Allometric releases of nitrogen and phosphorus from sediments mediated by bacteria determines water eutrophication in coastal river basins of Bohai Bay

Porous red mud ceramsite for aquatic phosphorus removal: Application in constructed wetlands

Red mud (RM) and spent oyster mushroom substrate (SOMS), by-products of industrial and agricultural production, can be recycled for polluted freshwater purification, bringing about a win-win situation. In this study, unacidified RM and RM acidified with oxalic acid (O-RM) and hydrochloric acid (H-RM), respectively, were mixed with SOMS to produce a porous ceramsite as a potential constructed wetlands (CWs) substrate. The results showed that the O-RM, H-RM, and RM ceramsites displayed fine compressive strengths of 7.75 ± 1.14, 8.40 ± 1.30, and 8.84 ± 0.69 MPa after calcining at 950 °C for 30 min, respectively. The phosphorus adsorption capacities of H-RM, O-RM, and RM ceramsite at a solid-liquid ratio of 25 g/L were 1.18 mg/g, 0.88 mg/g, and 1.06 mg/g, respectively. Toxicity release experiments showed that the ceramsites did not cause secondary environmental pollution, except for arsenic (ranging from 0.210 to 0.238 mg/L). The H-RM ceramsite was tested in a tidal flow-vertical flow CW (TF-VFCW) with Iris pseudacorus L. and Canna indica L plants. In the TF-VFCW, the average chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) removal rates were 81.01, 90.25, 66.90, and 77.32 %, respectively. Plant growth had less impact on COD and NH4-N removal but had greater limited TN and TP removal. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis confirmed that acid pretreatment and the incorporation of SOMS significantly increased the surface and interior porous structures of the ceramsite and enhanced phosphate adsorption by the polyhydroxyl aluminum-iron complex ions. Bacteroides and Campylobacter used the energy produced during polyhydroxyalkanoic acid (PHA) catabolism to absorb phosphorus. Therefore, the synergistic effect of the substrate, plants, and microorganisms achieved the removal of phosphorus from CWs and offered effective and environmentally friendly recycling of RM and SOMS.

Removal and recovery of nitrogen from anaerobically treated leachate based on a neglected HNAD nitrogen removal pathway: NH3 stripping

The heterotrophic nitrification aerobic denitrification (HNAD) process can withstand the environment with high NH4+-N concentration and complex components, and has the potential to be an effective scheme for nitrogen removal of anaerobically treated leachate from municipal solid waste incineration plant. But its mechanism is still unclear and the NH3 stripping process has received little attention. At the same time, the high concentration of NH4+-N in the anaerobically treated leachate also has great recycling potential. In this study, typical HNAD microorganisms were enriched and used for nitrogen removal from anaerobically treated leachate. A one-step system with a total nitrogen removal ratio of more than 98 % was constructed. Isotopic labeling experiments showed that nitrogen was not the main product. The important role of NH3 stripping in the HNAD system was defined, and 46.63 % nitrogen was recovered on this basis.

Long-term contamination of decabromodiphenyl ether reduces sediment multifunctionality: Insights from nutrient cycling, microbial ecological clusters, and microbial co-occurrence patterns

Despite the widespread detection of polybrominated diphenyl ethers in aquatic ecosystems, their long-term effects on sediment multifunctionality remain unclear. Herein, a 360-day microcosm experiment was conducted to investigate how decabromodiphenyl ether (BDE-209) contamination at different levels (0.2, 2, and 20 mg/kg dry weight) affects sediment multifunctionality, focusing on carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling. Results showed that BDE-209 significantly increased sediment total organic carbon, nitrate, ammonium, available phosphorus, and sulfide concentrations, but decreased sulfate. Additionally, BDE-209 significantly altered key enzyme activities related to nutrient cycling. Bacterial community dissimilarity was positively correlated with nutrient variability. Long-term BDE-209 exposure inhibited C degradation, P transport and regulation, and most N metabolic pathways, but enhanced C fixation, methanogenesis, organic P mineralization, inorganic P solubilization, and dissimilatory sulfate reduction pathways. These changes were mainly regulated by microbial ecological clusters and keystone taxa. Overall, sediment multifunctionality declined under BDE-209 stress, primarily related to microbial co-occurrence network complexity and ecological cluster diversity. Interestingly, sediment C and N cycling had greater impacts on multifunctionality than P and S cycling. This study provides crucial insights into the key factors altering multifunctionality in contaminated sediments, which will aid pollution control and mitigation in aquatic ecosystems.

