Nitrification In Sediments Research Articles

Sediment nitrate dissimilatory reduction processes in the river-lake ecotone of Poyang Lake, China: Mechanisms and environmental implications

Sediment nitrate dissimilatory reduction processes in the river-lake ecotone of Poyang Lake, China: Mechanisms and environmental implications

Distribution of nitrate (NO3−) and posphate (PO43-) in water, sediment and seaweed of Morowali distric marine waters

Abstract The seaweed market opportunity is very promising, this condition is in line with the national plan which positions Indonesia as the largest seaweed producer in the world. Seaweed production in Central Sulawesi, especially in Morowali district, has continued to decline since 2012-2021. The aim of the research was to examine the distribution of nitrates and phosphates in sea water, sediment and seaweed at seaweed cultivation sites around mining sites in Morowali District which is suspected to be the cause of this situation. Observation stations include South Bungku Waters, Bahodopi Waters, Witaponda Waters and Bumi Raya Waters. The results showed different nitrate and phosphate contents in sea water, sediment and seaweed. The nitrate content in waters throughout Morowali district ranged from 0.071 to 0.202 ppm, and phosphate from 0.001 to 0.013 ppm. The nitrate content in the sediment was in the range of 2.67-8.15 ppm and phosphate was in the range of 0.001-3.03 ppm. Meanwhile, the nitrate and phosphate content in seaweed was from 20.36 to 40.68 ppm and 1.39 to 8.37 ppm respectively. The data showed that the highest nitrate and phosphate content was in seaweed tallus, followed by sediment and the lowest nitrate and phosphate content in sea water. This indicates that the nitrate content of seawater, sediment and seaweed has exceeded the tolerance threshold for seaweed growth. However, the phosphate content in seawater was still relatively low, while in sediment and seaweed tallus has exceeded the threshold.

Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH4) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 106 copies g−1) was significantly higher than that of NC10 bacteria (2.1 × 106 copies g−1), the average potential rates of nitrite-DAMO (4.59 nmol 13CO2 g−1 d−1) and nitrate-DAMO (5.01 nmol 13CO2 g−1 d−1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH4 m−2 d−1, respectively, which accordingly achieved 15.07–24.95 mg m−2 d−1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH4 mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.

Vallisneria spiralis L. adaptive capacity improves pore water chemistry and increases potential nitrification in organic polluted sediments

BackgroundMacrophytes may modify benthic biodiversity and biogeochemistry via radial oxygen loss from roots. This condition contrasts sediments anoxia, allows roots respiration, and facilitates aerobic microbial communities and processes in the rhizosphere. Simultaneously, the rhizosphere can stimulate anaerobic microorganisms and processes via exudates or by favoring the build-up of electron acceptors as nitrate. As eutrophication often results in organic enrichment in sediments and large internal nutrients recycling, an interesting research question is to investigate whether plants maintain the capacity to stimulate aerobic or anaerobic microbial communities and processes also under elevated organic pollution.MethodsA manipulative experiment was carried out under laboratory-controlled conditions. Microcosms containing bare sediments and sediments transplanted with the macrophyte Vallisneria spiralis L. were created. The effect of the plant was investigated on sediments with moderate (8%) and elevated (21%) organic matter content, after an acclimatization period of 30 days. Chemical and physical parameters, microbial community composition and the potential rates of nitrification, denitrification and nitrate ammonification were measured at two different depths (0–1 and 1–5 cm) after the acclimatization period to evaluate the role of roots.ResultsVallisneria spiralis grew and assimilated pore water nutrients at the two organic matter levels and vegetated sediments had always nutrient-depleted porewaters as compared to bare sediments. Nitrifying microbes had a lower relative abundance and diversity compared to denitrifying bacteria. However, regardless of the organic content, in vegetated sediments nitrifiers were detected in deeper horizons as compared to bare sediments, where nitrification was confined near the surface. In contrast, potential denitrification rates were not affected by the presence of roots, but probably regulated by the presence of nitrate and by root-dependent nitrification. Potential nitrate ammonification rates were always much lower (< 3%) than potential denitrification rates.ConclusionsVallisneria spiralis affects N-related microbial diversity and biogeochemistry at moderate and elevated organic matter content, smoothing bottom water–pore water chemical gradients and stimulating nitrification and nitrogen loss via denitrification. These results suggest the possibility to deploy V. spiralis as a nature-based solution to counteract eutrophication in freshwater systems impacted by high loads of organic matter, for example, downstream of wastewater treatment plants.

