Quality Of Organic Matter Research Articles

Characterizing photochemical production carboxyl content of dissolved organic matters using absorbance spectroscopy combined with FT-ICR MS

Irradiation can significantly impact the structure, reactivity and environmental behavior of dissolved organic matter (DOM). The extent of these processes remains to be ascertained in more detail but the heterogeneity and site-specificity of DOM, and the lack of methods to characterize DOM at its environmentally-relevant concentrations make it a challenge. In this study, the differences of DOM response to photodegradation in four typical origins (i.e., surface water, sediment and intracellular and extracellular algal DOM) were tracked on the molecular-level using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Changes of the carboxyl and phenolic DOM moieties induced by irradiation were quantified by spectroscopic titrations, and the mechanism of functional groups affecting the changes of specific molecular composition was qualitatively proposed. The results demonstrated that intracellular algal organic matter (I-DOM) was most susceptible to photodegradation (ca. 63% DOM loss), then came extracellular algal organic matter (E-DOM) and surface water DOM (W-DOM) (ca. 15% DOM loss). Sediment DOM (S-DOM) was most resistant to irradiation, with a very small level of its mineralization. Lipids, lignin-like compounds and tannin-like compounds in I-DOM and E-DOM were relatively photo-labile. The photodegradation of lipids was related to the decarboxylation of carboxyl functional groups, while the photodegradation of tannin-like compounds was related to the rupture of phenolic functional groups. In comparison, the molecular composition of W-DOM and S-DOM was less affected by irradiation, which was also reflected in the fact that the carboxyl and phenolic functional groups were highly photo-resistant. This study showed that the photoactivity of DOM in surface water was closely related to the abundance of algae, so controlling the excessive reproduction of algae may have a positive effect on stability of quality and quantity of organic matter in surface water.

Marine and Not Terrestrial Resources Support Nearshore Food Webs Across a Gradient of Glacial Watersheds in the Northern Gulf of Alaska

Estuaries are among the most productive ecosystems on Earth, yet they are at risk in high-latitude regions due to climate-driven effects on the connected terrestrial and marine realms. Northern Hemisphere warming exceeds the global average and accelerates the melting of glaciers. As a result, the magnitude of freshwater discharge into estuaries may increase during the peak in glacial meltwater, ultimately affecting the riverine flux of organic matter (OM) from the land to coastal environments and food webs within. We investigated the extent to which terrestrial OM subsidizes nearshore food webs in northern Gulf of Alaska watersheds and if differences in the relative proportion of terrestrial versus marine OM supporting these food webs are explained by watershed glacial cover and/or by seasonal glacial discharge regimes. A stable isotope mixing model was employed to determine the contribution of marine (phytoplankton, macroalgae) and terrestrial (vascular plant) sources to the diets of grazing/detritivore and filter/suspension-feeding coastal invertebrates at the outflows of watersheds of varying glacial influence and across three distinct discharge periods. Additionally, a distance-based redundancy analysis was conducted to investigate the effects of watershed-characteristic (e.g., slope, vegetation cover) sourcing and transport of terrestrial OM on consumer diets. The diets of both feeding groups were predominantly marine (> 90%) and varied little among estuarine study sites at watersheds of different glacial cover or glacial discharge periods. Our findings suggest that terrestrial OM is not readily used by nearshore food webs in this productive study system, presumably due to the high quantity and quality of available marine OM.

The effect of shrubs admixture in pine forest stands on soil bacterial and fungal communities and accumulation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent toxic pollutants. The species composition of the stand is important in shaping the quality of soil organic matter and, consequently, the PAH content. The main purpose of the research was to determine the role of shrubs in shaping PAH accumulation in forest soils. The study covered the soils of the pine stands of the Rybnik Forest District, which experiences some of the highest deposition of industrial emissions in Europe. Pine stands with admixture of shrubs (alder buckthorn Frangula alnus and European hazelnut Coryllus avellana) growing in the same soil conditions were selected for the study. Samples for analyses were collected from the organic horizon (O) (from a depth of 0–7 cm) and humus mineral horizon (A) (from a depth of 7–15 cm). The organic C and total N concentrations, pH, alkaline cation content, soil enzyme activity and PAH content were determined. Additionally, the taxonomic composition of soil bacterial and fungal communities was determined. The highest activity of enzymes was noted in soils under influence of shrubs. The enzymatic activity was positively correlated with the content of total N, organic C, pH H2O and KCl and negatively with the C/N ratio. The highest PAH content was recorded in the soils of pine stands without the admixture of shrubs. Our research indicates the importance of shrubs in shaping the properties of surface horizons of forest soil and, consequently on the accumulation of PAHs. Shrubs stimulate biochemical activity of soils which results in lower PAHs accumulation by providing more easily decomposable organic matter.

