Irregular salt caverns are common in salt cavern storages around the world, accounting for more than 60 % of the salt caverns built in China. Previously, when evaluating the safety of irregular salt caverns under specific operating conditions, the target salt caverns were generally treated as regular or axisymmetric shapes. The significant influence of their real shapes on their operational safety was ignored. In order to accurately evaluate the safety of irregular salt caverns and to eliminate the influence of the irregular salt caverns shape on the evaluation results, software for generating irregular salt caverns was compiled using the C++ language. Geomechanical models of four typical irregular salt caverns in Jintan Salt Mine were constructed. The deformations, strains, and stresses of the four models are successfully calculated, and the corresponding calculation results are obtained, which proves the applicability and rationality of the software. The research results of this paper provide a new method and idea to overcome the difficulty of modeling irregular salt caverns.

Dissolved organic phosphorus (DOP) has been closely linked to microbial alkaline phosphatases (AP) whose affiliation and diversity is largely unknown in coastal waters. Here we assessed genetic diversity and abundance of bacterial alkaline phosphatases phoD and phosphate transporter phoD and explored how AP activity interacting with them along the salinity gradient of Pearl River Estuary (PRE), which was under heavy anthropogenic pressures. Partial least squares path modeling (PLS-PM) revealed the pathway from environmental variables (pH and salinity) to phoD-harboring bacterial taxa in particle-attached fraction and then to phoD gene copies was the determinant process for AP activity; while AP activity in free-living fraction was mainly controlled by the pathway from dissolved inorganic phosphorus (DIP) to phoD encoding community structure and its gene abundance. Our study highlighted the importance of diverse phoD phosphorus mineralizers, such as some members from Actinobacteria (Actinomadura), Alphaproteobacteria (unclassified Rhodobacteraceae, Roseovarius, Mesorhizobium) and Betaproteobacteria (Ralstonia), while pstS-harboring community was composed of picocyanobacteria. In the outer estuary with the lowest DIP concentration, AP level was activated substantially herein, which corresponded well with the spatial distribution of phoD and pstS gene abundance. High number of phosphatase and transporter genes potentially implied effective hydrolyzation rate of DOP to supplement inorganic phosphorus in the estuary. Researches on the characterization and transformation of DOP are insufficient owing to their complex composition and extraction difficulty. In the recent study, we applied Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to present a preliminary feature of DOP molecular composition in the PRE. The phosphoesters represented more than 95 % of total DOP, and CHOP compounds (mainly lipids) was a potential substrate for bacterial AP. Our study unveils the key biogeochemical role of AP for mineralizing specific DOP to support more phytoplankton biomass and emphasizes the supervision and management of both DOP and DIP entering the estuaries from land-based sources.

Biotin (vitamin B7) is a crucial cofactor for various metabolic processes and has significant applications in pharmaceuticals, cosmetics, and animal feed. Bacillus subtilis, a well-studied Gram-positive bacterium, presents a promising host for biotin production due to its Generally Recognized as Safe (GRAS) status, robust genetic tractability, and capacity for metabolite secretion. This study focuses on the metabolic engineering of B. subtilis to enhance biotin biosynthesis. Initially, the desthiobiotin (DTB) and biotin synthesis ability of different B. subtilis strains were evaluated to screen for suitable chassis cells. Subsequently, the titers of DTB and biotin were increased to 21.6 mg/L and 2.7 mg/L, respectively, by relieving the feedback repression of biotin synthesis and deleting the biotin uptake protein YhfU. Finally, through engineering the access tunnel to the active site of biotin synthase (BioB) for reactants and modulating its expression, the biotin titer was increased to 11.2 mg/L, marking an 1130-fold improvement compared to the wild-type strain. These findings provide novel strategies for enhancing the production of DTB and improving the conversion efficiency of DTB to biotin.

