Dissolved Organic Carbon Concentrations Research Articles

Vacuum ultraviolet irradiation for reduction of the toxicity of wastewater towards mammalian cells: Removal mechanism, changes in organic compounds, and toxicity alternatives

Vacuum ultraviolet (VUV, 185 + 254 nm) irradiation performs well for oxidation of model pollutants. However, oxidation of pollutants does not necessarily lead to a reduction in toxicity. Currently, a comprehensive understanding of the effect of VUV irradiation on the toxicity of real wastewater is still lacking. In this study, the influence of VUV irradiation on the toxicity of secondary effluents to Chinese hamster ovary (CHO) cells was investigated. The induction units of endogenous reactive oxygen species (ROS) and 8-hydroxyguanosine (8-OHdG) in cells continuously decreased with prolonged irradiation time. After 36 min of irradiation, the cytotoxicity and the genotoxicity of the secondary effluents were reduced by 57%–63% and 56%–61%, respectively. The UV (254 nm), •OH, and other substances generated during the VUV irradiation directly drive toxicity changes of wastewater. The contribution of •OH generated during VUV irradiation to the reductions in cytotoxicity and genotoxicity of the secondary effluents reached 72%–78% and 77%–84%, respectively. Hydroxyl radicals generated during VUV irradiation played an important role in the detoxification. The relative signal intensity of dissolved organic carbon (DOC) > 500 Da was partially removed, whereas that of DOC < 500 Da was small changed. Since the content of DOC > 500 Da in the samples was much lower than that of DOC < 500 Da, the removal of total DOC was only 15.8%-20.0% after 36 min of irradiation. The UV254 values and the fluorescence intensity values for different molecular weights (MWs) were all reduced effectively by VUV irradiation. Electron-rich organic compounds of all MWs were all sensitive to VUV irradiation. There were mono-linear relationships between changes in chemical indexes and changes in cytotoxicity or genotoxicity. The total fluorescence intensity (Ex: 220–420 nm, Em: 280–560 nm) was identified as the best indicator of the reduction in toxicity.

The changing nitrogen landscape of United States streams: Declining deposition and increasing organic nitrogen.

Air quality regulations have led to decreased nitrogen (N) and sulfur deposition across the conterminous United States (CONUS) during the last several decades, particularly in the eastern parts. But it is unclear if declining deposition has altered stream N at large scales. We compared watershed N inputs with N chemistry from over 2,000 CONUS streams where deposition was the largest N input to the watershed. Weighted change analysis showed that deposition declined across most watersheds, especially in the Eastern CONUS. Nationally, declining N deposition was not associated with significant large-scale declines in stream nitrate concentration. Instead, significant increases in stream dissolved organic carbon (DOC) and total organic N (TON) were widespread across regions. Possible mechanisms behind these increases include declines in acidity and/or ionic strength drivers, changes in carbon availability, and/or climate variables. Our results also reveal a declining trend of DOC/TON ratio over the entire study period, primarily influenced by the trend in the Eastern region, suggesting the rate of increase in stream TON exceeded the rate of increase in DOC concentration during this period. Our results illustrate the complexity of nutrient cycling that links long-term atmospheric deposition to water quality. More research is needed to understand how increased dissolved organic N could affect aquatic ecosystems and downstream riverine nutrient export.

A Pan‐Arctic Algorithm to Estimate Dissolved Organic Carbon Concentrations From Colored Dissolved Organic Matter Spectral Absorption

AbstractSampling for dissolved organic carbon (DOC) in the Arctic is challenging given the limited access and because it is not yet possible to measure with instruments deployed in situ. Compared to DOC, colored dissolved organic matter (CDOM) absorption spectroscopy is an easy‐to‐measure, relatively quick and cost‐effective approach which is often closely related to DOC concentrations in water samples. Here we present an algorithm based on quantitative and qualitative metrics of CDOM to provide DOC estimates derived from a Pan‐Arctic data set (n = 3,302) spanning rivers to deep ocean, with DOC ranging between 31 and 1,958 μM. The algorithm provided robust DOC estimates (r2 = 0.94; p &lt; 0.0001) and could reproduce DOC profiles and mixing plots across different locations in the Arctic Ocean. Besides its simplicity, this method is capable of capturing the extremely broad range of DOC within the strong gradients observed between Arctic riverine and marine systems.

