Sediment Accretion Research Articles

Selecting ecological attributes for managing within environmental limits: an example of a robust science-policy process in Aotearoa New Zealand

ABSTRACT Aotearoa New Zealand is experiencing continued environmental degradation despite its regulatory settings intended to improve environmental outcomes. A lack of clear environmental limits has made it hard to protect ecological integrity and reduce pressures from the cumulative effects of human activities, even more so in a changing climate. This article outlines an evidence-informed process for selecting attributes – i.e. measurable characteristics – of ecological integrity for use by policy makers in resource management across Aotearoa New Zealand. It describes criteria developed (including urgency and importance, suitability and feasibility) to select an initial suite of attributes through engagement with partners and stakeholders and substantial review. The new attributes are intended to fill key gaps not well covered by existing legislation. Seven new attributes were identified including indigenous vegetation cover, erodible soil stabilisation, sediment mud content, sediment accretion rate, nuisance macroalgae, and saltmarsh and seagrass extent. This small number of attributes are not sufficient on their own to protect ecological integrity by managing within environmental limits, but considered a necessary first step in managing priority issues. A more holistic suite of attributes could be developed later, building from this process that can be adapted depending on the details of any future resource management system.

Sea-level rise and extreme Indian Ocean Dipole explain mangrove dieback in the Maldives.

Mangrove forests enhance Small Island Developing States' resilience to climate change, yet in 2020, a mangrove dieback impacted ~ 25% of mangrove-containing islands in the Maldives. Using remote sensing, dendrology and sediment geochemistry, we document a significant decrease in mangrove health post-2020 (NDVI: 0.75 ± 0.09) compared to pre-2020 (0.85 ± 0.04; P < 0.0001). Dead trees showed reduced stomatal conductance (δ13C: -26.21 ± 0.11 ‰) relative to living ones (-27.66 ± 0.14 ‰), indicating salinity stress. Critically, sea-level rise (30.50 ± 23.30mm/year) outpaced mangrove sediment accretion (6.40 ± 0.69mm/year) five-fold between 2017 and 2020. We attribute this dieback to salinity stress driven by record-high sea levels in 2020, linked to an extreme positive Indian Ocean Dipole event. These findings reveal the vulnerability of mangrove ecosystems to rapid sea-level rise and highlights the urgent need for adaptive conservation strategies in Small Island Developing States.

Sediment accretion and nutrient enrichment enhance the growth and vegetative propagation of Phalaris arundinacea growing within a Carex thunbergii stand.

Sediment accretion (burial) and nutrient enrichment may exert a synergistic influence on the growth and distribution of macrophytes in floodplain wetlands; however, this phenomenon has rarely been examined. In this study, we investigated the effects of sediment accretion and nutrient enrichment on the growth and vegetative propagation of Phalaris arundinacea within a Carex thunbergii stand (one P. arundinacea ramet within 25 C. thunbergii ramets) using a factorial sediment burial (0, 3, and 6 cm) and nutrient addition (low, medium, and high) experimental design. High sediment burial (6 cm) without nutrient addition decreased the aboveground and total biomass of C. thunbergii but did not affect P. arundinacea, indicating that P. arundinacea is more tolerant to sediment burial than C. thunbergii. Moderate sediment burial (3 cm) with nutrient addition enhanced the aboveground and total biomass of P. arundinacea but did not affect C. thunbergii, indicating that P. arundinacea may gain a growth advantage over C. thunbergii under moderate sedimentation. High sediment burial with nutrient addition increased the number of rhizomes and ramets produced by P. arundinacea but did not affect C. thunbergii, indicating that the relative abundance of P. arundinacea may increase within the Carex community under high sedimentation conditions. Based on these results, it can be concluded that an increased sedimentation rate facilitates the invasion of P. arundinacea into Carex grasslands, and this invasion is further enhanced by nutrient enrichment. Therefore, management measures should be taken to reduce the sediment load and nutrient input to prevent Carex grasslands invasion by P. arundinacea and maintain the ecological function of floodplain wetlands.

