Accretion Rate Research Articles

Tidal Disruption Events through the Lens of the Cooling Envelope Model

The cooling envelope model for tidal disruption events (TDEs) postulates that while the stellar debris streams rapidly dissipate their bulk kinetic energy (“circularize”), this does not necessarily imply rapid feeding of the supermassive black hole (SMBH). The bound material instead forms a large pressure-supported envelope that powers optical/UV emission as it undergoes gradual Kelvin–Helmholtz contraction. We present results interpreting a sample of 15 optical TDEs within the cooling envelope model in order to constrain the SMBH mass M BH, stellar mass M ⋆, and orbital penetration factor β. The distributions of inferred properties from our sample broadly follow the theoretical expectations of loss-cone analysis assuming a standard stellar initial mass function. However, we find a deficit of events with M BH ≲ 5 × 105 and M ⋆ ≲ 0.5 M ⊙, which could result in part from the reduced detectability of TDEs with these properties. Our model fits also illustrate the predicted long delay between the optical light-curve peak and when the SMBH accretion rate reaches its maximum. The latter occurs only once the envelope contracts to the circularization radius on a timescale of months to years, consistent with delayed-rising X-ray and nonthermal radio flares seen in a growing number of TDEs.

Baryon-induced Collapse of Dark Matter Cores into Supermassive Black Holes

Nonlinear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest a ∼100 keV/c 2 fermion, which leads to ∼107 M ⊙ critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter core to SMBH formation and determines the accreted mass threshold that induces it. Baryonic gas density ρ b and velocity v b inferred from cosmological hydrosimulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than 1 Gyr. This process produces active galactic nuclei in galaxy mergers and the high-redshift Universe. For TXS 2116–077, merging with a nearby galaxy, the observed 3 × 107 M ⊙ SMBH, for Qb=ρb/vb3=0.125M⊙/(100kms−1pc)3 , forms in ≈0.6 Gyr, consistent with the 0.5–2 Gyr merger timescale and younger jet. For the farthest central SMBH detected by the Chandra X-ray satellite in the z = 10.3 UHZ1 galaxy observed by the James Webb Space Telescope (JWST), the mechanism leads to a 4 × 107 M ⊙ SMBH in 87–187 Myr, starting the accretion at z = 12–15. The baryon-induced collapse can also explain the ≈107–108 M ⊙ SMBHs revealed by JWST at z ≈ 4–6. After its formation, the SMBH can grow to a few 109 M ⊙ in timescales shorter than 1 Gyr via sub-Eddington baryonic mass accretion.

On the Durability of Icephobic Coatings: A Review.

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings.

The Coastline Change Pattern of Gresik Beach around the Madura Strait, Indonesia

The coastal region is characterized by dynamic changes in its coastline, which can be attributed to various factors. However, the main causes of change along the Gresik coast have yet to be thoroughly studied. Therefore, this research aims to examine the patterns of coastline change along the Gresik coast around the Madura Strait and the influence of wind-generated waves on them. Specifically, the study focuses on four coastal zones: Ujung Pangkah, Sidayu, Bungah, and Manyar districts. The research utilizes satellite imagery and geographic information systems (GIS) as well as methods for calculating ocean waves to analyze the coastline change patterns. The study also examines the impact of ocean wave energy on coastal abrasion and accretion. The findings revealed that the accretion rate in the study area was higher than the erosion rate. The accretion in the coastal area of Gresik is attributed to the flow of the Bengawan Solo River, which carries sediment from upstream. The accretion and abrasion areas for the entire period from 2002 to 2019 were 1063.16 ha and 425.23 ha, respectively. The study also found that the mangrove areas exhibit a higher rate of accretion than abrasion, indicating their potential as a reliable indicator of the effects of sea level rise resulting from global warming.This study revealed that the northern part of Ujung Pangkah District and Bungah District experienced the highest abrasion patterns, whereas no abrasion was observed in Sidayu District. Between 2002 and 2019, the abrasion areas in Ujung Pangkah and Bungah districts totaled 243.96 ha and 178.29 ha, respectively. Wind-generated waves were likely the primary cause of the abrasion in these areas, though other factors may also have contributed to coastline changes. It is essential to consider these factors for effective coastal management in the region.