Flow event size influences carbon, nutrient and zooplankton dynamics in a highly regulated lowland river

AbstractRiver regulation and water extraction has significantly altered flow regimes and reduced flood events in many inland river systems. Environmental flows have been adopted in many systems to mitigate the ecological impacts of river regulation, however a lack of knowledge regarding the interrelationship between flow regimes, carbon transport and instream productivity make prioritising water management difficult. To address this knowledge gap, we conducted a study on the Namoi River in the Murray-Darling Basin, Australia, monitoring changes in dissolved organic carbon (DOC), nutrient dynamics and planktonic food web structure during a period of variable flows. Nutrient and DOC concentrations were positively correlated with river discharge and zooplankton concentrations were highest post flow events. Planktonic chlorophyll-a, increased DOC concentration and higher discharge were the most influential drivers of change in zooplankton communities. Further, our results indicated that flow events increased production through both heterotrophic and autotrophic pathways, significantly boosting zooplankton concentration compared to base flow conditions across all measured flow events. We suggest even small in-channel flow events can be important for increasing basal and zooplankton production in rivers, and therefore should be protected or promoted by environmental flow management, particularly during drought conditions.

Seasonal and Storm Event‐Based Dynamics of Dissolved Organic Carbon (DOC) Concentration in a Mediterranean Headwater Catchment

AbstractThis study investigates the spatial and temporal dynamics of Dissolved Organic carbon (DOC) concentration in a Mediterranean headwater catchment (Turbolo River catchment, southern Italy) equipped with two multi‐parameter sondes providing more than two‐year (May 2019–November 2021) continuous high‐frequency measurements of several DOC‐related parameters. The sondes were installed in two nested sections, a quasi‐pristine upstream sub‐catchment and a downstream outlet with anthropogenic water quality disturbances. DOC estimates were achieved by correcting the fluorescent dissolved organic matter—fDOM—values through an original procedure not requiring extensive laboratory measurements. Then, DOC dynamics at the seasonal and storm event scales were analyzed. At the seasonal scale, results confirmed the climate control on DOC production, with increasing background concentrations in hot and dry summer months. The hydrological regulation proved crucial for DOC mobilization and export, with the top 10th percentile of discharge associated with up to 79% of the total DOC yield. The analysis at the storm scale using flushing and hysteresis indices highlighted substantial differences between the two catchments. In the steeper upstream catchment, the limited capability of preserving hydraulic connection over time with DOC sources determined the prevalence of transport as the limiting factor to DOC export. In the downstream catchment, transport‐ and source‐limited processes were observed almost equally. The correlation between the hysteretic behavior and antecedent precipitation was not linear since the process reverted to transport‐limited for high accumulated rainfall values. Exploiting high‐resolution measurements, the study provided insights into DOC export dynamics in nested headwater catchments at multiple time scales.

Spatially distributed tracer‐aided modelling to explore DOC dynamics, hot spots and hot moments in a tropical mountain catchment

AbstractTracer‐aided rainfall‐runoff modelling is a promising tool for understanding catchment hydrology, particularly when tracers provide information about coupled hydrological‐biogeochemical processes. Such models allow for predicting the quality and quantity of water under changing climatic and anthropogenic conditions. Here, we present the Spatially‐distributed Tracer‐Aided Rainfall‐Runoff model with a coupled biogeochemical reactive tracer module (STARR‐DOC) to simulate dissolved organic carbon (DOC) dynamics and sources. The STARR‐DOC model was developed and tested for a humid high Andean ecosystem (páramo) using high‐resolution hourly DOC and hydrometeorological data to simulate hourly discharge and DOC at a fine spatial (10 × 10 m) resolution. Overall, the model was able to acceptably reproduce discharge (KGE ~ 0.45) and stream DOC (KGE ~ 0.69) dynamics. Spatially distributed DOC simulations were independently compared using point DOC measurements for different soil types across the catchment, which allowed for identifying DOC production hot spots and hot moments. Results showed higher hydrological connectivity between slopes and valleys with increasing precipitation. Wetter conditions also favoured DOC production (wet month = 82 mg L−1, dry month = 5 mg L−1) and transport to the stream network (DOC concentrations: during events ~15 mg L−1, during baseflows ~4 mg L−1). Our results also suggest that minor changes in meteorological conditions directly affect páramo soil water dynamics and biogeochemistry. Knowledge of when and where DOC production in mountain catchments is greatest is important for water managers to understand when they make decisions about water security, especially considering climate change predictions for the Andean region.

