Sediment Ammonium Research Articles

Effects of salinity on nitrogen reduction pathways in estuarine wetland sediments

Denitrification, anammox, and DNRA are three important nitrogen (N) reduction pathways in estuarine sediments. Although salinity is an important variables controlling microbial growth and activities, knowledge about the effects of changing salinity on those three processes in estuarine and coastal wetland sediments are not well understood. Herein, we performed a 60-d microcosms experiment with different salinities (0, 5, 15, 25 and 35 ‰) to explore the vital role of salinity in controlling N-loss and N retention in estuarine wetland sediments. The results showed that sediment organic matter, sulfide, and nitrate (NO3−) were profoundly decreased with increasing salinity, while sediment ammonium (NH4+) and ferrous (Fe2+) varied in reverse patterns. Meanwhile, N-loss and N retention rates and associated gene abundances were differentially inhibited with increasing salinity, while the contributions of denitrification, anammox, and DNRA to total nitrate reduction were apparently unaffected. Moreover, denitrification rate was the most sensitive to salinity, and then followed by DNRA, while anammox was the weakest among these three processes. In other words, anammox bacteria showed a wide range of salinity tolerance, while both denitrification and DNRA reflected a relatively limited dynamic range of it. Our findings could provide insights into temporal interactive effects of salinity on sediment physico-chemical properties, N reduction rates and associated gene abundances. Our findings can improve understanding of the effects of saltwater incursion on the N fate and N balance in estuarine and coastal sediments.

Does invasive submerged macrophyte diversity affect dissimilatory nitrate reduction processes in sediments with varying microplastics?

Nitrogen removal is essential for restoring eutrophic lakes. Microorganisms and aquatic plants in lakes are both crucial for removing excess nitrogen. However, microplastic (MP) pollution and the invasion of exotic aquatic plants have become increasingly serious in lake ecosystems due to human activity and plant-dominant traits. This field mesocosm study explored how the diversity of invasive submerged macrophytes affects denitrification (DNF), anammox (ANA), and dissimilatory nitrate reduction to ammonium (DNRA) in lake sediments with varying MPs. Results showed that invasive macrophytes suppressed DNF rates, but DNRA and ANA were less sensitive than DNF to the diversity of invasive species. Sediment MPs increased the biomass of invasive species more than native species, but did not affect microbial processes. The effects of MPs on nitrate dissimilatory reduction were process-specific. MPs increased DNF rates and the competitive advantage of DNF over DNRA by changing the sediment environment. The decoupling of DNF and ANA was also observed, with increased DNF rates and decreased ANA rates. The study findings suggested new insights into how the invasion of exotic submerged macrophytes affects the sediment nitrogen cycle complex environments.

Nitrogen loading resulting from major floods and sediment resuspension to a large coastal embayment

Major floods pose a severe threat to coastal receiving environments, negatively impacting environmental health and ecosystem services through direct smothering with sediment and nutrient loading. This study examined the short and long-term impacts of the February 2022 major flood event on mud extent and sediment nitrogen flux in Moreton Bay (the Bay), a large, sub-tropical embayment in Southeast Queensland, Australia. Short-term impacts were assessed three days after the flood peak by sampling surface water at 47 sites in the direction of the predominant circulation pattern. Longer-term impacts were assessed by undertaking an intensive sediment survey of 223 sites and a nutrient flux experiment using sediment core incubations to simulate calm and resuspension conditions for the four key sediment classes. Short-term impacts revealed elevated turbidity levels extended across the Bay but were highest at the Brisbane River mouth, ammonium concentrations varied inversely with surface turbidity, whereas nitrate concentrates closely tracked surface turbidity. The sediment survey confirmed fine sediment deposition across 98 % of the Bay. Porewater within the upper 10 cm contained a standing pool of 280 t of ammonium, with concentrations more than three orders of magnitude higher than overlying surface waters. The nutrient flux experiment revealed an order of magnitude higher sediment ammonium flux rate in the sandy mud sediment class compared to the other sediment classes; and for simulated resuspension conditions compared to calm conditions for sand, muddy sand, and mud sediment classes. Scaling across the whole Bay, we estimated a mean annual sediment flux of 17,700 t/year ammonium, with a range of 13,500 to 21,900 t/year. Delivery of fine sediments by major floods over the last 50 years now impact >98 % of the benthic zone and provide a major loading pathway of available nitrogen to surface waters of Moreton Bay; representing a significant threat to ecosystem health.