Assessment of Riverbank Erosion and Accretion and its Impact on the People of Chairman Ghat, Noakhali, Bangladesh

Nestled within the vastness of the Meghna deltaic plain, Noakhali, and in particular, Chairman Ghat, stand as poignant examples of Bangladesh's intricate relationship with environmental challenges. The significance of the Meghna deltaic plain cannot be overstated, as it shapes the very fabric of the nation's landscape. However, this geographic richness comes hand-in-hand with vulnerability, and nowhere is this more apparent than in the relentless grip of riverbank erosion. Chairman Ghat, in Noakhali, epitomizes the struggle against this natural force, making it a focal point for understanding and addressing the profound impact of riverbank erosion in the region. The primary objective of this research work is to assessing river bank erosion & accretion and examine its the potential impact in the chairman Ghat area. In order to achieve this goal, this study employs remote sensing and GIS techniques to assess the erosion and accretion rates of Chairman Ghat on the Noakhali coast from 2000 to 2022 and conduct household survey to examine the socioeconomic impacts of river erosion on the local population. The findings revealed that Over the past 22 years, the Meghna estuary experienced a total of 667.0 km2 of erosion and 689.1 km2 of accretion. Chairman Ghat area alone witnessed a net erosion rate of 4.2 km2 per year during the specified period, resulting in a loss of 117.7 km2 of land, while only 25.3 km2 of new land was added. From household survey it is found that the adverse effects of riverbank erosion on the local community are evident, leading to the loss of vital agricultural lands, homesteads, and property damage that cannot be easily recovered. Consequently, a significant portion of the affected population is compelled to migrate, thereby exacerbating their socio-economic plight as they are forced to change professions. This research sheds light on the extent of riverbank erosion in Chairman Ghat, Noakhali, and elucidates its profound socioeconomic implications on the lives of the local inhabitants. The findings of the study will help to enhance our understanding of the specific impact of river erosion enabling the development of targeted strategies to protect vulnerable communities' lives, livelihoods, and environments. It will also promote cohesive coastal zone management, implementing robust measures that counteract the destructive consequences of riverbank erosion, thereby ensuring the sustainable development and resilience of these crucial ecosystems.

Multiwavelength detection of an ongoing FUOr-type outburst on a low-mass YSO

ABSTRACT During the pre-main-sequence evolution, Young Stellar Objects (YSOs) assemble most of their mass during the episodic accretion process. The rarely seen FUOr-type events are valuable laboratories to investigate the outbursting nature of YSOs. Here, we present multiwavelength detection of a high-amplitude eruptive source in the young open cluster VdBH 221 with an ongoing outburst, including optical to mid-infrared time series and near-infrared spectra. The initial outburst has an exceptional amplitude of >6.3 mag in Gaia and 4.6 mag in Ks, with a peak luminosity up to 16 L⊙ and a peak mass accretion rate of 1.4 × 10−5 M⊙ yr−1. The optical to infrared spectral energy distribution of this object is consistent with a low-mass star (0.2 M⊙) with a modest extinction (AV < 2 mag). A 100-d delay between optical and infrared rising stages is detected, suggesting an outside-in origin of the instability. The spectroscopic features of this object reveal a self-luminous accretion disc, very similar to FU Orionis, with a low line-of-sight extinction. Most recently, there has been a gradual increase in brightness throughout the wavelength range, possibly suggesting an enhancement of the mass accretion rate.

