Coastal Systems Research Articles

Urbanisation and boating are the main contributors to underwater soundscapes in three temperate estuaries

Anthropogenic noise has been identified as one of the most harmful forms of global pollutants impacting both terrestrial and aquatic ecosystems. As global populations continue to increase, coastlines are seeing substantial increases in the level of urbanisation. Although measures are in place to minimise stress on fauna, they rarely consider the impact of anthropogenic noise. In Australia, New South Wales (NSW) estuaries have seen extensive increases in urbanisation in recent years. Yet, there remains minimal baseline data on their soundscapes to determine if noise pollution is a threat. This research provides a first assessment of baseline sounds across a temporal and seasonal scale. Recreational boating was the primary soundscape contributor in estuaries, and estuaries with higher urbanisation levels contained higher sound levels. This research provides useful information for managers of NSW estuaries and is of global relevance in an era of increasing generation of anthropogenic noise in estuarine and coastal systems.

Removing development incentives in risky areas promotes climate adaptation

As natural disasters grow in frequency and intensity with climate change, limiting the populations and properties in harm’s way will be key to adaptation. This study evaluates one approach to discouraging development in risky areas—eliminating public incentives for development, such as infrastructure investments, disaster assistance and federal flood insurance. Using machine learning and matching techniques, we examine the Coastal Barrier Resources System (CBRS), a set of lands where these federal incentives have been removed. We find that the policy leads to lower development densities inside designated areas, increases development in neighbouring areas, reduces flood damages and alters local demographics. Our results suggest that the CBRS generates substantial savings for the federal government by reducing flood claims in the National Flood Insurance Program, while increasing the property tax base in coastal counties.

Birds influence vegetation coverage and structure on sandy biogeomorphic islands in the Dutch Wadden Sea

Small uninhabited islands form important roosting and breeding habitats for many coastal birds. Previous studies have demonstrated that guano can promote ecosystem productivity and functionality on island ecosystems. Here, we assess the role of external nutrient input by coastal birds on the vegetation structure and coverage on sandy biogeomorphic islands, where island-forming processes depend on vegetation-sedimentation feedbacks. As a first step, we investigated whether breeding birds affect vegetation productivity on sandy back-barrier islands in the Wadden Sea. Using a combination of bird observations and plant stable isotope (δ15N) analyses, we demonstrate that (i) breeding birds transport large quantities of nutrients via their faecal outputs to these islands annually and that (ii) this external nitrogen source influences vegetation development on these sandy, nutrient-limited, islands. Based on these results we discuss how this avian nutrient pump could impact island development and habitat suitability for coastal birds and discuss future directions for research. In general, we conclude that avian subsidies have the potential to affect both the ecological and biogeomorphic functioning of coastal soft-sediment systems. However, the strength and scale of especially these biogeomorphic interactions are not fully understood. For the conservation of both threatened coastal birds and sandy back-barrier islands and the design of appropriate management strategies, we argue that three-way interactions between birds, vegetation and sandy island morphodynamics need to be further elucidated.

Examining hydro-morphological modulations in proximity to a drain's estuarine outlet, case study: Kitchener Drain, Northern Coast of Egypt

In recent years, the Kitchener Drain has been affected by littoral erosion and sedimentation at the estuary where its discharge enters the Mediterranean Sea. Several measures have been taken to mitigate the impact of these problems. From 1993 to 2007, four stages of hard protection work were finished, including the construction of groins and detached breakwaters along the drain's eastern and western shores. Work on these projects began in 1992. At the drain outlet, dredging works are still proceeding. Nevertheless, shoreline instability continues even after these efforts. The Coastal Modelling System (CMS) was used to figure out what effect the ongoing hard work had on the erosion and accretion hot spot near the drain's output. The CMS-flow and CMS-wave steering modules are part of the CMS, a two-dimensional model of hydrodynamic circulation. To begin mitigating this effect, we ran the simulation beginning in 2012 and experimented with different calibration settings. After the calibration phase, the research area was subsequently simulated for five years. This study aims to assess the current state of affairs concerning the stabilization of the outflow sedimentation process and the erosion that is taking place on the eastern and western sides. In addition to that, we offered alternate structural modulation scenarios that incorporate both hard and soft structures. We looked at plenty of different possibilities. The scenario with the 600-meter-long jetty and sand nourishment was the most similar to the original coastal characteristics. Regarding a sediment reduction to ‐5706.99 m3 from ‐15321.70 m3 (at benchmark) computed at the outlet zone, this scenario was the most similar to the shoreline's initial appearance. Reducing sediment from ‐133433 m3 (at benchmark) to ‐114512 m3 was also achieved on the western side. Despite this, it was determined that the stability of the coastline would be influenced subtly by this circumstance.