Dense vegetation hinders sediment transport toward saltmarsh interiors

AbstractTo save saltmarshes and their valuable ecosystem services from sea level rise, it is crucial to understand their natural ability to gain elevation by sediment accretion. In that context, a widely accepted paradigm is that dense vegetation favors sediment accretion and hence saltmarsh resilience to sea level rise. Here, however, we reveal how dense vegetation can inhibit sediment accretion on saltmarsh platforms. Using a process‐based modeling approach to simulate biogeomorphic development of typical saltmarsh landscapes, we identify two key mechanisms by which vegetation hinders sediment transport from tidal channels toward saltmarsh interiors. First, vegetation concentrates tidal flow and sediment transport inside channels, reducing sediment supply to platforms. Second, vegetation enhances sediment deposition near channels, limiting sediment availability for platform interiors. Our findings suggest that the resilience of saltmarshes to sea level rise may be more limited than previously thought.

Organic Carbon Reaction Kinetics in Bioturbated Sediments

AbstractMost organic carbon delivered to the seafloor is degraded within the bioturbated layer. Theory and empirical evidence have shown that organic carbon reactivity relates to the age of a particle. However, due to particle mixing, the age‐depth linear relation induced by sediment accretion is obfuscated. Here we combine a Lagrangian particle tracking model that resolves the age distribution of particles in the bioturbated zone and couple it to age‐dependent organic carbon degradation. Depth profiles for organic carbon concentration, reactivity and degradation rate are presented for sediments receiving low and high reactivity organic carbon in coastal, continental slope and deep‐sea environments. Our results show that a simple first‐order kinetics model suffices for well‐mixed sediments and systems receiving pre‐processed materials. A reactive continuum approach is needed for poorly mixed sediments receiving highly reactive organic carbon and for sediments below the bioturbated layer.

Proximity to inlet channel drives spatial variation in sediment carbon across a lagoonal seagrass meadow

Seagrass meadows can be sinks for organic carbon, but estimates of global organic carbon stocks are complicated by substantial spatial variability in organic carbon burial observed within meadows. To improve estimates of organic carbon burial in seagrass meadows, it is necessary to understand the causes of the spatial heterogeneity. This study investigated relationships between spatial patterns in sediment organic carbon storage and accretion rates, hydrodynamics, and proximity to sources of organic carbon in a current-dominated Zostera marina Linnaeus meadow in Menemsha Pond, Massachusetts, USA. Sediment and velocity measurements were conducted at six stations along a 150-m transect across the meadow oriented perpendicular to the pond's unvegetated inlet channel. The meadow's edge near the channel had higher organic carbon than the channel as well as the highest organic carbon within the meadow. With increasing distance from the meadow's edge, all of the following decreased: sediment organic and total carbon, sediment accretion rates, peak tidal velocity, sediment trap mass deposition rate, and the relative contribution of non-seagrass sources to sediment organic carbon. Lower tidal velocities farther from the inlet channel reduced sediment resuspension, consistent with lower sediment trap mass deposition, which should enhance organic carbon content and organic carbon accretion rates. However, the opposite trend of decreasing organic carbon content (>50 % across the transect) and decreasing accretion rates with distance from channel was observed. This suggested that the local hydrodynamic intensity was not controlling organic carbon accretion, which was instead constrained by supply limitation and controlled by the lagoon-scale flow circulation.

Variations in litterfall dynamics, root biomass, and sediment accretion in restored and recolonized mangroves in Leyte, Philippines

