Particulate Organic Matter Research Articles

Seaweed (Porphyra) cultivation enhances production of autochthonous refractory dissolved organic matter in coastal ecosystems

Seaweed cultivation contributes to coastal carbon sequestration making it a compelling strategy to mitigate global climate change. Porphyra (commonly known as nori) is an economically important seaweed known to have high release rates for biogenic dissolved and particulate organic matter (DOM and POM). However, the impact of Porphyra cultivation on coastal organic matter dynamics remains unclear. To fill this knowledge gap, we conducted investigations examining the quantity and optical properties of DOM and POM, microbial community structures and relevant environmental factors along a continuum from a subtropical river through its adjacent coastal Porphyra cultivation zone during the cultivation and non-cultivation periods. Dissolved organic carbon (DOC) concentration was significantly elevated during the cultivation versus non-cultivation period, while particulate organic carbon (POC) concentration decreased, thereby resulting in a higher DOC/POC ratio in the water column. Endmember mixing analysis further suggested that autochthonous organic matter dominated in the coastal cultivation zone during both periods, with limited inputs of terrestrial organic carbon. Redundancy analysis revealed that more microbial modules mediated organic matter transformations during the cultivation period, leading to a 169% higher estuarine addition of microbially-sourced humic-like C3 compared to the non-cultivation period. Our findings demonstrate that Porphyra cultivation enhanced coastal carbon sequestration by promoting the autochthonous production and transformation of refractory DOM, which has important implications for the sustainable management and development of coastal blue carbon strategies.

Coupling between landward and seaward fringes of sandy beaches: algal deposits on the upper beach influence biogeochemistry and faunal assemblages in the swash zone

Energy subsidies from the sea typically underpin ocean-exposed sandy beach ecosystems. Strandings of detached macroalgae – ‘wrack’ – can be a spectacular form of such cross-ecosystem transfers of organic matter that sustain consumers in the recipient shore system; this has given rise to a model of wrack promoting the diversity and abundance of invertebrates, with scaling effects on upper trophic levels.However, most wrack is often wave-cast to the upper beach, whereas a distinct part of the shore fauna is limited to the ocean fringe of beaches – the ‘swash zone’. This has the potential to create a spatial asymmetry between the location of subsidies (concentrated at the landwards fringe) and the location of some of the putative recipients distributed at the ocean fringe.Here, we tested whether the fauna of the swash zone can benefit from wrack subsidies, by sampling fauna and algal deposits on a range of beaches in NW Spain. We also measured the potential functional link between algal wrack and nutrients released from wrack during decay.Wrack decay increased nutrient concentrations, and it is the combination of wrack cover, nutrient levels, and sediment coarseness that jointly drove variation in the assemblage structure of the swash fauna among beaches. Similarly, the density of the swash fauna and species richness increased markedly at higher nutrient levels and wrack cover.Filter feeders were an important compartment in the food web of the swash macrofauna; we hypothesize that wrack deposits in the upper beach enhance food availability for this trophic guild via increasing nutrients in the water column, stimulating primary production and providing particulate organic matter derived from algal decay. Besides, several polychaetes and peracarid species function as secondary consumers and detritus feeders that plausibly benefit, directly or indirectly, on the particulate organic matter that accumulates on the sediment surface or percolates into the interstitial environment.These findings expand the ‘wrack enhancement’ model to include the promotion of consumers at the ocean edge of sandy shores; it also contains a cross-shore linkage via decomposition processes that favourably change the nutrient regime across all the beach face and thereby couple the swash zone with the upper strandline.

Soil nutrients and pH modulate carbon dynamics in particulate and mineral-associated organic matter during restoration of a Tibetan alpine grassland

Soil nutrients and pH modulate carbon dynamics in particulate and mineral-associated organic matter during restoration of a Tibetan alpine grassland

Sources and fate of particulate organic matter along the river-estuary-coastal ocean continuum: Constraints from amino acid and amino sugar carbon isotopes

Sources and fate of particulate organic matter along the river-estuary-coastal ocean continuum: Constraints from amino acid and amino sugar carbon isotopes

Warmer Climate Reduces the Carbon Storage, Stability and Saturation Levels in Forest Soils

