Organic Carbon Supply Research Articles

Seasonal Variation in Flow and Metabolic Activity Drive Nitrate and Carbon Supply and Demand in a Temperate Agricultural Stream

AbstractIn‐stream biogeochemical processing, typically associated with base flow conditions, has recently been assessed at higher discharges, aided by high frequency monitoring. However, the potential for nutrient and carbon processing is still largely unknown in streams impacted by agriculture, representing major pathways for eutrophication and diffuse pollution. In this study, we measured solute concentrations and gross primary productivity (GPP) and ecosystem respiration (ER) to infer nitrate (NO3−) and dissolved organic carbon (DOC) supply and demand across contrasting hydrological conditions. As expected, solute supply greatly surpassed in‐stream biological demand for both NO3− and DOC for intermediate to large discharges. However, during four consecutive weeks in summer, lowered NO3− supply and high metabolic activity led to a 60% and 31% reduction in stream NO3− and DOC export. We also compared metabolism‐discharge versus solute concentration‐discharge patterns during storm events to better understand biogeochemical responses to high flows. Metabolic rates showed a contrasting response to storm events: ER increased while GPP decreased following declines in NO3− concentrations. The positive correlation between GPP and NO3− concentrations suggests that GPP suppression can be partially attributed to decreased NO3− availability during storm events. This study supports the idea that agricultural streams have a limited capacity to biologically process DOC and NO3−. However, it also emphasizes that the balance between supply and demand can vary from severe saturation to limitation, depending on seasonal fluctuations in discharge and metabolic activity, highlighting the crucial role of mitigating pollution at its source during hydrologically active periods to improve water quality.

Impact of freeze-thaw cycles and influent C/N ratios on N2O emissions in subsurface wastewater infiltration systems

Subsurface wastewater infiltration system (SWIS) is important source of N2O emission, biological denitrification process relies on organic carbon source as electron donor, enabling denitrifying reductase (NAR, NIR, NOR, and N2OR) to reduce nitrate nitrogen to N2. However, freeze-thaw cycles cause changes in soil structure through physical and biological processes that increase organic matter availability and microbial activity, thereby accelerating upper (aerobic) organic matter degradation. This leads to carbon deficiency in the lower (anaerobic) layer, which reduces denitrification efficiency increasing N2O production and emissions. This study investigated effects of influent C/N ratios on N2O emissions from SWIS under freeze-thaw stress, and changes in denitrifying reductase and microbial communities. Results showed that as influent C/N ratio increased from 6:1–10:1, average TN removal of SWIS decreased from 89.59 % to 84.95 %, while N2O emission rate decreased from 0.106 mg·m−2·h−1 to 0.0333 mg·m−2·h−1, a reduction of 68.61 %. Meanwhile, N2OR activity increased by 29.95 % with C/N ratio increasing from 6 to 10, showing a significant reduction of N2O. High-throughput sequencing results revealed that Proteobacteria and Firmicutes showed a linear relationship with influent C/N. As C/N increased from 6 to 8 and 10, Proteobacteria relative abundance increased from 22.24 % ± 1.79–32.51 % ± 2.51 % and 39.59 % ± 3.45 %, while Firmicutes relative abundance decreased from 31.73 % ± 7.87–3.34 % ± 0.27 % and 2.19 % ± 0.07 %. These results indicated that sufficient supply of organic carbon provided abundant electron donors for denitrifying reductases in freeze-thaw-affected SWIS, promoting influent NO3--N reduction and decreasing N2O release rates. Conversely, under low C/N ratio conditions, electron acceptance capacity of N2OR was limited and N2OR activity was inhibited, resulting in N2O accumulation and emission. SynopsisThis paper shows how increasing the organic carbon supply in SWIS can reduce N2O emissions and improve nitrogen removal under freeze-thaw stress.