Litterfall production and decay, root biomass, and sediment accretion dynamics were investigated from restored ‘planted’ (R5, R8, R15, and R30 stands) and recolonized stands (C5, C12, and C20 stands) to investigate patterns in primary productivity, belowground biomass, and sediment accretion dynamics. Litterfall data was collected using litter traps over 12 months, while decay kinetics was investigated using a litterbag experiment. Root biomass and sediment accretion data were collected using makeshift acrylic corers. Litterfall production increased as stands aged, and tended to stabilize as it matured in restored (R8: 10.05 Mg/ha/yr; R30: 6.1 Mg/ha/yr) and recolonized stands (C5: 18.75 Mg/ha/yr; C20: 9.05 Mg/ha/yr). Leaf litter decay rates (K/d) showed no pattern with stand age, although the recolonized stands (range: 0.059–0.113 K/d) had lower decay rates compared to the restored (range: 0.073–0.123 K/d) and natural stands (range: 0.064–0.123 K/d). Root biomass declined with age in restored stands (R5: 67.16 Mg/ha, R30: 49.67 Mg/ha), but increased in recolonized stands (C5: 5.41 Mg/ha, C20: 19.50 Mg/ha). Very high rates of sediment accretion were found in younger restored (R5: 10.1 cm/yr) and recolonized stands (C5: 8.1 cm/yr) than mature stands (R30: 6.3 cm/yr; C20: 4.3 cm/yr). Our results showed disparities of patterns in mangrove vegetation growth in recolonized stands and huge potential contribution on mangrove productivity when these areas are effectively restored.

Parasites disrupt a keystone mutualism that underpins the structure, functioning, and resilience of a coastal ecosystem

AbstractParasites can alter the traits or densities of mutualistic partners, potentially destabilizing mutualistic associations that underpin the structure, functioning, and stability of entire ecosystems. Despite the potentially wide‐ranging consequences of such disruptions, no studies have directly manipulated parasite prevalence and/or intensity in a mutualistic partner, nor quantified the resulting community‐level effects. Here, we investigated the effects of a common trematode parasite (Cercaria opaca) on the strength of a keystone facultative mutualism in western Atlantic salt marshes between the foundational marsh cordgrass, Spartina alterniflora, and the ribbed mussel, Geukensia demissa. Cordgrass increases mussel survivorship and growth through shading, while mussels enhance cordgrass growth by producing nutrient‐rich biodeposits. This mutualistic association also creates conditions that enhance biodiversity and ecosystem functioning, and mediates the ability of foundational plants to resist and recover from extreme drought. We used lab and field assays to show how increasing infection with trematode metacercariae negatively influenced mussel biodeposit production, as well as the strength of mussel shells and byssal attachments. By conducting a field manipulation using experimentally infected mussels, we demonstrated that the mutualistic benefits of mussels to cordgrass growth decreased with increasing trematode infection intensity—a pattern likely generated by reduced mussel biodeposition and enhanced mortality. Additionally, increasing parasite loads in mussels led to predictable decreases in the abundances of benthic invertebrates, as well as in key ecosystem characteristics and process rates (i.e., redox potential and sediment accretion). Finally, a survey of five North Carolina salt marshes demonstrated that infection with C. opaca was most common in mussels in areas experiencing cordgrass die‐off due to drought, and that infection intensity decreased with distance from die‐off areas. Because the mussel–cordgrass mutualism underpins marsh ecosystem resilience to drought‐associated die‐off, our results suggest that parasitism may depress recovery from these disturbances. Although this is the first experimental demonstration of parasites indirectly altering community structure and functioning by undermining an ecologically influential mutualism, this type of relationship could be common in nature, given that parasites frequently infect influential mutualists.

Iron species and sulfur isotopic compositions of authigenic pyrite in deep-sea sediments at southern Hydrate Ridge, Cascadia margin (ODP Leg 204): implications for non-steady-state depositional and diagenetic processes

Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steady-state depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the δ34S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite δ34S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite δ34S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record.