Quantitative characterization of the effect of compaction rate on ammonium release from clayey sediments

Ammonium-rich pore water will release from clayey sediments into adjacent aquifers during aquitards compaction, which can adversely affect groundwater quality. Differences in the rate of groundwater exploitation can lead to differences in the rate of compaction of aquitards, which may, to some extent, affect the release of chemical components of the pore water from the aquitard. However, the effect of the compaction rate of aquitards on the process of ammonium release from clayey sediments is poorly understood. Three groups of indoor compaction experiments were conducted to identify the effect of compaction rate on ammonium release from clayey sediments during compaction. The results showed that the compaction rate and sediment liquid limit exert a clear controlling effect on the release rate and internal change process of ammonium in clayey sediments. The increase in the ammonium release rate was approximately proportional to the increase in the compaction rate. When the moisture content of the clayey sediments exceeds the liquid limit, the ammonium concentration in pore water increases mainly due to the mineralization of organic matter containing nitrogen and the dissolution of the carbonate-bound ammonium. When the moisture content drops to the liquid limit, the ammonium concentration in pore water begins to decrease. Because the increase in the compaction rate weakened sediment mineralization and accelerated pore water release, the main forms of ammonium released from the sediment change from organic sulfide-bound ammonium and carbonate-bound ammonium to carbonate-bound ammonium and ion-exchanged ammonium. The results of this study have important significance for the management of groundwater quality in groundwater exploitation areas.

Functional composition outweighs taxonomic and functional diversity in maintaining ecosystem properties and processes of mangrove forests

AbstractBiodiversity loss can have significant consequences for human well‐being, as it can affect multiple ecosystem properties and processes (MEPP) that drive ecosystem services. However, a comprehensive understanding of the link between environmental factors, biodiversity, and MEPP remains elusive, especially in mangrove ecosystems that millions of people along tropical coastlines worldwide depend upon. Here, we collated a comprehensive dataset on forest inventory, plant traits, and environmental factors across 93 plots in the Sundarbans Reserved Forests, Bangladesh. The functional composition (FC) of leaf area showed a stronger positive association with MEPP, being determined by total biomass and productivity of the mangroves, sediment organic carbon, and ammonium, phosphorus, and potassium contents of the sediment, than species richness (SR) or functional diversity (FD). Further, FC mediated a strong negative association of sediment salinity, and a positive association of SR, with MEPP. The similar but opposite total associations of SR and sediment salinity with MEPP suggest that species‐rich mangroves could offset the negative impacts of rising salinity on MEPP. When focusing on a single aspect of MEPP, both FD and FC mattered, with the FD of leaf area showing a strong association with mangrove productivity and sediment potassium content, while the FC of leaf litter nitrogen showed the strongest associations with sediment ammonium and phosphorus contents. Therefore, to sustain mangrove ecosystems as a reliable nature‐based solution for climate change mitigation, conservation and (re‐)establishment projects should prioritize regionally dominant species with high leaf area and nitrogen content, plus functionally different species to support the ecosystem processes and services provided by mangroves.