Dissolved organic nitrogen (DON) has recently been recognized as an important nitrogen source for marine phytoplankton. However, the composition, sources, and biogeochemical cycling of DON in coastal ecosystems remain poorly understood. This study investigates the spatial distribution and seasonal variability of DON in Daya Bay, a subtropical semi-enclosed bay in the northern South China Sea. We measured DON concentrations, the DIN:DIP ratio, and the spectral characteristics of dissolved organic matter (DOM), including a(350), SUVA254, and fluorescence components. Our findings reveal clear seasonal differences in the controlling factors for DON distribution: in summer, land-based sources and biological activities dominate, whereas in winter, oceanic circulation and its associated water mass mixing play a predominant role. The combined spectral indexes suggest that the transformation of DON is significantly more active in summer than in winter. Additionally, most stations exhibited low DIN:DIP ratios (<16) and relatively high chlorophyll a concentrations (>2 μg/L) during the summer months, while DIP concentrations in Daya Bay remained generally low (<1 μmol L-1). This suggests that phytoplankton may assimilate DON, potentially leading to algal blooms and changes in population structure. Overall, these findings highlight the potential role of DON in the coastal nitrogen budget and phytoplankton dynamics, emphasizing the need for further investigation.

Coastal nitrogen enrichment significantly contributes to the decline of seagrass health and habitat, thereby diminishing its capacity to capture and sequester carbon (i.e., Blue Carbon). However, the consequences to blue carbon stocks due to sublethal changes in chemical recalcitrance of seagrass organic matter (OM) caused by nitrogen enrichment is unknown. In this study, we investigated the effects of nitrogen-loading on the chemical composition of meadow-forming Thalassia hemprichii. We found that the amino acid content in seagrass leaves and rhizomes increased with nitrogen loading, while the total labile OM and refractory OM (i.e., cellulose and lignin) content in seagrass leaves, sheaths, and roots generally decreased with nitrogen loading. Additionally, cellulose and lignin within sheath tissues showed a threshold response whereby refractory OM dropped when leaf nitrogen content (i.e., indicator of nitrogen loading) exceeded 2.2%. The rhizome labile OM and cellulose content also peaked at 2.2% leaf nitrogen content but subsequently reduced to a minimum at similar to 2.9% leaf nitrogen. The threshold of 2.2% leaf nitrogen content, equivalent to 43 similar to 72 mu M dissolved inorganic nitrogen concentration in sediment pore water, may be utilized to forecast the contribution of seagrass refractory OM to sediments. It was estimated that high nitrogen loading could result in a loss of 309-645 kg ha(-1) of refractory OM inputs in this study sites. The findings underscore that nitrogen enrichment has sublethal but significant negative impacts on carbon cycling via the reduction of refractory OM in seagrass biomass, consequently weakening the autochthonous contribution of seagrass to long-term carbon sequestration.

Dissolution trapping CO2 is thought to be a permanent storage mechanism in deep saline aquifers. Brine saturated with CO2 sinks to the bottom of the aquifer due to density-driven flow and is replaced by fresh brine with the remaining dissolution potential. This convective process persists and can effectively slow the spread of the CO2 plume, thereby reducing the risk of leakage. The density-driven convection process is sensitive to reservoir heterogeneity. In this paper, the dynamics of dissolved CO2 in a fractured saline aquifer are studied using a three-dimensional discrete fracture network matrix (DFM) model. The fracture density and heterogeneity between fractures are systematically analyzed. The highly connected fracture network provides preferential channels for the CO2-rich plume to migrate to deeper regions of the aquifer. Several cases show that the increase of fracture density can effectively increase the dissolution flux in the domain, but the effect becomes less significant when the quantity exceeds a threshold value. The effects of two heterogeneous patterns (the density of high-permeability channels in the system and the correlation of the fracture aperture with the geometric size) in determining dissolution trapping are discussed. The heterogeneity of the fracture aperture is beneficial to finger formation and depth development. The results of this study increase the understanding of the dissolved carbon dioxide and plume dynamics in the fractured saline aquifers used for carbon sequestration.