Chronic increasing nitrogen and endogenous phosphorus release from sediment threaten to the water quality in a semi-humid region reservoir

The water quality in the drinking water reservoir directly affects people's quality of life and health. When external pollution input is effectively controlled, endogenous release is considered the main cause of water quality deterioration. As the major nitrogen (N) and phosphorus (P) sources in reservoirs, sediment plays a vital role in affecting the water quality. To understand the spatial and temporal variation of N and P in the sediment, this study analyzed the current characteristics and cumulative effects of a semi-humid reservoir, Yuqiao Reservoir, in North China. The N and P concentrations in the reservoir sediment were decreased along the flow direction, while the minimum values were recorded at the central sediment profile. External input and algal deposition were the main factors leading to higher sediment concentrations in the east (Re-E) and west (Re-W) areas of reservoir sediment profiles. According to the long-term datasets, the peaks of both sediment total nitrogen content and deposition rate were observed in the 2010s, which has increased about three times and six times than in the1990s, respectively. Therefore, the increase in phosphorus concentration may be the main reason for eutrophication in water in recent years. The mineralization of organic matter has a significant promoting effect on releasing N and P from sediments, which will intensify eutrophication in water dominated by P and bring huge challenges to water environment management. This study highlights that the current imbalance in N and P inputs into reservoirs and the endogenous P release from sediment will have a significant impact on water quality.

Trophic level plays an enhanced role in shaping microbiota structure and assembly in lakes with decreased salinity on the Qinghai-Tibet and Inner Mongolia Plateaus

Plateau lakes characterized by salinization and eutrophication are essential aquatic ecosystems. A myriad of microorganisms serve as crucial biological resources in plateau lakes and drive the elemental cycles of these ecosystems. Currently, there is a paucity of knowledge regarding the impacts of salinization and eutrophication dynamics on the microbiota in plateau lakes. Here, high-throughput sequencing of the 16S ribosomal RNA genes (V4 region) was used to characterize microbial community structure and assembly in plateau lakes with different salinities and trophic levels. Water samples were collected at 191 sites across 24 lakes on the Qinghai-Tibet and Inner Mongolia Plateaus in northern China. The results showed that high salinity considerably reduced microbial alpha-diversity and niche breadth while increasing within-group similarity among various lake types. High salinity additionally decreased the complexity of microbial networks and enhanced network robustness. The assembly of microbial communities was primarily governed by deterministic processes in high-salinity and eutrophic low-salinity lakes. At decreased salinity, trophic level played a leading role in shaping microbial community structure, and the ecological processes shifted from deterministic processes driven by high salinity to eutrophication-driven deterministic processes. The biomarkers also varied from taxa adapted to high-salinity environments (e.g., Nanoarchaeaeota, Rhodothermia) to those suited for living in freshwater and low-salinity habitats (e.g., Alphaproteobacteria, Actinobacteria). In the case of eutrophication, Actinobacteria, Chloroflexi, and Cyanobacteria became the dominant taxa. Our findings indicate that decreased salinity enables trophic level to play an enhanced role in shaping microbial community structure and assembly in plateau lakes. This study enriches our knowledge about the ecological impacts of salinization and eutrophication in plateau lakes.

Guiding the landscape patterns evolution is the key to mitigating river water quality degradation

Consensus has emerged that landscape pattern evolution significantly impacts the river environment. However, there remains unclear how the landscape pattern evolves possible to achieve a balance between land resource use and water conservation. Thus, simulating future landscape patterns under different scenarios to predict river eutrophication level is critical to propose targeted landscape planning programs and alleviate river water quality degradation. Here, we coupled five water quality parameters (TOC, TN, NO3--N, NH4+-N, TP), collected from October 2020 to September 2021, to construct the river eutrophication index (EI) to assess river water quality. Meanwhile, based on redundancy analysis, patch-generating land use simulation model, and stepwise multiple linear regression model comprehensively analyze the Fengyu River watershed landscape patterns evolution and their impact on river eutrophication. Results indicated that current rivers reach eutrophic levels, and EI reaches 40.7. The landscape patterns explain 88.2 % of river eutrophication variation, while the LPI_Con metric is critical and individually explained 21.5 %. Furthermore, eutrophication in the watershed will increase in 2040 under the natural development (ND) scenario, and the EI will reach 44.4. In contrast, farmland protection (FP) scenarios and environmental protection (EP) scenarios contribute to mitigating eutrophication, the EI values are 38.2 and 38.1, respectively. The results provide a potential mechanistic explanation that river eutrophication is a consequence of unreasonable landscape pattern evolution. Guiding the landscape patterns evolution based on critical driver factors from a planning perspective is conducive to mitigating river water quality degradation.