Degradation and accumulation of organic matter in euxinic surface sediments

The impact of oxygen on the preservation of organic matter in marine surface sediments is still controversial. We revisited this long-standing debate by determining the burial efficiency of sedimentary organic matter in the Black Sea, the largest anoxic and euxinic basin in the modern ocean. Surface sediments were sampled in the Danube paleodelta on the northwestern margin of the Black Sea at 420–1550 m water depth. Steady-state modeling of solid species (particulate organic carbon and nitrogen) and solutes (ammonium, sulfate, and total alkalinity) in sediments was performed to quantify rates of mass accumulation, particulate organic matter (POM) degradation, and POM burial. We develop a novel analytical model to quantify these rates applying an inverse modelling approach to down core data accounting for molecular diffusion, sediment burial and compaction. Our model results indicate that 56.7 ± 6.6 % of the particulate organic matter deposited in the study area is not degraded in surface sediments but accumulates below 10 cm sediment depth. This burial efficiency is substantially higher than those previously derived for seafloor areas underlying oxygenated bottom waters. Hence, our study confirms previous studies showing that euxinic bottom water conditions promote the preservation of particulate organic matter in marine sediments.

Releasing mechanism of ammonium during clayey sediments compaction and its impact on groundwater environment

Compaction of clayey aquitard would release pore water containing high levels of ammonium to adjacent aquifers, potentially affecting the concentration of groundwater ammonium. However, the releasing process and impact effect of ammonium within clayey aquitard during compaction remain unknown. Four groups of pre-experiments and two groups of simulation experiments were conducted to reveal the releasing mechanism of ammonium during clayey sediment compaction. (1) The results of Experiment A simulating continuous sedimentation conditions showed that the sediment ammonium transferred into pore water sequentially through desorption of ion exchange form, degradation of organic matter, and simultaneous release of mineral-bound ammonium. The concentration of pore water ammonium was 3.54–8.20 mg N/L, with a significant periodical variation due to sediment ammonium transformation. The lower moisture content (<42.4 %) in the later stage of compaction inhibited the biological transformation of ammonium, and the change in mineral structure caused the isomorphic replacement of K to capture ammonium, resulting in a decrease in ammonium concentration in released pore water. (2) The results of Experiment B simulating artificial compaction conditions (such as land subsidence) showed that the pore water ammonium was primarily caused by desorption of ion exchange form ammonium due to changes in pore structure and moisture content. The ammonium concentration in pore water was 4.72–9.91 mg N/L, with a significant increase in response to a large change in pressure in the short term. (3) The estimate results in the Chen Lake wetland suggested that the contribution of clayey aquitard compaction to groundwater ammonium concentration in the adjacent aquifer would be 2.68–4.29 mg N/L, which accounted for a considerable portion of groundwater ammonium concentration and was far higher than that of advection and diffusion. The findings of this study reveal the releasing mechanism of ammonium during clayey sediments compaction, in which reaction products may affect adjacent aquifers.

Impact of reservoir operation policies on nitrogen cycling processes and water quality dynamics in a large water supply reservoir

Reservoir operation policies affect reservoir nitrogen (N) cycling and budgets through complex influences on physical and biogeochemical processes in water and sediment. However, the underlying influencing mechanisms, especially the impact of operations on sediment processes, remain unclear. This study combines a coupled hydrodynamic-eutrophication-sediment model and a reservoir operation model to clarify reservoir operation impact on N cycling processes in water and sediment as well as impact on stored and discharged water quality. Three typical reservoir operation policies (i.e., standard, hedging, and eco-friendly) were selected to create operation scenarios. The hydrodynamic-eutrophication-sediment model was used to simulate N cycling processes and N concentrations in stored and discharged water under each scenario. Using China's Danjiangkou Reservoir as a case study, results revealed that reservoir operation policies significantly affected spatiotemporal dynamics of N cycling processes and water quality. Specifically, reservoir sediment acted as a N source, contributing to annual net release of 9.5–16.1 Gg N. Higher water levels promoted sediment ammonium release through effects on reservoir submerged area and sediment temperature. Moreover, denitrification processes in water and sediment collectively contributed to annual N removal of 14.0–16.9 Gg N. Annual N removal was greater in the higher water level scenario despite its lower denitrification rate per unit area. Additionally, these processes and hydrodynamic conditions combine to affect N forms and concentrations. The N concentration in the lower water level scenario was generally higher, risking algal bloom outbreaks in the shallow-water zone. This study is intended to help guide reservoir operation policymaking to account for N management while also coordinating water quantity and quality targets.

