Variability Of Organic Matter Research Articles

Exploring soil pedogenesis through frequency-dependent magnetic susceptibility in varied lithological environments

AbstractThe use of percent frequency-dependent magnetic susceptibility (χfd%) is well-established for detecting superparamagnetic (SP) components in fine-grained soils and sediments. This study employs χfd% as a direct indicator of pedogenetic processes in soils from the Moroccan Rif region. Three soil transects (T1, T2, and T3), each comprising four soil cores with depths reaching 100 to 120 cm, were sampled from distinct lithological formations within an area subject to moderate to intense erosion. A total of 272 soil samples were collected and analyzed using MS2 Bartington Instruments, providing values to calculate χfd% and identify ultrafine ferrimagnetic minerals (SP, < 0.03 μm). In Quaternary fluvial terraces (T1) soils, approximately 60% of the samples indicate a mixture of SP, multidomain (MD), and Single Stable Domain (SSD) magnetic grains, while 30% contained coarser MD grains. Only 10% of the samples exhibit predominantly superparamagnetic (SP) grains. Soils on marly substrates (T2) showed 90% of samples with a combination of SP, MD, and SSD, and just 10% had SP grains. In contrast, soils from Villafranchian sandy deposits displayed χfd% values exceeding 10% in over 50% of samples, indicating that almost all iron components consist of SP grains. Physico-chemical analyses of the soils in profiles T1, T2, and T3 reveal distinct characteristics, including variations in clay content, organic matter, nutrient levels, and proportions of free and total iron. These results are important for understanding soil evolution and pedogenesis, with profiles T1 and T3 showing advanced development marked by high mineral iron, clay, and organic matter content. In contrast, profile T2 reflects a weak stage, influencing nutrient availability and contributing to overall soil dynamics in the respective profiles. The results of this study suggest that magnetic susceptibilities in these samples primarily originate from pedogenetic sources, revealing significantly advanced pedogenesis compared to T1 and T2 soils. The findings of this study align with previous research on soil erosion and degradation in the region, demonstrating that soils developed on terraces and marly substrates are more degraded and less stable than those on sandy substrates. This study underscores the utility of magnetic susceptibility as a rapid and effective indicator for initial soil assessment and gauging the degree of pedogenesis.

An in-depth Analysis of Soil Quality and Heavy Metal Contamination in the vicinity of the Visakhapatnam Municipal Solid Waste Dumpsite

The study conducts a comprehensive analysis of soil quality and heavy metal contamination in the vicinity of the Visakhapatnam Municipal Solid Waste Dumpsite, with a focus on the Gajuwaka municipality. The research addresses the escalating global concerns arising from improper waste disposal practices and their environmental repercussions. The Gajuwaka dumpsite, receiving diverse waste types, poses significant threats due to the leaching of heavy metals into the soil, impacting environmental components and human health. The study employs a robust experimental methodology involving soil sampling, metal extraction and Atomic absorption spectroscopy for elemental analysis. Waste characterization reveals the predominant presence of organic fractions and inert materials in the dumpsite. Seasonal physicochemical analysis of soil samples indicates variations in pH, moisture content, soil texture, organic matter and nutrient availability. Metal content generally decreases during the post-monsoon period. Phytotoxicity analysis of selected plant species demonstrates their capacity to accumulate heavy metals, particularly lead. The study emphasizes the urgent need for effective waste management practices, continuous soil monitoring and community engagement to mitigate environmental and health risks associated with waste dumping sites. The findings underscore the critical importance of sustainable waste management and environmental health. The study contributes valuable insights into the complex challenges posed by improper waste disposal practices and provides a foundation for the development of comprehensive strategies aimed at addressing environmental concerns.