Optimal balance of organic detritus and feed for fish growth and water quality improvement through regulating nutrients cycling

In order to explore the effects of different feed composition on the nutrient level and microbial loop structure in aquaculture ponds, a field simulation experiment in aquaculture ponds was conducted by adding different proportions (0%, 20%, 40% and 60%) of bagasse to fish feed for combined feeding. The addition of bagasse significantly reduced the levels of various forms of nitrogen and phosphorus in the water, especially with the addition of 60% bagasse. In the treatments without addition and with 20% bagasse added, nitrogen and phosphorus levels remained relatively high, which should be attributed to the decomposition of feed and the release of sediment, ultimately stimulating the abundant reproduction of algae. Bacterial growth was limited due to insufficient supply of organic carbon, and the growth of fish relied more on the components of the feed. With the addition of 60% bagasse, the high organic carbon and low nitrogen and phosphorus levels could not support the growth of phytoplankton, bacteria, and zooplankton. It is inferred that organic carbon may be more degraded into carbon dioxide, ultimately limiting the growth of fish. Adding 40% bagasse achieved a balanced level of carbon, nitrogen, and phosphorus, establishing a healthy and stable microbial loop structure (including phytoplankton, bacteria, and zooplankton). Most nutrients were converted into plankton, which then became natural food for fish, ensuring complete nutrient utilization. This is beneficial for both water quality improvement and fish reproduction. Therefore, adding a moderate proportion of bagasse to the feed can maximize the effects of water quality improvement, fish reproduction, and even the quality of fish meat.

Anthropogenic and climatic impacts on historic sediment, carbon, and phosphorus accumulation rates using 210Pbex and 137Cs in a sub-watershed linked to Zarivar Lake, Iran

To estimate a watershed’s response to climate change, it is crucial to understand how human activities and climatic extremes have interacted over time. Over the last century, the Zarivar Lake watershed, Iran, has been subjected to various anthropogenic activates, including deforestation and inappropriate land-management practices alongside the implementation of conservation measures like check dams. To understand the effects of these changes on the magnitude of sediment, organic carbon (OC), and phosphorus supplies in a small sub-watershed connected to the lake over the last century, a lake sediment core was dated using 210Pbex and 137Cs as geochronometers. The average mass accumulation rate (MAR), organic carbon accumulation rates (OCAR), and particulate phosphorus accumulation rates (PPAR) of the sediment core were determined to be 6498 ± 2475, 205 ± 85, and 8.9 ± 3.3 g m−2 year−1, respectively. Between the late 1970s and early 1980s, accumulation rates were significantly higher than their averages at 7940 ± 3120, 220 ± 60, and 12.0 ± 2.8 g m−2 year−1 respectively. During this period, the watershed underwent extensive deforestation (12%) on steep slopes, coinciding with higher mean annual precipitations (more than double). Conversely, after 2009, when check dams were installed in the sub-watershed, the sediment load to the lake became negligible. The results of this research indicate that anthropogenic activities had a pronounced effect on MAR, OCAR, and PPAR, causing them to fluctuate from negligible amounts to values twice the averages over the last century, amplified by climatic factors. These results imply that implementing climate-smart watershed management strategies, such as constructing additional check dams and terraces, reinforcing restrictions on deforestation, and minimum tillage practices, can facilitate protection of lacustrine ecosystems under accelerating climate change conditions.Graphical

The distribution of particulate organic matter in the heterogeneous soil matrix - Balancing between aerobic respiration and denitrification

Denitrification, a key process in soil nitrogen cycling, occurs predominantly within microbial hotspots, such as those around particulate organic matter (POM), where denitrifiers use nitrate as an alternative electron acceptor. For accurate prediction of dinitrogen (N2) and nitrous oxide (N2O) emissions from denitrification, a precise quantification of these microscale hotspots is required. The distribution of POM is of crucial importance in this context, as the local oxygen (O2) balance is governed not only by its high O2 demand but also by the local O2 availability.Employing a unique combination of X-ray CT imaging, microscale O2 measurements, and 15N labeling, we were able to quantify hotspots of aerobic respiration and denitrification. We analyzed greenhouse gas (GHG) fluxes, soil oxygen supply, and the distribution of POM in intact soil samples from grassland and cropland under different moisture conditions. Our findings reveal that both proximal and distal POM, identified through X-ray CT imaging, contribute to GHG emissions. The distal POM, i.e. POM at distant locations to air-filled pores, emerged as a primary driver of denitrification within structured soils of both land uses. Thus, the higher denitrification rates in the grassland could be attributed to the higher content of distal POM. Conversely, despite possessing compacted areas that could favor denitrification, the cropland had only small amounts of distal POM to stimulate denitrification in it. This underlines the complex interaction between soil structural heterogeneity, organic carbon supply, and microbial hotspot formation and thus contributes to a better understanding of soil-related GHG emissions.In summary, our study provides a holistic understanding of soil-borne greenhouse gas emissions and emphasizes the need to refine predictive models for soil denitrification and N2O emissions by incorporating the microscale distribution of POM.