Temporal and Spatial Variation Characteristics and Influencing Factors of Bacterial Community in Urban Landscape Lakes

Urban landscape lakes are closely related to human activity, but there are limited studies on their bacterial community characteristics and risks to human health. In this study, four different types of urban landscape lakes in Xi'an were selected, and the bacterial community structures in different seasons were analyzed by Illumina Nova high-throughput sequencing technology. Seasonal variations in bacterial communities were analyzed by linear discriminant analysis, STAMP difference analysis, and nonmetric multidimensional scaling. Redundancy analysis was used to investigate the influencing factors. Furthermore, the metabolic functions of bacterial communities were predicted by Tax4Fun. There were clear seasonal differences in the α-diversity of bacteria, with bacterial diversity being higher in winter than in summer in the four urban landscape lakes, and the diversity of different water sources was different; the distributions of Proteobacteria, Actinobacteria, Chloroflexi, and Verrucomicrobia had significant seasonal differences; and the dominant bacteria at the genus level had obvious temporal and spatial differences. Furthermore, a variety of environmental factors had an impact on bacterial communities, and temperature, DO, and nitrogen were the primary factors affecting the seasonal variation in bacteria. There are also significant seasonal differences in the metabolic functions of bacterial communities. These results are helpful for understanding the current status of bacteria in the aquatic environments of such urban landscape lakes.

Development of yeast and microalgae consortium biofilm growth system for biofuel production

Background

The current study aimed to develop a laboratory-scale biofilm photobioreactor system for biofuel production.

Scope & Approach

During the investigation, Jute was discovered to be the best, cheap, hairy, open-pored supporting material for biofilm formation. Microalgae & yeast consortium was used in this study for biofilm formation.

Conclusion

The study identified microalgae and yeast consortium as a promising choice and ideal partners for biofilm formation with the highest biomass yield (47.63 ± 0.93 g/m2), biomass productivity (4.39 ± 0.29 to 7.77 ± 0.05 g/m2/day) and lipid content (36%) over 28 days cultivation period, resulting in a more sustainable and environmentally benign fuel that could become a reality in the near future.

Nutrients and Environmental Factors Cross Wavelet Analysis of River Yi in East China: A Multi-Scale Approach

The accumulation of nutrients in rivers is a major cause of eutrophication, and the change in nutrient content is affected by a variety of factors. Taking the River Yi as an example, this study used wavelet analysis tools to examine the periodic changes in nutrients and environmental factors, as well as the relationship between nutrients and environmental factors. The results revealed that total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH4+-N) exhibit multiscale oscillation features, with the dominating periods of 16-17, 26, and 57-60 months. The continuous wavelet transform revealed periodic fluctuation laws on multiple scales between nutrients and several environmental factors. Wavelet transform coherence (WTC) was performed on nutrients and environmental factors, and the results showed that temperature and dissolved oxygen (DO) have a strong influence on nutrient concentration fluctuation. The WTC revealed a weak correlation between pH and TP. On a longer period, however, pH was positively correlated with TN. The flow was found to be positively correct with N and P, while N and P were found to be negatively correct with DO and electrical conductance (EC) at different scales. In most cases, TP was negatively correlated with 5-day biochemical oxygen demand (BOD₅) and permanganate index (COD_Mn). The correlation between TN and COD_Mn and BOD₅ was limited, and no clear dominant phase emerged. In a nutshell, wavelet analysis revealed that water temperature, pH, DO, flow, EC, COD_Mn, and BOD₅ had a pronounced influence on nutrient concentration in the River Yi at different time scales. In the case of the combination of environmental factors, pH and DO play the largest role in determining nutrient concentration.

