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The onset of the Late Holocene subepoch, marked by the 4.2 ka BP event, is characterized by drought along the equatorial regions and cooling trends near the poles, as evidenced by lower sea surface temperatures in the northern North Atlantic. However, the occurrence and significance of this event remain controversial, with inconsistent verification across different regions. A comprehensive review of over 30 studies examining climate proxies such as peat deposits, lake sediments, and tree rings from Sweden, spanning 5000 to 3500 cal a BP, reveals some recurring patterns. These studies extend from northern to southern Sweden, and many of these suggest a shift towards wetter, colder, or both wetter and colder climate around 4500–4000 cal a BP. Despite these indications, variations in the reliability and replication of climate proxies introduce substantial uncertainty. Additionally, several parts of Sweden lack sufficient proxy data. As a result, there is no clear evidence of a widespread, uniform climate change across Sweden during 4500–4000 cal a BP. The temporal variability of these changes, ranging from decadal to millennial scales, further complicates the identification of a single climatic event. The climate patterns in Sweden during this period align with the broader northern North Atlantic region, where both supportive and contradictory evidence exists for climate changes around 4200 cal a BP. The absence of consistent findings across multiple proxies and regions suggests that the 4.2 ka BP event was not a globally synchronous event but may represent a complex interplay of regional climatic shifts. [ABSTRACT FROM AUTHOR]

Aims: Peat is used as a major ingredient of growing media in horticulture. Peat extracted from bogs can be acidic and low in nutrient availability and is therefore mixed with liming agents, nutrients, surfactants, perlite and so on. This study aims to estimate the rates at which raw peat and the modified peat ('growing media') decompose to release carbon dioxide (CO2), to estimate the release of carbon (C) from liming agents and to estimate how peat biogeochemistry is changed. Methods: We obtained 28 and 24 samples of raw peat and 24 growing media from four peat extraction companies in Canada. Growing media were treated with horticultural additives. We incubated the samples under laboratory conditions, measuring CO2 production, tracer using δ 13 C - CO 2 , pH, C, nitrogen (N) content and humification indices (HIs) from infrared technology called Fourier transform-mid infrared (FT-MIR). Results: C:N ratio, pH, dissolved organic carbon, bulk density and C content differed significantly (P < 0.05) between raw peats and growing media. There was more than a doubling of total CO 2 production from growing media compared to raw peat. HIs show higher values for the growing media, which could result from spectral band shifts in the growing media because of increased cation availability. δ 13 C - CO 2 as a tracer showed an average 22% of the total CO 2 production orginated from added carbonate materials. Conclusion: Our results provide the rates (0.15 ± 0.017mgCO2-Cg−1d−1) at which horticultural peat decomposes and on the source of emitted CO 2 . This will improve current estimates CO2 emissions from horticultural peat. [ABSTRACT FROM AUTHOR]

Organic inputs are key to increasing soil organic carbon in agricultural soils. This study aimed to unravel the process of mineralization and humification of chicken manure (CM) and composted kitchen waste (KW) using an in situ litterbag incubation experiment. The results indicated that over 50%, 64% to 72%, and 62% to 85% of the initial mass, carbon and nitrogen, respectively, were lost through incubation with a marked loss occurring during the first 28 days. Increased humic acids (HAs), humus (HS) and degree of humification, along with a decrease in the level of fulvic acids and precursors for humic substances were observed through incubation. By comparison, CM demonstrated higher carbon and nitrogen conservation efficiencies and greater humification compared to KW. Additionally, a higher degree of humifaction and larger quantities of HAs and HS were not favorable for carbon and nitrogen conservation. Further structural equation modeling indicated that microbial community had a strong effect on carbon loss and nitrogen release, while stoichiometric properties of organic inputs were the main determinant of the mineralization and humification processes. These findings will enhance understanding of litter decomposition in soils and provide valuable references for soil carbon sequestration with organic inputs. [ABSTRACT FROM AUTHOR]