Impacts of agricultural drainage on the quantity and quality of tropical peat soil organic matter in different types of forests

Tropical peatlands serve as huge carbon (C) pools in the global C balance, and degradation due to agricultural use is a major concern. The objective of the present study was to examine the relationship between the C loss rate in agriculturally drained tropical peat soils in relation to groundwater level (GWL) and the chemical structure of the resulting soil organic matter (SOM). Soil mesocosms containing three peat soils collected from three forest types in Malaysia, Mixed peat swamp (MPS), Alan Batu (ABt), and Alan Bunga (ABg) forests, which are classified based on dominant plant species, species diversity, and forest structure, were buried in an oil palm plantation for a period of five years. Soil samples packed in the top layer (0–20 cm depth) and the bottom (60–80 cm depth) layer were then analyzed and the results were compared with the initial values for these soils. Weight loss, total C and N contents, ash content, and pyrophosphate solubility index (PSI; an index of the degree of humification) were measured. Changes in the chemical structure of the SOC were investigated using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy with phase-adjusted spinning side bands and thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry (THM-GC/MS). The C loss in the MPS forest soil, 2–12%, was smaller than that in the ABt and ABg forest soils, 20–37%, especially in the bottom layer. The higher C loss in the ABt and ABg soils, without significant difference between the top and bottom layers, can be attributed to the greater accumulation of less decomposed plant components as evidenced by the larger yields of lignin-derived phenols and polysaccharide-related compounds in THM-GC/MS analysis. The C composition as estimated by 13C NMR did not vary during incubation of the ABt and ABg soils while the yields of lignin-derived and other phenols as well as polysaccharide-related compounds in THM-GC/MS were decreased, especially in the top layer. These findings suggest that plant components with a low degree of decomposition are susceptible to drainage regardless of their structure. The progression of the oxidative degradation of lignin in the top layer of all soils was also suggested by the increases in PSI and the vanillic acid/vanillin ratio. The % O-alkyl C and % alkyl C may control the rate of C loss positively and negatively, respectively. PSI also appears to be useful for roughly estimating the decomposability of tropical peat SOM in various GWLs.

Anthropogenic land uses influence stream dissolved organic matter quality more than decomposition rates and macroinvertebrate diversity

In the era of the Anthropocene, streams and rivers are among the most heavily impacted ecosystems due to the influence of catchment land use on stream water quality and ecological condition. In practice, structural and functional indicators collected by biomonitoring programs are underused and thus limited in their ability to offer practical insight into functional-based restoration approaches. Here we applied a novel combination of indicators—cotton strip decomposition, benthic invertebrate sampling together with dissolved organic matter (DOM) composition — to determine if streams highly impacted by urbanized and agricultural land use across Windsor-Essex (southwestern Ontario, Canada) were consistent across season, anthropogenic land use or some combination of both. Overall, our results suggest that urbanized and agricultural streams are indeed degraded at a similar level, with high decomposition rates and low levels of macroinvertebrate diversity. Moreover, DOM quality proved to be the most predictable indicator spatially and seasonally, integrating insights from both decomposition and macroinvertebrate indices. Microbial humic-like DOM correlated positively with decomposition rates, and negatively with invertebrate species richness. Our findings show that functional changes in stream ecological condition can be effectively tracked by structural indicators, namely DOM composition. DOM offers a cost-effective approach to assessing ecosystem health and should be explored as a reliable indicator in monitoring programs and to inform functional-based indicators in ecosystem restoration.

