Depth Distribution Patterns Research Articles

Fluctuations in abundance of the striped venus clam Chamelea gallina in the southern Adriatic Sea (Central Mediterranean Sea): knowledge, gaps and insights for ecosystem-based fishery management

An assessment on the fluctuations in abundance of the striped venus clam (Chamelea gallina) in the southern Adriatic Sea (Central Mediterranean Sea), and the northern Gargano area, has been conducted through both historical information and recent data from monitoring surveys during the period 1997–2019. Production trends, conditions of the commercial stock biomass, and depth distribution pattern of juveniles and commercial sizes were analysed testing temporal differences. Moreover, the exploitation of the clam beds and recruitment events were investigated in 2018–2019. Changes in abundance were analysed using non-parametric tests for both juvenile (length class, LC < 22 mm) and commercial (LC ≥ 22 mm) fractions. Hydrodynamic changes, temperature and salinity variations were explored using a 3D hydrodynamic numerical model (MIKE 3 FM-HD) and statistical analysis, as well as changes in benthic assemblages impacted by hydraulic dredges were investigated through PERMANOVA and other multivariate analysis.The results showed a temporal decline of production and biomass of C. gallina during the 1997–2019 period, and a regression of the depth limit in the clams’ distribution towards shallower waters. A significant reduction in juveniles was observed during 2018–2019 with a very limited recruitment. The fishing exploitation showed high impacts on the commercial stock and benthic assemblages in the summer of 2018. Overall, water currents were predominantly directed offshore in 2018, during the C. gallina spawning period. This could affect the larval dispersal and settlement on unsuitable bottoms. Anomalies in temperature (high peaks in August 2018, > 28 °C) and salinity (low values in spring 2018, < 37 PSU) could have induced stress and mortality events on the entire clam bed in the study area. This first study highlights the need to integrate environmental information in the assessment of commercial stocks of clams in the Adriatic Sea, to better understand climate change effects on the fluctuations and to support effective ecosystem-based fishery management.

Insights into swordfish (Xiphias gladius) movement patterns and habitat utilization off the coast of northern Chile

This study reports on the fine-scale movements of swordfish (Xiphias gladius) tagged off of the Antofagasta region of northern Chile, where harpoon fishing operations date back more than seven millenia. The study was conducted within a highly productive swordfish foraging area where movements and habitat use remain poorly characterized. Swordfish were outfitted with both data storage and satellite-linked archival tags scheduled for short (&lt;30 days) and longer-term (&gt;100 days) data collection. All tags were deployed on basking swordfish using harpoon-based methods across two field seasons in March 2019 and April 2022 around oceanic fronts and offshore seamounts. Fine-scale depth and temperature data were recorded over 145 days from four adult swordfish (100-200 kg). Swordfish exhibited regionally unique diurnal behaviors with greater average daytime depths than those recorded at night (78.0 ± 66.5 and 12.7 ± 4.9 m, respectively). The average daytime depths were shallower than those previously documented for other Pacific regions, including Chile's offshore waters. Daytime basking was observed on 76% of the daily records (110 out of 145 days) and accounted for approximately 12% of the collective daylight hours. Findings align with previous swordfish tagging studies and suggest that depth distribution patterns vary considerably depending on regional oceanographic conditions. Movement data are compared with previous studies, and we discussed relative to regional fishing operations.

Kinetic reactive transport explains distinct subsurface deposition patterns of pollutants in sediments. The case of the Sellafield-derived 236U, 137Cs and 239,240Pu in the Esk Estuary, UK