Optimizing coastal protection: Nature-based engineering for longitudinal drift reversal and erosion reduction

Traditional hard engineering solutions have shown weaknesses in mitigating erosion processes in vulnerable coastal areas, contributing in some cases to their aggravation, which makes it necessary to study innovative nature-based engineering solutions. This research deals with an in-depth analysis of hydro-morphodynamic modelling results for optimizing the geometry of maritime structures under longitudinal drift reversal conditions by mimicking and manipulating natural processes to promote wave energy dissipation and sediment retention through wave deformation due to obstacle interposition. The solutions draw inspiration from the full-scale observation data of two examples of longitudinal drift reversal. Additionally, numerical simulations were developed for predicting wave climate near the Iberian Peninsula shoreline under different scenarios. Hydrodynamics and morphodynamics modelling results are discussed based on the impact of a specific storm, considering different characteristics of protection structures, followed by parametric sensitivity analysis and comparative studies performed with an optimized solution. Results indicated this solution contributed to sediment accumulation downdrift near the shoreline, as there is no interruption of the longitudinal drift compared to traditional protection structures. At the alignment, the structure also improved nearshore sediment accretion, reduced areas of erosion relative to a no-structure scenario and exhibited behaviour akin to an emerged structure with its crest level. Compared to wholly submerged structures, it becomes a relevant coastal protection alternative, as it guarantees excellent protection on the adjacent coastal zone by safeguarding against tidal variations induced by storm surges and mean sea level rise due to climate change. Furthermore, there is a positive effect to help promote biodiversity whenever the structure is located in an intertidal zone. Despite the enormous computational effort required in the hydro-morphodynamic modelling process, this study shows that it is possible to create innovative engineering coastal solutions to induce longitudinal drift reversal and reduce erosion near the shoreline.

Drivers of dune formation control ecosystem function and response to disturbance in a barrier island system.

Barrier islands are landscape features that protect coastlines by reducing wave energy and erosion. Quantifying vegetation-topographic interactions between adjacent habitats are essential for predicting long-term island response and resilience to sea-level rise and disturbance. To understand the effects of dune dynamics on adjacent interior island ecosystem processes, we quantified how sediment availability and previous disturbance regime interact with vegetation to influence dune building and ease of seawater and sediment movement into the island interior on two US mid-Atlantic coast barrier islands. We conducted field surveys of sediment accretion, vegetative cover, and soil characteristics in dune and swale habitats. Digital elevation models provided assessment of water flow resistance from the mean high water mark into the island interior. We found that geographic location impacted sediment accretion rates and Panicum amarum (a species increasing in abundance over time in the Virginia barrier islands) accreted sediment at a significantly lower rate compared to other dune grasses. Dune elevation impacted the ease of seawater flow into the island interior, altering soil chlorides, annual net primary productivity, and soil carbon and nitrogen. Our work demonstrates the importance of incorporating biological processes and cross-island connectivity into future scenario modeling and predictions of rising sea-levels and increased disturbance.

Late Quaternary Surface Displacements on Accretionary Wedge Splay Faults in the Cascadia Subduction Zone: Implications for Megathrust Rupture

Because splay faults branch at a steep dip angle from the plate-boundary décollement in an accretionary wedge, their coseismic displacement can potentially result in larger tsunamis with distinct characteristics compared to megathrust-only fault ruptures, posing an enhanced hazard to coastal communities. Elsewhere, there is evidence of coseismic slip on splay faults during many of the largest subduction zone earthquakes, but our understanding of potentially active splay faults and their hazards at the Cascadia subduction zone remains limited. To identify the most recently active splay faults at Cascadia, we conduct stratigraphic and structural interpretations of near-surface deformation in the outer accretionary wedge for the ~400 km along-strike length of the landward vergence zone. We analyze recently acquired high-frequency sparker seismic data and crustal-scale multi-channel seismic data to examine the record of deformation in shallow slope basins and the upper ~1 km of the surrounding accreted sediments and to investigate linkages to deeper décollement structure. We present a new fault map for widest, most completely locked portion of Cascadia from 45 to 48°N latitude, which documents the distribution of faults that show clear evidence of recent late Quaternary activity. We find widespread evidence for active splay faulting up to 30 km landward of the deformation front, in what we define as the active domain, and diminished fault activity landward outside of this zone. The abundance of surface-deforming splay faults in the active outer wedge domain suggests Cascadia megathrust events may commonly host distributed shallow rupture on multiple splay faults located within 30 km of the deformation front.

