Particulate Organic Matter Concentrations Research Articles

Environmental factors as drivers of the spatial distribution of the copepods Eurytemora affinis affinis and Eurytemora velox in the Scheldt tributaries.

The main tributaries of the Scheldt estuary offer an interesting setting to study the response of organisms to various environmental conditions. The Bovenscheldt and the Dender are closed to tidal entrance by locks, and are hence essentially fresh water systems with low turbulence. The Durme and the Rupel, with its two sub-tributaries (the Beneden-Nete and the Dijle), receive estuarine water at each tide and as such, present a fresh-brackish water gradient according to the geographic location of their confluence with the estuary and the tidal phase. This paper aims (1) to determine the spatial-temporal distribution of two calanoid copepod species: Eurytemora affinis affinis (Poppe, 1880) and E. velox (Lilljeborg, 1853) in these tributaries and (2) the environmental conditions favoring each species development. Species distribution and abundance data, collected in the four tributaries between 2018 and 2021 are analyzed by Generalized Linear Mixed Models (GLMM) and the results are interpreted in the context of ecosystem functioning. A spatial structuring between E. affinis affinis and E. velox was revealed. Whilst E. affinis affinis develops best in the tidal tributaries such as the Durme and Rupel, E. velox is more typical of the non-tidal ones: the Bovenscheldt and the Dender. The tidal tributaries have high Particulate Organic Matter (POM) concentrations due to tidal turbulence, and hence generally lower oxygen concentrations than the non-tidal ones (< 10-11 mg L-1). Factors favoring E. affinis affinis development in the tidal tributaries are higher chlorinity, pH and diatom abundance than in the non-tidal ones. In the non-tidal tributaries, with lower POM concentrations, phytoplankton activity more strongly influences the overall oxygen balance, with oxygen concentrations often rising above 10-11 mg L-1 and sometimes showing high variability. The results suggest that E. affinis affinis might suffer from hyperoxia-induced oxidative stress under these high oxygen conditions and advocate the necessity to include this aspect in further research. E. velox, which is most abundant in those tributaries, seems to be more tolerant to hyperoxia and strong fluctuations in O2 concentrations than E. affinis affinis.

Potential gains in soil carbon and nitrogen as a result of systems perenniality: Insights from on‐farm experiments and soil organic matter fractions

AbstractUnderstanding soil organic matter (SOM) dynamics along gradients of land intensification is critical to guide conservation goals towards improvements in soil carbon (C) and nitrogen (N) storage. In this study, we clarified (a) how the C and N concentrations within SOM fractions of distinct ecological relevance responded to soil management representing a cropland‐grassland gradient and (b) how these operationally defined fractions affected soil physicochemical and biological properties. We compared sites with annual row crop rotations with and without cover crops (i.e. cropland soils) with perennial grassland sites (i.e. reference soil) by sampling near‐surface soils from statewide on‐farm cover crop experiments replicated across four agro‐ecoregions in Midwest USA. Soil management had a significant main effect on C and N content in SOM fractions, but responses were site‐ and fraction‐specific. We found that C content of free particulate organic matter and water‐extractable organic matter (WEOM) of reference soils were 58%–76% and 31%–59% greater than those of the cropland soils in two of the four sites. Differences in N content of WEOM because of soil management were observed in two of the four sites. These reference soils had between 40% and 60% greater N than cropland soils. Additionally, the N content of aggregate occluded POM (o‐POM) of reference soils was three times greater than those of the cropland soils in one of the four sites. Broadly across bulk and SOM fractions, high declines in cropland C and N relative to reference soils were observed in non‐irrigated and strip‐till sites and coarse‐texture soils. Free and o‐POM C and N were strongly associated with aggregate stability, water infiltration and enzyme activity, whereas C and N contents of WEOM and MAOM were correlated with soil's ability to hold onto essential nutrients (e.g. calcium, magnesium, potassium and sodium). Although the potential of cover crops to drive changes on ecologically meaningful SOM fractions is less pronounced in the short (3 year) term, the findings demonstrate the potential of continuous living cover as an approach to agroecosystem design to improve soil functions closely related to SOM characteristics.