The kinetics of the uptake of pollutants by solids in sediments interacts with transitional eddy diffusivity in the pore fluid, leading to different depth-distribution patterns. This work aims to gain insights into the still poorly understood behaviour in the marine environment of the anthropogenic 236U, a recently postulated tracer of water masses. It is hypothesized that the transition from mobile U(VI) to highly particle-reactive U(IV) in the anoxic zone of the sediment produces a subsurface deposition pattern. A novel numerical model for kinetic reactive transport in sediments, which merges diagenetic processes for transport and box models for the uptake, is used for concept demonstration. It is applied to synthetic environments with high eddy diffusivity to obtain the singular depth-distribution patterns of pulsed inputs of tracers that mimic the anthropogenic 239,240Pu, 137Cs, and 236U. While the first is retained in the upper cm, the second shows an exponential penetration pattern over few cm, and 236U is deposited with a Gaussian-like pattern centred below the transition to the anoxic zone. These patterns are then merged into a diagenetic model to compute the depth distribution at decadal or centennial scales of dissolved and particle-bound inputs of these radiotracers. It is successfully applied to a real case using literature data for a sediment core from the Esk Estuary, UK, affected by radioactive releases from the Sellafield nuclear reprocessing plant. This work provides insight into until now poorly understood field data and provides a novel view of broad implications in the study of the behaviour of pollutants in surficial aquatic sediments.

Influence of terrigenous supply from the African continent on sedimentary CaCO3 distribution in the Southeast Atlantic Ocean

AbstractTerrigenous materials are transported to the ocean via various pathways, which can modify the weight contents of calcium carbonate (wt% CaCO3) in marine sediment and mask CaCO3 dissolution profiles, especially in ocean margins. Although the effect of terrigenous dilution on marine CaCO3 has long been established, there is still a lack of quantitative assessment on how the terrigenous input shapes sedimentary CaCO3 depth distribution features. In this study, we focus on the CaCO3 depth distribution patterns on the seafloor in the Southeast Atlantic Ocean. Based on an up‐to‐date compilation of surficial sedimentary CaCO3 content data and a simple conceptual model, the regional dilution effect of terrigenous supply from the African continent on the basinal sedimentary CaCO3 depth distribution is quantified. Our results show that the flux of noncarbonate materials needed to reproduce the carbonate distribution decreases with distance to the African continent. The noncarbonate flux to pelagic sediment in the Southeast Atlantic Ocean is on the same order of magnitude of the dust deposition rate, while the flux to marginal sediment is intensified as a consequence of the fluvial discharge. Moreover, enhanced dissolution of CaCO3 is found in marginal regions, which is due to faster rates of deep (boundary) currents than those in the pelagic ocean. These new insights help to distinguish the dilution impact from carbonate dissolution patterns and will advance research on land–ocean interaction and paleoclimate/environment reconstructions in ocean margins.

Biogeography of Southern Ocean prokaryotes: a comparison of the Indian and Pacific sectors.

SummaryWe investigated the Southern Ocean (SO) prokaryote community structure via zero‐radius operational taxonomic unit (zOTU) libraries generated from 16S rRNA gene sequencing of 223 full water column profiles. Samples reveal the prokaryote diversity trend between discrete water masses across multiple depths and latitudes in Indian (71–99°E, summer) and Pacific (170–174°W, autumn‐winter) sectors of the SO. At higher taxonomic levels (phylum‐family) we observed water masses to harbour distinct communities across both sectors, but observed sectorial variations at lower taxonomic levels (genus‐zOTU) and relative abundance shifts for key taxa such as Flavobacteria, SAR324/Marinimicrobia, Nitrosopumilus and Nitrosopelagicus at both epi‐ and bathy‐abyssopelagic water masses. Common surface bacteria were abundant in several deep‐water masses and vice‐versa suggesting connectivity between surface and deep‐water microbial assemblages. Bacteria from same‐sector Antarctic Bottom Water samples showed patchy, high beta‐diversity which did not correlate well with measured environmental parameters or geographical distance. Unconventional depth distribution patterns were observed for key archaeal groups: Crenarchaeota was found across all depths in the water column and persistent high relative abundances of common epipelagic archaeon Nitrosopelagicus was observed in deep‐water masses. Our findings reveal substantial regional variability of SO prokaryote assemblages that we argue should be considered in wide‐scale SO ecosystem microbial modelling.