Neoproterozoic transition from subduction to breakup along the margin of the Rodinia supercontinent: Sedimentary evidence from the northwestern Tarim Block, Northwest China

The Tarim Block, northwest China, was positioned on the periphery of Rodinia during the Neoproterozoic Era, and preserves a geological archive chronicling the assembly and breakup of the supercontinent. Due to its antiquity and limited exposure, sedimentary records along the margin of the Rodinia supercontinent remain sparsely documented. This study focuses on the Xifangshan and Dongqiaoenbrak formations, the oldest sedimentary units in the northwestern Tarim Block, which comprise a Neoproterozoic sedimentary record at the supercontinent margin during the transition from subduction to breakup. A comprehensive analysis employing sedimentology, petrology, elemental geochemistry, and UPb detrital zircon chronology was undertaken, to elucidate paleoenvironment, parent rocks, and tectonic-sedimentary evolution. Findings show that the Neoproterozoic witnessed the subduction of an oceanic plate beneath the Tarim Block, resulting in the formation of a continental margin magmatic arc. The Xifangshan Formation, deposited during the late phase of this arc (with the earliest sedimentary age recorded at 770 Ma), represents a submarine fan dominated by turbidity currents. Around 760 Ma, rapid crustal uplift occurred, and the tectonic setting gradually shifted from subduction to rift, giving rise to the coastal alluvial fan sedimentary system observed in the Dongqiaoenbrak Formation. Both the Xifangshan and Dongqiaoenbrak Formations record deposition in an oxic to suboxic marine environment with moderate salinity, influenced by a semiarid to semihumid palaeoclimate. The continental margin arc served as the primary source for sedimentation in both formations, and a few magmatic products linked to extension (syenite, monzonite) were also cannibalized into the sedimentary system of Dongqiaoenbrak Formation. This transition from a turbidite system to a coastal alluvial fan represents a sedimentary response to the subduction-to-breakup dynamics along the margin of the Rodinia supercontinent.

The Contribution of Mesoscale Convective Systems to the Coastal Rainfall Maximum over West Africa

Abstract This study examines the behaviors of coastal mesoscale convective systems (MCSs) to understand why the maximum climatological rainfall appears offshore of West Africa using satellite measurements. West Africa has a higher amount of rainfall offshore than inland during the monsoon season, but the reason for this offshore rainfall maximum remains unclear. MCSs that propagate offshore from coastal West Africa can develop into high-impact weather events in the eastern Atlantic, yet we know little about the MCS transitions across coastlines. Therefore, better understanding of how MCSs evolve during the coastal-to-maritime transition and contribute to the offshore climatological rainfall maximum over West Africa is key to advancing the knowledge of high-impact weather in this coastal region. The offshore rainfall can be contributed by either offshore-propagating MCSs generated over land or the MCSs initiated over the ocean. While continental MCSs are known to have more intense deep convection, their frequency of propagating offshore is found to be small. Instead, we find that the offshore environment supports the frequent formation of maritime MCSs, leading to their dominant contribution to offshore rainfall. However, an exception is found for the 8°–10°N offshore area, where the presence of high terrain generates MCSs with intense rainfall that more frequently propagate offshore and enhance offshore rainfall. These MCSs also often intensify their rainfall and expand in size as they move offshore. These results suggest that understanding the frequency, intensity, and transition of MCS generated over land and the ocean is key to better comprehending and simulating the rainfall activity over the coastal-to-marine transition zone.