Humic substances are highly valuable molecules known to promote several soil functions and plant growth. The present study describes the extraction and characterization of humic and fulvic acid from composts prepared from different proportions of rice straw, sea weed, fish waste and cow dung. The results showed a compost recovery of 60–64.8% and a composting duration of 65–110 days, with significant differences among the treatments. The type and proportion of feed stock significantly influenced the total N, P, Ca, Mg and K contents of the compost, with the highest values occurring in T2, followed by T3 and T1; however, there were no significant differences in Fe, Zn or Mn. The recovery of humic substances (HS) varied from 7.52 to 9.41%, with a significantly greater recovery occurring in T2 than in T3 and T1, while cow dung addition (T4) had the lowest recovery. The addition of sea weed and fish waste increased the total N, P, K, Ca and Mg contents of the HS plants, while the lowest E4/E6 ratio was recorded in T2, followed by T3 and T4, indicating strong humification, which was greater than that in T4 and T5. The FTIR spectrum of humic acid (HA) exhibited typical distinguishing bands in addition to absorption bands at 2374, 1723, 1360, 1120 and 757 cm−1, which are specific to T2 and T3, indicating the presence of diverse carbon compounds and amines and a consequently high degree of humification. The strong absorption peaks in the 1030–1080 cm−1 region for T3 and T2 were attributed to S–O and C–O stretching of sulfoxide and primary alcohol groups, whereas the additional peak at 1120 cm−1 in T3 was ascribed to C–O stretching of secondary alcohol groups. Unlike those in the HA spectra, the fulvic acid (FA) extract peak was more intense at 3320–3330 cm−1, 1630–1650 cm−1 and 610–640 cm−1, which indicated the presence of more oxygen-containing active groups. Resynthesized HSs with more mineralized plant nutrients increased in quality, indicating the technical feasibility of the valorization of organic wastes for the extraction of HA and FA with greater agronomic value. [ABSTRACT FROM AUTHOR]

This study focuses on geochemical research into humic acids and humification processes in lakes of West Antarctica, specifically King George Island and Marie Byrd Land. Humic acids were extracted from recent sediments of Antarctic lakes and analysed using high-precision laboratory methods. The experiments included examining the elemental composition and molecular structure of the humic acids. The results show that the organic matter in sediments of the studied lakes has undergone complete humification processes. However, the molecular structure of humic acids is characterized by a predominance of aliphatic fragments and a significant amount of polysaccharides, which is typical of humic substances in the cold climates of Arctic and Antarctic regions. Thus, the humic substances of Antarctic lakes were found to have a very low degree of maturity and were non-resistant to mineralization. These findings are valuable for understanding the full chain of organic matter transformation processes in Antarctic ecosystems and the global carbon cycle on Earth. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil acidification due to the long-term application of nitrogenous fertilizers and the consequent impact on crop growth have been frequently reported. The effects of acidification on soil humus, charge, and microbial communities need to be studied. In this experiment, fertilizer drenching was used to simulate the effects of multiple years of fertilizer application on the black soil. The results showed that 25 years of soil acidification treatment resulted in a decrease of 8.97% in the content of stable humus and led to a decrease of 58% and 51.18% in the humic acid (HA) content and degree of humification (PQ) value in stable humus, respectively. In addition, soil acidification leads to a significant decrease in total negative charge (CEC8.2) and variable negative charge (CECv), with both decreasing by 63.28% and 88.67%, respectively, at 25 years. Acidification treatments affected both soil microbial community abundance and diversity, with a significant decrease in Acidobacteriota and Gemmatimonadota abundance and an increase in Bacteroidia abundance and Acidobacteriota abundance at 25 years. [ABSTRACT FROM AUTHOR]