Phytoplankton Community Response to Environmental Factors along a Salinity Gradient in a Seagoing River, Tianjin, China

A river-estuary ecosystem usually features a distinct salinity gradient and a complex water environment, so it is enormously valuable to study the response mechanism of living organisms to multiple abiotic factors under salinity stress. Phytoplankton, as an important part of aquatic microorganisms, has always been of concern for its crucial place in the aquatic ecosystem. In this study, phytoplankton data and 18 abiotic factors collected from 15 stations in Duliujian River, a seagoing river, were investigated in different seasons. The results showed that the river studied was of a Cyanophyta-dominant type. Salinity (SAL) was the key control factor for phytoplankton species richness, while water temperature (WT) was critical not only for species richness, but also community diversity, and the abundance and biomass of dominant species. Apart from WT, the abundance and biomass of dominant species were also driven by total nitrogen (TN), nitrate (NO₃^-), pH, and water transparency (SD). Moreover, total dissolved phosphorus (TDP), pH, and chemical oxygen demand (COD) were crucial for community diversity and evenness. The bloom of dominant species positively associated with TDP led to lower diversity and evenness in autumn. In addition, when available nitrogen was limited, Pseudoanabaena sp. could obtain a competitive advantage through the N₂ fixation function. Increased available nitrogen concentration could favor the abundance of Chlorella vulgaris to resist the negative effect of WT. The results show that Oscillatoria limosa could serve as an indicator of organic contamination, and nutrient-concentration control must be effective to inhibit Microcystis bloom. This could help managers to formulate conservation measures.

The Effect of Rainfall on Aquatic Nitrogen and Phosphorus in a Semi-Humid Area Catchment, Northern China

The impact of rainfall on water quality may be more important in semi-arid regions, where rainfall is concentrated over a couple of months. To explore the impact of rainfall changes on water quality, e.g., nitrogen (TN) and phosphorous (TP), the diversion from Luan River to Tianjin Watershed in the northern semi-humid area was selected as the study area. TN and TP concentrations in rivers and the Yuqiao Reservoir during the three-year high-flow season (2019-2021) were analyzed. The response relationship and influencing factors among the watershed's biogeochemical process, rainfall, and water quality were clarified. The results showed that rainfall in the high flow season mainly controlled the river flow. The concentration of TN and TP in the inflow rivers is regulated by rainfall/flow, while the concentration of TN and TP in the water diversion river has different variation characteristics in the water diversion period and other periods. The lowest annual concentrations of TN and TP were observed in the normal year, while the highest annual concentration was observed in the wet year, indicating that the hydrological process drove the nutrient transport in the watershed. For the tributaries, the Li River catchment contributed a large amount of N and P to the aquatic environment. For the reservoir, the extreme TN concentrations were the same as the tributaries, while the extremes of TP concentrations decreased from the dry year to wet year, which was in contrast to the tributaries. The spatial variation of TN and TP concentrations in the reservoir showed that the concentration decreased following the flow direction from the river estuary to the reservoir outlet. Considering climate change, with the increase of rainfall in North China in the future, the TN and TP transport fluxes in the watershed may continue to increase, leading to the nitrogen and phosphorus load of the downstream reservoir. To ensure the impact of the increase of potential N and P output fluxes in the watershed on the water quality of the reservoir area, it is necessary to strengthen the effective prevention and control of non-point source pollution in the watershed.

Effects of Terrestrial Inputs on Mesozooplankton Community Structure in Bohai Bay, China

Zooplankton play a pivotal role in connecting primary producers and high trophic levels, and changes in their temporal and spatial distribution may affect the entire marine ecosystem. The spatial and seasonal taxonomic composition patterns of mesozooplankton in Bohai Bay were investigated in relation to a number of water parameters. Bohai Bay is a eutrophic semi-enclosed bay with dynamic physico-chemical conditions influenced by terrestrial inputs and seawater intrusion. The results showed that under the condition of terrigenous input, the diversity of mesozooplankton species near the eutrophic Haihe River Estuary and Jiyun River Estuary was lower than that in the central Bohai Bay, with gelatinous Oikopleura dioica as the dominant species. The mesozooplankton diversity was highest in the bay mouth affected by seawater intrusion, and the dominant oceanic species, mainly copepods Corycaeus affinis, Calanus sinicus, and Oithona similis, entered the inner bay from the bay mouth. Meanwhile, the abundance of mesozooplankton in summer was significantly higher than that in autumn. Compared with historical data, the dominant species in Bohai Bay has evolved from arrow worm Sagitta crassa to copepod Paracalanus parvus, probably due to global warming, indicating the effects of human activities on the succession of mesozooplankton community.