Shoreline dynamics over last three decades and predictions for 2032 and 2042: a spatial analysis along the coastal stretch of Aruvi Aru and Kal Aru estuaries in Mannar district, Sri Lanka

ABSTRACT The North-Western coastal stretch of the Aruvi Aru and Kal Aru estuaries in Sri Lanka's Mannar district faces increasing vulnerability due to coastal erosion, but comprehensive research has been lacking until now. This study aims to analyze shoreline changes from 1988 to 2022 and forecast future changes until 2042. Landsat satellite images and statistical parameters such as LRR and AoR were used to calculate erosion and accretion rates. The maximum erosion rate was −4.7 to −5.3 m/year, while accretion ranged from 9.6 to 10.3 m/year. The Kalman filter model predicted further erosion in Vankalai West (45 m by 2042) and accretion in Pathaikaddumunai (78 m by 2042). Certain areas, including Vankalai, Naruvilikulam, and Kondachchikudah, were identified as high-risk zones prone to erosion. The study suggests implementing this technique for comprehensive coastal management strategies in Sri Lanka.

The blue carbon of southern southwest Atlantic salt marshes and their biotic and abiotic drivers

Coastal vegetated ecosystems are acknowledged for their capacity to sequester organic carbon (OC), known as blue C. Yet, blue C global accounting is incomplete, with major gaps in southern hemisphere data. It also shows a large variability suggesting that the interaction between environmental and biological drivers is important at the local scale. In southwest Atlantic salt marshes, to account for the space occupied by crab burrows, it is key to avoid overestimates. Here we found that southern southwest Atlantic salt marshes store on average 42.43 (SE = 27.56) Mg OC·ha−1 (40.74 (SE = 2.7) in belowground) and bury in average 47.62 g OC·m−2·yr−1 (ranging from 7.38 to 204.21). Accretion rates, granulometry, plant species and burrowing crabs were identified as the main factors in determining belowground OC stocks. These data lead to an updated global estimation for stocks in salt marshes of 185.89 Mg OC·ha−1 (n = 743; SE = 4.92) and a C burial rate of 199.61 g OC·m−2·yr−1 (n = 193; SE = 16.04), which are lower than previous estimates.

Probing supermassive black hole growth and its dependence on stellar mass and star formation rate in low-redshift galaxies

ABSTRACT We present an improved study of the relation between supermassive black hole growth and their host galaxy properties in the local Universe (z < 0.33). To this end, we build an extensive sample combining spectroscopic measurements of star formation rate (SFR) and stellar mass from Sloan Digital Sky Survey, with specific Black Hole accretion rate (sBHAR, $\lambda _{\mathrm{sBHAR}} \propto L_{\rm X}/\mathcal {M}_{\ast }$) derived from the XMM–Newton Serendipitous Source Catalogue (3XMM–DR8) and the Chandra Source Catalogue (CSC2.0). We find that the sBHAR probability distribution for both star-forming and quiescent galaxies has a power-law shape peaking at log λsBHAR ∼ −3.5 and declining towards lower sBHAR in all stellar mass ranges. This finding confirms the decrease of active galactic nucleus (AGN) activity in the local Universe compared to higher redshifts. We observe a significant correlation between $\log \, \lambda _{\rm sBHAR}$ and $\log \, {\rm SFR}$ in almost all stellar mass ranges, but the relation is shallower compared to higher redshifts, indicating a reduced availability of accreting material in the local Universe. At the same time, the BHAR-to-SFR ratio for star-forming galaxies strongly correlates with stellar mass, supporting the scenario where both AGN activity and stellar formation primarily depend on the stellar mass via fuelling by a common gas reservoir. Conversely, this ratio remains constant for quiescent galaxies, possibly indicating the existence of the different physical mechanisms responsible for AGN fuelling or different accretion mode in quiescent galaxies.