Characterization and function of particulate organic matter: Evidence from lakes undergoing ecological restoration

Particulate organic matter (POM) plays a crucial role in the organic composition of lakes; however, its characteristics remain poorly understood. This study aimed to characterize the structure and composition of POM in Lake Baiyangdian using many kinds of techniques and investigate the effects of different extracted forms of POM on water quality. The suspended particulate matter in the lake had complex compositions, with its components primarily derived from aquatic plants and their detritus. The organic matter content of the suspended particulate matter was relatively high (organic carbon content 27.29–145.94 g/kg) for the sum of three extractable states (water-extracted organic matter [WEOM], humic acid, and fulvic acid) and one stable bound state (humin). Spatial distribution analysis revealed that the POM content in the water increased from west to east, which was consistent with the water flow pattern influenced by the Baiyangdian water diversion project. Fluorescence spectroscopy analysis of the WEOM showed three prominent peaks with excitation/emission wavelengths similar to those of dissolved organic matter peaks. These peaks were potentially initial products of POM conversion into dissolved organic matter. Furthermore, the intensity of the WEOM fluorescence peak (total fluorescence peak intensity) was negatively correlated with the inorganic nitrogen concentration in water (p < 0.01), while the intensity of the HA fluorescence peak showed a positive correlation with the inorganic nitrogen concentration (p < 0.01). This suggested that exogenous organic matter inputs led to the diffusion of alkaline dissolved nitrogen from sediment into water, while degradation processes of aquatic plant debris contributed to the decrease in inorganic nitrogen concentrations in the water column. These findings enhance our understanding of POM characteristics in shallow lakes and the role of POM in shallow lake ecosystems.

Exploring contribution of phytoplankton cell death to settleable particulate organic carbon in the East China Sea in spring

Phytoplankton's death contributes to marine settleable particulate organic matter (POM). In this study, we used laboratory cultivation of different algal species to identify a positive correlation between the cumulative number of dead algal cells and POC>75 (carbon content of the settleable POM). The contribution coefficient of cell death to POC>75 varied among different algal species. Additionally, the field survey and incubation experiment were conducted in the East China Sea (ECS) to explore the spatial-temporal correlation between phytoplankton death and POC>75. The results concluded that phytoplankton death was the main factor controlling POC>75. In the ECS, the relationship between the surface cumulative mass of POC>75 and the cumulative number of dead cells followed: Cumulative mass of POC>75(mg) = 0.487 × Cumulative number of dead cells (/104) + 0.069. This study provided a methodology to quantitatively explain the relationship between phytoplankton death and settleable POM.

Coupling scales in process‐based soil organic carbon modeling including dynamic aggregation

AbstractBackgroundCarbon storage and turnover in soils depend on the interplay of soil architecture, microbial activities, and soil organic matter (SOM) dynamics. For a fundamental understanding of the mechanisms that drive these processes, not only the exploitation of advanced experimental techniques down to the nanoscale is necessary but also spatially explicit and dynamic image‐based modeling at the pore scale.AimWe present a modeling approach that is capable of transferring microscale information into macroscale simulations at the profile scale. This enables the prediction of future developments of carbon fluxes and the impact of changes in the environmental conditions linking scales.MethodWe consider a mathematical model for CO2 transport across soil profiles (macroscale), which is informed by a pore‐scale (microscale) model for C turnover. It allows for the dynamic, self‐organized re‐arrangement of solid building units, aggregates and particulate organic matter (POM) based on surface interactions, realized by a cellular automaton method, and explicitly takes spatial effects on POM turnover such as occlusion into account. We further include the macroscopic environmental conditions water saturation, POM content, and oxygen concentration.ResultsThe coupled simulations of macroscopic transport and pore‐scale carbon and aggregate turnover reveal the complex, nonlinear interplay of the underlying processes. Limitations by diffusive transport, oxygen availability, texture‐dependent occlusion and turnover of OM drive CO2 production and carbon storage.ConclusionsThis emphasizes the need for such micro–macro models exchanging information on different scales to investigate and quantify the effects of structural changes, variations in environmental conditions, or degradation processes on carbon turnover.