Identification of ammonium source for groundwater in the piedmont zone with strong runoff of the Hohhot Basin based on nitrogen isotope

Groundwater with high ammonium concentration (HANC groundwater), mostly caused by anthropogenic pollution, is widely distributed in China, which could also result from natural geological genesis. Groundwater in the piedmont zone with strong runoff in the central Hohhot Basin has featured its excessive ammonium concentration since the 1970s. Currently, chemical factories also serve as potential pollution sources. In this study, based on the nitrogen isotopic technique and combined with hydrochemical methods, the sources of high concentration ammonium in the groundwater was identified. The HANC groundwater is mainly distributed in the alluvial-proluvial fan and the interfan depression in the western and central parts of the study area, and a maximum ammonium concentration of 529.32 mg/L was observed in the groundwater in the mid-fan of the Baishitou Gully (BSTG) alluvial-proluvial fan. Although the BSTG mid-fan is part of the piedmont zone with strong runoff, some of the HANC groundwater in this area still presents the typical hydrochemical characteristics in the discharge area. Moreover, an extremely high concentration of volatile organic compounds was observed in groundwater in the BSTG alluvial-proluvial fan, which indicated significant anthropogenic pollution. Besides, 15N-NH4+ is enriched in groundwater in the BSTG root-fan and the interfan depression, which is consistent with the situation of organic nitrogen and exchangeable ammonium in natural sediments, as well as the natural HANC groundwater in other regions of China. These δ15N-NH4+ values indicate that the ammonium of the groundwater in the BSTG root-fan and the interfan depression is derived from natural sediments. The 15N-NH4+ in groundwater is depleted in the BSTG mid-fan, and the δ15N-NH4+ values are similar with those of the pollution sources from the chemical factories in the mid-fan. Both hydrochemical and nitrogen isotopic characteristics indicate significant pollution in the mid-fan, but the ammonium pollution is limited to the area near the chemical factories.

Post-dredging nitrogen dynamics at the sediment–water interface: the shallow, eutrophic Mogan Lake, Turkey

The sedimentation and resuspension of various forms of nitrogen in wetlands determines the direction of the nitrogen dynamics. Mogan Lake, in the Gölbaşı Special Environmental Protection Area, is one of the most important Ramsar-nominated wetlands in Turkey. Lake management applications have been performed by the local managers since 2008, including sediment cleaning activities such as dredging. In this context, the aim was to quantitatively predict the nitrogen dynamics (ammonium and nitrate release/ uptake in the positive and/or negative direction) at the sediment–water interface, which has not been addressed in the eutrophication and sediment-related studies conducted to date on the lake in question. Sediment ammonium and nitrate flux were estimated to be between -9.16 and 0.36 µg m-2 d-1 and between -67.2 and 35.16 µg m-2 d-1, respectively. The estimations for sediment nitrogen flux in Mogan Lake did not show a regular seasonal or spatial fluctuation. Our results demonstrate that low nitrogen release levels in Mogan Lake do not pose a threat to its nutrient level. In conclusion, both monitoring and reducing external loading is still the top priority for a long-term recovery of water quality in the process of freshwater ecosystems.

Diffusive gradients in thin films for transfer of phosphorus, nitrate and ammonium in lake sediments