The heterogeneity of natural rock leads to complex mechanical behaviors, and affects the accuracy and repeatability of laboratory rock mechanics test results. 3D printing (3DP) technology can rapidly reproduce 3D models with complex structure and good consistency, which can effectively reduce the interference of heterogeneity for natural rock specimens and improve the repeatability of rock mechanics test results. However, the current studies on the similarity of 3DP materials are mostly phenomenological, lacking similarity evaluation of physical attributes and mechanical properties. In this study, the analogues of natural sandstone are prepared using 3DP technology, and the differences in physical indexes and mechanical behaviors between 3DP specimen and sandstone are described. The results show that 3DP specimen have brittle characteristics similar to natural sandstone. The deformation characteristics and failure modes of 3DP specimen are similar to those of sandstone. The uniaxial compressive strength and cohesion of 3DP specimen meet the similarity, the elastic modulus is slightly lower, and the Poisson's ratio and internal friction angle are significantly insufficient.

Salt cavern is one of the best storage for hydrogen, compressed air, and natural gas. However, the current physical/numerical simulation-based construction design cannot yield optimal solutions due to the complex correlation of multiple construction parameters. This paper proposes a novel machine-learning-enabled method for the geometry prediction and design optimization during salt cavern construction. A dataset of 1197 simulations of salt cavern construction is collected using our previously developed program. Construction parameters are included as inputs, and the simulated cavern geometries as outputs. A Gated Recurrent Unit model is selected and well-trained from 600 artificial neural network models. The model achieves a mean absolute error of 1.6m in the test dataset and of 2.83m for the geometric prediction of cavern JT52 in Jintan, meeting the field design requirements. Furthermore, an optimized construction design method is proposed by looping generating construction parameters, shape prediction, and deviation calculation until the deviation meets requirements. It succeed in designing an ideal ellipsoid cavern in approximately 51 min, with a capacity ratio fc 31 % larger than those of the field caverns. This approach demonstrates the potential for machine learning methods to serve as the third generation of construction design methods after physical and numerical modeling.

Seagrass ecosystems have received a great deal of attention for contributing to uptake of atmospheric CO2, and thereby helping to mitigate global climate change ('blue carbon'). Carbon budgets for seagrass ecosystems are developed by estimating air-sea CO2 fluxes. Data for air-sea CO2 flux for tropical seagrass ecosystems are lacking, which is problematic for constraining global seagrass carbon budgets. Here, we sought to address this important data gap for tropical seagrass ecosystems (dominated by Thalassia hemprichii and Enhalus acoroides) from the Hainan Island of South China Sea, while also testing what the main factors driving the variations of air-sea CO2 fluxes are. We found that air-sea CO2 fluxes exhibited a U-shape diurnal variability from 6 a.m. to 6 a.m. of the next day, with the highest and lowest air-sea CO2 fluxes values at early morning and afternoon, respectively. Biological processes were the driving force for mediating diurnal variations of seawater pCO2. The pCO2, sea in different seasons displayed a trend of increasing from spring, reaching maximum in summer and then a decreasing trend after summer, where water temperature, wind speed and seagrass growth mainly drove the variations. This resulted in net uptake of CO2 in all seasons except during summer in our study seagrass ecosystems, with greater negative values found in autumn (-3.63 +/- 0.76 mmol m- 2 d-1) than those in winter (-2.84 +/- 0.60 mmol m- 2 d-1). While the nutrient loading induced seagrass biomass changes (especially the seagrass T. hemprichii), which mediated the air-sea CO2 fluxes changes among different seagrass meadows. Net annual CO2 uptake potential under low nutrient loading (-0.77 +/- 0.16 mol m- 2 yr- 1) was 23-54 % greater than high nutrient loading seagrass meadows, with the average annual air-sea CO2 flux of the three seagrass meadows as-0.64 +/- 0.13 mol m- 2 yr- 1. These results suggest that tropical seagrass meadows of Hainan Island are a significant CO2 sink of atmospheric CO2, but this capacity can be diminished by nutrient loading. Scaling up, we estimate the annual atmospheric CO2 uptake by seagrass meadows of Hainan Island (total area 55.28 km2) was 1544 t of CO2 yr-1, equivalent to the annual emissions from the wholesale, retail, accommodation and catering industries of 164,000 tourists in Hainan Island. With carbon neutrality becoming an important part of global climate governance, this study provides timely information for capitalising on the ability of seagrasses to contribute to natural climate solutions.