The transition between coastal and offshore areas in the North Sea unraveled by suspended particle composition

Identifying the mechanisms that contribute to the variability of suspended particulate matter concentrations in coastal areas is important but difficult, especially due to the complexity of physical and biogeochemical interactions involved. Our study addresses this complexity and investigates changes in the horizontal spread and composition of particles, focusing on cross-coastal gradients in the southern North Sea and the English Channel. A semi-empirical model is applied on in situ data of SPM and its organic fraction to resolve the relationship between organic and inorganic suspended particles. The derived equations are applied onto remote sensing products of SPM concentration, which provide monthly synoptic maps of particulate organic matter concentrations (here, particulate organic nitrogen) at the surface together with their labile and less reactive fractions. Comparing these fractions of particulate organic matter reveals their characteristic features along the coastal-offshore gradient, with an area of increased settling rate for particles generally observed between 5 and 30 km from the coast. We identify this area as the transition zone between coastal and offshore waters with respect to particle dynamics. Presumably, in that area, the turbulence range and particle composition favor particle settling, while hydrodynamic processes tend to transport particles of the seabed back towards the coast. Bathymetry plays an important role in controlling the range of turbulent dissipation energy values in the water column, and we observe that the transition zone in the southern North Sea is generally confined to water depths below 20 m. Seasonal variations in suspended particle dynamics are linked to biological processes enhancing particle flocculation, which do not affect the location of the transition zone. We identify the criteria that allow a transition zone and discuss the cases where it is not observed in the domain. The impact of these particle dynamics on coastal carbon storage and export is discussed.

Deciphering the role of particulate organic matter in soil nitrogen transformation in rice–rapeseed and rice–wheat rotation systems

Crop rotation affects the decomposition of soil organic matter (SOM) and thereby alter the composition of SOM fractions. It remains unclear how different SOM fractions impact soil nitrogen (N) transformation in various rotation systems. The aim of this study was to ascertain the role of particulate organic matter (POM)-a labile SOM fraction-in soil N transformation under various crop rotations. A paired plot experiment was conducted under two common cropping patterns, i.e., rice–rapeseed rotation (RR) vs. rice–wheat rotation (RW). Soil chemical composition and organic matter fraction before rice transplanting were compared between RR and RW systems after four years of crop rotations (2017–2021). With the same N inputs, the rice yield and N uptake under RR were 16.4 % and 13.2 % higher than those under RW, respectively. Compared with RW, RR resulted in higher carbon (C) and N contents in soil POM, despite minimal differences in total SOM. A larger potentially mineralizable N pool and a higher N mineralization rate occurred under RR than under RW, based on the results of soil net mineralization experiment. When POM was incubated alone, its contribution to potentially mineralizable N was 65.1 % and 61.3 % in RR and RW soils, respectively. Infrared spectroscopy revealed that in contrast with RW, RR promoted the accumulation of organic matter with high bioavailability (e.g., amides, carbohydrates, polysaccharides) in soil POM. This might be responsible for the higher gross mineralization and nitrification rates but lower gross immobilization rate under RR than under RW. Consequently, RR not only increased the contents of POMC and POMN but also improved the quality of POM fraction in soils. Findings of the present study demonstrate that POM plays a distinct role in soil N mineralization in various rotation systems. The discrepancy in POM content and composition resulting from various crop rotations leads to differences in soil N mineralization, which in turn affects the N supply and rice yield.

Straw return plus zinc fertilization increased the accumulations and changed the chemical compositions of mineral-associated soil organic carbon

Agricultural zinc (Zn) fertilization can markedly promote organo-Zn complex formation, especially when combined with straw. However, how soil organic carbon (SOC) conversion responds to Zn and/or straw plus Zn has received little attention. Here, we explored the SOC, particulate organic carbon (POC), mineral-associated organic carbon (MAOC), as well as the OC chemical compositions’ responses in a field experiment site created in 2016. The following treatments were control (CK, no straw return and no Zn fertilization), straw return (St), Zn fertilization (Zn), and straw return combined with Zn fertilization (St+Zn). The results of our three-year study indicated that MAOC content under St+Zn increased by 4.4–6.4%, which led to a slight SOC accumulation (3.7–7.4%) compared to that of St alone. After including straw return with Zn fertilization, the Zn content of particulate organic matter and that of mineral-associated organic matter (ZnMAOM) both increased and thus helped MAOC formation. The chemical compositions of POC and MAOC were affected mainly by straw return and Zn fertilization, respectively. Both the Zn and St+Zn treatments had increased relative hydroxyl C contents and reduced O-alkyl C contents in MAOC, compared to that of CK and St, and the ZnMAOM content best explained the changes. In both the POC and MAOC fractions, the aromatic C to aliphatic C ratio decreased in Zn treatments compared to those in CK. Altogether, Zn’s effects on SOC and its fractions were closely linked to straw return, and Zn aids in MAOC and SOC accumulations when applied with straw.