There is a lack of the understanding of the transfer of phosphate (PO4-P), ammonium (NH4-N) and nitrate (NO3-N) at the millimeter scale in sediments related to internal loadings in the semi-arid and cold Lake Hulun in China. In this paper, a passive sampling technique-diffusion gradients in thin films (DGT) has been used for the biogeochemical behaviors and dynamic transfer of PO4-P, NH4-N and NO3-N in sediments in this lake. The two-sided DGT probe (AMP-TH&ZrO-Chelex) and ZrO DGT piston are designed for sediment/water interface. Based on change characters of DGT concentration profiles (nutrients, Fe and Mn) related to redox status and chemical properties, N and P mobilizations are derived. The reductive dissolution of Mn(IV) or Fe(III) (oxyhydr)oxides accounts for subsequent P release is corresponded with the oxic or anoxic status in sediment layers; Fe(III)-reduction is the main reason for P remobilization. The breakdown of algae biomass deposited on the uppermost sediment and phosphatase enzymes activity enhanced by NH4-N also lead to P remobilization. In sub-anoxic or anoxic layer, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) induce exchangeable ammonium (NH4ex) enrichment and NH4-N release, while, anammox depletes NH4-N mobility. Aerobic nitrification results in NO3-N remobilization. Organic matter favors NH4-N release. DGT induced fluxes in sediments (DIFS) model is used to derive the labile P pool (51.5–465.5 cm3 g−1), resupply constant (0.186–0.734), response time (54–11,070 s) and Dspt rate (32–382,517 nmol cm−3 d−1) for describing dynamic P transfers with two opposite types of “slow” and “fast” resupplies. The diffusive fluxes across sediment/water interface in ranges of 67.9–498.7 μg m−2 d−1 (PO4-P), −1416–106.8 (NH4-N) and –2147–301.1 μg m−2 d−1 (NO3-N) and DIFS parameters can be used for release risks in lake regions and the sediment remediation strategies are recommended.

Experiment on Sediment Ammonia Nitrogen Release of Chaohu Lake in Varying Hydrodynamic Disturbance

Shallow water has low depth, and hydrodynamic conditions may change with the effect of wind and waves, resulting in sediment suspension and pollutant release. To investigate the influence of sediment incipient motion on ammonia nitrogen (NH3-N) release in shallow lakes under hydrodynamic disturbance, we monitored ammonia nitrogen concentration in the overlying water of sediments in Chaohu Lake under static, weak, and strong disturbance conditions and analyzed the ammonia nitrogen release rate based on the these concentrations. In static condition, the sediment particles on the surface moved individually (individual movement), and the ammonia nitrogen release rate was 9.59 mg/m2/day. When the disturbance was weak and a small proportion of sediment particles started to move (small movement), the ammonia nitrogen release rate increased to 34.21 mg/m2/day. When the disturbance was further strengthened, and most of the sediment particles moved (general movement), the ammonia nitrogen release rate was 77.04 mg/m2/day. Distribution showed that the release rate varied the most in the western area followed by the eastern area, and the central area had the lowest release rate. The daily release of ammonia nitrogen in Chaohu Lake ranged from 8742.3 kg to 61,008.59 kg. In this experiment, we combined sediment movement and pollutant release, which provides a new reference for the study of pollutant release in shallow lakes and for ammonia nitrogen management in other shallow lakes.

Occurrence of nitrite-dependent anaerobic methane oxidation bacteria in the continental shelf sediments

Nitrite-dependent anaerobic methane oxidation (N-damo) is a key bioprocess coupling global carbon and nitrogen cycles and is mediated by NC10 bacteria. So far, the distribution of N-damo bacteria in marine sediments has rarely been reported. In this study, the sediments from the Bohai Sea, Yellow Sea and East China Sea were taken as the research objects, and the ecological distribution of N-damo bacteria was investigated by quantitative PCR and amplicon sequencing. Quantitative PCR results demonstrated that the highest average copy number of N-damo bacterial 16S rRNA gene was in the Bohai Sea, followed by the East China Sea, while the lowest was observed in the Yellow Sea. Based on the OTU numbers, the N-damo bacterial diversity was highest in East China Sea, followed by the Bohai Sea, while lowest in the Yellow Sea. The N-damo bacterial community structure exhibited an obvious spatial distribution among the three seas. Sediment nitrite nitrogen content is the key environmental factor affecting the abundance and diversity of N-damo bacteria, and sediment ammonia nitrogen content is the key environmental factor affecting the community structure of N-damo bacteria.