Denitrification dominates dissimilatory nitrate reduction across global natural ecosystems.

Denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are three competing processes of microbial nitrate reduction that determine the degree of ecosystem nitrogen (N) loss versus recycling. However, the global patterns and drivers of relative contributions of these N cycling processes to soil or sediment nitrate reduction remain unknown, limiting our understanding of the global N balance and management. Here, we compiled a global dataset of 1570 observations from a wide range of terrestrial and aquatic ecosystems. We found that denitrification contributed up to 66.1% of total nitrate reduction globally, being significantly greater in estuarine and coastal ecosystems. Anammox and DNRA could account for 12.7% and 21.2% of total nitrate reduction, respectively. The contribution of denitrification to nitrate reduction increased with longitude, while the contribution of anammox and DNRA decreased. The local environmental factors controlling the relative contributions of the three N cycling processes to nitrate reduction included the concentrations of soil organic carbon, ammonium, nitrate, and ferrous iron. Our results underline the dominant role of denitrification over anammox and DNRA in ecosystem nitrate transformation, which is crucial to improving the current global soil N cycle model and achieving sustainable N management.

Analysis of the Rate and Nutrient Content of Sediment in The Coral Transplantation Installation Vertical Method on Samalona Island, Makassar City

Samalona Island is a small island that administratively belongs to the inner zone of the Spermonde Islands region with low live coral cover. One effort to improve coral conditions is to carry out vertical transplantation, but hydro-oceanographic conditions are thought to be an inhibiting factor, including sediment. The research carried out aims to determine the suitability of oceanographic parameters, estimate sediment rates, and determine the phosphate and nitrate in sediments. The research method used a field experiment method by taking water and sediment samples and installing sediment traps for 15 days. The parameters measured in situ are temperature, pH, current speed, salinity, and dissolved oxygen, while the ex-situ test is the dry weight of sediment, TSS, nitrate, and phosphate concentrations. Data analysis uses descriptive statistics and is categorized according to the evaluation instrument used. The research results show that the values for temperature, pH, current speed, salinity, and dissolved oxygen meet the standard criteria for coral-based on PP 21/2022. The sediment rate during the research period was 0,003 – 0,015 gr/cm2/day, so it was categorized as having the potential damage to corals with a mild to severe impact level. The nitrate concentration in sediment ranges from 0,19 – 0,25 ppm while phosphate ranges from 0,35 – 0,72 ppm, so it can be said to be waters with a medium trophic level (mesotrophic). The current speeds and sediment rates potentially accelerate nutrient concentrations and cause sediment resuspension, thereby closing coral polyps, especially on corals closest to the substrate where vertical coral transplant installations are installed.

Exploration of the nitrification process in surface sediment of a hypereutrophic intertidal zone via hydroxylamine monitoring

Hydroxylamine is considered an indicator of nitrification, as it is both produced and consumed during the ammonium (NH4+) oxidation process. In this study, to explore the site of active nitrification and elucidate the factors controlling nitrification, hydroxylamine concentrations in the seawater and porewater of the hypereutrophic Yatsu tidal flat, eastern Japan, were measured using the iodine oxidation method with a Sep-Pak C18 cartridge. The concentrations over approximately 2 years indicated that nitrification was more active in the surface sediment than in seawater. This would support denitrification in the surface sediment via active nitrification–denitrification, which removes N. In addition, multiple linear regression analysis indicated that the concentration in porewater was positively correlated with the seawater parameters of nitrate (NO3−) concentration, NH4+ concentration, and temperature, while among porewater parameters, it was negatively correlated with the phosphate (PO43−) concentration and positively correlated with the NH4+ concentration. These relationships between hydroxylamine concentration and environmental factors suggest that porewater nitrification increases with higher temperature and NH4+ supply from seawater and porewater, as well as under oxic conditions. Our results demonstrate that hydroxylamine is a useful indicator of sediment nitrification in the hypereutrophic intertidal zone.