Impacts of temperature and fluid seepage on organic matter composition in sediments of an active hydrothermal basin

Marine sediments are one of the largest organic carbon (OC) sinks on Earth. Yet, major knowledge gaps remain in our understanding of sedimentary OC cycling, particularly regarding temperature-induced alteration processes of OC from different sources. Here, we investigate OC-rich sediments of Guaymas Basin (Gulf of California) across two hydrothermal areas, one with only conductive geothermal heating and the other additionally experiencing seepage of hydrocarbon-rich fluids from deeper layers. We use Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) to investigate diagenetic OC changes and show that cold control sites in both hydrothermal areas are dominated by similar contributions of lipid-derived compounds, nitrogenous (likely protein-derived) compounds, carbohydrates, and polyaromatic hydrocarbons (PAHs). These OC compound groups are largely derived from phytoplankton detritus from overlying water. Conductively heated sediments, which reach in situ temperatures of ∼ 80 °C, have similar general OC compositions and contents to these cold sites, but show evidence of diagenetic modifications of individual carbohydrate groups in deeper layers. By contrast, strong decreases in carbohydrate and nitrogenous compound abundances at the seep sites indicate that these compound groups are not only modified but also selectively degraded at the higher temperatures (>80 °C) of these sites. Increases in pyrolysis products of PAHs, prist-1-ene, and alkanes with depth, moreover, show that import of OC by deep hydrothermal fluids contributes significantly to sedimentary OC pools mainly in deeper layers of these sites. Our study provides the first comprehensive analysis of major OC compound groups in Guaymas Basin sediment and indicates that the supply of OC by hydrothermal fluid flow only has minor impacts on particulate organic matter compositions at the seafloor, even at active seep sites. We furthermore show that temperatures up to ∼ 80 °C already result in thermochemical modifications of organic matter (OM) that are potentially linked to the onset of kerogen formation. The sequence and time scales of chemical modifications and activations in relation to temperature are an important subject for future investigations.

It's time to broaden what we consider a 'blue carbon ecosystem'.

Photoautotrophic marine ecosystems can lock up organic carbon in their biomass and the associated organic sediments they trap over millennia and are thus regarded as blue carbon ecosystems. Because of the ability of marine ecosystems to lock up organic carbon for millennia, blue carbon is receiving much attention within the United Nations' 2030 Agenda for Sustainable Development as a nature-based solution (NBS) to climate change, but classically still focuses on seagrass meadows, mangrove forests, and tidal marshes. However, other coastal ecosystems could also be important for blue carbon storage, but remain largely neglected in both carbon cycling budgets and NBS strategic planning. Using a meta-analysis of 253 research publications, we identify other coastal ecosystems-including mud flats, fjords, coralline algal (rhodolith) beds, and some components or coral reef systems-with a strong capacity to act as blue carbon sinks in certain situations. Features that promote blue carbon burial within these 'non-classical' blue carbon ecosystems included: (1) balancing of carbon release by calcification via carbon uptake at the individual and ecosystem levels; (2) high rates of allochthonous organic carbon supply because of high particle trapping capacity; (3) high rates of carbon preservation and low remineralization rates; and (4) location in depositional environments. Some of these features are context-dependent, meaning that these ecosystems were blue carbon sinks in some locations, but not others. Therefore, we provide a universal framework that can evaluate the likelihood of a given ecosystem to behave as a blue carbon sink for a given context. Overall, this paper seeks to encourage consideration of non-classical blue carbon ecosystems within NBS strategies, allowing more complete blue carbon accounting.