Temporal profiling resolves the drivers of microbial nitrogen cycling variability in coastal sediments

Here we describe the potential for sediment microbial nitrogen-cycling gene (DNA) and activity (RNA) abundances to spatially resolve coastal areas impacted by seasonal variability in external nutrient inputs. Three sites were chosen within a nitrogen-limited embayment, Port Phillip Bay (PPB), Australia that reflect variability in both proximity to external nutrient inputs and the dominant form of available nitrogen. At three sediment depths (0–1; 1–5; 5–10 cm) across a 2 year study key genes involved in nitrification (archaeal amoA and bacterial β-amoA), nitrite reduction (clade I nirS and cluster I nirK, archaeal nirK-a), anaerobic oxidation of ammonium (anammox 16S rRNA phylogenetic marker) and nitrogen fixation (nifH) were quantified. Sediments impacted by a dominance of organic nitrogen inputs were characterised at all time-points and to sediment depths of 10 cm by the highest transcript abundances of archaeal amoA and archaeal nirk-a. Proximity to a dominance of external nitrate inputs was associated with the highest transcript abundances of nirS which temporally co-varied with seasonal changes in sediment nitrate. Sediments isolated from external inputs displayed the greatest depth-specific decrease in quantifiable transcript abundances. In these isolated sediments bacterial β-amoA transcripts were temporally associated with increased sediment ammonium levels. Across this nitrogen limited system variability in the abundance of bacterial β-amoA, archaeal amoA, archaeal nirk-a or nirS transcripts from the sediment surface (0–1 and 5 cm) demonstrated a capacity to improve our ability to monitor coastal zones impacted by anthropogenic nitrogen inputs. Specifically, the spatial detection sensitivity of bacterial β-amoA transcripts could be developed as a metric to determine spatiotemporal impacts of large external loading events. This temporal study demonstrates a capacity for microbial activity metrics to facilitate coastal management strategies through greater spatial resolution of areas impacted by external nutrient inputs.

The role of sulfur cycle and enzyme activity in dissimilatory nitrate reduction processes in heterotrophic sediments

The dissimilatory nitrate (NO3−) reduction processes (DNRPs) play an important role in regulating the nitrogen (N) balance of aquatic ecosystem. Organic carbon (OC) and sulfur are important factors that influence the DNRPs. In this study, we investigated the effects of sulfur cycle and enzyme activity on DNRPs in the natural and human-modified heterotrophic sediments. Quarterly monitoring of anaerobic ammonium oxidation, denitrification (DNF), and dissimilatory NO3− reduction to ammonium (DNRA) in sediments was conducted using 15N isotope tracing method. qPCR and high-throughput sequencing were applied to characterize the DNF and DNRA microbial abundances and communities. Results showed that instead of the OC, the glucosidase activity (GLU) was the key driver of the DNRPs. Furthermore, instead of the ratio of OC to NO3−, the GLU and the ratio of OC to sulfide (C/S) correctly indicated the partitioning of DNRPs in this study. We deduced that the sulfur reduction processes competed with the DNRPs for the available OC. In addition, the inhibitory effect of sulfide (final product of the sulfur reduction processes) on the DNRPs bacterial community were observed, which suggested a general restrictive role of the sulfur cycle in the regulation and partitioning of the DNRPs in heterotrophic sediments.

Effects of AM Fungi and Grass Strips on Soil Erosion Characteristics in Red Sandstone Erosion Areas in Southern China