Reshaping the plastisphere upon deposition: Promote N2O production through affecting sediment microbial communities in aquaculture pond

Microplastics (MPs) could provide vector for microorganisms to form biofilm (plastisphere), but the shaping process of MPs biofilm and its effects on the structure and function of sedimentary microbial communities especially in aquaculture environments are not reported. For this, we incubated MPs biofilm in situ in an aquaculture pond and established a sediment microcosm with plastisphere. We found that the formation of MPs biofilm in surface water was basically stable after 30 d incubation, but the biofilm communities were reshaped after deposition for another 30 d, because they were more similar to plastisphere communities incubated directly within sediment but not surface water. Moreover, microbial communities of MPs-contaminated sediment were altered, which was mainly driven by the biofilm communities present on MPs, because they but not sediment communities in proximity to MPs had a more pronounced separation from the control sediment communities. In the presence of MPs, increased sediment nitrification, denitrification and N2O production rates were observed. The K00371 (NO2-⇋NO3-) pathway and elevated abundance of nxrB and narH genes were screened by metagenomic analysis. Based on structural equation model, two key bacteria (Alphaproteobacteria bacterium and Rhodobacteraceae bacterium) associated with N2O production were further identified. Overall, the settling of MPs could reshape the original biofilm and promote N2O production by selectively elevating sedimental microorganisms and functional genes in aquaculture pond.

Microbial communities and nitrogen cycling in Litopenaeus vannamei and Mercenaria mercenaria polyculture ponds

The nitrogen cycling has an important ecological role in aquaculture ponds, and microbes mainly carry out the related processes. To better reveal the microbial community and nitrogen cycling processes in shrimp and clam polyculture ponds, we analyzed the microbial communities of water and sediment of four ponds containing Litopenaeus vannamei with different stocking densities of Mercenaria mercenaria (LM, 0 ind/m2; LM-L, 17.4 ind/m2; LM-M, 34.8 ind/m2; LM-H, 52.2 ind/m2) from May to September. Additionally, the possible reaction rates and gene abundances involved in nitrogen cycling were determined in sediments of LM and LM-M in July. The results showed that the dominant phyla in the water included Proteobacteria, Cyanobacteria, and Bacteroidetes and in sediment were Proteobacteria, Desulfobacterota, and Chloroflexi. According to principal coordinate analysis, microbial communities of water and sediment significantly differed with and without M. mercenaria. The LEfSe analysis indicated that nitrogen cycling processes in the water of L. vannamei ponds were denitrification and dissimilatory nitrate reduction to ammonium (DNRA), while nitrification and denitrification were observed in the water of L. vannamei-M. mercenaria polyculture ponds. In the sediments of L. vannamei ponds, DNRA was dominant process, whereas in the sediments of L. vannamei-M. mercenaria polyculture ponds, DNRA, incomplete nitrification and denitrification were identified. Compared with LM, LM-M increased the nitrification rate and enhanced nitrate reduction with denitrification and anaerobic ammonium oxidation (anammox) instead of DNRA in sediments. The abundance of genes involved in nitrification and denitrification was significantly enriched in the sediments of LM-M. These results suggest that L. vannamei-M. mercenaria polyculture ponds may enhance nitrifying bacteria and denitrifiers, promoting nitrification and denitrification in sediment. This study helps understand shrimp polyculture ponds’ microbial community composition and nitrogen cycling.

Dynamics of Benthic Nitrate Reduction Pathways and Associated Microbial Communities Responding to the Development of Seasonal Deoxygenation in a Coastal Mariculture Zone.