Understanding Climate Change and Anthropogenic Impacts on the Salinization of Low‐Lying Coastal Groundwater Systems

AbstractFresh coastal groundwater is a valuable water resource of global significance, but its quality is threatened by saltwater intrusion. Excessive groundwater abstraction, sea‐level rise (SLR), land subsidence and other climate‐related factors are expected to accelerate this process in the future. The objective of this study is to (a) quantify the impact of projected climate change and (b) explore the role of individual hydrogeological boundaries on groundwater salinization of low‐lying coastal groundwater systems until 2100 CE. We employ numerical density‐dependent groundwater flow and salt transport modeling for this purpose, using Northwestern Germany as a case. Separate model variants are constructed and forced with climate data, that is, projected SLR and groundwater recharge, as well as likely ranges of other hydrogeological boundaries, including land subsidence, abstraction rates and drain levels. We find that autonomous salinization in the marsh areas, resulting from non‐equilibrium of the present‐day groundwater salinity distribution with current boundary conditions, is responsible for >50% of the salinization increase until 2100 CE. Sea‐level rise, land subsidence and drain levels are the other major factors controlling salinization. We further show that salinization of the water resources is a potential threat to coastal water users, including water suppliers and the agrarian sector, as well as coastal ecosystems. Regional‐scale uplifting of drain levels is identified as an efficient measure to mitigate salinization of deep and shallow groundwater in the future. The presented modeling approach highlights the consequences of climate change and anthropogenic impacts for coastal salinization, supporting the timely development of mitigation strategies.

Effects of groundwater pumping on pore water flow and salt transport in tide‐controlled unconfined coastal aquifers

AbstractUnconfined coastal aquifers are a main pathway for land‐sourced solutes to enter the oceans. The migration of these solutes in aquifers is highly affected by the groundwater flow and salt transport processes, which are, to a great extent, controlled by tides. While many studies have examined how tidal oscillations would influence the subsurface hydrodynamics in coastal aquifers, most of them ignored the potential impact of groundwater pumping, a common practice in coastal areas to satisfy the demand for freshwater. This study, by means of laboratory experiments and numerical simulations, explored the combined effects of tides and groundwater pumping on the pore water flow and salinity distributions in an unconfined coastal aquifer. The results show that, in a tide‐controlled aquifer, the addition of groundwater pumping would exacerbate the degree of seawater intrusion and lead to wider spreading and deeper penetration of the upper saline plume. Moreover, groundwater pumping would enhance the tide‐driven circulation in the upper saline plume and weaken the density‐driven circulation in the saltwater wedge, ultimately leading to the reduction in total submarine groundwater discharge. These findings may promote a deep insight into the complex coastal groundwater systems experiencing human activities, and provide guidance for better evaluating the environmental impact of groundwater pumping.

Geochemistry of coastal geothermal systems from southern Baja California peninsula (Mexico): Fluid origins, water-rock interaction and tectonics

The Baja California peninsula forms the western margin of the Gulf of California (GC) rift system, which is an active tectonic setting manifested by seismicity and numerous geothermal sites. The present study examines the geochemistry of thermal fluids (major ions and gas species, δ18O-δD, δ13C, 3He/4He) from the southern tip of the peninsula (Los Cabos Block, LCB). Sampling was mostly focused on the coastal thermal manifestations in the towns of Buenavista and El Sargento, but other sites further inland are also included for broadening the scope of the study. The main objectives include: (i) characterize water-rock interactions and other processes controlling the fluid composition, (ii) constrain solute geothermometry estimates through multi-step geochemical modeling, and (iii) discuss the fluid origins in terms of tectonics and regional shear-wave velocity anomalies in the upper lithosphere. The geothermal systems in the area have a tectonic origin and result from fluid circulation along regional faults that penetrate the upper crust through the granitic basement. Mixing between the thermal fluids and seawater at the coast is clearly illustrated through major ions and δ18O-δD relationships. Reconstruction of the pre-mixing chemical compositions indicates a low-salinity fluid at Buenavista (Cl = 104–109 mg L−1) and a saline fluid at El Sargento (Cl = 7169 mg L−1). The geochemical modeling allows us to validate these endmember compositions and to address a common issue when using solute geothermometry, which is the uncertainty on the state of equilibrium of the thermal fluid with respect to wall-rock minerals. The corresponding results reveal contrasting thermal regimes at depths (Buenavista: 101–122 °C, El Sargento: 212–220 °C), likely associated with differences in geothermal gradient and fluid circulation depth. Our gas samples have among the lowest He isotopic ratios (0.07–0.95 Ra) in the Baja California peninsula, indicating that the origin of helium is mainly crustal. Shear wave tomography demonstrates that the study area is associated with two low velocity regions, one in the crust and the other one in the upper mantle. Our results favor the hypothesis that the heating of fluids is produced by lower-crustal flow driven by strong topographic gradients along the rifted margin. This study provides new insights into the origin of the thermal anomalies in the LCB and the adjacent GC rift system.