As one of the most serious soil erosion areas in China, red sandstone erosion areas in southern China have been seriously affected by abundant annual rainfall. To understand the effects of AM fungi and different grass strips on soil erosion characteristics in red sandstone erosion areas in southern China, we selected Cynodon dactylon, Lotus corniculatus, Zoysia japonica, and Astragalus sinicus. Two treatments were carried out for each grass: AM was the soil in its original state, and CK was the soil in which the original AM fungi were eliminated. Taking CK treatment as the control group, any changes of runoff and sediment yield and nutrient loss under different grass strip conditions were measured. The total yield of runoff and sediment in the four grass strips under CK treatment was greater than that of AM. The runoff ammonium nitrogen loss concentration in AM treatment was smaller than in CK treatment under continuous scouring. The ammonium nitrogen loss concentration of sediment during continuous scouring showed a decreasing trend. Under AM treatment, the loss concentration of sediment ammonium nitrogen showed a decreasing trend compared with the CK treatment. The percentage of sediment particles &gt;2 mm in the four grass strips was significantly larger for CK treatment than AM treatment (p &lt; 0.05), and except for Cynodon dactylon, the percentage of sediment particles in the size range of 1–2 mm for other grass strips was significantly larger for CK treatment than for AM treatment (p &lt; 0.05); the percentage of sediment particles at 0.02–0.25 mm was significantly smaller for CK treatment than for AM treatment (p &lt; 0.05). The mean weight diameter (MWD) of sediments produced by the four grass strips under simulated scouring showed an overall increasing trend with increased scouring time. The mean weight diameter (MWD) of sediments produced under CK treatment was larger than that of AM treatment. The fractal dimension (D) of sediments showed a decreasing trend with increased scouring time. These results showed that AM fungi can promote the growth of plant roots, strengthen soil anchoring, protect large particle aggregates in soil under rainfall scouring, and reduce soil erosion and nutrient loss in red sandstone erosion areas in southern China. Cynodon dactylon and Zoysia japonica were more prominent than Lotus corniculatus and Astragalus sinicus in inhibiting soil erosion in red sandstone erosion areas.

Sources and fate of organic matter in a hypersaline lagoon: A study based on stable isotopes from the Pulicat lagoon, India

Stable carbon (δ13C) and nitrogen (δ15N) isotopes of organic matter (OM) in bed sediments and suspended solids are thoroughly investigated in the Pulicat lagoon, India, in pre-South West (SW) monsoon (June 2018) and post-North East (NE) monsoon (March 2019) to understand the response of OM in salt stress conditions. A near absence of an external supply of water and intense evaporation, as suggested by higher hydrogen and oxygen isotope values (δD and δ18O) of the lagoon water, led to hypersaline conditions in the lagoon. Despite a long period of osmotic stress, a high OM concentration in suspended solids in post-NE monsoon suggests that autochthonous production is unaffected by salt stress conditions. Locally at different sites, the difference in δ13C (−4.9‰ to +1.4‰) and δ15N (−4.1‰ to +1.6‰) values of OM between suspended solids and bed sediments are higher in pre-SW monsoon compared to post-NE monsoon. The negative isotopic difference is caused by benthic respiration of OM and cation exchange with clay bound ammonium in bed sediments, whereas the positive difference is the result of cellulose decomposition in areas dominated by seagrasses. However, in post-NE monsoon, wind-induced re-suspension of bed sediments reduce the differences in δ13C (−2.3‰ to −0.1‰) and δ15N (−2.1‰ to +3‰) values. The source apportionments of δ15N values suggest inputs from sewage and fertilizers. Additionally, seagrass-detritus dislodged by fishing activities favors primary production. Overall, we suggest that the impact of the hypersaline conditions on in-situ productivity can be suppressed if wind activity and nutrient re-cycling are dominant. The present study is unique as it addresses the processes that operate in a hypersaline lagoon during the short-term failure of monsoon.

Assessing citric acid-derived luminescent probes for pH and ammonia sensing: A comprehensive experimental and theoretical study

The present work reports on the assessment of luminescent probes derived from citric acid (CA) and β-aminothiols (namely, l-cysteine (Cys) and cysteamine) for instrumental and smartphone-based fluorimetric sensing purposes. Remarkably, the evaluated luminescent probes derived from natural compounds showed pH-dependent dual excitation/dual emission features. Both fluorophores hold promise for the ratiometric fluorimetric sensing of pH, being especially convenient for the smartphone-based sensing of pH via ratiometric analysis by proper selection of B and G color channels. Time dependent density functional theory (TDDFT) calculations allowed to substantiate the pH dependent structure-property relationship and to unveil the critical role of the CA derived carboxyl group, these findings contributing to the fundamental knowledge on these systems for the rational design of new fluorophores and in establishing fluorescence sensing mechanisms of CA-derived systems. Besides, paper-based devices modified with CA-Cys were implemented in a three-phase separation approach for sensitive and selective ammonia sensing, yielding a remarkable enrichment factor of 389 and a limit of detection of 37 μM under optimal conditions. The proposed approach was successfully applied to the determination of ammonia nitrogen and extractable ammonium in water samples and marine sediments, respectively.