Biochar addition plays an important role in manure composting, but its driving mechanism on microbial succession and humification process of human excreta composting is still unclear. In the present study, the mechanism of biochar addition was explored by analysing the humification process and microbial succession pattern of human excreta aerobic composting without and with 10% biochar (HF and BHF). Results indicated that BHF improved composting temperature, advanced the thermophilic phase by 1 d, increased the germination index by 49.03%, promoted the growth rate of humic acid content by 17.46%, and raised the compost product with the ratio of humic acid to fulvic acid (HA/FA) by 16.19%. Biochar regulated the diversity of fungi and bacteria, increasing the relative abundance of Planifilum, Meyerozyma and Melanocarpus in the thermophilic phase, and Saccharomonospora, Flavobacterium, Thermomyces and Remersonia in the mature phase, which accelerates the humification. Bacterial communities' succession had an obvious correlation with the total carbon, total nitrogen, and temperature (P < 0.05), while the succession of fungal communities was influenced by the HA/FA and pH (P < 0.05). This study could provide a reference for the improvement of on-site human excreta harmless by extending the thermophilic phase, and facilitating the humification in human excreta compost with biochar addition. [ABSTRACT FROM AUTHOR]

This study investigates the biogeochemical and environmental characteristics of humic acids isolated from sediment samples of five lakes located in the European taiga zone. Sediment samples were analyzed using advanced techniques, including CHN analysis, solid-state 13C-NMR spectroscopy, and FTIR spectroscopy. The results show that the humic acids from the studied lake sediments exhibit lower degrees of aromaticity compared to those in terrestrial soils, indicating a lower degree of humification under aquatic reducing conditions. This suggests that aquatic environments favor the preservation of relatively labile organic compounds. The affinity of metals to form complexes with the humic acids varied among the lakes, with metals such as Co, Pb, V, and Sb forming stable chelate complexes, while Mn and Cd exhibited higher geochemical mobility. The findings provide insight into the role of humic substances in controlling the distribution and mobility of metals in aquatic ecosystems, contributing to our understanding of biogeochemical processes in taiga lake environments. [ABSTRACT FROM AUTHOR]

Introduction: Humus can be formed during composting through biological pathways, nonetheless, the mechanisms through which bacterial and fungal communities govern the development of humus in compost with the addition of biochar remain uncertain. Methods: In this study, compost with cow dung and maize stover as feedstock was employed as a control group, and compost with 10% biochar added on top of the feedstock was adopted as a treatment group to investigate the effect of bacterial and fungal communities on humus formation during biochar composting. Results and Discussion: The results demonstrated that the humic acid content increased by 24.82 and 25.10% at the cooling and maturation stages, respectively, after adding biochar. Besides, the degree of polymerization content in the maturation stage was elevated by 90.98%, which accelerated the humification process of the compost. During the thermophilic and maturity stages, there was a respective increase of 51.34 and 31.40% in reducing sugar content, suggesting that the inclusion of biochar could furnish ample reducing sugar substrate for the Maillard reaction. The addition of biochar reduced the number of humus precursorassociated genera by 35, increased the number of genera involved in humus synthesis by two, and enhanced the stability of the cross-domain network between bacteria and fungi, which confirms that microorganisms contribute to the humification process by decreasing humus precursor consumption as well as increasing humus synthesis with the addition of biochar. Additionally, adding biochar could enhance the humification capacity of the compost pile by dominating the Maillard reaction with reducing sugars as the substrate and strengthening the function of humus synthesis-associated genera. This study enhances our comprehension of the regulatory pathways of biochar in the humification process during composting. [ABSTRACT FROM AUTHOR]

Fertility and soil balance cannot be maintained without the presence of organic matter and the addition of new quantities of plant residues or chemical and organic fertilizers, as plants extract significant amounts of nutrients from the soil each year. Therefore, the application of manure can be considered a good source for increasing the potential fertility of the soil. This study addresses on the fertilization with manure derived from cattle and sheep farming activities on the typical chernozem soil from the Romanian Plain. The effects of using these organic fertilizers are mainly observed in the behavior of nitrogen (N) and phosphorus (P) in the soil, as they are the main nutrients that influence agricultural crop yields. Potassium (K) has a secondary role, but along with pH and other macronutrients, it improves the physical and biological properties of the soil, as evidenced by the appearance and formation of a positive humus balance and an improvement in the NPK content of the soil. Following the application of manure over a period of more than five years, changes in the physical-chemical indicators are observed, such as the bulk density of soil which decreases from 1.28 g/cm³ to 1.17 g/cm³, or the humus that increases from 2.07 % to 2.57 %, after five years of manure action. [ABSTRACT FROM AUTHOR]