Defining an exposure index along the Schleswig-Holstein Baltic Sea coast

A wind exposure index (EI), which indicates the main physical driver of a coastal system, was developed along the Schleswig-Holstein Baltic Sea (SH) coast – Germany, to demonstrate the highly dynamic coastal stretches (i.e., potential erosion hotspots). The approach used three steps to define more accurate EIs. Initially, a representative wind year (RWY), which has similar physical characteristics as in the long-term data, was defined by analysing measured wind data from 2000 to 2019 at four stations distributed in the entire area of interest. The RWY was identified by a statistical comparison of wind speeds in 5 classes and 36 directional sectors between summer to summer yearly wind and the overall data. The selected RWY spanned from 01.09.2016 to 31.08.2017 and showed a reasonable agreement with the overall data (Skill = 0.77 and rmsd = 0.56 m/s). Next, high spatiotemporal nearshore hydrodynamics over the RWY were predicted using a model nesting approach of two domains in Delft3D. The predicted nearshore hydrodynamics indicated fair agreements with the measured data (R2: 0.87–0.90 for water levels and 0.75–0.86 for wave heights). Finally, the predicted water level and wave height time series in the nearshore area (∼ 5 m MSL depth) were used for the analysis of the EI adopting a 2-step procedure capturing short- and long-term correlations as well as seasonal long-range dependencies of the time series. This approach allows to model the clustering behaviour of extreme values of both parameters and provides reasonable EIs along the SH coast. The exposed areas display high EIs (e.g., 1 at the east of Fehmarn), while sheltered areas and bays have low values (e.g., 0 at Eckernförde Bay). The higher the EI the stronger the coastal dynamics and thus strong erosion can be expected. Interestingly, the EI varies considerably even along the exposed coastal stretches with long fetches, which indicates the sensitivity of the EI to the local morphology, which determines the nearshore hydrodynamics. Therefore, a definition of the EI based on nearshore hydrodynamics provides an accurate index of local physical drivers of a coastal system. The developed approach can be adopted to any coast, and provides useful information on the potential erosion areas for the coastal managers.

Nuclear and Radiological Material Smuggling in the Indian Ocean: Implications for India’s Coastal Security

Incidents of nuclear and radiological smuggling in the Indian Ocean are a matter of concern. Attempts to smuggle nuclear material within India have also been reported as recently as 2021. Indian security agencies previously have also seized natural uranium in coastal states such as Gujarat, Maharashtra and Bengal indicating how vulnerable the Indian coast is to radiological and nuclear smuggling. The Nuclear Security Index has also consistently ranked India below China and Pakistan despite their poor record on nuclear non-proliferation. These facts highlight concerns regarding the possible misuse of nuclear and radiological material by criminal and terrorist networks. Since India is targeted by terrorist groups and lies in the vicinity of countries and routes that see frequent nuclear and radiological trafficking, there are inevitable implications for the Indian coastal security system. This article identifies and analyses these security implications and argues for a beefing up of India’s coastal security.