Estuaries receive substantial amounts of terrestrial dissolved organic nitrogen (tDON), which will be transported from the freshwater to the oceanic terminus through vigorous exchange processes. However, the intricate migration and transformation dynamics of tDON during this transportation, particularly at a molecular level, remain constrained. To address this knowledge gap, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used for the analysis of DON molecular composition in the Pearl River Estuary (PRE), a river -dominated estuarine system influenced by intensified anthropogenic activities in southern China. The results showed a pronounced spatial -temporal variation in DON concentration in the study area. At the molecular level, tDON exhibited reduced unsaturation and aromaticity, coupled with an elevated abundance of DON compounds containing one-nitrogen atom (1 N -DON, 53.17 %) and compounds containing carbon, hydrogen, oxygen, nitrogen, and sulfur (CHONS) (27.46 %). It was evident that lignin was depleted while more oxygenated tannin compounds were generated in the freshwater -seawater mixing zone. This transformation is attributed to heightened biological activities, likely influenced by the priming effect of terrestrial nutrient inputs. In summer, the prevailing plume combined with biological activities in the strong mixing area and outer estuary increased the abundance of 3 N -DON molecules and a concurrent rise in the abundance of DON compounds containing only carbon, hydrogen, oxygen, and nitrogen (CHON), DON compounds containing carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus (CHONSP), and CHONS. This trend also underscores the expanding role of marine plankton and microbes in the utilization of DON compounds containing carbon, hydrogen, oxygen, nitrogen, and phosphorus (CHONP). These findings provide details of tDON transformation processes at the molecular level in a river -dominated estuary and underline the estuarine hydrodynamics involved in transporting and altering DON within the estuary.

Dissolution trapping is a permanent and safe mechanism for geological carbon sequestration. An increase in density caused by the dissolution of CO2 into brine can trigger a density-driven convection process. In this study, the effect of fracture roughness on the density-driven convection process in heterogeneous saline aquifers is numerically analyzed by using a three-dimensional rough fracture-matrix model. The results show that the variation of the fracture aperture, a microscale heterogeneity phenomenon, can result in the change of the macroscopic flow characteristics. The rough fracture surface intensifies the convection inside the fracture and makes the migration path of the solute more tortuous. The spatial variability of the aperture generates the merging of convective fingers and suppresses the development of weak convective fingers, thus further enhancing the longitudinal extent of convective mixing. It is indicated that neglecting roughness during the flux growth stage can lead to an underestimation of dissolved fluxes by about 20%. The consideration of fracture roughness variation can contribute to the better understanding and prediction of the dynamics of dissolved CO2 in real reservoirs.

3D printing is widely adopted to quickly produce rock mass models with complex structures in batches, improving the consistency and repeatability of physical modeling. It is necessary to regulate the mechanical properties of 3D-printed specimens to make them proportionally similar to natural rocks. This study investigates mechanical properties of 3D-printed rock analogues prepared by furan resin-bonded silica sand particles. The mechanical property regulation of 3D-printed specimens is realized through quantifying its similarity to sandstone, so that analogous deformation characteristics and failure mode are acquired. Considering similarity conversion, uniaxial compressive strength, cohesion and stress–strain relationship curve of 3D-printed specimen are similar to those of sandstone. In the study ranges, the strength of 3D-printed specimen is positively correlated with the additive content, negatively correlated with the sand particle size, and first increases then decreases with the increase of curing temperature. The regulation scheme with optimal similarity quantification index, that is the sand type of 70/140, additive content of 2.5‰ and curing temperature of 81.6 ℃, is determined for preparing 3D-printed sandstone analogues and models. The effectiveness of mechanical property regulation is proved through uniaxial compression contrast tests. This study provides a reference for preparing rock-like specimens and engineering models using 3D printing technology.