Uncovering the role of oxygen on organic carbon cycling: insights from a continuous culture study with a facultative anaerobic bacterioplankton species (Shewanella baltica)

Deoxygenation is tied to organic carbon (Corg) supply and utilization in marine systems. Under oxygen-depletion, bacteria maintain Corg respiration using alternative electron acceptors such as nitrate. Since anaerobic respiration’s energy yield is lower, Corg remineralization may be reduced and its residence time increased. We investigated the influence of oxygen and alternative electron acceptors’ availability on Corg cycling by heterotrophic bacteria during a continuous culture experiment with Shewanella baltica, a facultative anaerobic γ-Proteobacteria in the Baltic Sea. We tested six different oxygen levels, from suboxic (<5 µmol L-1) to fully oxic conditions, using a brackish (salinity=14 g L-1) media supplied with high (HighN) or low (LowN) inorganic nitrogen concentrations relative to glucose as labile Corg source. Our results show that suboxia limited DOC (glucose) uptake and cell growth only under LowN, while higher availability of alternative electron acceptors seemingly compensated oxygen limitation under HighN. N-loss was observed under suboxia in both nitrogen treatments. Under HighN, N-loss was highest and a C:N loss ratio of ~2.0 indicated that Corg was remineralized via denitrification. Under LowN, the C:N loss ratio under suboxia was higher (~5.5), suggesting the dominance of other anaerobic respiration pathways, such as dissimilatory nitrate reduction to ammonium (DNRA). Bacterial growth efficiency was independent of oxygen concentration but higher under LowN (34 ± 3.0%) than HighN (26 ± 1.6%). Oxygen concentration also affected dissolved organic matter (DOM) cycling. Under oxic conditions, the release of dissolved combined carbohydrates was enhanced, and the amino acid-based degradation index (DI) pointed to more diagenetically altered DOM. Our results suggest bacterial Corg uptake in low-oxygen systems dominated by S. baltica can be limited by oxygen but compensated by high nitrate availability. Hence, suboxia diminishes Corg remineralisation only when alternative electron acceptors are lacking. Under high nitrate:Corg supply, denitrification leads to a higher N:C loss ratio, potentially counteracting eutrophication in the long run. Low nitrate:Corg supply may favour other anaerobic respiration pathways like DNRA, which sustains labile nitrogen in the system, potentially intensifying the cycle of eutrophication. Going forward, it will be crucial to establish the validity of our findings for S. baltica in natural systems with diverse organic substrates and microbial consortia.

Soil Chemical and Physical Attributes in Recovering Areas in the Southern Amazon

The recovery of soil quality and forest regeneration is of fundamental environmental importance, especially in the Amazon biome. The objective was to evaluate the contribution of soil’s physical and chemical attributes in degraded areas in recovery process with different ages and compared to adjacent degraded areas cultivated with grassland, in the Southern Amazon. For this, was used areas located in the south of the Brazilian Amazon and four different areas were chosen, with 6 years of recovery (APP-6), 3 years (APP-3), degraded (APPD) area and degraded areas cultivated with grassland (DP). With emphasis on the physical variable bulk density soil showed averages of 1.37± 0.052 g cm-3 (APP-6), 1.49± 0.066 g cm-3 (APP-3), 1.55± 0.055 g cm-3 (APPD) and 1.67±0.077 g cm-3 (DP), respectively, and there was a decrease in soil density with longer area recovery time. As for the soil chemical variable of P observed averages of 18.46±2.74 mg kg-1(APP-6), 2.86±1.73 mg kg-1 (APP-3), 1.46±0.69 mg kg-1 (APPD) and 1.1±0.20 mg kg-1 (DP), there was a high increase in P in areas with longer recovery time. Study of comparison of means, was possible to elucidate the relationships between the soli’s chemical and physical attributes in the four areas studied. The results showed a greater supply of organic carbon, phosphorus, exchangeable cations (K+, Ca+ 2 and Mg+2) to APP-6 in relation DP. APPD e APP-3 areas. Similarly, the improvement in the physical attributes of total porosity and the bulk density of the soil in the area of APP-6 years of recovery, in comparison with the other areas (DP, APP-3 e APPD).

Metabolic response to a heterologous poly-3-hydroxybutyrate (PHB) pathway in Phaeodactylum tricornutum.