PRECIPITATION DATA FROM GOOGLE EARTH ENGINE (GEE) IN REVETMENT DRAINAGE EVALUATION IN KALIANDA

Floods can occur frequently if there are no organized and constant changes in land use. Flood issues in Waymuli, South Lampung, has been occurring due to changes in land use in the area. Prior studies regarding drainage of coastal revetments may have been done before. However, the analysis was done using precipitation data from GEE and therefore, new findings as the solution for the flood problems in the region were necessary. The main objective of this research is to assess the extent of success of drainage system management using rainfall information obtained via GEE. The method used was by evaluating the capability of the drainage system using data from GEE, which involve identifying and measuring the drainage capacity with the HEC-RAS application. This study conclude that the use of GEE can be accurately used to evaluate revetment drainage. Rainfall in the last two years were 54.0340 mm, 81.8905 mm in the last five years, and 104.0784 mm in the last ten years. However, GEE results show that the highest rainfall recorded in September 2022 was 46.857 mm. Based on the HEC-RAS evaluation, it was also found that the drainage system does not have the capacity to drain rain within a 2-year period. It can be concluded that the function of the drainage system in this area is to support the coastal revetment system, not as the main drainage system.

Hydrodynamic and turbulence associated with tidal bore propagation in an amazonian macrotidal system

The study analyzed the hydrodynamic and turbulence characteristics of the Tidal Bore (TB) associated with Sucuriju River Coastal System (SRCS), a macrotidal estuarine system located north of the Amazon River mouth. Two points were sampled using ADCP at a frequency of 0.5 Hz for 13 hours, one at the mouth (P1) and the other upstream (P2). The Tidal Gauge (TG) located at the mouth collected tidal data continuously for three months at a 30-second rate. The instantaneous hydraulic jump velocities (HJ) and the hydraulic jump resultant (HJRES) were calculated for TG. The Tidal Bore Froude Number (Fr), Turbulent Kinect Energy – TKE (q2/2), TKE Production (Pτ), Reynolds stress (τx and τy), and Quantity S were calculated for P1 and P2. Over 70 TB occurrences were identified during spring tides, with the highest HJRES of 2.23 observed in March. The U̅ component showed greater results during ebb tide, reaching 1.48 and 1.00 m s−1 for P1 and P2 respectively, with a rapid current inflow associated with TB. The highest TKE and Reynolds stress parameters were observed during ebb tide, with TKE reaching up to 1.80 J m−3 in P1 and 1.12 J m−3 in P2. After the TB these values decreased to almost zero, resulting in lower energy associate with a rapid increase in water level, indicates a transition from supercritical (Fr>1) to subcritical flow (Fr<1). Based on the Fr value, the TB showed characteristics of a Weak Breaking Tidal Bore / Breaking Bore in P1 (1.2 or 1.3 < Fr < 1.5), and Cross waves / shock waves / undular bore for P2 (1.0 < Fr < 1.2 or 1.3).

Analysis of the spatial evolution of coastal defense patterns in the Ming Dynasty based on long-time-series Wokou invasions (Zhejiang)

As a famous coastal defense heritage in the world’s military history, the maritime defense heritage of China’s Ming Dynasty represents the highest achievement of China’s ancient coastal military defense. There is a relative lack of holistic research on this defense system from its establishment to stabilization. Additionally, there is a lack of comparative research on the combination of Wokou invasions and defense patterns from a spatio-temporal perspective. The study aims to offer insights into the temporal and spatial evolution of ancient military defense heritage and investigate the significance of Ming Dynasty coastal defense. This study focuses on Zhejiang, a key coastal defense during the Ming Dynasty. Using GIS tools, it analyzes the spatio-temporal evolution characteristics of Wokou invasions and defense mode in the process of Zhejiang coastal defense from its establishment to its perfection by using GIS analytical tools, and explores the driving factors of the dynamic adjustment of this coastal defense system. The results show that: (1) Hongwu 1 to 31 (1368–1398) witnessed the construction of a 12-area defense system, encompassing Wei and Suo citadels. This followed a multi-point defense strategy, with Wei citadels controlling the coastline and Suo citadels supporting them; (2) Hongwu to Wanli (1368–1588) saw the evolution of five defense modes, evolving from decentralized to centralized and then to a coexistence of both. This culminated in the establishment of 4–6 Defense Mode (4 Canjiang and 6 Bazong); (3) the evolution of the defense paradigm is largely driven by Wokou incursions and is an adaptation from small-scale, short-duration infestations to large-scale, long-duration infestations. The findings show that the Ming Dynasty’s coastal defense system in China was flexible and adaptive, evolving to meet changing defense needs.