The impact of gas accretion and AGN feedback on the scatter of the mass–metallicity relation

ABSTRACT The gas-phase metallicity of galaxies encodes important information about galaxy evolution processes, in particular star formation, feedback, outflows, and gas accretion, the relative importance of which can be extracted from systematic trends in the scatter of the mass–metallicity relation (MZR). Here, we use a sample of low-redshift (0.02 < z < 0.055) galaxies from SDSS to investigate the nature of the scatter around the MZR, the observables and physical processes causing it, and its dependence on galaxy mass. We use cold gas masses inferred from optical emission lines using the technique of Scholte & Saintonge (2023) to confirm that at fixed stellar mass, metallicity and gas mass are anticorrelated, but only for galaxies up to M* = 1010.5 M⊙. In that mass regime, we find a link between the offset of a galaxy from the MZR and halo mass, using the amplitude of the two-point correlation function as a proxy for halo mass; at fixed stellar mass, the most gas-poor galaxies reside in the most massive haloes. This observation is consistent with changes in gas accretion rates onto galaxies as a function of halo mass, with environmental effects acting on satellite galaxies also contributing. At higher stellar masses, the scatter of the MZR does no longer correlate with gas or halo mass. Instead, there is some indication of a link with AGN activity, as expected from models and simulations that metallicity is set by the interplay between gas in- and outflows, star formation, and AGN feedback, shaping the MZR and its scatter.

Dissecting cosmological filaments at high redshifts: emergence of spaghetti-type flow inside DM haloes

ABSTRACT We use high-resolution zoom-in simulations to study the fueling of central galaxies by filamentary and diffuse accretion at redshifts, z ≳ 2. The parent haloes were chosen with similar total masses, log (Mvir/M⊙) ∼ 11.75 ± 0.05, at z = 6, 4, and 2, in high/low overdensity environments. We analyse the kinematic and thermodynamic properties of circumgalactic medium (CGM) within few virial radii, Rvir, and down to the central galaxy. Using a hybrid d-web/entropy method we mapped the gaseous filaments, and separated inflows from outflows. We find that (1) The CGM is multiphase and not in thermodynamic or dynamic equilibrium; (2) filamentary and diffuse accretion rates and densities decrease with lower redshifts, and inflow velocities decrease from $200-300\, {\rm {km\, s}^{-1}}$ by a factor of 2; (3) temperature within the filaments increases inside Rvir, faster at lower redshifts; (4) filaments show a complex structure along their spines: a core radial flow surrounded by a lower density envelope. The cores exhibit elevated densities and lower temperature, with no obvious metallicity gradient in the cross sections. Filaments also tend to separate into different infall velocity regions and split density cores, thus producing a spaghetti-type flow; (6) inside the inner $\sim 30\, h^{-1}$ kpc, filaments develop the Kelvin–Helmholtz instability which ablates and dissolves them, and triggers turbulence along the filaments, clearly delineating their spines; (7) finally, the galactic outflows affect mostly the inner ∼0.5Rvir ∼ 100 h−1 kpc of the CGM.

Spectral and temporal features of GX 13+1 as revealed by AstroSat

ABSTRACT GX 13+1, a neutron star low-mass X-ray binary that exhibits the properties of both atoll and Z sources, is studied using data from Soft X-ray Telescope and Large Area X-ray Proportional Counter (LAXPC) onboard AstroSat. The source traces a ν shaped track in its hardness-intensity diagram (HID). Spectral modelling of the data in the 0.7–30.0 keV energy range, with the model – $\tt {constant}$ × $\tt {tbabs}$ × $\tt {thcomp}$ × $\tt {bbodyrad}$ + $\tt {relxillNS}$, yields orbital inclination angle (θ) of 77$\substack{+10\\-8}$°. Flux resolved spectral analysis reveals the ν shaped pattern in the plots of spectral parameters kTe, kTbb, and Γ versus Fbol, closely resembling the pattern traced in LAXPC HID. This indicates changes in the spectral properties of the corona and the boundary layer/accretion disc. Assuming that the accretion disc truncates at the Alfvén radius, the upper limit of the magnetic field strength (B) at the poles of neutron star in GX 13+1 is calculated to be 5.10 × 108 G (for kA = 1 and η = 0.1), which is close to that of atoll sources. Furthermore, thickness of the boundary layer is estimated to be 5.70 km, which results in the neutron star radius value of ≲14.50 km. Quasi-periodic oscillations (QPOs) at 56 ± 4 and 54 ± 4 Hz are detected in Regions D and E of HID, respectively. The frequencies of these QPOs are similar to the characteristic frequency of horizontal branch oscillation and these do not exhibit a positive correlation with mass accretion rate.