While numerous studies have examined the effects of direct and carbonized straw return on soil fertility, most focus on short-term impacts. Long-term research is needed to understand how these practices affect soil fertility and organic carbon transformation, providing guidance for the use of straw and biochar in agriculture. This study examined the long-term effects of corn straw (CS), straw biochar (BIO), and biochar-based fertilizer (BF) applied over 5, 10, and 15 years on soil aggregates, organic carbon, and humus composition in a peanut field microplot experiment. Using pig manure compost (PMC) as a control, we assessed soil water-stable aggregate distribution, carbon content in soil and aggregates, and organic carbon's infrared spectral characteristics. The goal was to understand how different straw utilization methods impact soil carbon retention and humus composition for sustainable agricultural practices. The results showed that the straw biochar (BIO) had a significantly better long-term effect on increasing the proportion and stability of large soil aggregates compared to direct straw return (CS) and biochar-based fertilizer (BF). After ten years of continuous fertilization, the organic carbon content in soils treated with BIO was higher than that in soils treated with CS. After fifteen years of continuous fertilization, the organic carbon content in soils treated with BF was similar to that of the CS treatment. Additionally, humus carbon primarily accumulated in the 2–0.25 mm aggregates (SMA), and the BIO treatment significantly improved the quality of soil humus. FTIR spectra indicated that the long-term application of BIO and BF increased the proportion of aromatic carbon in the soil, enhancing the stability of soil organic carbon. Long-term application of carbonized straw returns improved soil organic carbon, aggregate stability, and humus quality, contributing to carbon sequestration. Fertilization duration directly and indirectly regulated humus formation through its impact on organic carbon and aggregates, while organic materials influenced humus indirectly. [ABSTRACT FROM AUTHOR]

Chemical composition of volcanic soils has been studied in the Southern Kuril Islands (Iturup, Kunashir, Shikotan), which undergo recurrently ash falls of mainly basic composition upon volcanic eruptions. The total content of metals (K, Ca, Mg, Na, Ba, Cu, Co, Cd, Cr, Fe, Mo, Ni, Pb, Sc, Sr, V, and Zn) and the concentrations of their mobile forms extracted by the ammonium acetate buffer at pH 4.80 have been determined. The total contents of Sc, V, Fe, and Zn are 1.5–5 times higher than their natural abundances in the upper layer of the Earth's crust (clarkes), whereas the contents of Cr, Ni, Sr, and Ba are 2–10 times lower. The soils show contrasting pH distribution (3.75–7.81) providing for the mobility of metals. The maximum activity of radial and lateral migration leading to radical differentiation of the genetic soil horizons by their chemical composition in different catenary positions is observed at low pH values; the coefficients of radial and lateral migration can rise up to 12 and 29, respectively. The results of factor analysis have revealed the leading role of soil-forming rocks in the formation of soil chemical composition (about 63% of sample variance); whereas humus formation, transformation of mineral and organic substances in soils, and hydrothermal activity exert a lesser effect. Soils formed on intermediate and mafic rocks of the Cenozoic volcanic massif are characterized by the Ca–Mg–Na paragenetic association; those formed on deposits of liparite–dacite complex are specified by the Ba–K–Pb–Mo association; on gabbroid rocks, by the Ni–Cr–Cu association; and on psammite, by the V–Sc–Fe–Co association. The Mo–Pb paragenesis is typical for the areas of current hydrothermal activity. The influence of placer formation on the chemical composition of soils in the coastal areas of Iturup and Shikotan Islands is shown. The distribution of mobile forms is associated with chelate-formation processes, geochemical barriers of acid–base, sorption, and redox types. Local soil pollution mainly related to the operation of motor vehicles has been identified. The areas of Krabozavodskoe and Yuzhno-Kuril'sk settlements show elevated concentrations of Ba, Sr and K due to the activities of fish processing plants; and the area of Kuril'sk city manifests elevated concentrations of Cr, Ni, Cu, Co, Zn and Pb, the source of which being the repair base. The calculated index of soil toxicity probability (MERMQ), as well as the results of biotesting for Daphnia magna and Chlorella vulgaris attest to the low soil toxicity. This is explained by the low population density and low economic development of the islands. [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]