Thermal evolution of biochar in nature: A potential mode to enhance the self-cleaning of environmental DOC

Biochar often undergoes multiple thermal processes. Thermal evolution is described in this study as the process by which biochar in the environment changes again in a thermal environment. In this study, the thermal evolution process of biochar was studied by characterization test. The results showed that the oxygen content in biochar increased after thermal evolution, mainly due to functional groups such as O-H and C-O, while the functional groups of CO did not change significantly. Micro-pores will be generated in biochar after thermal evolution, which will increase the surface area and significantly enhance the adsorption capacity. The biochar was added to natural water to observe how biochar enhanced the removal of dissolved organic carbon (DOC). The concentration of DOC was reduced by about 6.68 mg/L by SB 800, and most of the components were humus, which indicated that the thermal evolution of biochar promoted the removal of DOC. The Electron spin resonance (ESR) test shows that after thermal evolution, biochar has more oxygen-containing carbon center persistent free radicals due to the increase of C-O functional groups in biochar. Under visible light, persistent free radicals in oxygen center are formed by electron transition, which can undergo a variety of reactions with water to form reactive oxygen species.

Enzyme Activity and Dissolved Organic Carbon Content in Soils Amended with Different Types of Biochar and Exogenous Organic Matter

Biochars are proposed as a strategy for long-term carbon sequestration. High resistance for decomposition, low decay rate and long estimated lifetime allow for stable forms of carbon to be retained in the environment. Nevertheless, the application of pyrolyzed feedstock, particularly along with exogenous organic matter, may affect carbon dynamics in soil through the introduction of labile compounds and the stimulation of extracellular enzymes. The aim of this research was to evaluate the influence of biochars and unprocessed organic amendments in two agricultural soils on the dissolved organic carbon (DOC) content and activity of three enzymes involved in carbon turnover. In the incubation experiment, the activity of dehydrogenase, β-glucosidase, and cellulase and the DOC content were measured on days 30, 60, 90, 180, and 360. The addition of biochars stimulated dehydrogenase and β-glucosidase, while cellulase was suppressed. Fresh biomass enhanced the activity of the enzymes through a priming effect. DOC content was the highest in treatments with high enzyme activity, suggesting that it acted as a source of energy for microbes. The findings suggest that the biochar properties and the presence of exogenous organic matter affect microbial response in soil, which might be crucial for carbon sequestration. However, long-term studies are recommended to fully understand the mechanisms that determine the response of soil biota to biochar.

Stabilization of organic carbon in top- and subsoil by biochar application into calcareous farmland

Biochar is recognized for its role in carbon sequestration and emission mitigation in farmland topsoil. However, the mechanisms by which biochar affects soil organic carbon (SOC), its composition, and stability, in the topsoil (0–20 cm) and subsoil (140–160 cm) remain unclear. Applying biochar to the calcareous farmland topsoil significantly increased the topsoil SOC contents by 33 % after a decade, with a 5 % increase in dissolved organic carbon (DOC) contents (topsoil) and a substantial increase of 162 % in subsoil DOC contents. Additionally, humic substances showed an increase of 24 % (topsoil), while low-molecular-weight water-extracted DOC exhibited a remarkable increase of 142 % in the subsoil. The application of biochar significantly increases the contents of SOC, DOC, and microbial biomass carbon (MBC) in the topsoil, as well as SOC and DOC contents in the subsoil. However, a slight decrease is observed for MBC content in the subsoil. Biochar-amended soil significantly suppressed enzyme activity in the topsoil and decreased α diversity in topsoil and subsoil while increasing the content of mineral-associated soil organic matter (MAOM). These observed changes are conducive to stabilizing SOC, emphasizing MAOM formation as a primary mechanism for carbon sequestration in both topsoil and subsoils. This study provides evidence that biochar contributes to the long-term organic carbon sequestration in calcareous farmland, highlighting the importance of considering both topsoil and subsoil when evaluating the dynamic impacts of biochar on SOC.