Control of landscape position on organic matter decomposition via soil moisture during a wet summer

Sustainable cropland management requires preservation of soil organic matter (SOM). In spite of in depth understanding gained from ample field and laboratory studies, we have a poor understanding of landscape scale spatial variation of fresh organic matter (OM) decomposition and its conversion into soil organic carbon (SOC). Particularly, local topographic position may be expected to co-control these processes via soil hydrology. In this study, we sought to identify if such control is significant by setting up a field experiment with two contrasting positions across 10 gently sloping cropland fields covering three different soil texture groups, i.e. loamy sand, (sandy) loam and silt loam. We wanted to link OM decomposition to within-field differences in soil moisture, whilst keeping variation in other soil and management factors minimal. Specifically, mesocosms with 13C enriched ryegrass (the OM source) were incorporated in the fields for ten weeks and afterwards, soil was separated into > 500 µm, 53 – 500 µm and < 53 µm sized fractions. Overall, we found that lower located positions were wetter than higher positions with average differences of 11 %, 20 % and 16 % in water-filled pore space for the loamy sand, (sandy) loam and silt loam soil, respectively. Mineralization of added OM was surprisingly independent of landscape position, even though moisture conditions appeared wetter than optimal at the low but not at the high landscape positions. Remaining ryegrass residues > 500 µm did follow local topography-driven gradients in soil moisture with higher amounts in low landscape positions. In other words, drier conditions at high landscape positions improved coarse OM decomposition, with consequently more ryegrass-carbon (C) ending up in finer soil fractions (< 500 µm). Additionally, soil texture affected decomposition of the smallest fraction (< 53 µm) with a stabilizing effect for finer-textured (silt loam) soils. We conclude that, despite significant contrasts in moisture conditions between landscape positions, within-field spatial variability of OM mineralization was overall limited during the observed wet summer period. Nevertheless, landscape position affected the quality of remnant unmineralized C, with relatively more conversion of freshly added OM into OM associated with silt and clay at the drier higher positions, potentially improving the long-term stability of SOM. Likewise observations under different weather conditions are needed to evaluate the necessity of precise modelling of local soil hydrology for predicting SOC stock evolution on the landscape scale.

Shallow lake response to Holocene climate variation in south-central Minnesota, USA

Sedimentary deposits in lakes across the upper Midwest record the co-evolution of climate and biogeochemistry since the retreat of the Laurentide Ice Sheet at the end of the last glacial period. Here, we report on a Holocene lake sediment record from Chub Lake, a shallow (3 m depth) eutrophic lake system in south-central Minnesota. High-resolution elemental data from scanning XRF along with variations in organic matter, carbonate minerals, clastic material, biogenic silica, charcoal, and carbon isotopes reveal internally consistent patterns of hydroclimatic influence on this shallow lake system from 11,300 years BP to present. In particular, authigenic carbonate mineral formation and preservation in Chub Lake appears to be well suited as a moisture proxy beginning around 9700 BP up until ∼2300 BP, when a combination of more humid climates and basin-infilling change the hydrology of Chub Lake. This work emphasizes the importance of evaluating shallow lake sediment records both as important archives of climate proxies and case studies on how changing climates impact aquatic systems.

Bacterial Communities across Multiple Ecological Niches (Water, Sediment, Plastic, and Snail Gut) in Mangrove Habitats.

Microbial composition across substrates in mangroves, particularly in the Middle East, remains unclear. This study characterized bacterial communities in sediment, water, Terebralia palustris snail guts, and plastic associated with Avicennia marina mangrove forests in two coastal lagoons in the Sea of Oman using 16S rDNA gene MiSeq sequencing. The genus Vibrio dominated all substrates except water. In the gut of snails, Vibrio is composed of 80-99% of all bacterial genera. The water samples showed a different pattern, with the genus Sunxiuqinia being dominant in both Sawadi (50.80%) and Qurum (49.29%) lagoons. There were significant differences in bacterial communities on different substrata, in particular plastic. Snail guts harbored the highest number of unique Operational Taxonomic Units (OTUs) in both lagoons, accounting for 30.97% OTUs in Sawadi and 28.91% OTUs in Qurum, compared to other substrates. Plastic in the polluted Sawadi lagoon with low salinity harbored distinct genera such as Vibrio, Aestuariibacter, Zunongwangia, and Jeotgalibacillus, which were absent in the Qurum lagoon with higher salinity and lower pollution. Sawadi lagoon exhibited higher species diversity in sediment and plastic substrates, while Qurum lagoon demonstrated lower species diversity. The principal component analysis (PCA) indicates that environmental factors such as salinity, pH, and nutrient levels significantly influence bacterial community composition across substrates. Variations in organic matter and potential anthropogenic influences, particularly from plastics, further shape bacterial communities. This study highlights the complex microbial communities in mangrove ecosystems, emphasizing the importance of considering multiple substrates in mangrove microbial ecology studies. The understanding of microbial dynamics and anthropogenic impacts is crucial for shaping effective conservation and management strategies in mangrove ecosystems, particularly in the face of environmental changes.