Dissolved Carbon Concentrations and Emission Fluxes in Rivers and Lakes of Central Asia (Sayan–Altai Mountain Region, Tyva)

The carbon (C) cycle in inland waters, including carbon concentrations in and carbon dioxide (CO2) emissions from water surfaces, are at the forefront of biogeochemical studies, especially in regions strongly impacted by ongoing climate change. Towards a better understanding of C storage, transport and emission in Central Asian mountain regions, an area of knowledge that has been extremely poorly studied until now, here, we carried out systematic measurements of dissolved C and CO2 emissions in rivers and lakes located along a macrotransect of various natural landscapes in the Sayan–Altai mountain region, from the high mountains of the Western Sayan in the northwest of Tyva to the arid (dry) steppes and semideserts in the intermountain basins in the southeast of Tyva on the border with Mongolia. New data on major hydrochemical parameters and CO2 fluxes (fCO2) gathered by floating chambers and dissolved organic and inorganic carbon (DOC and DIC, respectively) concentrations collected over the four main hydrological seasons allowed us to assess the current C biogeochemical status of these water bodies in order to judge possible future changes under climate warming. We further tested the impact of permafrost, river watershed size, lake area and climate parameters as well as ‘internal’ biogeochemical drivers (pH, mineralization, organic matter quality and bacterial population) on CO2 concentration and emissions in lakes and rivers of this region and compared them with available data from other subarctic and mountain settings. We found strong environmental control of the CO2 pattern in the studied water bodies, with thermokarst lakes being drastically different from other lakes. In freshwater lakes, pCO2 negatively correlated with O2, whereas the water temperature exerted a positive impact on pCO2 in large rivers. Overall, the large complexity of counteracting external and internal drivers of CO2 exchange between the water surfaces and the atmosphere (CO2-rich underground DIC influx and lateral soil and subsurface water; CO2 production in the water column due to dissolved and particulate OC biodegradation; CO2 uptake by aquatic biota) precluded establishing simple causalities between a single environmental parameter and the fCO2 of rivers and lakes. The season-averaged CO2 emission flux from the rivers of Tyva measured in this study was comparable, with some uncertainty, to the C uptake fluxes from terrestrial ecosystems of the region, which were assessed in other works.

Spatial-temporal variation of soil organic matter decomposition potential in China

Soil organic matter decomposition is an essential process of the ecosystem biogeochemical cycle. However, the comprehension of soil organic matter decomposition mechanisms at a large-scale level remains relatively inadequate, especially due to the high variability in organic matter quality, which poses challenges for standardized analysis of decomposition. Therefore, in this study, standardized cotton strips (to represent cellulose) and wooden sticks (to represent lignin) were used to conduct field research on the decomposition potential of soil organic matter, comparing the mass loss of these standardized materials across 23 sites situated in different climate types in China. After 6 months of incubation, the decomposition rate of both substrates displayed an increasing trend from north to south and a decreasing trend from east to west, driven by variations in temperature and precipitation at a large scale. However, the decomposition pattern of wooden sticks along the latitude exhibited a reversal during summer, with a positive correlation between mass loss per unit temperature and latitude, possibly attributable to reduced constraints on decomposer activity at high latitudes in summer. These results suggest that the decomposition ability of decomposers is more powerful at high latitudes compared with the decomposers at low latitudes. Random forest analysis showed that decomposers, soil conditions and climate had significant effects on the decomposition of standardized organic matter at the large-scale. Notably, as decomposition progressed, the relative influence of the decomposers on the cotton strips mass loss significantly increased, while for wooden sticks, the relative influence of climate significantly increased. In summary, this study provides crucial evidence for the spatial characteristics and temporal dynamics of soil organic matter decomposition in large-scale patterns.

Pedobiological properties of a lignite spoil heap in the Provence coal mine basin (south-east of France)

The aim of this study was to investigate the bio-physico-chemical properties of soils developed on dumps originating from lignite extraction and to decipher the respective roles of the geomorphology and the presence of lignite on the biogeochemical characteristics of these soils. Soils from the Armand spoil heap, located in Peypin (Bouches-du-Rhône, France), and natural neighboring Mediterranean soils without lignite were sampled and compared. Lignite presence was assessed by 13C CPMAS NMR spectroscopy allowing for the quantification of C pools such as aromatic C groups, which are characteristic signature of lignite. Physico-chemical (texture, pH, organic C, carbonate, total N, total S, CEC), mineralogical and biological (enzyme activities: β-glucosidase, arylsulfatase, acid phosphatase, arylamidase, lipase and fluorescein diacetate hydrolase; Oxitop basal respiration and Biolog® catabolic profile) parameters were analyzed in the two types of soil. Microbial activities were higher in the natural soils than in the spoil heap soils, while spoil heap samples exhibited enriched aromatic-C pools. Some variables exhibited a gradient along the slope: carbonate and sand contents were larger at the bottom of the heap while clay content, CEC, organic C and C/N ratio were larger at the top of the heap. On the contrary, microbiological activities did not follow any structured pattern according to the slope and appeared distributed as patches. Variance partitioning combined with multiple linear regressions demonstrated that the 13C NMR quality of soil organic matter was the main structuring factor of microbial properties, which were in most cases reduced by the presence of lignite.