The marine diatom Phaeodactylum tricornutum is an emerging host for metabolic engineering, but little is known about how introduced pathways are integrated into the existing metabolic framework of the host or influence transgene expression. In this study, we expressed the heterologous poly-3-hydroxybutyrate (PHB) pathway using episomal expression, which draws on the precursor acetyl coenzyme-A (AcCoA). By experimentally perturbing cultivation conditions, we gained insight into the regulation of the endogenous metabolism in transgenic lines under various environmental scenarios, as well as on alterations in AcCoA flux within the host cell. Biosynthesis of PHB led to distinct shifts in the metabolome of the host, and further analysis revealed a condition-dependent relationship between endogenous and transgenic metabolic pathways. Under N limitation, which induced a significant increase in neutral lipid content, both metabolic and transcriptomic data suggest that AcCoA was preferably shunted into the endogenous pathway for lipid biosynthesis over the transgenic PHB pathway. In contrast, supply of organic carbon in the form of glycerol supported both fatty acid and PHB biosynthesis, suggesting cross-talk between cytosolic and plastidial AcCoA precursors. This is the first study to investigate the transcriptomic and metabolomic response of diatom cell lines expressing a heterologous multi-gene pathway under different environmental conditions, providing useful insights for future engineering attempts for pathways based on the precursor AcCoA. KEY POINTS: • PHB expression had minimal effects on transcription of adjacent pathways. • N limitation favoured native lipid rather than transgenic PHB synthesis. • Glycerol addition allowed simultaneous lipid and PHB accumulation.

Persistent hot spots of CO2 and CH4 in coastal nearshore environments

AbstractNearshore environments are typically supersaturated with the potent greenhouse gases methane and carbon dioxide, due to intense remineralization of the elevated supply of organic carbon in these systems. These environments are characterized by overlapping biogeochemical gradients and heterogeneous morphology, and the overall spatial variability in nearshore greenhouse gas concentrations remains unclear. We measured surface water partial pressures of carbon dioxide and methane synoptically with water quality parameters in the coastal Baltic Sea, covering two ice‐free seasons. The high‐frequency flow‐through data revealed sites with recurring very high partial pressures of carbon dioxide and methane (i.e., hot spots) scattered around the 50 km × 40 km study area, exceeding overall partial pressure averages by 455 μatm (CH4) and 2396 μatm (CO2). High partial pressures were linked with elevated inputs of allochthonous and autochthonous organic matter, underpinning the major role of organic enrichment of coastal environments in global carbon cycling.

Oxic methane production from methylphosphonate in a large oligotrophic lake: limitation by substrate and organic carbon supply.

Methane is an important greenhouse gas that is typically produced under anoxic conditions. We show that methane is supersaturated in a large oligotrophic lake despite the presence of oxygen. Metagenomic sequencing indicates that diverse, widespread microorganisms may contribute to the oxic production of methane through the cleavage of methylphosphonate. We experimentally demonstrate that these organisms, especially members of the genus Acidovorax, can produce methane through this process. However, appreciable rates of methane production only occurred when both methylphosphonate and labile sources of carbon were added, indicating that this process may be limited to specific niches and may not be completely responsible for methane concentrations in Flathead Lake. This work adds to our understanding of methane dynamics by describing the organisms and the rates at which they can produce methane through an oxic pathway in a representative oligotrophic lake.

Rapid Expansion of Fixed Nitrogen Deficit in the Eastern Pacific Ocean Revealed by 50‐Year Time Series

AbstractClimate change is expected to increase the strength of ocean Oxygen Deficient Zones (ODZs), but we lack a detailed understanding of the temporal or spatial variability of these ODZs. A 50‐year time series in the Eastern Tropical North Pacific (ETNP) ODZ revealed that it has strengthened by 30% from 1994 to 2019. We subdivided the ODZ into a core and a deep layer based on potential density and revealed that different processes control the magnitude of fixed nitrogen loss between these regions. We postulate that the depth of the upper ETNP ODZ water mass, the 13°C Water, influences the organic carbon supply to the core ODZ and therefore its strength. We correlated the maximum fixed nitrogen loss in the core ODZ with a nearby sedimentary nitrogen isotope record and found that this recent increase in the magnitude of fixed nitrogen loss occurred only a few times over the last 1,200 years. Using this correlation, we derived the first confidence interval for the natural variability of the maximum fixed nitrogen loss within the ETNP ODZ, which has a range of 3.3 μmol kg−1 (p = 0.01). While the current increase is only comparable to two previous events, it is within the confidence interval for natural variability (p = 0.03). The deep ODZ also strengthened from 2016 to 2019 by approximately 30%, but this increase occurred more rapidly than the core ODZ, and this dramatic increase was not observed over the rest of the 40 years. Climate‐driven intensification could lead to unprecedented changes in the ETNP ODZ within the next decade.