Significant benthic fluxes of bioavailable dissolved amino acids to the ocean: Results from the East/Japan Sea

AbstractWe measured dissolved organic carbon (DOC) and total dissolved amino acid (TDAA) in seawater and sediment porewater of the Ulleung Basin in the East/Japan Sea. The DOC and TDAA concentrations were 1.1‐ and 1.4‐fold higher in the euphotic zone, and 11‐ and 43‐fold higher in sediment porewater, respectively, than those in the deep ocean. Consequently, in the deep ocean, TDAA and DOC input fluxes from porewater were 2‐ and 0.4‐fold of those from the euphotic zone, respectively. This larger contribution of benthic flux for TDAA and its shorter residence time in the benthic boundary layer (BBL) (1.3 ± 0.9 yr) seem to result in steep TDAA increases in the BBL, although DOC concentrations remained relatively uniform throughout the entire deep ocean. AA‐derived indices also show enhanced bioavailability of dissolved organic matter in the BBL. Benthic inputs seem to supply a significant amount of bioavailable TDAA to the deep ocean, fueling microbial activity.

The amelioration and improvement effects of modified biochar derived from Spartina alterniflora on coastal wetland soil and Suaeda salsa growth

Exotic species Spartina alterniflora (S. alterniflora) are widely invaded in the coastal zones of China and threaten the native ecosystem functions. In this study, phosphorus-magnesium modified BC (P–Mg modified BC) included PA-Mg-BC and DAP-Mg-BC derived from S. alterniflora were successfully prepared by co-pyrolysis of biomass and diammonium phosphate (DAP) or phosphoric acid (PA) and magnesium oxide (MgO). The preparation process markedly improved the surface morphologies, P loading amount, and P-containing functional groups of modified BC. The characterization results indicated that stable and low-solubility Mg–P complex formed on the surface of PA-Mg-BC and DAP-Mg-BC, which delayed the rapid release of P. Moreover, the MgO improved the buffering capacity of PA-Mg-BC and DAP-Mg-BC to competitive anions (SO42− and CO32−) during P release. Meanwhile, pot experiment showed that the suitable applications of PA-Mg-BC and DAP-Mg-BC could improve soil quality and fertility by enhancing SOC, DOC, TN, TP and AP contents, as well as β-glucosidase activities. The amended soil pH and salinity compared to the original soil also declined through precipitation and acid-base neutralization. In addition, P–Mg modified BC could improve bacterial community structure and promote the growth and biomass of Suaeda salsa (S. salsa). This study could provide a feasible method for realizing ecological restoration of coastal wetland and resource utilization of S. alterniflora.

The apoptosis of Chlorella vulgaris and the release of intracellular organic matter under metalimnetic oxygen minimum conditions

Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris (C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L, 3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days, respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the release of IOM during the development of MOM.

Top-down control over dissolved organic carbon in the bottom water of the Weddell Sea and its implication for the continental shelf pump

Dense water out of the Antarctic shelves is expected to drive the transport of carbon into the deep Southern Ocean via the formation of Antarctic Bottom Water. However, bottom water formation’s capacity to sequester carbon into the deep ocean is poorly constrained. Here, dissolved organic carbon (DOC), dissolved black carbon (DBC), and particulate organic carbon (POC) were examined to reveal the influence of the Weddell Sea Deep Water (WSDW) on DOC transport during its flowing out of the Weddell Sea. High DOC concentrations (>60 μM-C) and low DBC/DOC ratios (<1.5%) were observed in surface water near the South Orkney Islands, ascribing to sea ice melt-induced phytoplankton blooms. Seawater at the mid-deep depths exhibited a higher DOC concentration (averaging 48.1 ± 3.7 μM-C) than the incoming water source, resulting from the release of DOC from sinking particles. Bottom water had higher DOC concentration compared to the mid-deep layer water (t-test, p < 0.005), while the DBC concentrations were comparable. In addition, the excess DOC (relative to WSDW) in bottom water showed a close relation with POC in surface water. These results reveal a top-down control over the DOC concentration in bottom water through a quick sinking of diatom detritus and subsequently solubilization in bottom water and/or sediment. With an estimate, the WSDW carries 5.1 ± 2.8 Tg-C/yr of excess DOC out of the Powell Basin, representing an important carbon source to the deep Southern Ocean. This study highlights the key role of the Antarctic continental shelf pump in carbon sequestration.