AbstractForest soils store about one‐fifth of the global terrestrial biosphere carbon stock. However, our understanding of how soil geochemical, plant and microbial factors regulate forest soil organic carbon (SOC) storage, stability, and saturation levels remains limited. Here, we conducted a sampling campaign across a 5000‐km natural forest transect in China, measuring climate, geochemical factors and SOC fractions with varying stability. Additionally, we compiled a global data set of SOC fractions in major forest biomes. Our field survey and global synthesis consistently demonstrate that warmer climates not only reduce the content of labile particle organic matter (POM), but also decrease the typically stable mineral‐associated organic matter (MAOM), leading to a significant decline in total soil carbon storage. Additionally, warmer climates promote the crystallization of Fe/Al oxides, which decreases the formation efficiency of Fe/Al oxide associated organic complexes. Consequently, the mineralogical carbon saturation level declines from boreal forests (37%) to tropical forests (25%). Our findings underscore that, beyond the well‐established climate impacts, soil geochemical properties play a pivotal role in shaping forest SOC composition and saturation levels across latitudes. This highlights that colder regions harbor larger and more stable carbon pools, and that ongoing climate warming and associated soil geochemical properties shift could potentially lead to a decline in soil carbon storage and its capacity to mitigate climate change.

Long-term cropping system effects on soil organic matter fractions and enzyme activities in a cool oceanic climate

Information about soil organic matter fraction and enzyme activity responses to agricultural management may help guide decisions that sustain crop productivity and soil health. We measured carbon and nitrogen in bulk soil, mineral-associated organic matter, particulate organic matter, water-extractable organic matter, and the potential activity of β-glucosidase, N-acetyl-β-d-glucosaminadase, acid phosphomonoesterase and arylsulfatase in three cropping systems after: 1) 21-years of conventional- or no-tillage silage corn monoculture (0-20-cm); and 2) six years of nitrogen fertilization with or without nitrification inhibitors and 3) nine years of 100 or 200% the recommended broadcast or fertigation nitrogen rate in two distinct mature highbush blueberry systems (0-15-cm). Soil organic carbon, particulate organic carbon, particulate organic nitrogen, water-extractable nitrogen and arylsulfatase activity were 17%, 38%, 50%, 25% and 68% greater, respectively, with no-tillage than conventional tillage. Particulate organic carbon accumulated with two decades of no-tillage, which increased soil organic carbon without altering mineral-associated organic carbon. Nitrification inhibitors did not impact any soil organic matter fraction or enzyme activity after six years in a mature highbush blueberry system. Broadcasted nitrogen led to higher soil organic carbon than fertigation, but excessive application (200% vs 100% rate) depleted soil organic carbon, accumulated reactive nitrogen and reduced potential activity of N-acetyl-β-d-glucosaminadase, acid phosphomonoesterase and arylsulfatase after nine years in a mature highbush blueberry system. Excessive nitrogen may deplete organic carbon and cause reactive nitrogen accumulation in soil of mature highbush blueberry systems. Intensive agricultural management has trade-offs for carbon and nitrogen cycling that should be balanced with sustainable crop production.

Integrated Analysis of Indoor Air Quality and Fungal Microbiota in Educational Heritage Buildings: Implications for Health and Sustainability

Indoor air quality is paramount for the health and well-being of individuals, especially in enclosed spaces like office buildings, schools, hospitals, and homes where people spend a significant amount of time. Ensuring good indoor air quality is not only essential for reducing symptoms such as headaches, eye and respiratory irritation, fatigue, and difficulty in concentration, but it is also a key component of sustainable building practices aimed at promoting long-term health and environmental balance. This study aims to explore the impact of the microclimate and fungal microbiota on the health and cognitive performance of occupants in a university classroom, which is part of a cultural heritage building. The research delves into various microclimatic parameters, including temperature, relative humidity, CO2, volatile organic compounds, O2, and particulate matters (PM2.5 and PM10), to understand their influence on the development of microbiota and the manifestation of symptoms associated with Sick Building Syndrome. Over the course of a year-long investigation, microbiological samples were collected, revealing the presence of 19 fungal species, with Cladosporium, Alternaria, and Aureobasidium being the most prevalent genera. These species were found to thrive in an environment characterized by inadequate ventilation, posing potential health risks to occupants, such as allergic reactions and respiratory infections. Microclimatic parameter values such as mean temperature of 22.9 °C and mean relative humidity of 38.5% indicated moderate conditions for fungal proliferation, but occasional high levels of PM2.5 and CO2 indicated periods of poor indoor air quality, negatively influencing the comfort and health of the occupants. The questionnaires completed by 190 students showed that 51.5% reported headaches, 44.2% frequent sneezing, and 43.7% severe fatigue, linking these symptoms to increased levels of CO2 and PM2.5. The novelty of the study lies in the integrated approach to indoor air quality assessment in a heritage educational building, highlighting the need for improved ventilation and air management to enhance health and cognitive performance, while emphasizing sustainable indoor environment management that balances occupant well-being with the preservation of cultural heritage.