Rotifer distribution patterns in relation to dissolved organic matter in the middle reaches of Huai River Basin during the dry season.

Increased dissolved organic matter (DOM) may induce water browning and affect zooplankton communities by changing photochemical environment, microbial food web, and bioavailability of organic carbon supply. However, little is known about the relationship between DOM components and rotifers in natural rivers, relative to the cladocerans and copepods. Here, we investigated the spatial patterns of rotifer distribution in relation to DOM by collecting forty-four water samples from four areas in the middle reaches of Huai River Basin. Results revealed that DOM was described by two humic-like and two protein-like components. There were significant differences in the composition and diversity of rotifer communities among areas, which might be related to autochthonous and allochthonous DOM as well as geographical distances. Specifically, rotifer communities were mainly related to molecular weight, substituents on the aromatic ring, humification level, and protein-like materials. Autochthonous and fresh DOM was positively associated with rotifer abundance and richness, and terrigenous humic-like substances were positively associated with rotifer diversity and evenness. There was a reciprocal effect between rotifer and DOM. Our findings will contribute to the understanding of the possible effects of water browning on rotifer communities, providing new insights into the key role of DOM and rotifer in the energy transfer of aquatic systems.

Semi-continuous production of polyhydroxybutyrate (PHB) in the Chlorophyta Desmodesmus communis

Polyhydroxyalkanoates (PHAs) are promising alternatives that accumulate as energy and carbon storage material in various microorganisms, including bacteria and microalgae, being biodegradable and suitable for a wide variety of applications. Among these compounds, the most prevalent and well-characterized biopolymer is polyhydroxybutyrate (PHB), which belongs to the short-chain PHAs.The present study was designed to evaluate algae-based PHB production in two Chlorophyta (Desmodesmus communis and Chlorella vulgaris) under a two-phase nutritional mode of cultivation, namely a phototrophic growth phase (PGP) and a mixotrophic stress phase (MSP) with N,P-depleted media and organic carbon supply (i.e., glucose or sodium acetate, NaOAc). The highest PHB productivity (0.11 g PHB/g biomass/d; 0.015 g PHB/L/d), corresponding to 32.1 % w/w of intracellular PHB, was observed for D. communis after 3 days of cultivation under mixotrophic conditions in batch cultures (e.g., low light, phosphorus-free medium, 1 g/L of NaOAc). A scaled-up cultivation (10 L) was set up to evaluate for the first time PHB yields and biomass composition in a semi-continuous system. A PHB content of 34 % w/w was achieved on day 8, corresponding to a maximum PHB productivity of 0.10 g PHB/g biomass/d (or 0.011 g PHB/L/d), which increased up to 54 % w/w on day 15. The biomass was composed of about 30 % w/w proteins, 6 % w/w polysaccharides, and 11 % w/w lipids, which can be valorised from a biorefinery perspective. The scaled-up D. communis cultivation in 10 L PBRs confirmed the potential utilization of this algal species for PHB production with productivity up to 2-times higher than those reported for several cyanobacterial species and similar to the maximum value obtained with batch cultures in previous works performed with Scenedesmaceae.