Intensive mariculture activities result in eutrophication and enhance coastal deoxygenation. Deoxygenation profoundly influences nitrate reduction processes and further the fate of nitrogen (N) in coastal systems. Herein, 15N isotope labeling, real-time PCR, and high-throughput sequencing techniques were jointly used to investigate the participation and seasonal dynamics of sediment nitrate reduction pathways and the succession of functional microbial communities during the development of seasonal deoxygenation in a coastal aquaculture zone. Denitrification dominated benthic nitrate reduction (46.26-80.91%). Both denitrification and dissimilatory nitrate reduction to ammonium were significantly enhanced by summer deoxygenation (dissolved oxygen levels fell to 2.94 ± 0.28 mg L-1), while anammox remained unchanged. The abundance of the nitrous oxide reductase gene nosZ increased during deoxygenation. The community of the nosZ gene was sensitive to deoxygenation, with Azospirillum and Ruegeria accounting for the majority. Pelobacter was overwhelming in the nrfA gene (encoding dissimilatory nitrite reductase) community, which was less affected by deoxygenation. The variations of benthic nitrate reduction processes were driven by bottom water oxygen combined with temperature, chlorophyll a, and microbial gene abundances and community compositions. Our results implicated that seasonal oxygen-deficient zones could be substantial N sinks of coastal ecosystems and important for N balance. Effective management measures need to be developed to avoid further exacerbation of coastal deoxygenation and maintain the sustainable development of mariculture.

Community assembly of comammox Nitrospira in coastal wetlands across southeastern China.

Complete ammonia oxidizers (comammox Nitrospira) are ubiquitous in coastal wetland sediments and play an important role in nitrification. Our study examined the impact of habitat modifications on comammox Nitrospira communities in coastal wetland sediments across tropical and subtropical regions of southeastern China. Samples were collected from 21 coastal wetlands in five provinces where native mudflats were invaded by Spartina alterniflora and subsequently converted to aquaculture ponds. The results showed that comammox Nitrospira abundances were mainly influenced by sediment grain size rather than by habitat modifications. Compared to S. alterniflora marshes and native mudflats, aquaculture pond sediments had lower comammox Nitrospira diversity, lower clade A.1 abundance, and higher clade A.2 abundance. Sulfate concentration was the most important factor controlling the diversity of comammox Nitrospira. The response of comammox Nitrospira community to habitat change varied significantly by location, and environmental variables accounted for only 11.2% of the variations in community structure across all sites. In all three habitat types, dispersal limitation largely controlled the comammox Nitrospira community assembly process, indicating the stochastic nature of these sediment communities in coastal wetlands. IMPORTANCE Comammox Nitrospira have recently gained attention for their potential role in nitrification and nitrous oxide (N2O) emissions in soil and sediment. However, their distribution and assembly in impacted coastal wetland are poorly understood, particularly on a large spatial scale. Our study provides novel evidence that the effects of habitat modification on comammox Nitrospira communities are dependent on the location of the wetland. We also found that the assembly of comammox Nitrospira communities in coastal wetlands was mainly governed by stochastic processes. Nevertheless, sediment grain size and sulfate concentration were identified as key variables affecting comammox Nitrospira abundance and diversity in coastal sediments. These findings are significant as they advance our understanding of the environmental adaptation of comammox Nitrospira and how future landscape modifications may impact their abundance and diversity in coastal wetlands.

Interplay of legacy irrigation and nitrogen fertilizer inputs to spatial variability of arsenic and uranium within the deep vadose zone

The vadose zone is a reservoir for geogenic and anthropogenic contaminants. Nitrogen and water infiltration can affect biogeochemical processes in this zone, ultimately affecting groundwater quality. In this large-scale field study, we evaluated the input and occurrence of water and nitrogen species in the vadose zone of a public water supply wellhead protection (WHP) area (defined by a 50-year travel time to groundwater for public supply wells) and potential transport of nitrate, ammonium, arsenic, and uranium. Thirty-two deep cores were collected and grouped by irrigation practices: pivot (n = 20), gravity (n = 4) irrigated using groundwater, and non-irrigated (n = 8) sites. Beneath pivot-irrigated sites, sediment nitrate concentrations were significantly (p < 0.05) lower, while ammonium concentrations were significantly (p < 0.05) higher than under gravity sites. The spatial distribution of sediment arsenic and uranium was evaluated against estimated nitrogen and water loading beneath cropland. Irrigation practices were randomly distributed throughout the WHP area and presented a contrasting pattern of sediment arsenic and uranium occurrence. Sediment arsenic correlated with iron (r = 0.32, p < 0.05), uranium negatively correlated to sediment nitrate (r = −0.23, p < 0.05), and ammonium (r = −0.19 p < 0.05). This study reveals that irrigation water and nitrogen influx influence vadose zone geochemistry and mobilization of geogenic contaminants affecting groundwater quality beneath intensive agricultural systems.