Abrupt shift in the organic matter input to sediments in Lake Liangzi, a typical macrophyte-dominated shallow lake in Eastern China, and its response to anthropogenic impacts

Understanding the historical variations in organic matter (OM) input to lake sediments and the possible mechanisms regulating this phenomenon is important for studying carbon cycling and burial in lake systems; however, this topic remains poorly addressed for macrophyte-dominated lakes. To bridge these gaps, we analyzed bulk OM and molecular geochemical proxies in a dated sediment core from Lake Liangzi, a typical submerged macrophyte-dominated lake in East China, to infer changes in OM input to sediments over the past 169 years due to the intensification of human activities in the catchment. A relatively primitive OM input pattern was observed in ca. 1841–1965, during which the lowest hydrogen index (HI), short-chain n-alkane abundance, and n-C17/n-C16 alkane indicated minimal input from phytoplankton, whereas the high Paq (proxy of aquatic macrophyte input) and long-chain n-alkane abundance suggested dominant and subordinate inputs from submerged and emergent macrophytes, respectively. OM input transitioned during ca. 1965–1993, with the highest Paq and lowest long-chain n-alkane abundance, indicating an increase of submerged macrophyte input and concurrent decline of emergent macrophyte input, probably caused by hydrological regulation practices and land reclamation in the 1960s, respectively. A further shift in OM input was observed since ca. 1993, characterized by the beginning of an increase in phytoplankton input, as indicated by the greater HI, short-chain n-alkane abundance, and n-C17/n-C16 alkane in sediments. Moreover, a lower Paq and higher abundance of long-chain n-alkanes indicated a decline in input from submerged macrophytes and an elevated input from terrestrial plants. The increase in αβ-hopane abundance and homohopane index value indicated that petroleum-sourced OM was first introduced into the sediments. The causes of these OM input changes included nutrient influx associated with domestic and industrial discharge, aquaculture within the lake, and widespread deforestation and land clearance in the catchment.

Spatial patterns of organic matter content in the surface soil of the salt marshes of the Venice Lagoon (Italy)

Abstract. Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity.

AI can empower agriculture for global food security: challenges and prospects in developing nations.

Food and nutrition are a steadfast essential to all living organisms. With specific reference to humans, the sufficient and efficient supply of food is a challenge as the world population continues to grow. Artificial Intelligence (AI) could be identified as a plausible technology in this 5th industrial revolution in bringing us closer to achieving zero hunger by 2030-Goal 2 of the United Nations Sustainable Development Goals (UNSDG). This goal cannot be achieved unless the digital divide among developed and underdeveloped countries is addressed. Nevertheless, developing and underdeveloped regions fall behind in economic resources; however, they harbor untapped potential to effectively address the impending demands posed by the soaring world population. Therefore, this study explores the in-depth potential of AI in the agriculture sector for developing and under-developed countries. Similarly, it aims to emphasize the proven efficiency and spin-off applications of AI in the advancement of agriculture. Currently, AI is being utilized in various spheres of agriculture, including but not limited to crop surveillance, irrigation management, disease identification, fertilization practices, task automation, image manipulation, data processing, yield forecasting, supply chain optimization, implementation of decision support system (DSS), weed control, and the enhancement of resource utilization. Whereas AI supports food safety and security by ensuring higher crop yields that are acquired by harnessing the potential of multi-temporal remote sensing (RS) techniques to accurately discern diverse crop phenotypes, monitor land cover dynamics, assess variations in soil organic matter, predict soil moisture levels, conduct plant biomass modeling, and enable comprehensive crop monitoring. The present study identifies various challenges, including financial, infrastructure, experts, data availability, customization, regulatory framework, cultural norms and attitudes, access to market, and interdisciplinary collaboration, in the adoption of AI for developing nations with their subsequent remedies. The identification of challenges and opportunities in the implementation of AI could ignite further research and actions in these regions; thereby supporting sustainable development.