Assessment of kerogen types and source rock potential of Lower Jurassic successions in the Mandawa Basin, SE Tanzania

Variability in organic matter types and quality of source rock intervals across evolving rift-basins has been the focus of previous studies, which have shown that due to dynamic sedimentary regimes and water depths such source intervals occur sporadically and restricted to specific stratigraphic horizons. Such heterogeneous settings require detailed geochemical analysis to document variations in source quality. This study presents a comprehensive geochemical analysis of source rock intervals in Lower Jurassic successions (Mbuo, Nondwa and Mihambia Formations) in the Mandawa Basin, on-shore Tanzania, in order to constrain organic matter types and quality. Organic matter richness was measured by Total Organic Carbon (TOC) analysis, while quality and thermal maturity of organic matter was assessed by programmed pyrolysis, complemented by organic carbon isotope analysis (δ13Corg) of sediment samples collected from outcrops, cores, and cuttings samples. TOC and programmed pyrolysis datasets from existing literature were synthesized in this study to better understand organic matter quality and thermal maturity evolution on regional scale. These data were examined in relation to paleogeography to gain insight into the factors regulating the distribution of organic matter quality within the Mandawa Basin.Average TOC contents in Lower Jurassic sediments fluctuate from 0.31 to 4.83 wt% with an average of 1.4 wt%, whereas, kerogen yield (S2) and hydrogen index (HI) remain generally low, with values ranging from 0.01 to 8.6 (mg HC/g rock) with an average (0.92 mg HC/g rock) as well as from 2 to 233 (mg HC/g TOC) with an average of 46 (mg HC/g TOC), respectively. Organic matter is composed mainly of type III (gas prone) to IV (inert) kerogens with lesser admixture of type II-III kerogen (oil-gas prone), which have been deeply buried and undergone a wider range of thermal diagenesis, from early to overmature stage. The δ13Corg isotopic composition of organic matter is consistent with kerogen typing, indicating terrestrial organic matter with a heavier signature during sea level low stands. Upon marine incursions δ13Corg shifts to isotopically more depleted marine organic matter. This implies that the investigated source intervals have poor to fair source potential. Only a few intervals of limited thickness in the Upper Mbuo, Nondwa, and Mihambia Formations of the Mita Gamma-1 and East Lika-1 wells, as well as in the Lower Mbuo Formation in the Mbuo-1 well, have been locally enriched. The enrichment is attributed to periodic marine ingressions that have persisted since the Pliensbachian period and suggests the presence of oil generation potential.A comparison of TOC and programmed pyrolysis borehole data from this study to those compiled from literature in a paleogeographical context reveals high spatial variability. The southeastern and northwestern parts of the study area have the highest source potential, indicating high organic matter productivity in the dysoxic to anoxic water column, which promoted the preservation of organic matter. In contrast, the eastern and western parts generally show low source potential, indicating degraded organic matter and significant terrestrial influxes from emergent land that were deposited in shallow, mixed oxygenated water with low to moderate organic matter productivity.