In the recent study, we investigated the seasonal variations in root exudation and microbial community structure in the rhizosphere of seagrass Enhalus acoroides in the South China Sea. We found that the quantity and quality of root exudates varied seasonally, with higher exudation rates and more bioavailable dissolved organic matter (DOM) during the seedling and vegetative stages in spring and summer. Using Illumina NovaSeq sequencing, we analyzed bacterial and fungal communities and discovered that microbial diversity and composition were influenced by root exudate characteristics s and seagrass biomass, which were strongly dependent on seagrass growth stages. Certain bacterial groups, such as Ruegeria, Sulfurovum, Photobacterium, and Ralstonia were closely associated with root exudation and may contribute to sulfur cycling, nitrogen fixation, and carbon remineralization, which were important for plant early development. Similarly, specific fungal taxa, including Astraeus, Alternaria, Rocella, and Tomentella, were enriched in spring and summer and showed growth-promoting abilities. Overall, our study suggests that seagrass secretes different compounds in its exudates at various developmental stages, shaping the rhizosphere microbial assemblages.

Seagrass beds are susceptible to deterioration and heavy metals represent a crucial impact factor. The accumulation of heavy metal in two tropical seagrass species were studied in South China in this study and multiple methods were used to identify the heavy metal sources. E. acoroides (Enhalus acoroides) and T. hemperichii (Thalassia hemperichii) belong to the genus of Enhalus and Thalassia in the Hydrocharitaceae family, respectively. Heavy metal concentrations in the two seagrasses followed the order of Cr > Zn > Cu > Ni > As > Pb > Co > Cd based on the whole plant, and their bioconcentration factors were 31.8 +/- 29.3 (Cr), 5.7 +/- 1.3 (Zn), 7.0 +/- 3.8 (Cu), 3.0 +/- 1.9 (Ni), 1.2 +/- 0.3 (As), 1.7 +/- 0.9 (Pb), 9.1 +/- 11.1 (Co) and 2.8 +/- 0.6 (Cd), indicating the intense enrichment in Co and Cr within the two seagrasses. The two seagrasses were prone to accumulate all the listed heavy metals (except for As in E. acoroides), especially Co (BCFs of 1124) and Cr (BCFs of 2689) in the aboveground parts, and the belowground parts of both seagrasses also accumulated most metals (BCFs of 27) excluding Co and Pb. The Pb isotopic ratios (mean Pb-208/Pb-204, Pb-207/Pb-204 and Pb-206/Pb-204 values of 38.2054, 15.5000 and 18.3240, respectively) and Cd isotopic compositions (delta Cd-114/110 values ranging from -0.09 parts per thousand to 0.58 parts per thousand) within seagrasses indicated the anthropogenic sources of Pb and Cd including coal combustion, traffic emissions and agricultural activities. This study described the absorption characteristics of E. acoroides and T. hemperichii to some heavy metals, and further demonstrated the successful utilization of Pb and Cd isotopes as discerning markers to trace anthropogenic origins of heavy metals (mainly Pb and Cd) in seagrasses. Pb and Cd isotopes can mutually verify and be helpful to understand more information in pollution sources and improve the reliability of conclusion deduced from concentrations or a single isotope.

Anthropogenic activities and natural erosion caused abundant influx of heavy metals (HMs) and organic matter (OM) into estuaries characterized by the dynamic environments governed by tidal action and river flow. Similarities and differences in the fate of HM and OM as well as the influences of OM on HMs remain incomplete in estuaries with seasonal human activity and hydrodynamic force. To address this gap, dissolved HMs (dHMs) and fluorescence dissolved OM (FDOM) were investigated in the Pearl River Estuary, a highly seasonally anthropogenic and dynamic estuary. It aimed to elucidate the effects of hydrodynamic conditions and DOM on the seasonal fate of dHMs via the multivariate statistical methods. Our findings indicated dHMs and FDOM exhibited consistently higher levels in the upper estuarine and coastal waters in both seasons, predominantly controlled by the terrestrial/anthropogenic discharge. In the wet season, dHMs and humic-like substances (HULIS) were positively correlated, showing that dHMs readily combined with HULIS. This association led to a synchronous decrease offshore along the axis of the estuary and the transport following the river plume in the surface affected by the salt wedge. Contrarily, dHMs were prone to complex with protein-like components impacted by the hydrodynamics during the dry season. Principal Component Analysis (PCA) results revealed the terrestrial/anthropogenic inputs and the fresh-seawater mixing process were the most crucial factors responsible for the fate of dHM in wet and dry seasons, respectively, with DOM identified as a secondary but significant influencing factor in both seasons. This study holds significance in providing valuable insights into the migration, transformation, the ultimate fate of dHMs in anthropogenically influenced estuaries, as well as the intricate dynamics governing coastal ecosystems.