Hydrology, rather than wildfire burn extent, determines post‐fire organic and black carbon export from mountain rivers in central coastal California

AbstractCoastal mountain rivers export disproportionately high quantities of terrestrial organic carbon (OC) directly to the ocean, feeding microbial communities and altering coastal ecology. To better predict and mitigate the effects of wildfires on aquatic ecosystems and resources, we must evaluate the relationships between fire, hydrology, and carbon export, particularly in the fire‐prone western United States. This study examined the spatiotemporal export of particulate and dissolved OC (POC and DOC, respectively) and particulate and dissolved black carbon (PBC and DBC, respectively) from five coastal mountain watersheds following the 2020 CZU Lightning Complex Fires (California, USA). Despite high variability in watershed burn extent (20–98%), annual POC, DOC, PBC, and DBC concentrations remained relatively stable among the different watersheds. Instead, they correlated significantly with watershed discharge. Our findings indicate that hydrology, rather than burn extent, is a primary driver of post‐fire carbon export in coastal mountain watersheds.

Spatial-temporal distribution and source apportionment of riverine dissolved organic carbon in the Miyun section of the Chaobai River in Beijing, China

Dissolved organic carbon (DOC) is indicative of water quality in drinking source water and has an impact on drinking water treatment. Exploring occurrence of DOC in drinking source water is of great significance for the drinking water safety in Beijing. This study elucidated spatial-temporal DOC dynamics in the Miyun section of Chaobai River in Beijing of China and identified sources of DOC based on DOC fluorescent spectral characteristics. Results showed that the average riverine DOC concentration was 30.60 mg/L. DOC concentrations in the Miyun section of the Chaobai River were 30.40, 30.24, and 31.09 mg/L in spring, summer and autumn, respectively. DOC concentrations at the three segments of the Miyun section of the Chaobai River (the Chaohe River, the Baihe River and the Chaobai River) were 29.93, 30.29 and 32.57 mg/L, respectively. Land use contributed to DOC variations rather than season and river segment. Significant increases in DOC concentration were observed in river water flowing through farmland and urban areas, and DOC concentration presented the highest after flowing through the farmland area. The results of FI, HIX and BIX showed that DOC mainly came from endogenous sources such as aquatic biological activities, and was less affected by terrestrial inputs. Special attentions ought to be paid on prevention and control of endogenous DOC inputs.

Mechanisms of 137Cs leaching based on long-term observations in forested headwater catchments in Yamakiya, Fukushima Prefecture, Japan

Dissolved radiocesium (mainly 134Cs and 137Cs) is thought to be leached mainly from suspended sediment in downstream rivers, while organic matter, such as leaf litter, contributes to catchments in forested headwater streams. It is also known that dissolved 137Cs in headwater streams exhibit seasonal variation with water temperature. Some mechanisms have been proposed as the causes: ionic competition of potassium ion (K+) and ammonium ion (NH4+), leaching associated with the decomposition of organic matter, and thermodynamic adsorption-desorption processes. We investigated the relationship between K+ and the dissolved organic carbon (DOC) concentrations and seasonal changes in dissolved 137Cs concentration using a large number of samples from a headwater's small catchments. We examined temporal trends in 137Cs concentrations in coarse organic matter, suspended sediments, and dissolved forms at four sites (one decontaminated site and three undecontaminated sites) in the Yamakiya area since 2011. The distribution coefficients (Kdcss and Kdorg) of dissolved 137Cs concentrations relative to suspended sediment and coarse organic matter 137Cs concentrations were calculated, and differences in temporal changes due to decontamination were investigated. In addition, we examined the relationship between water temperature and DOC, K+, NH4+ and 137Cs concentrations in the headwater catchments. The suspended sediment 137Cs concentrations at the decontaminated headwater site (IBO) decreased significantly after decontamination and remained low thereafter. In contrast, dissolved 137Cs concentrations decreased temporarily during the decontamination period, but returned to pre-decontamination levels. Almost no NH4+ has been detected in headwater streams in our catchments. In the SET and ISH watersheds, where the distance from the groundwater spring is short, a correlation was found between DOC concentration and dissolved 137Cs concentration. In contrast, in the IBO watershed, where the distance from the groundwater spring is long, temperature dependence and a good correlation between K+ and 137Cs were observed. Therefore, microbial decomposition of organic matter may have a significant effect on the seasonal variation of dissolved 137Cs in forested headwater streams at short distances from the spring, but the influence of competing ions is expected to increase gradually as the water flows downstream.