Complex drivers of geomorphic response and habitat formation revealed in multiyear monitoring of Cosumnes River experimental floodplain reconnection

In this study, we examine a novel levee breach experiment that reconnected a floodplain along the Cosumnes River, California to determine the decadal impact of removing 250 meters of levee and assess the recruitment of large wood. This is the latest study in an ongoing series of investigations 40 years in the making along the largest river on the western slope of the Sierra Nevada without a major dam. We present the findings of this multi-modal investigation here by first measuring the geomorphic alteration of the floodplain surface to quantify the depletion and accretion of sediment across the excavated site. We then identify and quantify the deposition of large wood. Results indicate initiation of anastomosing channel formation and distinct areas of large wood recruitment supporting a naturally evolving lateral levee. Accretion resulted in more than 25,000 m3 of sediment deposition within the original excavation site, the development of multiple sand splays, and natural recruitment of native riparian tree species. We conclude by discussing implications following other approaches to floodplain restoration as a Nature-based Solution. In episodic flow regimes, like in California’s Mediterranean-montane hydroclimatic regime, restoring lateral hydrologic connectivity facilitates ecosystem function. Large flood pulse events drive sediment dynamics and geomorphic heterogeneity while enriching biodiversity through biogeochemical fluxes and habitat creation on reconnected floodplains that store floodwaters and reduce peak discharge. These findings support the importance of long-term monitoring efforts of floodplain restoration.

Spatial and temporal variation in long-term sediment accumulation in a back-barrier salt marsh

In situ persistence of salt marshes in the face of sea-level rise relies on their ability to maintain substrate elevation through sufficient vertical accretion of sediment. However, sedimentation rates in salt marshes vary spatially and temporally, which complicates the assessment of their ability to keep up with sea-level rise. Here, we explore the spatial and temporal variation in sediment accumulation in a single back-barrier salt marsh site. Using one-time in situ measurements at the landscape scale, we obtained synoptic information of elevation and sediment thickness over the entire salt marsh in a chronosequence over centuries. Repeated measurements along short elevation transects (0.3–0.9 m +MHT) revealed decadal changes, complementing the broader marsh data with detailed information on elevation, thickness of the marsh deposits and accumulation rates. Thickness of the deposits was largely related to the elevation gradient: the sediment layer was thinner at the higher marsh (near the dunes and far away from the intertidal flats), and thicker at the lower marsh (near the intertidal flats). Moreover, the thickness of the layer increased with salt marsh age along the chronosequence, and age accounted for 72 % of variability in sediment accumulation. The rate of sediment accumulation was higher than the local rate of sea-level rise in the younger marsh, whereas it was equal to the rate of sea-level rise in the older marsh. In the older salt marsh, sediment accumulation was lower, possibly due to autocompaction in the thicker, older layers. Both at the landscape scale and along short elevation transects within individual drainage basins, sediment accumulation decreased with distance to sediment supply routes. However, their relative importance depended on the scale of observation. Distance to creeks accounted for 17 % of the variability in sediment accumulation at the landscape scale, compared to 4 % at the smaller scale. Similarly, the influence of distance to intertidal flats varied from 1 % at the landscape scale to 13 % at the smaller scale. Our main findings indicate that lower-elevation older marshes and higher-elevation younger marshes far away from sediment sources are at risk of not keeping pace with the local rate of sea-level rise and are potentially vulnerable to increased flooding.

Mangrove density and delta formation in Segara Anakan Lagoon as an impact of the riverine sedimentation rate