Snowpack Distribution Using Topographical, Climatological and Winter Season Index Inputs

A majority of the annual precipitation in many mountains falls as snow, and obtaining accurate estimates of the amount of water stored within the snowpack is important for water supply forecasting. Mountain topography can produce complex patterns of snow distribution, accumulation, and ablation, yet the interaction of topography and meteorological patterns tends to generate similar inter-annual snow depth distribution patterns. Here, we question whether snow depth patterns at or near peak accumulation are repeatable for a 10-year time frame and whether years with limited snow depth measurement can still be used to accurately represent snow depth and mean snow depth. We used snow depth measurements from the West Glacier Lake watershed, Wyoming, USA, to investigate the distribution of snow depth. West Glacier Lake is a small (0.61 km2) windswept (mean of 8 m/s) watershed that ranges between 3277 m and 3493 m. Three interpolation methods were compared: (1) a binary regression tree, (2) multiple linear regression, and (3) generalized additive models. Generalized additive models using topographic parameters with measured snow depth presented the best estimates of the snow depth distribution and the basin mean amounts. The snow depth patterns near peak accumulation were found to be consistent inter-annually with an average annual correlation coefficient (r2) of 0.83, and scalable based on a winter season accumulation index (r2 = 0.75) based on the correlation between mean snow depth measurements to Brooklyn Lake snow telemetry (SNOTEL) snow depth data.

Photosynthetic performances of two deep‐water canopy‐forming fucoid algae across a depth gradient: Interspecific variability and short‐term adaptation to the light environment

AbstractDeep‐water canopy‐forming algae Gongolaria montagnei var. compressa and Ericaria zosteroides (Fucales: Ochrophyta) co‐exist in mixed populations, the first taxa dominating at the upper limit of distribution (20 m) and the second at the lower limit (40 m). This depth distribution pattern is consistent with the photosynthetic performances of both taxa, with E. zosteroides showing higher photosynthetic efficiency (α) and lower light at saturation (Ik) and compensation (Ic) than G. montagnei var. compressa. Neither photosynthesis at saturation (Pmax) nor dark respiration showed any significant change at the species level. G. montagnei v. compressa showed higher Pmax and α at 20 and 40 m, but E. zosteroides did not follow the same trend, although both Ik and Ic decreased with depth in this species, pointing to an increased capacity of E. zosteroides to show photo‐adaptation. Each species maintained its Psat values when transplanted from the depth where it was dominant to the depth where it was secondary, but in the case of G. montagnei var. compressa it decreased its Psat when transplanted from 40 to 20 m and in the case of E. zosteroides it increased its Psat when transplanted from 20 to 40 m. These results point to a better photosynthetic performance of E. zosteroides than G. montagnei var. compressa at low‐light conditions, information that can be used to improve success in restoration action plans.

Bacteriophage-host depth distribution patterns in soil are maintained after nutrient stimulation in vitro

Previous research has revealed the ecological importance of viruses in different ecosystems. However, bacteriophage-host distribution patterns in soil depth profiles have not been investigated. Environmental factors such as nutrient availability and physiological stress can impact the mode (either lytic or lysogenic) of viral reproduction and subsequent influence of virus infection on ecological processes. Soil depth profiles with distinct geochemical properties are ideal models to investigate the virus-host relationships as a function of environmental trophic status and cell abundance. Batch enrichment experiments using soil collected at varying depths (0–140 cm) as inoculum were performed to explore the interactions between viruses and co-occurring microbial hosts under nutrient stimulation. Both viral and bacterial abundance increased in the nutrient media compared with those in the original soils. Bacterial abundance was similar in mixed-cultures of soils regardless of sampling depth, whereas viral abundance was negatively correlated with the depth of soil samples which caused a decreasing virus-to-bacteria ratio. The lysogenetic fraction increased with soil depth in a similar manner as in the original soils assessed directly without nutrient stimulation. The bacterial diversity decreased with soil depth, and was influenced primarily by soil type, viral abundance, and virus-to-bacteria ratio. The bacterial communities were dominated by Bacilli, Beta-, Gamma-Proteobacteria, and Clostridia after nutrient stimulation. Viral and bacterial community structure also varied with soil horizons (i.e., depth). The results showed that the patterns for virus-host interactions shaped by the geochemical properties in the original environment were conserved or similar after in vitro nutrient stimulation. These findings suggest that short-term changes in trophic status alone may not significantly alter the balance of viral reproductive strategies in terrestrial ecosystems as in the antecedent environmental conditions that the host community has long adapted to, and other factors such as stress, host diversity or adaptation may be necessary to trigger community-level shifts in the interactions between viruses and hosts that responded most favorably to nutrient addition.