Random defects at different scales are the crucial cause of damage evolution and cascade transfer in rocks. For a large-scale underground cavern, the rock mesoscopic heterogeneity and macroscopic random joints are inevitable factors of rock stability, which needs to be further studied. In this study, a multi-scale analysis method for the stability of jointed rock mass in large underground caverns is proposed. The statistical damage theory is used to describe the mesoscopic heterogeneous rock damage. Monte Carlo simulation and measured joint geometric information are combined to reconstruct the macroscopic random joint network of rock mass. The integrated analysis of mesoscopic heterogeneity of rock and the macroscopic response of random jointed rock mass is performed by Rock Failure Process Analysis (RFPA) system. The research shows that the existence of joint affects the failure mode of rock mass and strengthens the heterogeneity. The representative elementary volume (REV) of jointed rock mass and its equivalent mechanical parameters are determined and used in the stability analysis of a large-scale underground cavern project. Results show a good agreement with the in-situ monitoring deformation of surrounding rock mass, which verifies the effectiveness of the rock mass multi-scale analysis method.

Excessive anthropogenic nitrogen inputs lead to the accumulation of nitrogen, and significantly impact the nitrogen transformation processes in estuaries. However, the governing of nitrogen during its transport from terrestrial to estuary under the influence of diverse human activities and hydrodynamic environments, particularly in the fresh-seawater mixing zone, remains insufficient researched and lack of basis. To address this gap, we employed multi-isotopes, including δ15N-NO3-, δ18O-NO3-, δ15N-NH4+, and δ15N-PN, as well as microbial function analysis, to investigate the nitrogen transformation processes in the Pearl River Estuary (PRE), a highly anthropogenic and terrestrial estuary. Principle component analysis (PCA) confirmed that the PRE could clearly partitioned into three zone, e.g., terrestrial area (T zone), mixing area (M zone) and seawater area (S zone), in terms of nitrogen transportation and transformation processes. The δ15N-NO3- (3.38±0.60‰) and δ18O-NO3- (6.35±2.45‰) results in the inner estuary (T area) indicate that NO3-attributed to the domestic sewage and groundwater discharge in the river outlets lead to a higher nitrification rate in the outlets of the Pearl River than in the reaching and seawater intrusion areas, although nitrate is rapidly diluted by seawater after entering the estuary. The transformation of nitrogen in the T zone was under significant nitrogen fixation (0.61 ± 0.22 %) and nitrification processes (0.0043 ± 0.0032 %) (presumably driven by Exiguobacterium sp. (14.1 %) and Cyanobium_PCC-6307 (8.1 %)). In contrast, relatively low δ15N-NO3- (6.83 ± 1.24‰) and high δ18O-NO3- (22.13±6.01‰) imply that atmospheric deposition has increased its contribution to seawater nitrate and denitrification (0.53±0.13 %) was enhanced by phytoplankton/bacterial (such as Psychrobacter sp. and Rhodococcus) in the S zone. The assimilation of NH4 results from the ammonification of NO3- reduces δ15N-NH4+ (5.36 ± 1.49‰) and is then absorbed by particulate nitrogen (PN). The retention of nitrogen when fresh-seawater mixing enhances the elevation of δ15N-NH4+ (8.19 ± 2.19‰) and assimilation of NH4+, leading to an increase in PN and δ15N-PN (6.91 ± 1.52‰) from biological biomass (mainly Psychrobacter sp. and Rhodococcus). The results of this research demonstrate a clear and comprehensive characterization of the nitrogen transformation process in an anthropogenic dominated estuary, highlighting its importance for regulating the nitrogen dissipation in the fresh-seawater mixing process in estuarine ecosystems.