Effects of Low-Severity Fire on the Composition and Stability of Soil Organic Carbon in Permafrost Peatlands (Northeast China).

Climate change and human activity are increasing the frequency of wildfires in peatlands and threatening permafrost peatland carbon pools. In Northeast China, low-severity prescribed fires are conducted annually on permafrost peatlands to reduce the risk of wildfires. These fires typically do not burn surface peat but lead to the loss of surface vegetation and introduction of pyrogenic carbon. However, the long-term effects of repeated low-severity fires on soil carbon stability in these ecosystems remain unclear. Thus, we conducted low-severity prescribed fire experiments over 3 years in the permafrost peatlands of the Great Khingan Mountains. Our findings showed a gradual decline in the total carbon content, primarily due to the reduction in free particulate organic matter (fPOM). Initially, fPOM was higher in the burned sites but decreased with repeated burning. Chemical analyses revealed a 32% increase in the aromaticity of the fPOM at the burned sites, which diminished the thermal stability of the soil. Furthermore, both prescribed fires and the addition of pyrogenic carbon reduced biological stability while increasing enzyme activity and CO2 production, which was attributed to the introduction of post-fire pyrogenic carbon. These results suggest that low-severity fires compromise the stability of permafrost peatlands, particularly because the pyrogenic carbon input alters the chemical composition of the soil carbon fraction.

Physical drivers of bio-optical properties in the Guangdong-Hong Kong-Macao Greater Bay Area during the winter dry season

Understanding the variability of bio-optical properties in coastal seas is essential to assessing the impact of natural and anthropogenic activities on the quality of the coastal environments and their resources. This study investigated the vertical distribution of bio-optical properties and their potential driving forces in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) using a bio-optical dataset collected during the winter dry season. The hydrographic and biogeochemical properties observed across the GBA exhibited significant spatial variability, allowing the classification of the waters into three distinct regions: estuarine diluted water (EDW), Guangdong coastal current water (GCCW), and dense shelf water (DSW). Our findings show that EDW exhibited beam attenuation and optical backscatter coefficients an order of magnitude greater compared to the other two regions, which was attributed to factors such as higher concentrations of suspended particulate matter and organic material from estuarine sources. In contrast, the GCCW was characterized by lower salinity, temperature, and suspended particulate matter and displayed reduced turbidity near the coast, whereas nutrient-rich GCCW waters transported to the mid-shelf region supported increased phytoplankton biomass and a greater abundance of micro-phytoplankton. By exploring the bio-optical characteristics and their underlying processes in the GBA, this study enhances our understanding of the complex dynamics shaping the optical properties of coastal waters in this heavily urbanized region.

Temperate grassland conversion to conifer forest destabilises mineral soil carbon stocks.

Tree-planting is increasingly presented as a cost-effective strategy to maximise ecosystem carbon (C) storage and thus mitigate climate change. Its success largely depends on the associated response of soil C stocks, where most terrestrial C is stored. Yet, we lack a precise understanding of how soil C stocks develop following tree planting, and particularly how it affects the form in which soil C is stored and its associated stability and resistance to climate change. Here, we present changes in C and nitrogen (N) stored as mineral-associated organic matter (OM), occluded particulate OM, free particulate OM and dissolved OM, from four regional chronosequences of Scots pine (Pinus sylvestris L.) forests planted on former grasslands across Scotland. We found that c. 58-68 years after the plantation, bulk soil C and N stocks in the organic layer and the top 20cm of mineral soil decreased by half relative to unforested grasslands - a decrease roughly equivalent to a third of the simultaneous C gain in the tree biomass. This pattern was driven predominantly by a decrease in the amount of C and N stored as mineral-associated OM, an OM fraction considered as relatively long-lived. Our findings demonstrate the need to estimate C storage in response to tree planting based both on soil C stocks and tree biomass, as the use of the latter alone may significantly over-estimate net C benefits of tree planting on permanent grasslands.