Productivity-induced redox transition within the Niobrara formation, western Interior seaway, Colorado

Deposition of organic rich shale/marl within the Niobrara Formation during the Coniacian to Santonian Ocean anoxic event (OAE 3) within the Western Interior Seaway presents a unique record of variable organic carbon burial under a greenhouse climate. In order to understand the mechanisms behind the changes from low to high organic carbon burial, and how this high burial rate was sustained for over 3 Ma, productivity within the surface waters and subsequent preservation of organic matter within the sediments were investigated in this study. Based on the multiproxy approach adopted herein, the sedimentary record of the Niobrara Formation in northern Colorado can be separated into two distinct intervals: Interval 1 and Interval 2. Interval 1 is bioturbated, organic lean and oxic, with low to moderate trace metal enrichment except for Mn. Interval 2 is laminated, organic-rich, more enriched in trace metals U, V and Mo, and less enriched in Mn, typical of anoxia during deposition. The transition from oxic to anoxic conditions coincides with greater enrichments in TOC, Cu and Ni, suggesting enhanced productivity is associated with redox transitions within the Niobrara Formation. These local changes in productivity and redox conditions are sudden and coincide with recurring iron (Fe) and phosphorus (P)-rich bentonites, evidence of ash deposition that could have enhanced nutrient supply, productivity and accumulation of organic carbon. Consequently, perturbations of the global carbon cycle associated with OAE 3 were inferred to have occurred in Interval 2.High total Fe, total sulfur, Fe/Al, and trace metal enrichments in Interval 2 are intrinsically linked to prevalence of anoxic bottom-water conditions which enhanced burial of pyrite and organic matter. Results from productivity proxies and Fe–S–C ternary plots show that Fe limitation on pyrite formation under anoxic porewater enhanced organic carbon burial and preservation. This implies Fe enrichment within the sediments favored pyrite formation instead of organic matter sulfidization, leading to a complex relationship between S and organic carbon in the marine sediments during Niobrara deposition.

Verifying the applicability of PD/A unit for ultimate sidestream and mainstream polishing: Operating performance, granular characteristics and active microbes

Partial denitrification/anammox (PD/A) has been recently applied to co-treat domestic wastewater and nitrate-containing anammox effluent. However, studies regarding its performance without external organic supplement, spatial characteristics within sludge aggregates, and chronological changes of active microorganisms along PD/A cycle have rarely been reported. Herein, one-stage PD/A unit extremely and simultaneously polished anammox-pretreated reject water (NH4+-N: 65.4 ± 5.7 mg/L, COD: 199.7 ± 23.2 mg/L) and domestic wastewater (NO3−-N: 81.6 ± 7.8 mg/L, TN: 85.8 ± 8.9 mg/L, COD: 338.2 ± 29.0 mg/L) to 4.5 ± 2.1 mg/L without external organic carbon supply. Protective “granules-in-granule” aggregates with densely clustered anammox bacteria embedded in homogeneous denitrifying Thauera prevailed in PD/A system, surviving disadvantages from complex wastewater. Uronic acids and β-sheet proteins in outer extracellular matrix facilitated granulation and pollutants adsorption, while tryptophan- and aromatic-like proteins with tighter secondary structure in inner extracellular matrix maintained granular robustness. Importantly, succession of active microorganisms along the PD/A cycle was revealed by transcript-level analysis for the first time. In PD-period, stimulated Thauera contributed to rapid nitrite accumulation. In subsequent anammox-period, Ca.Brocadia was activated to conduct advanced nitrogen removal, which accompanied the timely nitrate-to-nitrite reduction by Thauera and Ca.Competibacter. Elusimicrobia was active throughout the PD/A cycle, which is conducive to eliminate the dependence of PD process on external carbon source by decomposing complex organics in actual wastewater. Protective granular structure, orderly activation and harmonious cooperation of functional consortia facilitated practical nitrogen removal rate of 0.6 ± 0.1 kg-N/m3/d under anoxic condition, which sheds light on engineering application of anammox technology.

Carbon supplementation in domestic sewage via mixing with paint booth effluent: Influence on the performance of bioremediation and algal biomass production from high-rate algal ponds