Organic farming systems affect carbon stocks but not soil structure and associated physical properties in a long-term farming trial on Chernozem

An asset of organic farming systems with diversified crop rotations, next to a cut in pesticide and mineral fertilizer application, is the built-up of organic carbon stocks in the long-term. In addition, the inclusion of deep-rooting legumes like alfalfa is known to improve soil structure and increase particulate organic matter contents in the subsoil. These views have been challenged recently ascribing limited potential for legume-based crop rotations to increase carbon stocks in Chernozems (Mollisols) due to limited accrual of mineral-associated organic carbon. Likewise, the direct impact of these legumes on soil structure and associated soil properties like water retention and transport has been questioned and linked to indirect effects instead.The objective of this study was to investigate the impact of legume-based crop rotations on carbon stocks and soil structure properties in the Flurweg II long-term farming systems trial (26 years) established on a Chernozem soil in Germany. We compared one conventional (INT) and two organic farming systems, with (O + M) and without (O - M) integrated livestock management. The three farming systems differ in biomass return via plant residues or farmyard manure as well as share and type of legumes in the eight-year crop rotation (INT: pea, O - M: faba bean and pea, O + M: biannual alfalfa). The comparison included yields, carbon stocks, soil physical properties and microstructure properties based on X-ray computed tomography of soil within and beneath the plow horizon. All farming systems underwent conventional plowing. In addition, we compared carbon stocks and microstructure properties with those from the nearby Westerfeld tillage trial with conventional and reduced tillage in a legume-free crop rotation.The carbon stocks in the plowed topsoil of the Flurweg II systems trial increased significantly with organic farming including livestock (INT: 53 ± 2 vs. O + M: 61 ± 2 t ha−1), but not without (O - M: 53 ± 4 t ha−1), likely because of farmyard manure application in the O + M system. This increase in topsoil carbon stocks is only moderate compared to the increase in topsoil carbon stocks in the Westerfeld tillage trial by switching from conventional to reduced tillage (53 vs. 70 t ha−1). The carbon stocks of the whole soil profile (down to 48 cm) in the Flurweg II systems trial tended to increase with organic farming irrespective of livestock integration (INT: 72 ± 5 t ha−1 vs. O ± M: 82–83 ± 7 t ha−1). Particulate organic matter (POM) contents and biopore diameter below the plow layer tended to increase with alfalfa in the crop rotation of the O + M farming system. However, the legacy effect four years after the presence or absence of alfalfa was only in the range of natural, spatial variability. As a result of similar soil microstructure there was also hardly any difference in hydraulic conductivity and no difference in soil mechanical properties between farming systems.This study shows that Chernozems in this region still have the capacity to increase POM contents and carbon stocks with climate-smart, regenerative agricultural management, but also demonstrate that this has limited effects on structural properties.

Cover crops and soil health in rainfed and irrigated corn: What did we learn after 8 years?

AbstractDuration of cover crop (CC) management, CC biomass production, and other factors could impact how CC affects soil health. We studied the 8‐year cumulative impacts of winter rye (Secale cereale L.) CC on soil physical, chemical, and biological properties in rainfed and irrigated no‐till corn (Zea mays L.)‐based systems in the western US Corn Belt. Average annual CC biomass production was 0.56 ± 0.51 Mg ha−1 at the rainfed site and 0.98 ± 0.95 Mg ha−1 at the irrigated site. After 8 years, CC improved particulate organic matter (POM) and mean weight diameter of water‐stable aggregates (MWD) compared with no CC in the 0–5 cm soil depth at both sites. Cover crop increased total POM concentration by 2.8 mg g−1 at the rainfed site and by 13.4 mg g−1 at the irrigated site, while it increased MWD by 0.39 mm at the rainfed site and by 0.79 mm at the irrigated site. Also, CC increased soil C at a rate of 0.125 Mg ha−1 year−1 in the 0–5 cm depth but only at the rainfed site. Cover crop affected neither water infiltration nor available water but improved microbial biomass. Changes in other properties were site‐dependent. Cover crop improved many soil properties after 8 years even though measurement taken after 4 years showed no significant effect of CC, which indicates CC slowly impacts properties in this environment. Low CC biomass production and high biomass input from corn‐based systems may explain the slow soil response. In general, winter rye CC enhances near‐surface soil properties in the long term.