Gene content of seawater microbes is a strong predictor of water chemistry across the Great Barrier Reef

BackgroundSeawater microbes (bacteria and archaea) play essential roles in coral reefs by facilitating nutrient cycling, energy transfer, and overall reef ecosystem functioning. However, environmental disturbances such as degraded water quality and marine heatwaves, can impact these vital functions as seawater microbial communities experience notable shifts in composition and function when exposed to stressors. This sensitivity highlights the potential of seawater microbes to be used as indicators of reef health. Microbial indicator analysis has centered around measuring the taxonomic composition of seawater microbial communities, but this can obscure heterogeneity of gene content between taxonomically similar microbes, and thus, microbial functional genes have been hypothesized to have more scope for predictive potential, though empirical validation for this hypothesis is still pending. Using a metagenomics study framework, we establish a functional baseline of seawater microbiomes across offshore Great Barrier Reef (GBR) sites to compare the diagnostic value between taxonomic and functional information in inferring continuous physico-chemical metrics in the surrounding reef.ResultsIntegrating gene-centric metagenomics analyses with 17 physico-chemical variables (temperature, salinity, and particulate and dissolved nutrients) across 48 reefs revealed that associations between microbial functions and environmental parameters were twice as stable compared to taxonomy-environment associations. Distinct seasonal variations in surface water chemistry were observed, with nutrient concentrations up to threefold higher during austral summer, explained by enhanced production of particulate organic matter (POM) by photoautotrophic picocyanobacteria, primarily Synechococcus. In contrast, nutrient levels were lower in winter, and POM production was also attributed to Prochlorococcus. Additionally, heterotrophic microbes (e.g., Rhodospirillaceae, Burkholderiaceae, Flavobacteriaceae, and Rhodobacteraceae) were enriched in reefs with elevated dissolved organic carbon (DOC) and phytoplankton-derived POM, encoding functional genes related to membrane transport, sugar utilization, and energy metabolism. These microbes likely contribute to the coral reef microbial loop by capturing and recycling nutrients derived from Synechococcus and Prochlorococcus, ultimately transferring nutrients from picocyanobacterial primary producers to higher trophic levels.ConclusionThis study reveals that functional information in reef-associated seawater microbes more robustly associates with physico-chemical variables than taxonomic data, highlighting the importance of incorporating microbial function in reef monitoring initiatives. Our integrative approach to mine for stable seawater microbial biomarkers can be expanded to include additional continuous metrics of reef health (e.g., benthic cover of corals and macroalgae, fish counts/biomass) and may be applicable to other large-scale reef metagenomics datasets beyond the GBR.D4ZFkyo-_x3xtsAViMg6HSVideo

Time and climate roles in driving soil carbon distribution and stability in particulate and mineral-associated organic matter pools.