The paint booth effluent (PBE) was used as a carbon supplement to evaluate the treatment of domestic sewage (DS) via microalgae biotechnology. The present study aimed to assess the performance of different mixtures of PBE and DS in the treatment and production of algal biomass in high-rate algal ponds (HRAPs), seeking to determine the optimal mixture between the effluents. The blends were: D1 (0% PBE, 100 % DS), D2 (18.75 % PBE, 81.25 % DS), D3 (37.5 % PBE, 62.5 % DS), D4 (56.25 % PBE, 43.75 % DS) and D5 (75% PBE, 25 % DS). As a result, in the D2 blend, with better carbon, nitrogen, and phosphorus ratio, there was a higher primary and total biomass productivity (0.08 g chl-α/m2.day and 2.0 g VSS/m2.day). The regression adjustment corroborated the results of the D2 mixture, showing PBE dosages between 18 and 25 % as better for algal growth. The insertion of PBE in the medium positively affected the bioremediation performance, increasing the removals with the addition of PBE. The nutrient and organic matter removal efficiencies ranged from values close to 50 %, of total organic carbon in the D1 mixture, and reaching 100 % in the removal of ammoniacal nitrogen. The D2 mixture stands out with the highest nitrogen recovery via the assimilation of organic nitrogen, reaching 19 % more in relation to the initial value. Thus, PBE contributed to the supply of organic carbon to the biomass, favoring the consortium between algae and bacteria.

Regulation of marine plankton respiration: A test of models

Plankton respiration is a major process removing oxygen from pelagic environments and constitutes one of the largest oxygen transformations in the sea. Where the O2 supplies due to dissolution, advection and oxygenic photosynthesis are not sufficient, hypoxic, or anoxic waters may result. Coastal waters with limited water exchange are especially prone to have low oxygen levels due to eutrophication and climate change. To support marine environmental management in a period of rapid climate change, we investigated the current knowledge of regulating plankton respiration based on field and experimental studies reported in the literature. Models for regulation of plankton respiration was tested on a three-year field data set. Temperature is the most reported predictor positively influencing plankton respiration (mean r2 = 0.50, n=15). The organic carbon supply driven by primary production has a similar coefficient of determination but fewer reported relationships (mean r2 = 0.52, n=6). Riverine discharges of dissolved organic carbon can override the influence of primary production in estuaries precluding effects of nutrient reductions. The median predictions of respiration regulation produced by current models vary by a factor of 2 from the median of observed values and extreme values varied even more. Predictions by models are therefore still too uncertain for application at regional and local scales. Models with temperature as predictor showed best performance but deviated from measured values in some seasons. The combined dependence of plankton respiration on temperature, phytoplankton production and discharge of riverine organic carbon will probably lead to increased oxygen consumption and reduced oxygen levels with projected climate change. This will be especially pronounced where increased precipitation is expected to enhance riverine discharges of carbon compounds. The biologically mediated transfer of carbon for long-term storage in deeper layers will slow down. Implementation of plankton respiration measurements in long-term ecological monitoring programs at water body and basin scales is advocated, which would enable future multivariate analyses and improvements in model precision across aquatic environments.

Are ancient seep environments distinguishable by benthic foraminiferal assemblages? A case study of the Cretaceous Western Interior Seaway

Methane cold seeps are food-rich seafloor habitats that served as oases for macrofaunal communities in the Cretaceous Western Interior Seaway (WIS). Although seep-obligate taxa occur at modern seeps, macrofaunal inhabitants were not endemic to seep environments in the WIS. Here we investigate benthic foraminiferal assemblages across the WIS and test whether benthic foraminifera from seeps are distinct from non-seep environments. We compile abundance data from Campanian to Maastrichtian seep, nearshore, and offshore environments and use constrained multivariate ordination to center our analysis on differences in assemblage composition as it relates to environment setting. Genus-level analysis reveals that offshore settings have more calcareous taxa than nearshore settings, which, in contrast, have representation from various agglutinated genera. Analyses of guilds and morphotypes disregard test-wall type and still find compositional differences among environments that indicate a nearshore–offshore gradient in organic carbon supply. We also find that seep assemblages are generally more similar to offshore assemblages than nearshore ones, reflecting their position near the central axis of the WIS. However, there are no genera, guilds, or morphotypes unique to seeps. We further compare between assemblages from immature, predominantly soft-ground seeps and mature, predominantly hard-ground seeps. We find compositional differences consistent with abated chemical stressors and a well-developed physical substrate associated with seep maturity. Thus, although seep environments draw their benthic foraminiferal faunas from the surrounding metacommunity, assemblages reflect the environmental differences present at seeps and could be used as an additional proxy for seep settings and seep maturity in the WIS.