Warming-dominated climate change impacts on soil organic carbon fractions and aggregate stability in Mollisols

Mollisols contain high amounts of soil organic carbon (SOC), which is highly susceptible to climate change; thus, climate change could indirectly influence soil aggregate stability, but the dominant factor affecting aggregate stability remains controversial. Here, a soil transplanting test from high-latitude to low-latitude locations was initiated in 2004 to investigate the influences of warming-dominated climate change (approximately 3–4.7 ℃) on the quantity and molecular composition of OC fractions in surface (0–20 cm) soils, aggregate stability changes and underlying mechanisms. Different initial soil organic matter (SOM) contents of 50.6 g kg−1 (SOM5), 58.8 g kg−1 (SOM6), and 108.9 g kg−1 (SOM11) were established in situ soils and in transplanted soils to simulate warming. The 15-year warming-dominated climate change presented no noticeable change in the SOC content in the lower SOM Mollisols (SOM5 and SOM6) but increased the SOC content by 13.3% in the higher SOM Mollisol (SOM11). In terms of labile OC fractions, warming-dominated climate change significantly increased the dissolved organic carbon (DOC) content by 20.1%–47.7% but reduced the easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC) contents by 22.1%–33.6%. Irrespective of any treatment, warming-dominated climate change decreased soil aggregate stability, as evidenced by the reduction in mean weight diameter (MWD) and geometric mean diameter (GMD) of 41.7%–79.3% and an increase in fractal dimension (D) of 28.6%–58.5%. For hierarchically organized soil aggregates, warming-dominated climate change increased the proportion and OC content of particulate organic matter inside free microaggregates (Fm-POM) as well as nonaggregated silt + clay-sized organic matter (nA-MOM). However, climate change decreased the proportion and OC content of silt + clay-sized fractions inside microaggregates within macroaggregates (mM-MOM). Of importance, warming-dominated climate change increased the amount of carbohydrates and decreased the amount of lignin in the mM-MOM, Fm-POM, and nA-MOM fractions. Therefore, we speculated that chemical protection by mineral association within macroaggregates and nA-MOM fractions and physical protection by the occlusion of POM within free microaggregates might be the primary mechanisms for SOC stabilization under long-term climate change in Mollisols. The long-term warming-dominated climate change results demonstrated a positive effect on SOC content in higher SOM Mollisols, DOC, carbohydrate C, free microaggregate-associated C and nonaggregated silt + clay-sized associated C but exhibited a negative effect on EOC, MBC, lignin C, silt + clay-sized inside microaggregates within macroaggregates C and aggregate stability. These variables all contributed to the reduction in soil aggregate stability and might act as sensitive indicators of warming-dominated climate change in Mollisols, which in turn affect farmland ecosystem C fluxes in response to further climate change.

Source, composition, and reactivity of particulate organic matter along the Changjiang Estuary salinity gradient and adjacent sea