KARAKTERISTIK DISTRIBUSI ZAT HARA NITRAT DAN FOSFAT PADA AIR DAN SEDIMEN DI ESTUARIA TANJUNG LIMAU KOTA BONTANG KALIMANTAN TIMUR

This research was conducted in May 2021 - January 2022. The purpose of this study was to determine the distribution of nitrate and phosphate content in water and sediment in the Tanjung Limau estuary, Bontang City, East Kalimantan. Sampling of water and sediment was carried out at 4 research stations using a random method which was then analyzed at the Water Quality Laboratory and Soil Science Laboratory of PPLH Mulawarman University. The results showed that the nitrate content in the water was 0.012-0.018mg/L, 4.20-9.09% in the sediment, while the phosphate in the water was 0.014-0.077 mg/L and the phosphate in the sediment was 0.021-0.030%. The results of the analysis show that the nitrate and phosphate content is higher at Station 1 and lower towards Station 4. There is a significant difference between the nitrate and phosphate content in the water and in the sediment. The content of nitrate and phosphate is mostly sourced from upstream of the river, namely in residential areas and mangrove forests.

Delineating Contaminant Hotspots Through Hydrochemical Assessment of a Severely Degraded Watershed in Nepal

This project deals with the environmental assessment of the Bagmati River in Kathmandu Valley, Nepal. Rapid population growth and urban development in recent decades have turned this river into a highly polluted water body. To delineate the contaminant hotspots, water and sediment samples were collected from eleven (11) sites along the river. Water samples were analysed for temperature, pH, total dissolved solids (TDS), conductivity, dissolved oxygen (DO), total suspended solids (TSS), turbidity, E. coli, biochemical oxygen demand (BOD), nitrate, total phosphorus (TP), chloride, and heavy metals in sediments. The data showed considerable degradation of the aquatic system. The TDS increased from 52 mg/L in Sundarijal (near source) to 595 mg/L near Teku (city center). Simultaneously, TSS increased from 43 mg/L to 1233 mg/L, with a contamination hotspot near the Thapathali area. DO quickly dropped below 2 mg/L at all sites near downtown. E. coli increased from 4000 MPN/100 mL in Sundarijal to 46,000 MPN/100 mL in Teku. The high levels of E. coli and the low DO were attributed to the direct disposal of sewage, house-hold trash, industrial effluents, and wastes from hospitals and slaughter houses. In recent years, sediment accumulation of heavy metals has also gone up, namely Cr (35%), Cu (59%), Fe (7%), Pb (7%), and Zn (25%). Phosphorus ranges from 0.2 mg/L at the source to 6.2 mg/L near the city. Phosphorus comes from the area’s wastewater treatment plant, industrial discharges, and sewage. From people’s survey results, 23% said they dispose off part or all of their trash into the river or directly on the street. The urban impact is also evident in the dramatic rise of dissolved Cl in water from the suburbs (26.2 mg/L) to the central city area (73 mg/L). Based on the results, areas near Teku, Thapathali, and Kalimati should be prioritised for immediate remedial measures. Urgent recommendations include dredging of stream sediments, contaminant source cutoff, stringent industrial regulations, and buffer strips and filter beds along the stream banks.