Abstract. Cahyo TN, Hartoko A, Muskananfola MR, Haeruddin, Hilmi E. 2024. Mangrove density and delta formation in Segara Anakan Lagoon as an impact of the riverine sedimentation rate. Biodiversitas 25: 1276-1285. Segara Anakan Lagoon (SAL) is in Southwestern of Central Java Province, Indonesia. The Western Part of SAL (WP-SAL) gets its sediment load from the Citanduy River. This research aimed to determine the temporal pattern of the shoreline, water body area, depth, delta formation, and mangrove density at WP-SAL. Shoreline data were extracted from a base map and the satellite imagery. Overlapping analysis of several shorelines and depth maps showed different results in terms of values or patterns. The western part of SAL had silted up and reached more than 85% in 161 years. The sediment accretion impacted the shoreline (between 177 ha yr-1 in 1999-2003), and the average decrease of the water bodies speed was 61 ha yr-1. The Pelawangan Barat waters (PBW) and the main lagoon had a decreasing depth because of the sediment deposits. The sedimentation also greatly impacts mangrove species distribution, clustering and association, and density and mangrove affinity. Mangrove density growth-based and the delta formation were formed and developed following the tidal pattern during floods and ebbs. It can be used to predict the future morphology of WP-SAL. The WP-SAL will be sediment filled and left the waterways channels, it was reached within 13.6 years from 2018, which would be in 2032.

Mangrove ecosystems’ role in climate change mitigation

Mangrove forests are crucial to ecosystems for their benefits, and role in climate change mitigation. Across marine and terrestrial boundaries, they shield coastal areas from tidal waves and storms, with dense roots that dissipate wave energy effectively. These roots also trap carbon-rich particles from the water, storing them in sediments and fostering sediment accretion and carbon burial. Mangrove ecosystems have declined over the past five decades, largely due to aquaculture. This decline reduces coastal resilience, exacerbating risks from storms, sea-level rise, and erosion, while releasing stored carbon as CO2 emissions. Mangrove degradation is crucial for climate mitigation. Mitigation strategies should prioritize conserving ecosystems with high carbon sequestration rates, reducing anthropogenic CO2 emissions, and rehabilitating mangrove habitats converted for aquaculture. We must expand our knowledge and understanding of the significance of mangroves in delivering coastal protection, how mangrove ecosystems serve as carbon sinks, how future changes could impact them, and how anthropogenic activities and climate change can impact their carbon storage.

System-scale dynamics of long-term sediment and phosphorus accumulation in contrasting valley-bottom wetlands in dryland landscapes of South Africa

Anthropogenic-induced acceleration of sediment and associated nutrients presents a serious challenge to water resource management across the globe. While wetlands are potential natural solutions, little is known of how well key wetland types attenuate downstream sediment fluxes and how these relate to local- and catchment-scale factors. This research aimed to develop an understanding of patterns and rates of sediment and phosphorus retention in valley-bottom wetlands in South Africa. The geomorphology, sedimentology and historical accretion rates of three wetlands which offered diversity in size, catchment position and degree of organic accumulation were compared to ascertain the impact of local- and catchment-scale factors. Estimates of sediment and associated phosphorus accumulation suggest higher rates in clastic sediment-dominated wetlands (1089–7655 g sediment m−2 yr−1, 0.4–1.6 g-P m−2 yr−1) compared to an organic sediment-dominated system (601–1308 g-sediment m−2 yr−1, 0.2–0.3 g-P m−2 yr−1). Sediment accretion rates generally increased longitudinally, indicating that distal wetland reaches act as sediment and phosphorus retention hotspots. Phosphorus distribution patterns were primarily attributed to variations in organic matter content and associated aluminium and iron complexing agents in fine-grained sediment deposits, while particle size distributions were less important. However, the relevance of individual complexing agents in phosphorus dynamics varied among wetlands with differing landscape conditions. Contrasts between these systems reflect variations in catchment lithology and hydroclimatic regime, which influence the relative magnitude of sediment supply and vegetation productivity. We postulate that intermediate-sized wetlands characterised by catchments around 900 ha in size, gentle longitudinal slopes (∼2 %), a high proportion of fine sediment deposition, limited organic matter breakdown, and a long vegetation growing season provide optimal conditions for sediment and phosphorus accumulation. This system-scale information is essential to guide management decisions to identify and prioritize within-catchment ‘hotspots’ of sediment and phosphorus retention.