Understanding the accumulation and stability of soil organic matter (SOM) pools as a function of time (i.e., soil age) and climate (i.e., precipitation and temperature) represents a crucial challenge. This study aims at investigating the effect of both climate and time on SOM distribution into particulate and mineral-associated organic matter (POM and MAOM, respectively), using two chronosequences located along a climate gradient. The contribution of POM and MAOM to soil organic carbon (SOC) storage differs between the climo-chronosequences and with depth. The ratio between MAOM and POM pools (MAOM/POM) ranges from 0.9 to 2.0 and from 1.4 to 3.5 in the wetter and cooler and in the drier and warmer chronosequence, respectively. Regardless of the chronosequence, the MAOM/POM ratio increases with depth, highlighting a more important role of the mineral-associated fraction in carbon storage in deeper soils. The concentration of organic carbon in mineral-associated (MAOC) and particulate (POC) pools along the soil profile in the wetter and cooler chronosequence is 2× and 3× higher, respectively, than in soils from the drier and warmer one. In particular, in the wetter and cooler chronosequence, MAOC and POC concentrations decrease with soil age. In the drier and warmer chronosequence, only POC concentration decreases with soil age, whereas MAOC concentration generally increases. The thermal stability of the MAOM fraction increases with soil age and depth only in the drier and warmer climatic conditions, whereas no differences with depth occur in the wetter and cooler chronosequence. Furthermore, the MAOM energy density decreases with soil depth and age in both chronosequences. Independently of the chronosequence, POM represents the most labile pool with higher energy density. In conclusion, time and climate play a different role in SOC distribution between the pools and on their relative stability. Soil age drives MAOM stability in drier and warmer conditions, whereas a wetter and cooler climate determines a higher SOC accumulation in both pools, although these greater carbon stocks are negatively correlated with their stability.

Differential use of multiple food sources at a bathyal benthic ecosystem in the central Sagami Bay revealed by amino acid nitrogen isotopic compositions

The nitrogen isotopic composition (δ15N) of amino acids can be used to estimate the trophic position of organisms with high precision compared to bulk tissue analyses, and shed light on potential food sources and food webs. Sagami Bay, Japan, is located at the tectonic plate boundary and have complex bottom topography, making multiple sources of organic matter to bathyal deep-sea ecosystems. Here, we applied this method to benthic animals (meiofauna, macrofauna, and megafauna) living at 1430 m deep in the central Sagami Bay, Japan. The δ15N value of phenylalanine (δ15NPhe) reflects the value of primary producers and was used to estimate the food sources of organisms, while the difference between δ15N value of glutamic acid (δ15NGlu) and δ15NPhe shifts between food source and consumer and was thus used to estimate the trophic position (TPGlu/Phe). The data obtained were interpreted together with previously reported values from benthic foraminifera of the same site for a holistic understanding of the food web. The trophic positions of organisms from the central Sagami Bay ranged mostly from 2.2 to 3.6, except hydrozoans (up to 4.3). Organisms with similar bulk tissue δ15N values sometimes exhibited different TPGlu/Phe values. The observed δ15NPhe varied greatly among benthic organisms in the central Sagami Bay (− 8.3‰ to 21.1‰), suggesting a wide variety of food sources exhibiting different δ15NPhe values. Given the location of the study site at the central part of the deep basin, various organic matter from terrestrial, planktic, coastal, upper bathyal, and perhaps chemosynthetic origins can be expected to accumulate and become available for bathyal benthic organisms. Furthermore, the cross-plot of δ15NPhe values and bulk tissue δ13C values, another indicator of food source, suggested that macro–megafauna examined rely on different organic matter than metazoan meiofauna and foraminifera, which rely on particulate organic matter and bulk sediments. Despite living in the same habitat, organisms of these two size classes may belong to independent food webs due to differences in feeding ecology.

Particle composition-based water classification method for estimating chlorophyll-a in coastal waters from OLCI images

The complex composition of seawater presents significant challenges for accurately estimating biogeochemical data through optical measurements, both in situ and via satellite data. To address the regional applicability of single bio-optical or remote sensing algorithms caused by these challenges, we explored a water optical classification method based on inherent optical properties and particle composition. The ratio of organic particulate matter to total suspended particulate matter concentration (POM/SPM) serves as an optical discriminator of water bodies based on the proportions of organic and mineral particles. The boundary value is determined by the relationship between the particulate backscattering coefficient bbp(λ) and POM/SPM. By analyzing in situ data collected from the coastal waters of Qinhuangdao in the Bohai Sea, China, we developed empirical algorithms to estimate both the POM/SPM ratio and chlorophyll-a (Chl-a) concentration, the latter being a key parameter derived from current ocean remote sensing that indicates phytoplankton abundance. The evaluation of our algorithms demonstrates that accounting for POM/SPM variations significantly improves Chl-a estimate accuracy across the optically-complex coastal waters near Qinhuangdao compared to algorithms that do not consider changes in particle composition, such as the well-known OC4Me algorithm. Furthermore, we determined the distribution of monthly averaged Chl-a concentration and POM/SPM ratio on the coast of Qinhuangdao, Bohai Sea, in 2023. Our results show, for the first time, that the monthly average variations of the POM/SPM ratio in the Bohai Sea and Chl-a concentrations exhibit pronounced seasonal fluctuations.