Peat Formation in Rewetted Fens as Reflected by Saturated n-Alkyl Acid Concentrations and Patterns

The conversion of cultivated fen peat soils into rewetted soils can mitigate global climate change. Specifically, carbon in newly formed peat can store atmospheric CO2 for a long time in soil, but alterations in the quality of soil organic matter are not well known. To shed light on the complex processes of peat degradation or new formation under dry or rewetting conditions, we investigated and quantified saturated n-alkyl acids as an indicator compound class of peatlands response to the contrasting management practices. The concentrations of saturated n-alkyl acids from two soil layers of the drained and rewetted were determined in two soil layers of drained and rewetted fenland types such as Alder Carr forest, coastal peatland, and percolation mire. The analytical methods were solvent extraction, methylation with tetramethylammonium hydroxide, and gas chromatography/mass spectrometry. The saturated n-alkyl acid distribution pattern showed that the concentrations of long C-chain lengths were larger by factors of up to 28 relative to the short C-chain lengths. The effect of rewetting was reflected by the ratios of the summed concentrations of long (n-C21:0 to n-C34:0) to short (n-C10:0 to n-C20:0) C-chain saturated n-alkyl acids for drained and rewetted peat soil samples. These ratios were consistently lower in samples from the rewetted sites, indicating a higher input of microbial bio- and necromass to soil organic matter, likely from algae and anaerobic bacteria, under rewetting. The results suggest that the enrichment of microbial biomass and necromass in rewetted soils may be an important contributor to the formation of new peat in fenlands, irrespective of fenland type.

Driving factors for soil C:N ratio in woody plant communities across northeastern Qinghai-Tibetan Plateau

Soil carbon: nitrogen ratio (Soil C:N ratio) is a crucial and stable indicator of soil organic matter quality, but little is known about how it is driven in woody plant communities on the northeastern Qinghai-Tibetan Plateau (QTP). For addressing the gap, we sampled 92 tree field plots and 200 shrub field plots during the plants’ growing seasons based on Vegetation Map of the People's Republic of China (1:1,000,000) to investigate the vegetations and soils. Our results showed that soil C:N ratios in tree communities were higher than those in shrub communities, with values of 14.58 ± 1.85 and 13.16 ± 1.66, respectively. Random forest (RF) algorithm and multiple comparison analysis further suggested that soil C:N ratios varied significantly among lifeforms and community types. Interestingly, our findings challenged the long-held view that climate had the most important impact on soil C:N ratios at the regional scale, as the hierarchy of importance for integrated factors was found to be soil > topography > biology > climate > lifeform for all woody plants. Pearson correlation analysis and ordinary least squares (OLS) regression analysis revealed that dissolved organic nitrogen (DON), ectomycorrhizal fungi (EcM) species proportion and downward shortwave radiation (Shwara) had significant positive correlations with soil C:N ratios in both lifeforms. The variation partitioning analyses (VPA) results showed that edaphic properties solely explained most of the variance. Multiple linear regression (MLR) models exhibited that dissolved total nitrogen (DTN) and DON were the main attributes influencing soil C:N ratios in tree communities while DON had the largest positive effect in shrub communities. Overall, these findings provide new insights into the regulatory mechanisms of C and N cycling in the woody plant communities of the northeastern QTP and shed light on the controlling factors of soil C:N ratios in this region.

Dynamics of dissolved organic matter (DOM) in waste stabilization ponds: Insights into co-treatment of sanitary sewage and landfill leachate

A thorough comprehension of dissolved organic matter (DOM) transformation in wastewater treatment plants is vital for their efficient operation and the production of high-quality effluent. However, little attention has been given to understanding DOM transformation and its potential impacts in stabilization pond systems, which heavily rely on biological processes. This study aims to fill this knowledge gap by investigating the transformations of DOM in stabilization ponds co-treating sanitary sewage and landfill leachate. A case study was conducted at the Ouro Branco WWTP in Brazil. Spectroscopic tools, including UV–Vis spectroscopy parameters (UV-254, URI), and molecular fluorescence (Excitation-Emission Matrix - EEM), were employed to assess the quality of organic matter. The findings revealed the prevalence of humic-like fluorophores associated with landfill leachate in all sampling points, including the final effluent. Notably, anaerobic ponds exhibited significantly higher fluorescence removal (peak A (80 %) > peak B (78 %) > peak C (76 %) > peak T (75 %)) compared to facultative ponds (peak T (29 %) > peak B (26 %) > peak C (19 %) > peak A (16 %)). The influent and final effluent displayed the most intricate DOM characteristics. While the influent characteristics were linked to the addition of landfill leachate, those of the final effluent were likely due to the release of soluble microbial products (SMPs).