Analysis of shoreline changes in the severe storm surge region of upper Coromandel coast, India, using Remote sensing (RS) and Geographic information system (GIS)

Coastlines have been subject to ongoing vulnerability from natural disasters, resulting in erosion and accretion occurring at varying intervals. The impacts of human activities and alterations in natural processes, including those induced by climate change, exacerbate the existing challenges faced along coastal regions. The present study aimed to analyze the changing shoreline along the Bapatla coastal tract in the upper coromandel coast of Andhra Pradesh due to erosion and accretion using the DSAS toolbar in ArcGIS software. Multiple statistical methods are available in DSAS; the present study confined attention to the end point rate (EPR), linear regression rate (LRR), and net shoreline movement (NSM) for this investigation. The Nizampatnam Mandal had the greatest erosion rate (-16.8 m/yr) and accretion rate (10.5 m/yr), according to EPR, as well as the highest erosion rate (-16.7 m/yr) and accretion rate (10.4 m/yr) according to LRR. As per NSM, between 1990 and 2020, the highest erosion and accretion was seen again in Nizampatnam. The shoreline at Nizampatnam either retreated by as much as -285.2 meters or advanced by 211.1 meters. The research indicated that the Bapatla district's shoreline is susceptible to erosion and accretion. The present investigation revealed that the coastal region of Bapatla district exhibits susceptibility to both erosion and accretion phenomena. The findings of the present study hold significant implications for professionals in the fields of coastal science, engineering, and administration. The findings are of utmost importance in the development of sustainable approaches for coastal management.

Constraints on Neutron Star Structure from the Clocked X-Ray Burster 1RXS J180408.9−342058

Type I X-ray bursts are rapid-brightening transient phenomena on the surfaces of accreting neutron stars (NSs). Some X-ray bursts, called clocked bursters, exhibit regular behavior with similar light-curve profiles in their burst sequences. The periodic nature of clocked bursters has the advantage of constraining X-ray binary parameters and physics inside the NS. In the present study, we compute numerical models, based on different equations of state and NS masses, which are compared with the observations of a recently identified clocked burster, 1RXS J180408.9−342058. We find that the relation between the accretion rate and the recurrence time is highly sensitive to the NS mass and radius. We determine, in particular, that 1RXS J180408.9−342058 appears to possess a mass less than 1.7M ⊙ and favors a stiffer nuclear equation of state (with an NS radius ≳12.7 km). Consequently, the observations of this new clocked burster may provide additional constraints for probing the structure of NSs.

Increasing carbon and nutrient burial rates in mangroves coincided with coastal aquaculture development and water eutrophication in NE Hainan, China

Mangroves sequester and store large area-specific quantities of blue carbon (C) and essential nutrients such as nitrogen (N) and phosphorous (P). Quantifying C and nutrient burial rates in mangroves across a centennial time span and relating these rates to mangrove habitat is fundamental for elucidating the role of mangroves in carbon and nutrient budgets and their responses to environmental changes. However, relevant data are very limited in China. In this study, we used the radionuclides (210Pb and 137Cs) to determine chronologies and C, N and P burial rates in two mangrove forests located at different geomorphologic settings in NE Hainan Island, China. We found that the temporal patterns of C, N and P burial rates since 1900 fitted a quadratic function with a notable increase after 1960s in both mangroves, which coincided with the rapid development of coastal aquaculture since 1960s in NE Hainan and the subsequent coastal water eutrophication in this area. Sediment accretion rate (SAR) and mass accumulation rate (MAR) stayed relatively steady in the open-coastal mangroves, while they increased exponentially in the estuarine mangroves since 1900. The estuarine mangroves had significantly higher SAR and C, N and P burial rates than the open-coastal mangroves. C, N and P burial rates averaged at 141.52 g m−2 a−1, 6.27 g m−2 a−1 and 1.14 g m−2 a−1, respectively in the estuarine core, and these rates averaged at 61.71 g m−2 a−1, 3.71 g m−2 a−1 and 0.43 g m−2 a−1, respectively in the open-coastal core. The results suggest that estuarine mangroves may be more capable of surviving accelerating sea level rise under climate change and play a greater role in C accumulation and nutrient filtering under anthropogenic nutrient enrichment than marine-dominated mangroves. Blue C burial may be enhanced by coastal water eutrophication, but such a relationship needs to be tested in further studies.