Machine Learning Predictions of Vertical Accretion in the Mississippi River Deltaic Plain

AbstractDeltaic landscapes consist of vast wetland systems that rely on sedimentation to maintain their elevation and ecological communities against relative sea‐level rise. In the Mississippi River Deltaic plain, rising relative sea level and anthropogenic activities are causing land loss that will continue unless vertical accretion of sediment on the wetland surface is enough to fill the accommodation space. Even though the fate of the Mississippi Deltaic plain is tied directly to vertical accretion, there is not yet a clear understanding of the system‐wide controls on this process. Here, we investigate vertical accretion in coastal Louisiana using a data set of 266 stations from the Coastwide Reference Monitoring System (CRMS). Using linear regression models, we analyze vertical accretion in freshwater‐intermediate, brackish, and saline marsh communities. Integrating results from these models into a Gaussian Process regression model, we predict controls on vertical accretion rates across the deltaic plain. Consistent with previous studies, our results suggest that tidal amplitude and flood depth are critical controls on vertical accretion. These effects are additive and marshes with high tidal amplitudes and flood depths experience the most vertical accretion. Interestingly, the normalized difference vegetation index is found to be important for predicting vertical accretion, but not because of an increase in biomass production, but because it records unique marsh communities and flooding regimes. This study emphasizes the importance of incorporating marsh specific information into predictive models for the vertical accretion of coastal wetlands and that better predictions of wetland accretion probably require denser observational data.

Influence of outer-rise faults on shallow décollement heterogeneity and sediment flux at the Japan trench

We investigate the impact of outer-rise normal fault subduction on the structural evolution of the décollement and frontal prism in a portion of the Japan trench that hosted the 2011 Tohoku earthquake. We use seismic reflection data to map the relative occurrence of sediment accretion, sediment subduction, and frontal tectonic erosion in the shallow portion of the subduction zone and correlate these deformation styles to the magnitude of outer-rise fault throw and incoming plate sediment thickness. These data reveal spatial heterogeneity in the modes of deformation over distances of 5-10 km that necessitate correlative heterogeneity in the geometry and composition of the shallow décollement over similar length-scales. We find that sediment accretion predominantly occurs in regions where incoming plate sediment thickness is greater than fault throw. In these areas, the décollement appears to be non-planar and compositionally homogenous. Conversely, frontal tectonic erosion and slope failures are predominantly observed in regions where fault throw is greater than sediment thickness. In these areas, the décollement may be planar but compositionally heterogeneous. Additionally, spatial variations in near trench slip appear to correlate with the dominant deformation modes, suggesting that both sediment thickness and outer-rise fault throw may be important controls on shallow megathrust behavior.

Investigation of the effects of small fishing ports on the shoreline: a case study of Samsun, Turkey

Shoreline change analysis is crucial for identifying coastal issues and understanding their underlying causes. This study focuses on investigating the coastal impacts of the Derekoy Fishing Port in Samsun, a city located on the Black Sea coast of Turkey. Temporal changes between 1984 and 2021 were analyzed using Landsat-5 TM/Landsat-8 OLI satellite images in conjunction with image processing and geographic information systems (GIS). Net shoreline movement (NSM), shoreline change envelope (SCE), end point rate (EPR), and linear regression rate (LRR) methods were used to investigate the changes in the shoreline. Polygon overlay analysis was utilized to determine the areas of erosion and accretion. The results indicate that prior to the port's construction, the coast remained relatively stable during the period of 1984–1995. However, sediment accretion occurred on the updrift side of the port, while erosion intensified on the downdrift side during the port's construction from 1995 to 2004. Despite the implementation of coastal protection structures to combat erosion, complete prevention was not achieved, and erosion shifted further eastward. Throughout 1984–2021, approximately 15.62 hectares of beaches were lost due to erosion, with a maximum value of -56.2 m recorded. The coastal erosion and the construction of coastal protection structures have disturbed coastal morphology and resulted in various environmental and socio-economic issues along the 19 Mayis and Atakum beaches. This study reveals the significant consequences of a small fishing port built without proper planning and adequate precautions, drawing attention to the problems.