The sources, distribution, and fate of particulate organic matter (POM) in estuaries are dynamic and complex, influenced by highly intensive human activities and high productivity. In this study, water samples were collected along the Changjiang Estuary salinity gradient and adjacent sea (CEAS) in February and May 2017. Particulate organic carbon (POC), particulate nitrogen (PN), the δ13C isotope values and major biochemical constituent (total particulate amino acids, TPAA) were measured. The concentrations of POC, PN, and TPAA showed an overall decreasing trend from the river end-member to the open sea; however, their maximum always occurred around the turbidity maximum zone (TMZ). Concentrations of POC and TPAA showed a negative correlation with salinity and a positive correlation with chlorophyll a, indicating that the variation in POM concentrations and composition was mainly controlled by both terrigenous input and in situ phytoplankton production. The δ13C values gradually increased from the river mouth to the open sea in both winter and spring, in contrast to the molar C/N, reflecting the transition from terrestrial POC to phytoplankton-derived fresh POC with increasing salinity. Major biochemical indicators of TPAA/POC (%) and the degradation index (DI), showed a gradual shift towards more bioactive POM with increasing salinity in spring, although low TPAA/POC (%) values appeared within the TMZ. In spring, POC reactivity was higher than in winter. The proportions of glycine (Gly) and serine (Ser) were higher in winter, indicating that POM had suffered extensive degradation. Based on a two end-member mixing model, the contribution of marine POC in spring (53 ± 14%) was significantly greater than in winter (39 ± 19%), indicating that phytoplankton-derived POM was dominant in spring, associated with the increase in phytoplankton biomass from winter to spring. Based on mass balance, a box model showed evidence of a net POC sink over the Changjiang estuary and its adjacent East China Sea shelf in both winter and spring, with a net POC budget of 20.49 ± 7.01 and 15.87 ± 6.57 kmol s−1, respectively. Results illustrate that the spatio-temporal distribution of POM varies distinctively and will further affect the variability in its composition and reactivity in the CEAS.

A classification-based approach to mapping particulate organic matter (POM) in inland water using OLCI images.

Particulate organic matter (POM) plays a major role in freshwater ecosystems by serving as a bridge for the conversion of various nutrients. The composition and sources of POM in inland lakes are complex, making it difficult to estimate its concentration accurately via remote sensing. Therefore, a classification-based method based on the sources and composition of POM is proposed for estimating POM concentrations in inland lakes. In this study, 379 samples were collected from ten lakes in the Yangtze River Delta (YRD) at different times. A water-type classification method based on OLCI [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] was developed for POM estimation based on biological and optical characteristics. Water type 1 is relatively clear, and POM may originate from aquatic vegetation or sediment. Water type 2 was dominated by inorganic suspended matter, and POM mainly originated from the attachment and entrainment of inorganic minerals. Water type 3 is an algae-dominated water body, and POM is mainly derived from fresh algal particles and the microbial degradation of phytoplankton. Therefore, specific POM estimation algorithms were developed for each water type. OLCI [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] were used for water type 1; [Formula: see text], [Formula: see text], and [Formula: see text] were adopted for water type 2; and [Formula: see text], [Formula: see text], and [Formula: see text] were selected for water type 3. Using an independent dataset to evaluate the estimation accuracy of the developed algorithm, the results show that the estimation performance of this algorithm is significantly improved compared to the two other algorithms used; the mean absolute percentage errors (MAPE) decreased from 72.56% and 52.21% to 32.61%, and the root mean square errors (RMSE) decreased from 3.05mg/L and 2.24mg/L to 1.75mg/L. A random error analysis of the atmospheric correction demonstrated that this algorithm is robust and can still perform well within a random error of 30%. Finally, this method was successfully applied to map the POM concentrations in the YRD using OLCI images acquired on November 12, 2020.

Ability of grazing fish to generate particulate organic matter derived from autochthonous primary production

AbstractGrazing fish play a role of controlling autochthonous primary production and converting it to secondary production by consuming benthic algae. Moreover, they will also provide autochthonous particulate organic matter (POM) for freshwater ecosystems by dislodging the benthic algal matrix while feeding. However, it has not been confirmed whether grazing fish induce POM production during their feeding on benthic algae. To verify this POM production during grazing by fish, short‐term (90 min) feeding experiments were conducted by introducing grazing fishPlecoglossus altivelisinto indoor aquaria with benthic algal mats. We found that the fish can generate POM by feeding on benthic algae. Although POM was generated in the aquaria where the fish had not grazed on the benthic algal mats at all, the concentration of POM in the aquaria increased with the frequency of the acts of scraping benthic algae by the fish. Furthermore, we observed that the fish egested faeces which corresponded to about 44% on average of the ingested benthic organic matter. In some cases, the fish generated POM that corresponded to 88% of the removed (dislodged and ingested) benthic organic matter through their feeding and defecation. This study suggested that grazing fish have a function of providing autochthonous POM to freshwater ecosystems both via dislodging benthic algae during feeding and through egestion of consumed benthic algae.