Three-dimensional space and time mapping reveals soil organic matter decreases across anthropogenic landscapes in the Netherlands

For restoring soil health and mitigating climate change, information of soil organic matter is needed across space, depth and time. Here we developed a statistical modelling platform in three-dimensional space and time as a new paradigm for soil organic matter monitoring. Based on 869 094 soil organic matter observations from 339,231 point locations and the novel use of environmental covariates variable in three-dimensional space and time, we predicted soil organic matter and its uncertainty annually at 25 m resolution between 0–2 m depth from 1953–2022 in the Netherlands. We predicted soil organic matter decreases of more than 25% in peatlands and 0.1–0.3% in cropland mineral soils, but increases between 10–25% on reclaimed land due to land subsidence. Our analysis quantifies the substantial variations of soil organic matter in space, depth, and time, highlighting the inadequacy of evaluating soil organic matter dynamics at point scale or static mapping at a single depth for policymaking.

Climate and soil factors co-derive the functional traits variations in naturalized downy thorn apple (Datura innoxia Mill.) along the altitudinal gradient in the semi-arid environment

Plant functional traits are consistently linked with certain ecological factors (i.e., abiotic and biotic), determining which components of a plant species pool are assembled into local communities. In this sense, non-native naturalized plants show more plasticity of morphological traits by adopting new habitat (an ecological niche) of the invaded habitats. This study focuses on the biomass allocation pattern and consistent traits-environment linkages of a naturalized Datura innoxia plant population along the elevation gradient in NW, Pakistan. We sampled 120 plots of the downy thorn apple distributed in 12 vegetation stands with 18 morphological and functional biomass traits during the flowering season and were analyzed along the three elevation zones having altitude ranges from 634.85 m to 1405.3 m from sear level designated as Group I to III identified by Ward's agglomerative clustering strategy (WACS). Our results show that many morphological traits and biomass allocation in different parts varied significantly (p < 0.05) in the pair-wise comparisons along the elevation. Likewise, all plant traits decreased from lower (drought stress) to high elevation zones (moist zones), suggesting progressive adaptation of Datura innoxia with the natural vegetation in NW Pakistan. Similarly, the soil variable also corresponds with the trait's variation e.g., significant variations (P < 0.05) of soil organic matter, organic carbon, Nitrogen and Phosphorus was recorded. The trait-environment linkages were exposed by redundancy analysis (RDA) that was co-drive by topographic (elevation, r = −0.4897), edaphic (sand, r = -0.4565 and silt, r = 0.5855) and climatic factors. Nevertheless, the influences of climatic factors were stronger than soil variables that were strongly linked with elevation gradient. The study concludes that D. innoxia has adopted the prevailing environmental and climatic conditions, and further investigation is required to evaluate the effects of these factors on their phytochemical and medicinal value.

Identification of acetic acid levels in ecoenzyme from organic materials of orange peel with acid-base titration method

This study aimed to elucidate the comparison of the levels of acetic acid and the pH of the ecoenzymes from organic matter variations of sweet and sour orange peels. The acetic acid is an organic compound containing a carboxylic acid group which is also widely applied in the health and industrial fields. Preparation of acetic acid from substrate products containing ethanol which can be obtained from fruit ingredients including oranges. One of the uses and management of organic waste, including vegetables and fruit, is by making ecoenzymes from fruit peels with a mixture of water and sugar. Fruit peels that can be used as organic ecoenzyme ingredients vary widely, so the content in ecoenzymes becomes very diverse and tends to be unstable. This type of research is descriptive. This study consisted of three stages, namely the manufacture of ecoenzymes from pasaman orange peel, gunung omeh, kaffir lime and lime in 7 variations (for 100 days), measurement of acetic acid levels and pH in the ecoenyzme samples for 14 days and 100 days. Acetic acid levels were determined using the acid-base titration method. The results of this study showed that the highest levels of acetic acid ecoenzyme in the 100-day fermentation were 5.53% in the sour orange group, while the lowest in the mixed ecoenzyme was 3.32%. The most acidic ecoenzyme pH was at 100 days of fermentation (pH ±3.5).