Microplastics are pollutants of global concern nowadays. However, the effects of microplastics addition to soil as a carbon source and the combined effects of microplastics and organic fertilizer on soil-dissolved organic matter (DOM) evolution are still unclear. This study focused on the evolution of DOM in soil with the addition of microplastics and investigated the variations in the content and composition of DOM in unfertilized and fertilized soil with different particle sizes of microplastics. It was observed that the TOC concentration of the soil DOM in the treatment with organic fertilizer and microplastics increased more (129.97–161.43 mg kg−1) than that in the treatment with microplastics alone (117.17–131.87 mg kg−1) and was higher than that in the original soil (95.65 mg kg−1). According to the humic acid relative abundance in DOM after 40 days of incubation, the humic acid relative abundance in DOM of the soil samples with microplastics and organic fertilizers addition was found to be higher than that in those with microplastic addition alone, reaching more than 80% in a short time. In conclusion, the TOC concentration of the soil DOM increased with the addition of microplastics, and the increase was more pronounced when organic fertilizers and microplastics were added together. Moreover, the soil humification increased to a higher level in the short term with the combined addition of microplastics and organic fertilizers, which was maintained during the long-term incubation process. [ABSTRACT FROM AUTHOR]

The novel awareness of humic matter as supramolecular associations of relatively small heterogeneous molecules has gained a consensus following the progressively larger number of experimental evidence present in the literature. This new understanding has implied that the humic molecules may be separated from each other by a sequential fractionation and be analytically identified one by one, thereby increasing our knowledge on their molecular structure. A method called Humeomics was thus conceived to solubilize not only unbound small molecules but also those bound in ester and ether linkages and allow to separate less chemically complex fractions easier to characterize. Humeomics was first successfully applied to humic extracts from soil, and then, directly to cropped and uncropped soils to reach a more detailed understanding of the soil Humeome, that is the molecular composition of the totality of soil humic molecules. Based on the increasing knowledge of the soil Humeome and on the general literature findings, a new perception was developed for the significance of Humification. A body of experimental evidence reveals, in accordance with the supramolecular nature of humus, that humification, rather than being the progressive increase of molecular mass of humic substances via a presumed but highly unlikely energy-intense formation of new covalent bonds, is nothing else than the selective accumulation in soil of hydrophobic molecular materials. In fact, the biotic transformation of fresh organic matter in soil progressively consumes the easily accessible hydrophilic biomolecules, whereas the hydrophobic components are firstly associated to each other and then squeezed out of the soil solution, thus being separated from the degrading biota by a spontaneous physical-chemical drive. This primary mechanism of chemical hydrophobic protection justifies the accumulation and persistent stabilization of natural organic matter in the environment and well integrates the process of secondary physical protection, the only one called so far to account for the stability of humus in soil. This review collates the literature advances in the establishment of both the supramolecular paradigm of soil humus and the real significance of Humification of natural organic matter. [ABSTRACT FROM AUTHOR]

Direct evidence-based approaches are vital in understanding the involvement of abiotic/biotic factors and evaluating the newly proposed theories on soil carbon (C) stabilization. Microaggregates (150–250 μm) collected from a corn system (>22 years; Kansas, USA), which had been under no-till with different nitrogen (N) treatments were analyzed (N treatments: manure/compost, urea, zero fertilizer). We studied C stabilization in free soil microaggregates (with preserved aggregate architecture), directly using scanning transmission X-ray microscopy coupled with near edge X-ray absorption fine structure (STXM-NEXAFS) spectroscopy. Submicron scale findings were complemented with bulk chemical analysis. The STXM-NEXAFS analysis revealed soil organic carbon (SOC) preservation inside nano- and micro-pores and organo–mineral association, various degrees of humification, and high molecular diversity. The presence of microbial-derived C was found in manure-/compost-added microaggregates highlighting the contribution of organic amendments in facilitating microbial diversity. The incidence of aragonite-like minerals suggested the biologically/chemically active nature of microaggregate cores. Bulk analysis of free microaggregates showed a higher concentration of SOC (6.5%), ammonium oxalate extractable Fe/Al/Si), and higher aliphaticity of humic acid in manure-/compost-added soils compared to inorganic fertilizer (3% SOC) and control (2.7% SOC) treatments. The co-existence of elements (calcium [Ca]/C, iron [Fe]/N, Fe/C, aluminum [Al]/C, and silicon [Si]/C) was partially supported by bulk chemical analysis that indicated a strong association between ammonium oxalate extractable Fe/Al/Si and SOC (R² = 0.63—0.77). Overall, our study provided direct/indirect evidence for the complex and interactive involvement of chemical, mineralogical, and biological mechanisms that may have been stimulated by the long-term addition of compost/manure in stabilizing SOC. [ABSTRACT FROM AUTHOR]