Groundwater level fluctuation caused by tide and groundwater pumping in coastal multi-layer aquifer system

This paper considered the groundwater head fluctuation induced by tide and pumping in the coastal multi-layered aquifer system. The multi-layered aquifer system comprises an unconfined aquifer, an upper confined aquifer, and a lower confined aquifer. An aquiclude exists between each two aquifers. All the layers terminate at the coastline. The new analytical solutions describing groundwater head variation in the coastal multi-confined aquifer system are derived. Superposition principle and image methods are used for the derivation of the analytical solutions. Analytical solutions of different situations of without considering pumping, of without considering tidal effect, and of N-layered confined aquifers are also derived. The impacts of the parameters of the initial phase shift of tide, pumping rate, position of the pumping well, storage coefficient, and transmissivity on the groundwater head fluctuation are discussed. The analytical solutions are applied with application examples in fitting field observations and parameter estimations. The estimated values of the hydraulic conductivities in the upper and lower confined aquifers are within the range of the values obtained from the field experiments. The fitted results of the analytical solutions capture the main characteristics of groundwater head fluctuation affected by the tide and groundwater pumping. The study of groundwater head fluctuation in the coastal zone is helpful to understand the mechanism of seawater intrusion under the influence of tide and groundwater pumping.

Effects of Diel Oxygen Cycling and Benthic Macrofauna on Sediment Oxygen Demand

This field study examined how sediment macroinfauna change patterns of sediment oxygen demand (SOD) throughout a diel oxygen cycle. Sediments with a greater faunal presence would be expected to have greater overall SOD, and at night may alter their behavior and influence SOD depending on their response to low-oxygen stress. Dynamic faunal bioturbation or bioirrigation behavior would also result in corresponding variation in SOD values on short time scales. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. Sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. Where more macroinfauna were present, they drove greater SOD during nightly low oxygen, presumably by enhancing their burrowing and irrigation activities. SOD was also more variable on a sub-diel timescale in sediments with more macroinfauna. Sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna, and their interaction produces heretofore unaccounted complexity in patterns of SOD particularly in shallow coastal systems. Extrapolations of temporally and spatially limited SOD measurements to a system-wide scale that do not account for the short-term and spatially variable effects of fauna may produce imprecise and misleading estimates of this critical ecosystem function.

Spatiotemporal changes of pelagic food webs investigated by environmental DNA metabarcoding and connectivity analysis.

Environmental DNA metabarcoding (eDNA metaB) is fundamental for monitoring marine biodiversity and its spread in coastal ecosystems. We applied eDNA metaB to seawater samples to investigate the spatiotemporal variability of plankton and small pelagic fish, comparing sites with different environmental conditions across a coast-to-offshore gradient at river mouths along the Campania coast (Italy) over 2 years (2020-2021). We found a marked seasonality in the planktonic community at the regional scale, likely owing to the hydrodynamic connection among sampling sites, which was derived from numerical simulations. Nonetheless, spatial variability among plankton communities was detected during summer. Overall, slight changes in plankton and fish composition resulted in the potential reorganization of the pelagic food web at the local scale. This work supports the utility of eDNA metaB in combination with hydrodynamic modelling to study marine biodiversity in the water column of coastal systems. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Phytoplankton Diversity, Spatial Patterns, and Photosynthetic Characteristics Under Environmental Gradients and Anthropogenic Influence in the Pearl River Estuary.

The Pearl River Estuary (PRE) is one of the world's most urbanized subtropical coastal systems. It presents a typical environmental gradient suitable for studying estuarine phytoplankton communities' dynamics and photosynthetic physiology. In September 2018, the maximum photochemical quantum yield (Fv/Fm) of phytoplankton in different salinity habitats of PRE (oceanic, estuarine, and freshwater zones) was studied, revealing a complex correlation with the environment. Fv/Fm of phytoplankton ranged from 0.16 to 0.45, with taxa in the upper Lingdingyang found to be more stressed. Community composition and structure were analyzed using 18S rRNA, accompanied by a pigment analysis utilized as a supplementary method. Nonmetric multidimensional scaling analysis indicated differences in the phytoplankton spatial distribution along the estuarine gradients. Specificity-occupancy plots identified different specialist taxa for each salinity habitat. Dinophyta and Haptophyta were the predominant taxa in oceanic areas, while Chlorophyta and Cryptophyta dominated freshwater. Bacillariophyta prevailed across all salinity gradients. Canonical correlation analysis and Mantel tests revealed that temperature, salinity, and elevated nutrient levels (i.e., NO3--N, PO43--P, and SiO32--Si) associated with anthropogenic activities significantly influenced the heterogeneity of community structure. The spatial distribution of phytoplankton, along with in situ photosynthetic characteristics, serves as a foundational basis to access estuarine primary productivity, as well as community function and ecosystem health.