Nitrification and denitrification processes in a zero-water exchange aquaculture system: characteristics of the microbial community and potential rates

​The zero-water exchange aquaculture has been identified as a promising method of farming to decrease the environment pressure of aquaculture and to increase profits. However, the ecological functions (e.g., nitrogen removal) and microbial biodiversity of the zero-water exchange pond aquaculture system are relatively understudied. In the present study, the zero-water exchange pond aquaculture system were constructed to investigated the microbial communities, sediment potential nitrification and denitrification production rates. And five functional genes (AOA amoA, AOB amoA, nirS, nosZ, and hzsB) were used to quantify the abundance of nitrifying and denitrifying microorganisms. The results showed that the sediment of the system had excellent potential nitrification-denitrification performance, with potential nitrification and denitrification rate were 149.77-1024.44 ng N g−1 h−1 and 48.32-145.01 ng N g−1 h−1, respectively. The absolute copy numbers of nitrogen functional genes and total bacterial 16S rRNA were 1.59×105-1.39×109 and 1.55×1010-2.55×1010copies g−1, respectively, with the dominant phyla, i.e., Proteobacteria, Actinobacteriota, Chloroflexi, Cyanobacteria, and Firmicutes. The relative abundances of the genera related to nitrification and denitrification, varied from 0.01% to 0.79% and from 0.01% to 15.54%, respectively. The potential nitrification rate was positively related to the sediment TOC concentration; and the potential denitrification rate had a positive correlation with sediment nitrate concentration. The genera Bacillus positively correlated with sediment NO3‐-N concentration, whereas Flavobacterium and Shewanella positively correlated with sediment NH4+-N concentration, which could be the functional bacteria for nitrogen removal. These findings may shed light on quantitative molecular mechanisms for nitrogen removal in zero-water exchange ponds, providing a sustainable solution to nitrogen pollution problem in the freshwater aquaculture 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.

Interactions between Phosphorus Enrichment and Nitrification Accelerate Relative Nitrogen Deficiency during Cyanobacterial Blooms in a Large Shallow Eutrophic Lake.

Regime shifts between nitrogen (N) and phosphorus (P) limitation, which trigger cyanobacterial succession, occur in shallow eutrophic lakes seasonally. However, the underlying mechanism is not yet fully illustrated. We provide a novel insight to address this from interactions between sediment P and nitrification through monthly field investigations including 204 samples and microcosm experiments in Lake Chaohu. Total N to P mass ratios (TN/TP) varied significantly across seasons especially during algal bloom in summer, with the average value being 26.1 in June and descending to 7.8 in September gradually, triggering dominant cyanobacterial succession from Microcystis to Dolichospermum. The regulation effect of sediment N/P on water column TN/TP was stronger in summer than in other seasons. Iron-bound P and alkaline phosphatase activity in sediment, rather than ammonium, contributed to the higher part of nitrification. Furthermore, our microcosm experiments confirmed that soluble active P and enzymatic hydrolysis of organic P, accumulating during algal bloom, fueled nitrifiers and nitrification in sediments. These processes promoted lake N removal and led to relative N deficiency in turn. Our results highlight that N and P cycles do not exist independently but rather interact with each other during lake eutrophication, supporting the dual N and P reduction program to mitigate eutrophication in shallow eutrophic lakes.

Effects of nitrogen input on N2O production and enzyme activity in Luoshijiang Wetland sediments, China

We examined the effects of nitrate (NO3--N) and ammonium (NH4+-N) input at different concentrations (0, 1, 5 and 25 mg·kg-1) on N2O production rate from the surface sediment (0-5 cm) of Luoshijiang Wetland, located upstream from Lake Erhai. The contribution of nitrification, denitrification, nitrifier denitrification, and other factors to the N2O production rate in sediments was studied by the inhibitor method. The relationships between N2O production and the activities of hydroxylamine (HyR), nitrate (NAR), nitric oxide (NOR), and nitrous oxide (NOS) reductases in sediments were analyzed. We found that NO3--N input significantly increased total N2O production rate (1.51-11.35 nmol·kg-1·h-1), which led to N2O release, whereas NH4+-N input decreased that (-0.80 to -0.54 nmol·kg-1·h-1), causing N2O absorption. NO3--N input did not change the dominant roles of nitrification and nitrifier denitrification in N2O production in sediments, but increased the contributions of these two factors to 69.5% and 56.5%, respectively. The NH4+-N input significantly changed N2O gene-ration process, and the nitrification and nitrifier denitrification changed from N2O release to uptake. There was a positive correlation between total N2O production rate and NO3--N input. NO3--N input significantly increased NOR activity and decreased NOS activity, thereby promoting N2O production. The total N2O production rate in sediments was negatively correlated with NH4+-N input. NH4+-N input significantly increased the activities of HyR and NOR, decreased NAR activity, and inhibited N2O production. Nitrogen inputs with different forms and concentrations changed the degree of contribution and mode of N2O production by affecting enzyme activities in sediments. NO3--N input significantly promoted N2O production, acting as a source of N2O, while NH4+-N input inhibited N2O production, resulting in an N2O sink.