Spatiotemporal variability and environmental effects of greenhouse gases, nutrients, and dissolved carbons in an ice-covered reservoir

Ice cover restructures the distribution of substances in ice and underlying water and poses non-negligible environmental effects. This study aimed to clarify the spatiotemporal variability and environmental effects of methane (CH4), nitrous oxide (N2O), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) in ice and water columns during different ice-covered periods. We surveyed the ice-growth, ice-stability, and ice-melt periods in an ice-covered reservoir located in Northeast China. The results showed that underlying water (CH4: 1218.9 ± 2678.9 nmol L−1 and N2O: 19.3 ± 7.3 nmol L−1) and ice (CH4: 535.2 ± 2373.1 nmol L−1 and N2O: 9.9 ± 1.5 nmol L−1) were sources of atmospheric greenhouse gases. N2O concentrations were the highest in the bottom water of the reservoir while CH4 accumulated the most below the ice in the riverine zone. These can be attributed to differences in the solubilities and relative molecular masses of the two gases. Higher concentrations of N2O, TN, TP, DOC, and DIC were recorded in the underlying water than those in the ice due to the preferential redistribution of these substances in the aqueous phase during ice formation. Additionally, we distinguished between bubble and no-bubble areas in the riverine zone and found that the higher CH4 concentrations in the underlying water than those in the ice were due to CH4 bubbles. In addition, we reviewed various substances in ice-water systems and found that the substances in ice-water systems can be divided into solute exclusion and particle entrapment, which are attributed to differences between dissolved and particulate states. These findings are important for a comprehensive understanding of substances dynamics during ice-covered periods.

Study on coupling of typical elements in surface water and groundwater in the middle reaches of the Yangtze River, China

Understanding the coupling relationship of typical elements between surface water (SW) and groundwater (GW) is helpful to the prevention of regional water environment pollution. In this study, the coupling of typical elements (C, N, P) of SW and GW in the middle reaches of the Yangtze River was comprehensively analyzed using multiple statistics and hydrogeochemical modeling methods. SW chemical characteristics was found similar with that of GW in the middle reaches of the Yangtze River with cluster analysis, and all sampling points was divided into two principal components based on principal component analysis. One principal component was more affected by the water-carbonate mineral interaction, the other one was greatly affected by anthropogenic activities. More interestingly, no fixed replenishment and discharge relationship was found between SW and GW in different seasons, which laid a foundation for the coupling of typical elements between SW and GW. Cl- in SW and GW had the same major source. In addition, almost identical water-carbonate reactions was found occurred in phreatic water (PGW) and confined water (CGW). As a link between SW and CGW, PGW may accept the supplies of the two waters at the same time, resulting the concentrations of δD, Cl-, DOC and HCO3– in PGW ranking between SW and CGW. Furthermore, Nitrogen and phosphorus were found to migrate between SW and GW, and a potential ammonium source in shallow aquitard which generated a large amount of ammonium. The coupling effect of nitrogen source input and transformation occurred in the process of nitrogen coupling between SW and GW, which increased the ecological risk of water environment. This study provided a scientific basis for the control of SW-GW pollution in the middle reaches of the Yangtze River, and supported the security of the water ecological environment in the Yangtze River Basin.

Selected Bacteria Are Critical for Karst River Carbon Sequestration via Integrating Multi-omics and Hydrochemistry Data.