The regulation pathways of biochar and microorganism in soil-plant system by multiple statistical methods: The forms of carbon participation in coastal wetlands

Coastal wetlands possess significant carbon storage capabilities. However, in coastal soil-plant systems augmented with biochar and microorganisms, the mechanisms of these amendments and carbon participation remain unclear. This study utilized pot experiments to explore how Enteromorpha prolifera biochar and Arbuscular mycorrhizal fungi (AMF) affect soil organic carbon (SOC), carbon-related microbes, photosynthetic and osmotic system of Suaeda salsa. The results showed biochar reduced exchangeable sodium percentage by 6.9% through adsorption and ion exchange, and increased SOC content by 34.4%. The abundance of carbon-related microorganisms (Bacteroidota and Chloroflexi) was increased and carbon metabolizing enzyme (cellulase and sucrase) activity in the soil was enhanced. AMF significantly improved plant growth compared with CK, as evidenced by the enhanced dry weight by 2.34 times. A partial least squares pathway model (PLS-PM) and correlation analysis suggested that the combined effect of biochar and AMF could be outlined as two pathways: soil and plant. Biochar increased SOC, improved the growth of soil carbon metabolizing microorganisms, and further promoted the activity of carbon-related enzymes. Additionally, AMF facilitated nutrient absorption by plants through root symbiosis, with biochar further enhancing this process by acting as a nutrient adsorber. These combined effects of biochar and AMF at soil and plant level enhanced the photosynthetic process of Suaeda salsa. The transport of photosynthetic products to the roots can increase the carbon storage in the soil. This study provides quantitative evidence supporting the increase of carbon storage in coastal wetland soil-plant systems through a combined application of biochar and AMF.

Impact evaluation of development plans in the Egyptian harbors on morphological changes using numerical simulation (case study: Damietta harbor, northeastern coast of Egypt)

The Egyptian government is grappling with the challenge of sedimentation in Damietta Harbor (DH), leading to expensive and recurring dredging operations for safe vessel navigation. This research examined the changes in the region's coastline, both before and after the port was established between 1977 and 1995. The impact of the government's policy to halt backfilling in the navigation lane on adjacent beaches until 2023 was also assessed using remote sensing (RS) and the Digital Shoreline Analysis System (DSAS) program, revealing varying yearly accretion and erosion rates. Following a shoreline movement tracking procedure, in the period from 1985 to 2023, the total areas undergoing erosion and accretion amounted to −1.36 km2 and +2.21 km2, respectively.To address the issue, the research team developed scenarios reflecting regional realities and conducted a numerical simulation using the Coastal Modeling System (CMS). Morphological alterations in the approach channel and pre- and post-port regions were monitored to assess the scenarios. The study also explored how deepening the navigation channel affected the annual sediment volume. Results showed that Scenario 5, involving breakwaters extension and the new western breakwater (NWBW), effectively controlled sediment. However, sedimentation increased with the deepening of the navigation channel. Scenario 7, with a 19 m deepening, exhibited slightly higher sediment volume by 21.75% but stood out for its capacity to handle large vessels. Additionally, the sedimentation in the navigation channel experienced a notable 72.1% decrease in Scenario 8, which portrays the anticipated final state of DH compared to the benchmark case.The study noted morphological changes from planned coastal constructions on the eastern side, including detached breakwaters (DBW) and Y-groins (Y-gs). Despite significant development costs, these structures were deemed insufficient to stabilize the shoreline. In summary, the research highlights the complexity of addressing sedimentation in DH, emphasizing the need for nuanced approaches in coastal management, and considering the consequences of deepening navigation channels.