Direct and Indirect Impacts of Disposable Face Masks and Gloves on Freshwater Benthic Fauna and Sediment Biogeochemistry

To reduce virus transmission, the use of personal protective equipment (PPE) increased substantially during the COVID-19 global pandemic. As a result, disposable face masks and gloves made from plastic polymers rapidly entered the environment, with little understanding of ecological impacts. Many plastic polymers sink to the bottom of freshwater bodies, either immediately or following biofouling and degradation, posing a potential risk to the benthos. We assessed the acute and chronic ecotoxicity of disposable polypropylene face masks and nitrile gloves on Lumbriculus variegatus, a benthic ecosystem engineer. In microcosm experiments, we also investigated direct impacts on sediment biogeochemistry and indirect impacts mediated by toxicity to L. variegatus. Exposure to fragments of both masks and gloves decreased vitality of L. variegatus. Gloves were acutely toxic, but mask toxicity was mediated by physical interactions. Glove fragments significantly decreased nitrogen removal and phosphorus release to the water column. Both materials suppressed the ecosystem engineering role of L. variegatus by decreasing its impact on microalgal primary production, net ecosystem metabolism, and sediment nitrate consumption. The influx of PPE to the environment may have profound and cascading negative impacts on benthic organisms and ecosystem function, suggesting the need for improved management of PPE litter.

Effects of dam building on the occurrence and activity of comammox bacteria in river sediments and their contribution to nitrification

The recent discovery of complete ammonia oxidizers (comammox) has fundamentally changed our understanding of nitrification. However, studies on the occurrence and activity of comammox bacteria and their contribution to nitrification remain unclear. Here, we investigated the abundance, activity, and diversity of comammox bacteria and their contribution to nitrification in sediments from dammed rivers in winter and summer. Our results indicated that comammox clade A was ubiquitous in all sediment samples and the community structure in comammox varied between the upper and lower reaches, but not on the time scale (winter and summer). Comammox activity in the dammed river sediments in summer was prominently higher than in winter (summer: 1.08 ± 0.52; winter: 0.197 ± 0.148 mg N kg−1 day−1). Furthermore, the activity of comammox bacteria in summer appeared higher in the vicinity of the dammed river and in the Sanjiang estuary, which is located downstream of the dammed river. The activity of ammonia-oxidizing bacteria (AOB) (0.77 ± 0.478 mg N kg−1 day−1) was higher compared to comammox (0.639 ± 0.588 mg N kg−1 day−1) and ammonia-oxidizing archaea (AOA) (0.026 ± 0.022 mg N kg−1 day−1) in both winter and summer. In terms of contribution to the nitrification process, AOB (winter: 67.13 ± 12.21 %; summer: 50.57 ± 16.14 %) outperformed comammox (winter: 28.59 ± 12.51 %; summer: 48.38 ± 16.62 %) and AOA (winter: <7.39 %; summer: <2.09 %). These findings indicated that the nitrification process in dammed river sediments was mainly dominated by AOB. Additionally, comammox activity was significantly affected by temperature and NH4+, suggesting that these variables were key determinants of the niche partitioning of comammox. Collectively, our findings provide novel perspectives into the widespread distribution and contribution of comammox to nitrification in dammed river ecosystems, thus broadening our understanding of the nitrification processes.