The following study examines the content and composition of soil organic carbon (SOC), focusing on the fractions of humic and fulvic acids under different vegetation types in Ruy Mountain, located in SW Bulgaria. Soil samples from surface horizons (0--10 cm) were analyzed to determine the total carbon, organic carbon, and the ratio of humic to fulvic acids. Results show significant variation in SOC, with the highest levels in soil under Fagus sylvatica (beech) forests and the lowest under Pinus sylvestris (pine) forests. The humic to fulvic acid ratio suggests that soils under beech forests have a higher humification degree. The study highlights the influence of vegetation on SOC composition and the importance of conserving natural vegetation for soil health and carbon sequestration. [ABSTRACT FROM AUTHOR]

Glomalin-related soil proteins (GRSP) play a crucial role in strengthening soil structure and increasing carbon (C) storage. However, the chemical stability of GRSP and related arbuscular mycorrhizal fungi (AMF) community response to fertilization remains unclear. This study investigated C and nitrogen (N) contents, three-dimensional fluorescence characteristics in GRSP, and AMF properties based on a field experiment that was subjected to 29 years of various fertilizations. The experiment included treatments with no fertilizer (CK), chemical fertilizer (NPK), manure (M), and manure combined with NPK (NPKM) treatments. Results showed that GRSP contained 37–49% C and 6–9% N, respectively. Compared with CK and NPK, the C and N proportions in GRSP significantly increased under M and NPKM. Using the parallel factor model, four fluorescent components of GRSP were identified: one fulvic acid-like component (C2), one tyrosine-like component (C4), and two humic acid-like components (C1, C3). Under M and NPKM, the fluorescent intensity of C2 and C4 decreased, while the humification index (HIX) increased relative to CK and NPK, indicating that organic fertilization could enhance the stability of GRSP. The C and N proportion in GRSP positively associated with soil organic C (SOC), total N (TN), available phosphorus (AP), AMF biomass, and diversity, while C2 and C4 showed negative associations. Structural equation modeling further revealed that manure-induced changes in pH, SOC, TN, and AP increased AMF biomass and diversity, thereby altering GRSP composition and stability. This study provides valuable insights into the compositional traits of GRSP, contributing to sustainable soil management and C sequestration in agroecosystems. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) is involved in many biogeochemical processes and plays an important role in aquatic ecosystems. This study integrated three-dimensional fluorescence excitation–emission matrix (EEM), fluorescence regional integration (FRI), and parallel factor analysis (PARAFAC) to better understand the distribution and component characteristics of DOM in the Yongding River and explore the response of DOM to natural and anthropogenic activities. The results showed that the relative abundance of fulvic-like materials of DOM in the river was the highest, with an average of 68.64%. PARAFAC identified three fluorescent components, namely, C1 (microbial humic-like components), C2 (terrestrial humic-like components), and C3 (protein-like components), and their changes with flow confirmed that the riverine DOM was generally influenced by microbial sources and terrestrial inputs. The upper reaches showed strong autochthonous characteristics and a high humification degree of DOM due to a fast flow rate, while the middle reaches showed biological or aquatic bacterial origin due to a moderate flow rate. The lower reaches of the river showed characteristics of biological and bacterial origin, most strongly influenced by human activities. The findings can help provide a basis for identifying DOM characteristics in the Yongding River basin and understanding the geochemical cycle of DOM at a regional scale. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)