Fatty Acids in Cnidaria: Distribution and Specific Functions.

The phylum Cnidaria comprises five main classes-Hydrozoa, Scyphozoa, Hexacorallia, Octocorallia and Cubozoa-that include such widely distributed and well-known animals as hard and soft corals, sea anemones, sea pens, gorgonians, hydroids, and jellyfish. Cnidarians play a very important role in marine ecosystems. The composition of their fatty acids (FAs) depends on food (plankton and particulate organic matter), symbiotic photosynthetic dinoflagellates and bacteria, and de novo biosynthesis in host tissues. In cnidarian lipids, besides the common FA characteristics of marine organisms, numerous new and rare FAs are also found. All Octocorallia species and some Scyphozoa jellyfish contain polyunsaturated FAs (PUFAs) with 24 and 26 carbon atoms. The coral families can be distinguished by specific FA profiles: the presence of uncommon FAs or high/low levels of common fatty acids. Many of the families have characteristic FAs: Acroporidae are characterized by 18:3n6, eicosapentaenoic acid (EPA) 20:5n3, 22:4n6, and 22:5n3; Pocilloporidae by 20:3n6, 20:4n3, and docosahexaenoic acid 22:6n3 (DHA); and Poritidae by arachidonic acid (AA) and DHA. The species of Faviidae show elevated concentrations of 18:3n6 and 22:5n3 acids. Dendrophylliidae, being azooxanthellate corals, have such dominant acids as EPA and 22:5n3 and a low content of DHA, which is the major PUFA in hermatypic corals. The major and characteristic PUFAs for Milleporidae (class Hydrozoa) are DHA and 22:5n6, though in scleractinian corals, the latter acid is found only in trace amounts.

Interseeding cover crop into an irrigated sandy loam for 6 years: Soil, crop, and economic response

AbstractInterseeding cover crops (CCs) may be a potential strategy to manage sandy soils, which are highly prone to degradation. However, how this practice affects CC biomass production and other ecosystem services in sandy soils over the traditional CC planting system (post‐harvest drilling) is still unclear. We studied how broadcast interseeded (32–67 days before crop harvest) winter rye (Secale cereale L.) CC affected CC biomass production, nitrate leaching potential, soil properties, crop yields, and farm income compared with post‐harvest drilled CC in an on‐farm irrigated no‐till corn (Zea mays L.)–soybean (Glycine max L.) experiment in a sandy loam in the western US Corn Belt for 6 years. Across the 6 years, interseeded CC produced 0.57 Mg ha−1 of biomass, while post‐harvest drilled CC produced 0.37 Mg ha−1. Nitrate leaching is a concern in sandy soils, but interseeded CC had mixed effects on soil nitrate concentration. Interseeded CC did not affect soil properties (particulate organic matter and organic C concentrations, and wet aggregate stability) and crop yields. Further, interseeded CC did not reduce farm income more than post‐harvest drilled CC. The limited effect of interseeded CCs is likely due to the relatively small increase in CC biomass production over the traditional CC planting system. Additional strategies including irrigation, drill interseeding, and planting green may boost interseeded CC biomass production and thus soil services in sandy soils. After 6 years, interseeded CC slightly boosted CC biomass production but minimally affected soils and crops, and both interseeded and post‐harvest‐drilled CCs reduced net income.

Polycyclic Aromatic Hydrocarbon Contents in Soil Organic Matter Fractions Along an Elevation Gradient in the French Alps

ABSTRACTPolycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic pollutants that accumulate in soils because of their high affinity for soil organic matter (SOM). As these pollutants are toxic to humans and the environment, a better understanding of their fate in the environment is required. This study aimed to assess the PAH distribution within soils according to different soil fractions: the free particulate organic matter (fPOM), the occluded particulate organic matter (oPOM) and the mineral‐associated organic matter (MaOM). PAH contents were measured in bulk soils and SOM fractions of alpine soils along an elevation gradient in the French Alps (Lautaret) from 1920 m to 2840 m a.s.l. A specific PAH distribution was identified, with highest PAH contents in the oPOM, followed by the fPOM, then the MaOM. Organic matter (OM) contents of each fraction can partly explain this distribution, but results of nuclear magnetic resonance (NMR) spectroscopy on fPOM and oPOM also highlighted a correlation between the PAH contents and the degree of decomposition of SOM. This indicates that the PAH distribution may be linked to the formation and transformation of fractions: (i) PAHs in the fPOM correspond to relatively recent deposits and mainly reflect the background contamination, (ii) in the oPOM are the PAHs that resist biodegradation during the transformation of fPOM into oPOM and accumulate in the oPOM; this accumulation may be further enhanced by the formation of aggregates. Finally, (iii) in the MaOM, the lower PAH contents can be explained by the different formation pathway of this fraction and its high degree of decomposition. As the PAH distribution may have an impact on their dynamics in soils, it should be taken into consideration in future research.

Using δ15N of Amino Acids and Nitrate to Investigate Particle Production and Transformation in the Ocean: A Case Study From the Eastern Tropical North Pacific Oxygen Deficient Zone

AbstractThe eastern tropical North Pacific oxygen deficient zone (ETNP‐ODZ) exhibits a distinct physical and biological environment compared to other oxygenated water columns, leading to a unique scenario of particulate organic matter (POM) production and vertical transport. To elucidate these biological pump processes, we present the first comparison of δ15N values of nitrate, phenylalanine (Phe), and glutamic acid (Glu) within two distinct size fractions of particles collected along a productivity gradient in the ETNP‐ODZ. Low δ15NPhe and δ15NGlu values in both particle pools at sites with prominent secondary chlorophyll maximum (SCM), compared to the ambient δ15N‐NO3−, suggest the presence of recycled N‐utilizing primary producers distinct from those at the primary chlorophyll maximum and their contribution to export. We observed reduced 15N enrichment of Phe in small particles and a narrower δ15NPhe disparity between the two particle size fractions compared to the results from oxic waters, likely due to slower heterotrophic microbial degradation of small particles. Unique δ15NPhe and δ15NGlu signatures of particles were found at the lower oxycline, potentially attributable to chemoautotrophic production and zooplankton mediation. These findings underscore the need for further investigations targeting particles generated at the SCM, their subsequent alteration by zooplankton, and the new production by chemoautotrophs. This will allow for a better evaluation of the efficiency of the biological pump in the globally expanding ODZs under contemporary climate change.

Fish Sludge as Feed in Circular Bioproduction: Overview of Biological and Chemical Hazards in Fish Sludge and Their Potential Fate via Ingestion by Invertebrates

ABSTRACTAquaculture farming discharges large volumes of fish sludge, consisting of particulate organic matter from feed spill and feces. Fish sludge from land‐based salmonid aquaculture systems can potentially be used to feed low‐trophic species such as marine polychaetes and insects. Further use of these invertebrates as feed may provide a more sustainable feed chain. However, food security must not compromise feed or food safety. The use of fish sludge as feed is currently not permitted in the European Union (EU). A regulatory assessment that considers the integration of fish sludge in the circular bioeconomy requires knowledge of the potential chemical and biological risks involved. This review has compiled data from existing literature on the occurrence of chemical and biological hazards, as well as the physical properties of fish sludge. The potential risks along this feed chain, from fish sludge to novel feed ingredient production, are discussed in light of the EU regulatory framework. Within the available, but scarce, literature on biological hazards in fish sludge, there is no clear evidence that fish sludge is unsafe for use as a feed material for invertebrates if treatment criteria established in the EU regulations are followed. Scarcity implies a level of uncertainty, but not necessary of risk. For the chemical hazards, some elements are of concern and may exceed regulatory limits, and there are limited data on the occurrence of organic pollutants. This review highlights considerable knowledge gaps concerning the use of fish sludge in a circular feed and food system.

Vertical biochemical composition of particulate organic matter in the Seychelles-Chagos Thermocline Ridge (SCTR), southwestern Indian Ocean

Vertical biochemical composition of particulate organic matter in the Seychelles-Chagos Thermocline Ridge (SCTR), southwestern Indian Ocean