Variations of Soil Organic Matter and Nutrients in Diverse Hilly Soils of Bandarban, Bangladesh

Functioning and positive interactions in an ecosystem depend on physical and chemical features of soil, along with nutrient status. These soil nutrients are vital for the growth and development of plants, playing a crucial role in various essential functions. The current study investigates the dynamic changes in soil nutrient patterns across different land use scenarios and soil depths at Bandarban Sadar Upazila, Chittagong Hill Tracts, Bangladesh. The research focuses on how soil nutrient levels are distributed in two soil depths (0-15 cm and 15-30 cm) among three different land use practices, such as forest land, agricultural land and barren land. About 90 soil samples from the study area were collected using a stratified random sampling design. The analysis reveals significant variations in soil pH, organic matter (OM), total nitrogen (TN), phosphorus (P), potassium (K), and sulfur (S) levels among these land use types and soil depths. The findings revealed that agricultural land typically exhibited higher levels of soil S content and pH, in contrast to forested areas where OM, TN, P, and K levels were comparatively more abundant. Again, barren land showed a relatively higher pH and S content than agricultural land and forest land. Additionally, the topsoil (0-15 cm) generally showed higher nutrient content than the deeper soil layer (15-30 cm). The investigation uncovered significant positive correlations of OM with soil nutrients such as TN, P, K &amp; S, indicating mutual influences on their availability. Overall, the research outcomes emphasize the importance of sustainable land management practices to maintain soil fertility and optimize soil productivity in this ecologically significant region.

Spatial variation of soil organic matter and metal mobility in wetland soils: Implications for biogeochemical processes in lateritic landscape

The evolution of the lateritic landscape over time changes the path of pedogenesis and soil hydrology. The occurrence of upland wetlands in the savannah flat plateau transforms well-drained lateritic soils into hydric soils enriched in organic matter. We investigated the composition of soil organic matter (SOM) produced in a wetland and their link with the mineral constituents of soil and their contribution to the mobility of Si, Fe, and Al in the soil. Six tranches were opened in a soil catena located from the plateau toward the center of the wetland, representing different hydromorphic features. Soil morphology was described, and chemical, physical and mineralogical analyses were performed to evaluate soil properties. Chemical fractionation of Soil Organic Matter (SOM) was performed and total organic carbon (TOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and water-extractable organic matter (WEOM) were determined in the soil horizons. Metal complexing properties of DOM were determined using an excitation-emission matrix of fluorescence. The occurrence of Fe eluviation in the superficial horizons, Fe2O3 enrichment in the mottled horizons, and ferricrete formation in the center of the wetland were observed. Geochemical transfer assessment and the variation of oxides within the horizons showed that Fe2O3 and SiO2 were more mobile than Al2O3, whose variability in the gley horizon reflected the mobility of Fe2O3 and SiO2. The stability constants of Al and Cu showed an increase with the depth for WEOM and SOM. The pattern of the organic carbon fraction varied according to the level of hydromorphy and soil depth. It was also observed an increase in the C/N ratio with depth, possibly related to the reduced bioavailability of DOC due to its adsorption with soil solids.

Downslope Weakening of Soil Revealed by a Rapid Robotic Rheometer

AbstractMoving down a hillslope from ridge to valley, soil develops and becomes increasingly weathered. Downslope variation in clay content, organic matter, and porosity should produce concomitant changes in soil strength that influence slope stability and erosion. This has yet to be demonstrated, however, because in situ measurements of soil rheology are challenging and rare. Here we employ a robotic leg as a mechanically sensitive and time‐efficient penetrometer to map soil strength along a canonical temperate hillslope profile. We observe a systematic downslope weakening, and increasing heterogeneity, of soil strength associated with a transition from sand‐rich ridge materials to cohesive valley bottom soil aggregates. Weathering‐induced changes in soil composition lead to physically distinct mechanical behaviors in cohesive soils that depart from the behavior observed for sand. We also demonstrate the promise that legged robots may use their limbs to sense and improve mobility in complex environments, with implications for planetary exploration.

