil, the concentration of diuron in both roots and stems of corn plants tended to decrease with the increase of aging time, and the enrichment coefficient of diuron in corn also tended to decrease in 0.1–5% biochar-amended soil. When aging time was 0 day and the biochar amendment in black soil was 0.1–5%, the accumulation concentration of diuron in earthworms decreased by 63%; the bioconcentration coefficient of diuron in earthworms in black soil with different levels of biochar decreased continuously with the increase of aging time.
Biochar is an efficient adsorbent for diuron and could significantly reduce the uptake of diuron by plants and earthworms from contaminated soil. Significant correlations indicated that regression analyses could be constructed between the bioconcentration factor and sorption coefficients to predict the bioavailability of diuron residues in soil to corns and earthworms. Biochar amendment could be used as an option to immobilize diuron in soil and protect non-target organisms from diuron contamination.
76. 题目: Microbial carbon use efficiency promotes global soil carbon storage
Soils store more carbon than other terrestrial ecosystems1,2. How soil organic carbon (SOC) forms and persists remains uncertain1,3, which makes it challenging to understand how it will respond to climatic change3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss5,6,7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways4,6,8,9,10,11, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.
77. 题目: What C:N ratios in soil particle-size fractions really say: N is preferentially sorbed by clays over organic C
Factors affecting soil organic carbon (SOC) retention in the tropics are relatively well known, but this is not the case for N retention and thus C:N ratios, a common proxy for organic matter stability. Recent data suggest that SOC and N concentrations vary with climate, whereas soil C:N ratios depend on particle-size fractions contents. However, such knowledge is still incipient for tropical soils, native vegetations and deeper soil layers, which are critical to understand how land use and climate change affect C and N fluxes. We assessed SOC, N and C:N ratios in bulk soils and sand, silt and clay fractions, and their correlations with other soil properties under native tropical forests in the highlands near Lavras, Brazil. Soil samples were collected to 1-m depth in soils of contrasting texture and mineralogy, formed on quartzite, sericite-schist, gabbro, itabirite, ironstone, meta-limestone, gneiss, and phyllite. Mean SOC and N concentrations were generally high, whereas mean soil C:N ratios varied from 9.5 to 18.7 among parent materials, and only in three soils C:N ratios varied considerably with depth. Enrichment factors (EFs) were generally < 1 in the sand and silt fractions for SOC and especially N. Conversely, EFs for clay were mostly > 1 for SOC and even higher (up to 6.58) for N. Such trend indicates that SOC and N are concentrated in clays, and more importantly, that N sorption is favored compared with SOC, and likely dependent on clay mineralogy. Soil C:N ratios decreased with increasing values of exchangeable bases, due to higher N in the most fertile soils, suggesting that a mechanism of R-NH3+ cationic sorption is likely involved. Our results suggest that soil N is a critical component of the overall stabilization of soil organic matter onto clays of tropical soils, deserving further investigation also under temperate climate and other zones.
78. 题目: Storage and controlling factors of soil organic carbon in alpine wetlands and meadow across the Tibetan Plateau
79. 题目: Artificial neural network implementation for dissolved organic carbon quantification using fluorescence intensity as a predictor in wastewater treatment plants
Although spectroscopic methods provide a fast and cost-effective means of monitoring dissolved organic carbon (DOC) in natural and engineered water systems, the prediction accuracy of these methods is limited by the complex relationship between optical properties and DOC concentration. In this study, we developed DOC prediction models using multiple linear/log-linear regression and feedforward artificial neural network (ANN) and investigated the effectiveness of spectroscopic properties, such as fluorescence intensity and UV absorption at 254 nm (UV254), as predictors. Optimum predictors were identified based on correlation analysis to construct models using single and multiple predictors. We compared the peak-picking and parallel factor analysis (PARAFAC) methods for selecting appropriate fluorescence wavelengths. Both methods had similar prediction capability (p-values >0.05), suggesting PARAFAC was not necessary for choosing fluorescence predictors. Fluorescence peak T was identified as a more accurate predictor than UV254. Combining UV254 and multiple fluorescence peak intensities as predictors further improved the prediction capability of the models. The ANN models outperformed the linear/log-linear regression models with multiple predictors, achieving higher prediction accuracy (peak-picking: R2 = 0.8978, RMSE = 0.3105 mg/L; PARAFAC: R2 = 0.9079, RMSE = 0.2989 mg/L). These findings suggest the potential to develop a real-time DOC concentration sensor based on optical properties using an ANN for signal processing.
80. 题目: Water-soluble organic carbon release from mineral soils and sediments in an irrigated agricultural system
Water interactions with soil and vegetation are greatly altered in agricultural watersheds compared to natural landscapes, which impacts sources and fates of organic carbon (OC). While mineral soil horizons in natural ecosystems primarily act as filters for dissolved organic carbon (DOC) leached from organic surface horizons, tilled soils largely lack an organic horizon and their mineral horizons therefore act as a source for both DOC and sediment to surface waters. Irrigated watersheds highlight this difference, as DOC and total suspended sediment (TSS) concentrations simultaneously increase during the low-discharge irrigation season, suggesting that sediment-associated OC may constitute a significant source of DOC. While water-soluble OC (WSOC) from sediments and soils has been found to be compositionally similar to stream DOC, these contributions remain poorly quantified in agricultural streams. To address this, we conducted abiotic solubilization experiments using sediments (suspended and bed) and soils from an irrigated agricultural watershed in northern California, USA. Sediments (R2 > 0.99) and soils (0.74 < R2 < 0.89) displayed linear solubilization behaviors over the range of concentrations tested. Suspended sediment from the irrigation season exhibited the largest solubilization efficiency (10.9 ± 1.6% TOCsediment solubilized) and potential (1.79 ± 0.26 mg WSOC g−1 dry sediment), followed by suspended sediment from a winter storm, then bed sediment and soils. Successive solubilization experiments increased the total release of WSOC by ∼50%, but most (88–97%) of the solid-phase OC remained insoluble in water. Using these solubilization potential estimates and measured TSS concentrations, we estimated that WSOC from suspended sediment in streams represented 4–7% of the annual DOC export from the watershed. However, field sediment export is much higher than what is represented by suspended sediment in the water column, therefore field-scale contributions from sediments could be much higher than estimated.