Mycorrhizal type affects forest nitrogen availability, independent of organic matter quality

Mycorrhizal type affects forest nitrogen availability, independent of organic matter quality

High-quality fine particulate organic matter drives SOM stocks: Insights from Mollisols in Northeast China

How the quantity and quality of particulate organic matter (POM) affect the mineral-associated organic matter (MAOM) accumulation and the aggregate stability has not been systematically studied, which limits the in-depth understanding of the relationship between POM and SOM stocks. This study investigated the changes in the biomass and C:N ratio of fine roots, the C contribution of POM to SOM and the C:N ratio of POM within different particle sizes in native grassland, plantations and croplands in the Mollisols region of Northeast China. Then, the influence of fine roots and POM characteristics on MAOM accumulation and aggregate stability was analyzed. The results showed that (1) the C contribution of fine POM (fPOM, 0.053–0.25 mm) to SOM and the C:N ratio of fPOM in the native grassland was significantly higher and lower than that in the other sites (P < 0.05), respectively. (2) The C contribution of MAOM to SOM and the mean weight diameter (MWD) of water-stable aggregates were significantly positively correlated with the C contribution of fPOM to SOM (P < 0.01), and negatively correlated with the fPOM C:N ratio (P < 0.01). (3) The effect of fPOM C:N ratio on MWD of water-stable aggregates was stronger compared to the C contribution of fPOM to SOM. (4) The fine roots biomass showed a significant indirect effect on the C contribution of MAOM to SOM and the MWD of water-stable aggregates by influencing the C contribution of fPOM to SOM (P < 0.05). In general, both the quantity and quality (C:N ratio) of fPOM were lower in other land use types than that in native grassland, which significantly affected the SOM stocks. At the same time, the fPOM was also a medium for the fine roots to affect the soil characteristics. Promoting the accumulation of fine POM and focusing on improving the quality of fine POM could be a promising measure to ensure food production and increase soil carbon stocks. Conservation tillage practices such as no-till may be effective.

Soil organic carbon accumulation and microbial carbon use efficiency in subalpine coniferous forest as influenced by forest floor vegetative communities

The importance of forest floor plants (herbs and mosses) and understory communities on soil C dynamics has been grossly understudied in forest ecosystems; however, there is currently very little knowledge on the impact of forest floor vegetation composition on soil organic C (SOC) accumulation and the microbial metabolic processes. To bridge this gap of knowledge, a forest floor vegetation-removal experiment involving nonvascular mosses (Pleurozium schreberi (PS); Rhizomnium tuomikoskii (RT); and Hylocomiastrum pyrenaicum (HP)) and vascular sedges (Carex sp., CS) was conducted in a subalpine coniferous forest on the eastern edge of Tibetan Plateau, to investigate the associations of different forest floor vegetation communities with mineral soil C accumulation and microbial physiology (C use efficiency (CUE) and microbial biomass turnover). Soils beneath the forest floor vegetative communities differed in soil C and nitrogen (N) concentrations and had distinctively different microbial community structure and physiology. Compared to bare soils, sedge soils had significantly greater SOC and dissolved organic C (DOC) accumulation, greater microbial DNA, biomass C and phospholipid fatty acids (PLFAs) concentrations, and higher microbial CUE and shorter microbial biomass turnover time. While effects of mosses differed among species, P. schreberi had similar effects as sedges, but the effects of H. pyrenaicum and R. tuomikoskii were minimal. Relative to bare soil, P. schreberi and Carex sp. soils were 61.5% and 51.6% higher in microbial CUE and had an obviously shorter microbial biomass turnover time. Variations in the level of DOC and PLFAs (rather than their portion relative to SOC) were the most important regulators of microbial CUE and biomass turnover rate in soils with different forest floor vegetation covers. These results highlight how differences in soil organic matter quality that are directly related to the forest floor vegetation community influence the microbial CUE and biomass turnover and the long-term soil C dynamics.