Fractionation of stable boron isotopes in alfisols: Application of a novel tool for tracing boron behavior in two soil profiles

Available boron (AB) and total boron (TB) in soil have distinct isotopic values, which are mainly influenced by the pH, organic matter and clay minerals, and can be used to explore the chemical behaviors of boron (B) in adsorption, weathering and eluviation processes. The B isotopic compositions of AB and TB in brown soil (slightly acidic) and cinnamon soil (neutral to slightly alkaline) profiles were investigated by multicollector inductively coupled plasma mass spectrometry. Variations in pH value and organic matter in the two soils directly affected the adsorption of B isotopes (dissolved 11B(OH)3 or 10B(OH)4-) in the aqueous solution, as shown by AB having an average negative δ11B value of −1‰ and a great range of −10.83‰ to +8.32‰ in the cinnamon soil. Furthermore, the long-term effects of adsorption and transportation processes were evidenced by the large range of δ11BTB values (-24.22‰ to +21.07‰) in the two soils. The topsoil layers with more organic matter and higher δ11B values indicated that B isotope fractionation occurred as a result of the input of rainfall, recycling of plant litter and the adsorption of organic matter and clay minerals. The lower δ11B values, the higher B contents and the element ratios in the underlying layers resulted from the weathering of different minerals and the adsorption of AB in the leaching process. This finding is supported by the relationship between AB and the clay/silt ratio, with more negative δ11B values being associated with finer clay particles via the adsorption of 10B(OH)4- in a weakly alkaline soil solution. The δ11B values in soils may be a useful tool for distinguishing geochemical cycling and processes and characterizing long-term processes that are difficult to assess.

Molecular compositional variation of organic matter deposited on the East Tasman Plateau during the Paleocene–Eocene thermal maximum

Molecular compositional variation of organic matter deposited on the East Tasman Plateau during the Paleocene–Eocene thermal maximum

Comparative analysis of soil organic matter fractions, lability, stability ratios, and carbon management index in various land use types within bharatpur catchment, Chitwan District, Nepal

BackgroundLand use and land cover changes have a significant impact on the dynamics of soil organic matter (SOM) and its fractions, as well as on overall soil health. This study conducted in Bharatpur Catchment, Chitwan District, Nepal, aimed to assess and quantify variations in total soil organic matter (TSOMC), labile organic matter fraction (CL), stable organic matter fraction (CS), stability ratio (SR), and carbon management index (CMI) across seven land use types: pastureland, forestland, fruit orchards, small-scale conventional agricultural land, large-scale conventional agricultural land, large-scale alternative fallow and conventional agricultural land, and organic farming agricultural land. The study also explored the potential use of the Carbon Management Index (CMI) and stability ratio (SR) as indicators of soil degradation or improvement in response to land use changes.ResultsThe findings revealed significant differences in mean values of TSOMC, CL, and CS among the different land use types. Forestland and organic farming exhibited significantly higher TSOMC (3.24%, 3.12%) compared to fruit orchard lands (2.62%), small scale conventional farming (2.22%), alternative fallow and conventional farming (2.06%), large scale conventional farming (1.84%) and pastureland (1.20%). Organic farming and Forestland also had significantly higher CL (1.85%, 1.84%) and CS (1.27%, 1.39%) compared to all other land use types. Forest and organic farming lands showed higher CMI values, while pastures and forests exhibited higher SR values compared to the rest of the land use types.ConclusionsThis study highlights the influence of various land use types on soil organic matter pools and demonstrates the potential of CMI and SR as indicators for assessing soil degradation or improvement in response to land use and land cover changes.