Accretion Flow Properties of EXO 1846-031 during Its Multi-peaked Outburst after Long Quiescence

We study the recent outburst of the black hole candidate EXO 1846-031, which went into an outburst in 2019 after almost 34 yr in quiescence. We use archival data from the Swift/XRT, MAXI/GSC, NICER/XTI, and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. The low-energy (2–10 keV) X-ray flux of the outburst shows multiple peaks, making it a multipeak outburst. Evolving type-C quasi-periodic oscillations are observed in the NICER data in the hard, hard-intermediate, and soft-intermediate states. We use the physical two-component advective flow (TCAF) model to analyze the combined spectra of multiple satellite instruments. According to the TCAF model, the accreting matter is divided into Keplerian and sub-Keplerian parts, and the variation in the observed spectra in different spectral states arises out of the variable contributions of these two types of accreting matter in the total accretion rate. Studying the evolution of the accretion rates and other properties of the accretion flow obtained from the spectral analysis, we show that the multiple peaks in the outburst flux arise out of the variable supply of accreting matter from the pile-up radius. We determine the probable mass of the black hole to be from the spectral analysis with the TCAF model. We also estimate the viscous timescale of the source in this outburst to be ∼8 days from the peak difference of the Keplerian and sub-Keplerian mass-accretion rates.

Detection of diffuse H i emission in the circumgalactic medium of NGC 891 and NGC 4565 - II

ABSTRACT We probe the neutral circumgalactic medium (CGM) along the major axes of NGC 891 and NGC 4565 in 21-cm emission out to ≳100 kpc using the Green Bank Telescope (GBT), extending our previous minor axes observations. We achieve an unprecedented 5σ sensitivity of 6.1 × 1016 cm−2 per 20 km s−1 velocity channel. We detect H i with diverse spectral shapes, velocity widths, and column densities. We compare our detections to the interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) obtained as part of the HALOGAS survey. At small impact parameters, $\gt 31\!-\!43~{{\ \rm per\ cent}}$ of the emission detected by the GBT cannot be explained by emission seen in the WSRT maps, and it increases to $\gt 64\!-\!73~{{\ \rm per\ cent}}$ at large impact parameters. This implies the presence of diffuse circumgalactic H i. The mass ratio between H i in the CGM and H i in the disc is an order of magnitude larger than previous estimates based on shallow GBT mapping. The diffuse H i along the major axes pointings is corotating with the H i disc. The velocity along the minor axes pointings is consistent with an inflow and/or fountain in NGC 891 and an inflow/outflow in NGC 4565. Including the circumgalactic H i, the depletion time and the accretion rate of NGC 4565 are sufficient to sustain its star formation. In NGC 891, most of the required accreting material is still missing.

A Centiparsec-scale Compact Radio Core in the Nearby Galaxy M60

M60, an elliptical galaxy located 16.5 Mpc away, has an active nucleus with a very low luminosity and an extremely low accretion rate. Its central supermassive black hole (SMBH) has a mass of M BH ∼ 4.5 × 109 M ⊙ and a Schwarzschild radius corresponding to R S ∼ 5.4 μas. To investigate the nature of its innermost radio nucleus, data from the Very Long Baseline Array (VLBA) at 4.4 and 7.6 GHz were reduced. The VLBA images reveal a compact component with total flux densities of ∼20 mJy at both frequencies, a size of ≤0.27 mas (99.7% confidence level), about 0.022 pc (50 R S) at 7.6 GHz, and a brightness temperature of ≥6 × 109 K. This suggests that the observed centiparsec-scale compact core could be attributed to a nonthermal jet base or an advection-dominated accretion flow (ADAF) with nonthermal electrons. The extremely compact structure also supports the presence of an SMBH in the center. Our results indicate that M60 is a promising target for broadband very long baseline interferometry observations at millimeter wavelengths to probe ADAF scenarios and tightly constrain the potential photon ring (about 28 μas) around its SMBH.