Weak seasonality in benthic food web structure within an Arctic inflow shelf region

The Arctic Ocean is characterized by pronounced seasonality in the quantity and quality of organic matter exported from the surface ocean. While it is well established that changes in food availability can alter the abundance, biomass and function of benthic organisms, the impact on food web structure is not well studied. We used bulk carbon and nitrogen stable isotope analysis to assess the quantity and quality of sediment organic matter and structure of the benthic food web in four seasons within the Northern Barents Sea (76°N − 82 °C). Despite a highly seasonal vertical flux, we found that the organic carbon and chlorophyll-a content of surface sediments was seasonally stable, suggesting a lack of seasonality in food availability at the seafloor. However, organic biomarkers indicate that the quality of sediment organic matter increased to a maximum in August and December, up to 6 months after the spring bloom. The seasonal stability of food quantity was mirrored in food-web structure (e.g., total isotopic range, number of trophic levels) which did not change significantly across sampling periods. We expected that suspension and deposit feeders would respond more readily to seasonal changes in food quality compared to predators. However, we observed no significant seasonal changes in the trophic levels or isotopic niche areas of benthic functional groups. The centroids of isotopic niches of all benthic functional groups shifted seasonally by <2 ‰ along the δ13C-axis, suggesting minimal shifts in carbon resource use. Because the northern Barents Sea experiences significant changes in seasonal sea ice cover, we expected that stable-isotope ratios of benthic organisms would show an increased consumption of sympagic-derived organic matter through less negative δ13C values in early spring and summer. However, only two taxa (the soft coral Gersemia spp. and bivalves in the family Yoldiidae) showed 13C-enrichment in spring or summer consistent with the assimilation of sympagic-derived organic matter, despite previous evidence suggesting widespread use of this carbon source. Overall, our results show that there is an apparent de-coupling in time between pelagic processes and benthic food-webs in which the accumulation and assimilation of high-quality organic matter occurs for benthos during the fall and early winter months when there is little to no fresh organic matter generated at the surface. This temporal mismatch highlights the importance of considering the timescales over which components of the marine ecosystem respond to short-term environmental changes and the methods employed to assess seasonality.

Soil organic matter carbon chemistry signatures, hydrophobicity and humification index following land use change in temperate peat soils

Peatlands play a critical role in the global carbon cycle, storing large amounts of carbon because of a net imbalance between primary production and the microbial decomposition of the organic matter. Nevertheless, peatlands have historically been drained for energy sources (e.g. peat briquettes), forestry, or agriculture - practices that could affect the quality of the soil organic matter (SOM) composition, hydrophobicity and humification index. This study compared the effect of land use change on the quality and composition of peatland organic material in Co-Offaly, Ireland. Specifically, drained and grazing peat (grassland), drained and forest plantation peat (forest plantation), drained and industrial cutaway peat (cutaway bog) and an undrained actively accumulating bog (as a reference for natural peatland) were studied. Fourier-transform infrared spectroscopy (FTIR) was used to examine the organic matter quality, specifically the degree of decomposition (DDI), carbon chemistry signatures, hydrophobicity and humification index. The ratio of hydrophobic to hydrophilic group intensities was calculated as the SOM hydrophobicity. In general, there is greater variance in the carbon chemistry signature, such as aliphatic methyl and methylene, C=O stretching of amide groups, aromatic C=C, strong H-bond C=O of conjugated ketones and O–H deformation and C– O stretching of phenolics and secondary alcohols of the peat samples from industrial cutaway bog samples than in the grassland and forest plantation samples. The hydrophobicity and the aromaticity of the soil organic matter (SOM) are significantly impacted by land use changes, with a trend of order active bog > forest plantation > industrial cutaway bog > grassland. A comparison of the degree of decomposition index of the peat from active bog showed a more advanced state of peat degradation in grassland and industrial cutaway bog and, to a lesser extent, in forest plantation.

Integrated analysis of aboveground and belowground indicators support a comprehensive evaluation of ecosystem recovery

Analyses of diverse aboveground and belowground indicators should underpin assessments of ecosystem recovery, yet monitoring many indicators is costly and their integration is challenging. Our objective was to combine indicators through a Bayesian hierarchical model to provide a comprehensive assessment of ecosystem status and identify a cost‐effective subset of indicators to provide an accurate estimate of ecosystem recovery. We assessed 59 aboveground–belowground indicators, classified into nine components of composition, structure, and function, to estimate the ecosystem status of restored rock spoils and reference forests in south‐eastern Australia. Overall ecosystem status, which integrates across ecosystem components and supporting indicators, was lower within restored forests but positively correlated with forest age. Reference forests had greater aboveground and belowground biotic structure, organic matter supply, and soil carbon stability, and trends were consistent among all of their supporting indicators. A subset of organic matter quality and nutrient cycling indicators were greater within restored forests, suggesting high ecosystem process rates, but that soil carbon may be more vulnerable to loss. Aboveground biotic structure was correlated with organic matter supply and quality, stability of soil carbon, the cycling of nutrients, and belowground biotic structure, providing evidence of aboveground–belowground coupling. A combination of four indicators representing belowground biotic structure, soil carbon stability, organic matter supply, and aboveground composition, provided a good estimate of ecosystem status at a third of the cost. Although ecosystem status can be monitored with a small set of indicators, a diversity of aboveground–belowground indicators provide a robust and comprehensive assessment of recovery.