High stability of autochthonous organic matter in inland aquatic ecosystems

Recalcitrant dissolved organic matter (RDOM) is a key component of ocean carbon sinks and it can be preserved in seawater for thousands of years. However, the fate of RDOM derived from the primary production in inland lake is unclear. In this study of Erhai lake in China, used the combination of δ13C, carbon/nitrogen (C/N) ratio, and optical spectroscopy analyses to constrain the variation of organic matter in the vertical direction (i.e., lake water → trap sediments → surface sediments → core sediments), to trace the burial process of RDOM. Two autochthonous components (C1, C2) and two allochthonous components (C3, C4) were identified in the water. High concentrations of C2 in winter and spring indicate that these two seasons provide favourable burial conditions for autochthonous dissolved organic matter. Three autochthonous components (C1, C2, C5) and three allochthonous components (C3, C4, C6) were identified in the sediments. The contributions of autochthonous organic matter were ∼49.9 ± 5.84 % (based on PARAFAC analysis) and ∼56.7 ± 5.62 % (based on the C/N ratio) in the sediment trap samples; 43.4 ± 8.84 % (based on PARAFAC analysis) and 40.8 ± 14.26 % (based on the C/N ratio) in the surface sediments; and 44.5 ± 14.4 % (based on PARAFAC analysis) and 48.4 ± 6.04 % (based on the C/N ratio) in the core sediments. Additionally, C2, which is the autochthonous component after microbial mineralisation, was preserved as a significant part of the RDOM in the water. Our results suggest that the mineralisation of autochthonous organic matter (OM) in the core sediments did not promote bacterial mineralization, and that the burial of OM on long timescales dependents primarily on its concentration rather than on its origin. Our results provide a new perspective for studying the stability of autochthonous OM and highlight a new direction for the study of the carbon sink of inland lakes.

Mapping Soil Organic Matter Using Different Modeling Techniques in the Dryland Agroecosystem of Huang-Huai-Hai Plain, Eastern China

Accurately mapping the spatial distribution and variation of soil organic matter (SOM) is of great significance for guiding regional soil management. However, the applicability and prediction performance of machine learning techniques in dryland agroecosystems still needs to be further studied. In this study, we collected a total of 733 topsoil samples from the farmland in Xiao County, Anhui Province, which is a typical dryland agroecosystem in the Huang-Huai-Hai Plain. Then, the environmental covariates were selected, and the ordinary kriging (OK), multiple linear stepwise regression (MLR), regression kriging (RK), radial basis function neural network (RBFNN), and random forest (RF) models were conducted to map the SOM content, and the optimal model was ascertained. The results demonstrated that the alkali-hydrolyzable nitrogen (26.11%), available potassium (17.73%), mean annual precipitation (13.26%), and pH (11.80%) were the main controlling factors affecting the spatial distribution of SOM in the study area. Meanwhile, the introduction of environmental covariates can effectively improve the SOM prediction accuracy, and the RF model (R2 = 0.48, MAE = 2.38 g kg−1, MRE = 12.99%, RMSE = 3.14 g kg−1) has a better performance than the RFBNN, MLR, RK, and OK methods. Although there are local differences in the spatial distribution of SOM predicted by the five methods, the overall spatial distribution of SOM was characterized by the low concentration area (13.44–20.00 g kg−1) distributed in the central and northwest of study area, and the high concentration area (24.00–28.95 g kg−1) distributed in the southeast. Overall, our study demonstrated that machine learning-based models could accurately predict the SOM content in dryland agroecosystem, and the produced maps function as baseline maps for sustainable agricultural management.

Effect of forest-based biochar on maturity indices and bio-availability of heavy metals during the composting process of organic fraction of municipal solid waste (OFMSW)

The main objective of this study was to investigate the effect of biochar on the composting process of the organic fraction of municipal solid waste (OFMSW) under real conditions. Different doses of biochar (1%, 3%, and 5%) were mixed with compost piles to evaluate the variation of temperature, moisture content (MC), organic matter (OM), carbon (C), nitrogen (N), C/N ratio, and heavy metal (HM) contents in comparison with the control treatment (with 0% biochar addition). The results of this study showed that the compost piles combined with different doses of biochar had higher MC. The use of biochar as an additive, even at low doses (1%), was able to increase the compost quality through the reduction of N losses during the composting process. The highest reduction of OM during the composting process was observed in the control pile (without biochar addition) by 48.06%, whereas biochar affected the biodegradability of OM and prevented the reduction of nutrients during the composting process under real conditions. The contents of HMs (Pb, Zn, Ni, Cd, and Cu) showed a significant reduction in all of the compost piles combined with biochar in comparison with the control treatment. Considering that in terms of all compost quality indicators, the piles combined with biochar can regarded as high standard product, the composts obtained from combining the OFMSW with different biochar doses have desirable features to be used as an amendment agent to improve agricultural soil quality.