Depositional dynamics and vegetation succession in self-organizing processes of deltaic marshes

Global deltaic marshes are currently facing a multitude of pressures, including insufficient sediment supply, rising sea levels, and habitat loss. Consequently, unraveling the internal regulatory mechanisms within deltaic marshes is of paramount importance. Here, we harness years of observational data and high-resolution numerical models to uncover depositional dynamics and vegetation succession in self-organizing processes of deltaic marshes. Our findings indicate that the colonization of salt marsh vegetation triggered a robust phase of growth in the initial stages of river deltas formation. However, as vertical accretion intensifies and inundation decreases, the delta is driven towards a state of critical slowing down due to insufficient sediment supply. We have captured a pivotal turning point in the evolution of deltaic marshes. In accordance with the critical submergence threshold we have established, when the inundation time of deltaic marshes exceeds 0.97 h/d, these salt marsh platforms sustain a higher annual growth rate. Conversely, when the inundation time of deltaic marshes falls below 0.97 h/d, the interannual accretion rate continues to decrease. Our research reveals that, in the absence of human disturbances, the deposition rate in deltaic marshes transitions from growth to decline. During this period, the delta undergoes an interesting succession of pioneer salt marshes (Suaeda salsa) and high-elevation salt marshes (Phragmites australis). Even without reductions in sediment input due to human activities, the vertical deposition rate within deltaic marshes will still shift from acceleration to deceleration under the influence of this internal negative feedback regulation. This adaptive capacity of marshes may foreshadow that when observing a slowdown in vertical accretion on deltaic marsh platforms, it cannot be solely attributed to reductions in sediment input caused by human activities.

Relative Effectiveness of a Radionuclide (210Pb), Surface Elevation Table (SET), and LiDAR At Monitoring Mangrove Forest Surface Elevation Change

AbstractSea-level rise (SLR) is one of the greatest future threats to mangrove forests. Mangroves have kept up with or paced past SLR by maintaining their forest floor elevation relative to sea level through root growth, sedimentation, and peat development. Monitoring surface elevation change (SEC) or accretion rates allows us to understand mangrove response to SLR and prioritizes resilient ecosystems for conservation or vulnerable ecosystems for restoration. We compared three methods to measure SEC and accretion in mangrove forests: 210Pb, surface elevation tables (SETs), and a terrestrial light detection and ranging system (compact biomass LiDAR—CBL). Lead-210 accretion rates were not significantly different than SET SEC rates and differences between the two methods (− 2 to 2 mm/year) were within the error of our measurements. Lead-210 only measures accretion in the upper meter of sediment and cannot capture deeper subsurface processes (e.g., subsidence, compaction) that SETs can. The lack of differences suggests the following: (1) surface processes in the active root zone are influencing forest floor elevation more than subsurface processes, (2) subsurface processes were not large enough to effect elevation, or (3) the SETs were not installed deep enough to capture subsurface processes. CBL SEC rates did not differ significantly from SET SEC rates. The larger spatial scale of the CBL scans resulted in significantly different SEC rates from some of the plots. This was due to the CBL measuring areas missed by the SET. The greater number of points measured by CBL (~ 30,000 vs 36) increased precision and lowered standard error. The traditional SET/rSET method is currently 3–10 × cheaper than the 210Pb or CBL method, respectively, and can accurately track changes in forest floor elevation. Costs of the use of LiDAR are likely to decrease in the future with the advent of newer and more cost-effective technology.