Macro-scale spatial modeling reveals the role of soil organic matter quality in CO2 emissions

Carbon dioxide (CO2) emissions from agricultural soils result from the interaction of various factors that regulate the quantity and quality of organic material. Our objective was to assess changes in soil CO2 fluxes following the renewal of degraded pastures using FTIR spectroscopy and a machine learning approach. Additionally, we aimed to understand the spatial distribution of organic compounds obtained from FTIR spectra bands and their correlations with soil attributes. The study was conducted in Selvíria, Mato Grosso do Sul, Brazil, in two areas dedicated to extensive beef cattle farming. Geostatistical grids were established in the study areas to evaluate CO2 emissions, and soil sampling was performed for FTIR spectral analysis and other soil attributes. The semi-quantitative analysis of the CH vibrational region involved spectral deconvolution guided by the positions of the peaks obtained from the second derivative and Gaussian curve fitting. Our results indicate that the relative abundance of compounds related to peaks at 2853 cm−1 and 2923 cm−1 showed linear and spatial correlations with CO2 emissions. Pasture renewal, followed by sorghum cultivation intercropped with Urochloa brizantha, resulted in increased soil pH up to 5.6 and reduced concentrations of compounds related to the aliphatic CH band. This management practice also led to a decrease in CO2 emissions to a range of 0.94 to 0.97 μmol m−2 s−1. The CH2 index, calculated as the ratio of peaks at 2853 cm−1 and 2923 cm−1, exhibited similar changes and could serve as an indicator of soil organic matter loss and CO2 emissions in these systems. Our findings suggest that FTIR organic compounds are spatially dependent and coupled with a machine learning approach is sensitive to distinguish chemical changes in soil organic groups and predict soil CO2 emissions.

Prediction of the distribution of soil properties in deep Colluvisols in different pedogeographic regions (Czech Republic) using diffuse reflectance infrared spectroscopy

Colluvisols form a significant part of the erosion–deposition soil catena mainly in undulating, agriculturally managed landscapes. Due to their sedimentary origin, they are soils with highly variable properties. For such diverse and often extremely deep soils, it is essential to capture the vertical distribution of properties in as much detail as possible. This study demonstrates the potential of the diffuse reflectance infrared spectroscopy (DRIFT) to derive accurate information on the stratigraphy and selected soil properties (soil organic carbon and calcium carbonate contents and aluminium and iron concentrations) of deep colluvial profiles in three regions in the Czech Republic with different dominant soil types (Chernozem, Luvisol, and Cambisol). The normalization of the spectrum using the quartz spectral band was found to be suitable for assessing the carbonate content in Chernozems and Luvisols (coefficients of determination (R2) were 0.89 and 0.88, respectively). The amount of organic carbon can be predicted from such normalized spectra with less confidence (R2 = 0.64). Organic matter quality as an indicator of their stability and maturity was computed from aliphatic compounds spectral bands (2930 cm–1) and aromatics and CO groups band around 1640 cm–1. The highest values of this indicator were found in Colluvisols in the Chernozem region (> 6, while, e.g., in the Cambisol region it is < 1), especially in the layers corresponding to the oldest sediments or buried in-situ horizons. In the Cambisol region, the buried B horizon was identified based on normalized (i) clays and Fe oxides bands and (ii) wider band of OH groups, which in this case is related to the content of iron oxyhydroxides. The study proved that the applied set of spectral parameters is an effective tool for the description of diverse soil parameters and for identification of the boundaries of individual soil layers. It is equally suitable for carbonate-free soils as well as for soils with higher carbonate contents, which usually cause difficulties in the interpretation of soil organic matter spectral parameters. It provides a comprehensive view of the soil and its mineral and organic components and can provide information that is difficult to measure by other methods.