Recalcitrant dissolved organic carbon (RDOC) produced by microbial carbon pumps (MCPs) in the ocean is crucial for carbon sequestration and regulating climate change in the history of Earth. However, the importance of microbes on RDOC formation in terrestrial aquatic systems, such as rivers and lakes, remains to be determined. By integrating metagenomic (MG) and metatranscriptomic (MT) sequencing, we defined the microbial communities and their transcriptional activities in both water and silt of a typical karst river, the Lijiang River, in Southwest China. Betaproteobacteria predominated in water, serving as the most prevalent population remodeling components of dissolved organic carbon (DOC). Binning method recovered 45 metagenome-assembled genomes (MAGs) from water and silt. Functional annotation of MAGs showed Proteobacteria was less versatile in degrading complex carbon, though cellulose and chitin utilization genes were widespread in this phylum, whereas Bacteroidetes had high potential for the utilization of macro-molecular organic carbon. Metabolic remodeling revealed that increased shared metabolites within the bacterial community are associated with increased concentration of DOC, highlighting the significance of microbial cooperation during producing and remodeling of carbon components. Beta-oxidation, leucine degradation, and mevalonate (MVA) modules were significantly positively correlated with the concentration of RDOC. Blockage of the leucine degradation pathway in Limnohabitans and UBA4660-related MAGs were associated with decreased RDOC in the karst river, while the Fluviicola-related MAG containing a complete leucine degradation pathway was positively correlated with RDOC concentration. Collectively, our study revealed the linkage between bacteria metabolic processes and carbon sequestration. This provided novel insights into the microbial roles in karst-rivers carbon sink.

Disentangling carcass size and climate effects on soil biogeochemistry during decomposition

When an animal dies the decomposition of its carcass releases multiple compounds that become available to soil microbiota altering soil biogeochemistry. This zone of affected substrate is characterized by significant changes to numerous soil biogeochemical parameters including pH, conductivity, microbial respiration rates, dissolved organic carbon (DOC), C/N ratios, carbon and nitrogen stable isotopes (δ13C and δ15N), and major/trace elemental concentrations. Although the effects of animal decomposition on these parameters have been recorded for various organisms and in a variety of ecosystems several knowledge gaps remain, including: the effect of carcass size; and decomposition effects in prairie ecosystems (i.e., semi-arid climates). the effect of carcass size; and decomposition effects in prairie ecosystems (i.e., semi-arid climates). Here, we investigate how soil biogeochemical parameters are affected by the decomposition of a horse carcass (~660 kg) in a prairie ecosystem in comparison to beavers (~18 kg) in a temperate forest. Three parameters were identified as significantly influenced by carcass size: conductivity, DOC, and microbial respiration rate. Average soil conductivity underneath the horse carcass was three to fifteen times higher than control soils and reached a maximum at 1114 ADD, while maximum soil conductivity values were observed after 160 ADD in beaver-associated soils. Maximum DOC concentrations were observed after 160 ADD in beaver-associated soil (67 ± 40 mg C gdw-1) and after 1114 ADD in horse-associated soil (326 ± 115 mg C gdw-1). Microbial respirations rates were both greater in horse-associated soil and longer-lasting compared to beaver-associated soil. Respiration rates were greatest in two of the three horse-associated soils after 1114 ADD (~733 µg CO2-C gdw-1 day-1), which significantly differs compared to beaver-associated soils (300 ± 90 µg CO2-C gdw-1 day-1 at 160 ADD). Taken together, these results demonstrate that larger carcasses result in a greater release of decomposition products, including C, and greater stimulation of soil heterotrophic communities. Other measured biogeochemical indicators of decay suggest a mixed influence due to carcass size and climate, notably δ15N values of the soil, and major element concentrations. Climate was revealed to be more important in controlling changes to pH and gravimetric moisture than carcass size, with baseline soil conditions and type playing critical roles. Additionally, in semi-arid regions such as western South Dakota, the role of wet-dry cycles on carcasses undergoing decomposition may help to explain the pulses observed with C concentrations and C cycling. This study provides the first direct comparison of soil biogeochemistry associated with the decomposition of two different sized taxa decayed in two different climates. Attempting to normalize climate data using ADD was found to be an imperfect system that does not account for all climate variables affecting decomposition. Unravelling patterns in decomposition can better help to constrain nutrient cycling in modern and ancient ecosystems.