Plant-herbivore interaction, susceptible to nutrient enrichment, is fundamental for maintaining a healthy and stable ecosystem. Hence, identifying nutrient thresholds may enable better management and monitoring of ecosystems. However, little information is available for the nutrient threshold for the susceptibility of seagrass, the only marine angiosperm, to herbivory. In present study, we investigated how nitrate enrichment altered the traits of dominant tropical seagrass Thalassia hemprichii at the physiological level (nutritional quality, chemical deterrents, and structural characteristics), changing its susceptibility to the herbivory of Cerithidea rhizophorarum. A set of multiple-choice feeding assays were conducted using nitrate-enriched seagrass pre-cultivated in the lab for 60 days. The present study found that the effect of nitrate enrichment on seagrass susceptibility to herbivory was non-linear, with a threshold effect. Low nitrate enrichment chemically and structurally defended seagrass, subsequently reducing herbivory, while continuously increasing nutrient enrichment crossing the threshold enhanced seagrass susceptibility to herbivory. Meanwhile, seagrass leaf total phenol and free fatty acid contents were the two dominant factors determining the herbivory preference of C. rhizophorarum. Overall, since anthropogenic nitrogen enrichment is increasing in intensity and frequency, our findings are significant for conservation and emphasize the importance of coastal eutrophication control.

Understanding the effect of hypergravity on the flow behavior in fractures is essential for using centrifuge modeling to study fluid flow and solute transport in fractured rock. Normal gravity (1 g) and hypergravity (N g) fracture flow experiments were carried out. The hypergravity effect on fracture flow was analyzed. The transition from linear to nonlinear flow was analyzed using the nonlinearity factor and the critical Reynolds number (Recr). The results showed that when the Reynolds number Re > Recr (162), the relationship between the total hydraulic gradient and the flow rate exhibited nonlinear flow behavior both in the 1 g and different N g experiments. The fitting curves of the total hydraulic gradient and the flow rate were similar, indicating that hypergravity had a negligible effect on fracture flow. Compared to the theoretical results that deduced from the Cubic law, the experimental results of 20, 25, and 30 g hypergravity experiments showed that the difference in the flow velocity was 0.08–2.93

In this study, we investigated the taxonomic composition of the bacteria and phytoplankton communities in the Pearl River Estuary (PRE) through Illumina sequencing of the V3-V4 region of the 16 S rRNA gene. Furthermore, their relationships as well as recorded environmental variables were explored by co-occurrence networks. Bacterial community composition was different in two size fractions, as well as along the salinity gradient across two seasons. Free-living (FL) communities were dominated by pico-sized Cyanobacteria (Synechococcus CC9902) while Exiguobacterium, Halomonas and Pseudomonas were predominantly associated with particle-associated (PA) lifestyle, and Cyanobium PCC-6307 exhibited seasonal shifts in lifestyles in different seasons. In wet season, bacterial community composition was characterized by abundance of Cyanobacteria, Actinobacteria, and Bac-teroidetes, which were tightly linked with high riverine inflow. While in dry season, Proteobacteria increased in prevalence, especially for Psychrobacter, NOR5/OM60 clade and Pseudomonas, which were thrived in lower water temperature and higher salinity. Moreover, we discovered that differences between PA and FL composition were more significant in the wet season than in the dry season, which may be due to better nutritional conditions of particles (indicated by POC%) in the wet season and then attract more diverse PA populations. Based on the analysis of plastidial 16 S rRNA genes, abundant small-sized mixotrophic phytoplankton (Dinophyceae, Euglenida and Haptophyta) were identified in the PRE. The complexity of co-occurrence network increased from FL to PA fractions in both seasons, which suggested that suspended particles can provide ecological niches for particle -associated colonizers contributing to the maintenance of a more stable community structure. In addition, the majority of phytoplankton species exhibited positive co-occurrences with both other phytoplankton species and bacterial counterparts, indicating the mutual cooperation between phytoplankton assemblages and specific bacterial populations e likely benefited from phytoplankton-derived organic compounds. This study enhances our understanding of the seasonal and spatial dynamics of bacterial communities and their potential relationship with phytoplankton assembly in estuarine waters.