Study on the Adsorption Relationship between Organic Matter and Particulate Matter in Water Distribution Pipes

In the process of water distribution, the secondary pollution of drinking water cannot be ignored. There are many organic substances in the water supply network, some of which exist in a dissolved state in the water as dissolved organic matter (DOM), and some of which are adsorbed on the particulate matter to form particulate organic matter (POM). With the flow of water, the particles will be brought into the end user, and threaten the life and health of the user. In this study, two forms of organic matter in distributed water were comprehensively analyzed through micro-filtration membrane filtration, ultrasonic extraction, C18 column solid phase extraction, and GC-MS detection, and their changes in the flow process were explored. The results show that, as the sampling point moves away from the water source, the DOM decreases and the POM increases, and in all there were fewer DOM species than POM, indicating that more organic matter existed on particulate matter or in particle form, and relatively less organic matter existed in a dissolved state. POM in water mainly includes alcohol, ketone, ester, nitrogen, sulfur compounds, and benzene, and the content of POM in different particle size ranges is not the same. Some small particle size ranges have a higher content of POM, while some large particle size ranges have a higher content of POM, which does not show obvious regularity.

The Inorganic Carbon Fixation Improved by Long-Term Manure Fertilization in Kastanozems under Rotation System of North China

In China, manure is the most abundant organic fertilizer product. Understanding the changes in soil inorganic carbon (SIC) resulting from long-term manure fertilization is vital for accurately evaluating agricultural soil carbon stocks and predicting global change. However, a comprehensive and quantitative understanding of the impacts of long-term fertilization on SIC is lacking. This study was conducted to assess the effects of SIC changes in topsoil (0–20 cm), aggregates of kastanozems and influencing factors under the potato-rape-naked oats cultivation system after 16 years of long-term different fertilization in Wuchuan station. The results showed that 16 years of application of manure promoted the fixation of SIC by 2.25 t ha−1–3.25 t ha−1. As soil organic carbon (SOC) content, exchangeable calcium and magnesium concentrations in free coarse particulate organic matter (cfPOM) increased, the crystallization of carbonate was promoted at the aggregate level. The distribution proportion of free-coarse particulate organic matter (cfPOM) and microaggregates in mineral-related organic matter (iMOM) were also increased which affected the content of SIC. However, the pH value of NPKM treatment was lower than that of M treatment, which reduced the amount of carbonate crystallization. Thus, the application of manure alone was the best way to promote the fixation of SIC in topsoil rather than manure combined with chemical NPK fertilize. This work provides a new insight into the conversion of inorganic carbon, which is beneficial to promote the sequestration of inorganic carbon.

Particulate Organic Matter Mobilization and Transformation Along a Himalayan River Revealed by ESI‐FT‐ICR‐MS

AbstractTracing pathways and transformations of particulate organic carbon from landscape sources to oceanic sinks is commonly done using the isotopic composition or biomarker content of particulate organic matter (POM). However, similarity of source characteristics and complex mixing in rivers often preclude a robust deconvolution of individual contributions. Moreover, these approaches are limited in detecting organic matter transformations. This impedes understanding of carbon cycling. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR‐MS) can simultaneously identify many molecular formulas from mixtures of organic matter, and provide direct information on its compositional variability. Here, we investigate how FT‐ICR‐MS can give insight into POM dynamics on a landscape scale, focusing on the trans‐Himalayan Kali Gandaki River, Nepal. Using molecular information, we identify source tracers in the solvent extractable lipid fraction of riverine POM, finding up to 102 indicative molecular formulas for individual sources. Further, we assess molecular transformations of the lipid fraction of POM during its transfer from litter into topsoil, and onwards into the river. A large number of shared mass formulas and a well‐preserved isoprenoidal patterns suggest efficient incorporation of litter into topsoil. In contrast, we observe a selective loss of mass formulas and a preferential export of formulas with low double bond equivalents and a low nominal oxidation state of carbon after organic matter entrainment in the river. Our results demonstrate the potential of FT‐ICR‐MS for source‐to‐sink studies, allowing detailed organic matter source characterization and discrimination, and tracking of molecular transformations along organic matter pathways spanning different spatial and temporal scales.