Response of Sediment Microbial Communities to the Rural Wastewater in the Pond-Ditch Circulation System

Microorganisms played important roles in nutrient removal in Pond-ditch circulation system (PDCS). However, dynamics of microbial community in the PDCS, and responses of rhizosphere and non-rhizosphere microbial community to rural wastewater remains unclear. In this paper, average operational taxonomic units numbers of sediment microbial varied from 10,254 to 17,112, and values in rhizosphere were higher than those of the non-rhizosphere (p &amp;lt; 0.05). Bacillus, Clostridium sensu stricto 1, and Geobacter were the predominant genera in PDCS sediment with relative abundances of 0.52–17.61%, 0.26–8.08%, and 0.20–4.58%, respectively. However, Bacillus, Clostridium sensu stricto 1, and Geobacter genera in rhizosphere were more abundant than those in non-rhizosphere at day 30. Chao 1 index ranged from 10,225 to 17,033 and showed significant positive correlations with all sediment properties (p &amp;lt; 0.05). Chao 1 and Shannon indices in rhizosphere were significant positively related to tartaric acid and total organic carbon, respectively; while significant correlation between Shannon and Simpson indices in non-rhizosphere and oxidation-reduction potential were detected (p &amp;lt; 0.05). Redundancy analysis suggested that lactic acids, proteins, and amino acids had strong positive effects on Geobacter and Clostridiu sensu stricto 12 in the rhizosphere; while Bacillus and Clostridium in non-rhizosphere were significantly affected by sediment ammonia nitrogen and nitrate nitrogen. Environmental variables accounted for 66.9 and 60.3% of the total variation for the microbial community of non-rhizosphere and rhizosphere sediments, respectively. Our results highlight that root exudates and sediment available N alter predominant genera in the rhizosphere and non-rhizosphere, respectively, which is benefit for optimizing removal efficiency of PDCSs in large-scale applications.

Sources and fate of excessive ammonium in the Quaternary sediments on the Dongting Plain, China

Excessive ammonia-nitrogen (N) in aquifers has caused groundwater pollution on the Dongting Plain (DTP), which seriously threatens the safety of drinking water. It is urgent and necessary to determine the sources and enrichment mechanisms of ammonia-N in groundwater. Carrying out water and soil collaborative research on a three-dimensional scale can more comprehensively analyze the sources of N, including natural and anthropogenic sources. In this study, surface and groundwater quality characteristics were examined from a total of 77 sites on the DTP. Two subsequent boreholes were drilled in the high ammonia concentration area and normal groundwater area, respectively, to compare the effects of anthropogenic activities. Indicators from hydrogeochemical and pedogeochemical analyses, as well as various isotopes, including δ15N-NH4+, δ15N-TON, δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δD-H2O, and δ13C-TOC were used to identify ammonium sources and transformation mechanisms in the strata. We found that the sediments were contaminated by manure and sewage in the aquifers, and part of the shallow groundwater was additionally contaminated by nitrogen fertilizers. Excessive ammonium-N was also detected in the deep aquitards and sediments, which were mainly dominated by mineralization. Ammonia oxidation (with weak hydroxylamine oxidation) is an important biogeochemical process in which ammonia and nitrate do not accumulate in oxidizing groundwater environments. However, heterotrophic nitrification (HN) and anaerobic ammonium oxidation (ANAMMOX) are the release mechanisms for excessive ammonium-N under reducing conditions. In addition, organic matter (OM) on the DTP had a wide range of biogeochemical proxies generated by phytoplankton within a lake, and the comparatively resilient terrestrial organic residues washed in from the surrounding terrestrial area. This study breaks through the conventional mechanisms for the release of excessive ammonium from sediments to aquifers, which provides new ideas for research on ammonium in sediments and ammonia in groundwater.