Using Mid-Infrared Spectroscopy to Optimize Throughput and Costs of Soil Organic Carbon and Nitrogen Estimates: An Assessment in Grassland Soils

Low-cost techniques, such as mid-infrared (MIR) spectroscopy, are increasingly necessary to detect soil organic carbon (SOC) and nitrogen (N) changes in rangelands following improved grazing management. Specifically, Adaptive Multi-Paddock (AMP) grazing is being implemented to restore grassland ecosystems and sequester SOC often for commercialization in C markets. To determine how the accuracy of SOC and N predictions using MIR spectroscopy is affected by the number of calibration samples and by different predictive models, we analyzed 1000 samples from grassland soils. We tested the effect of calibration sample size from 100 to 1000 samples, as well as the predictive ability of the partial least squares (PLS), random forest (RF) and support vector machine (SVM) algorithms on SOC and N predictions. The samples were obtained from five different farm pairs corresponding to AMP and Conventional Grazing (CG), covering a 0–50 cm soil depth profile along a latitudinal gradient in the Southeast USA. Overall, the sample size had only a moderate influence on these predictions. The predictive accuracy of all three models was less affected by variation in sample size when &gt;400 samples were used. The predictive ability of non-linear models SVM and RF was similar to classical PLS. Additionally, all three models performed better for the deeper soil samples, i.e., from below the A horizon to the –50 cm depth. For topsoil samples, the particulate organic matter (POM) content also influenced the model accuracy. The selection of representative calibration samples efficiently reduces analysis costs without affecting the quality of results. Our study is an effort to improve the efficiency of SOC and N monitoring techniques.

Performance of the Winged Pearl Oyster Pteria sterna (Gould, 1851), Maintained in Hanging Culture at Three Depths, in the Eastern Equatorial Pacific

This study evaluated the performance of P. sterna under suspended culture at three depths (2, 6, and 10 m). Juveniles (dorso-ventral length 42.6±0.94 mm) were placed in enclosures suspended on a long line in Palmar (Ecuador) from October 2018 to October 2019. The antero-posterior axis of the shells, the shell, softs tissues, and biofouling masses, and the survival rate, were determined during one year of culture. Chlorophyll-a, total particulate matter (TPM), particulate organic matter (POM), salinity and temperature were studied at each depth. At the end of the cultivation period, growth and survival rates did not show significant differences between water depths, with all oysters attaining dorso-ventral lengths of 102-106 mm. Principal components analysis (PCA) revealed a direct and significant relationship between the variance of soft tissue dry mass growth and chlorophyll a concentration, salinity, particulate organic matter (POM) concentration, and temperature, during the culture period evaluated. Thus, the results obtained indicate that the suspended culture of the winged oyster P. sterna in Ecuador can be carried out effectively within the range of 2 and 10 m of depth, obtaining relatively high yields (growth-survival).

Photochemical and microbial transformation of particulate organic matter depending on its source and size

Particulate organic matter (POM) in water systems can be converted into dissolved organic matter (DOM) through various pathways depending on its properties and transformation. Thus, information on the behavior of POM is crucial for fully understanding water systems and the carbon cycle. In this study, the effects of particle size and the source of POM, as well as photochemical and microbial changes in DOM characteristics subsequently released from POM were evaluated using various spectral indices, excitation-emission matrix combined with parallel factor analysis components, and principal component analysis. The amount of dissolved organic carbon (DOC) released from POM during suspension was significantly associated with the carbon content of POM (p < 0.05). The amount of DOC (mg-C/g-SS) decreased in mineral-bound POM as a result of microbial degradation but increased in biogenic POM as a result of microbial dissolution, owing to the structural differences in organic matter from different sources. Mineral-bound POM showed more DOC production by photochemical desorption than microbial degradation, whereas biogenic POM displayed the opposite trend. The DOM derived from fine POM had more humified terrestrial humic-like substances than those derived from coarse POM. Principal components 1 and 2 were associated with DOC production and degree of humification, respectively. The increase in the degree of aromaticity and humification of organic matter was higher in mineral-bound POM by photochemical desorption of highly humified organic matter and in the biogenic POM by microbial dissolution. In conclusion, this study was able to provide basic information on the transformation of POM, thus, it is expected to broaden the knowledge of the biogeochemical cycle of organic matter.