In Situ Estimates of Net Primary Production in the Western North Atlantic With Argo Profiling Floats.

The 14C incubation method for net primary production (NPP) has limited spatial/temporal resolution, while satellite approaches cannot provide direct information at depth. With chlorophyll‐a and backscatter measurements from BGC‐Argo floats, we quantified year‐round NPP in the western North Atlantic Ocean using both the Carbon‐based Productivity Model (CbPM) and Photoacclimation Productivity Model (PPM). Comparison with NPP profiles from 14C incubation measurements showed advantages and limitations of both models. CbPM reproduced the magnitude of NPP in most cases. However, in the summer the CbPM‐based NPP had a large peak in the subsurface, which was an artifact from the subsurface chlorophyll maximum caused by photoacclimation. PPM avoided the artifacts from photoacclimation, but the magnitude of PPM‐derived NPP was smaller than the 14C result. Different NPP distribution patterns along a North‐South transect in the Western North Atlantic Ocean were observed, including higher winter NPP/lower summer NPP in the south, timing differences in NPP seasonal phenology, and different NPP depth distribution patterns in the summer months. Using a 6‐months record of concurrent oxygen and bio‐optical measurements from two Argo floats, we also demonstrated the ability of Argo floats to obtain estimates of the net community production to NPP ratio, ranging from 0.3 in July to −1.0 in December 2016. Our results highlight the utility of float bio‐optical profiles and indicate that environmental conditions (e.g., light availability, nutrient supply) are major factors controlling the seasonality and spatial (horizontal and vertical) distributions of NPP in the western North Atlantic Ocean.

Combined chronological and mineral magnetic approaches to reveal age variations and stratigraphic heterogeneity in the Yangtze River subaqueous delta

Delta deposits show large spatial heterogeneity in terms of depositional rate and age, which is critical to the study of delta erosion in response to the declining fluvial sediment load observed at many river mouths in the world. In this study, we show that the magnetic susceptibility (χ) can be an indicator to reveal age variations and stratigraphic heterogeneity in the Yangtze River subaqueous delta. Ages of three short sediment cores (<2 m) collected at 20–32 m water depth from the Yangtze River subaqueous delta were determined using 210Pb, 137Cs, and optically stimulated luminescence (OSL) dating. In addition, depth variation of χ, which is influenced by post-depositional diagenesis and hence age, was used to roughly infer sediment ages among the cores in a simple way. The profiles of 210Pb, 137Cs, and OSL dating results indicate the spatial variability of ages, ranging from the last 100 years to >1700 years. The cores at shallow water depths are younger than those from deeper sites. Modern deposits (i.e., <100 years old) occur primarily at water depths shallower than ca. 30 m. The core in the northern part of the subaqueous delta shows much older ages than the core at the southern site with similar water depth, which is caused by their longer distance relative to the mouth of active sediment discharge distributary. Profile of χ confirms such spatial variation of ages in terms of depth distribution pattern and χ value. Older sediments (>800 a) show lower and uniform χ values due to the reductive dissolution of ferrimagnetic minerals, while younger sediments (<350 a) show higher χ values in the top layer but they decline with increasing depth. Considering the quick way of magnetic measurement, stratigraphic correlation based on χ can be used first to screen for cores before they are subjected to more detailed dating. This study shows that the methodological approach of combining sediment dating with magnetic measurement has great potential in revealing heterogeneous deltaic deposits.

RSDCN: A Road Semantic Guided Sparse Depth Completion Network

Laser radar (Lidar) plays an indispensable role in lots of security critical applications such as autonomous driving. However, the high sparsity and non-uniformity nature of the raw laser data brings large difficulties to reliable 3D scene understanding. Traditional depth completion methods suffer from the highly ill-conditioned nature of the problem. A novel end-to-end road semantic guided depth completion neural network with a special designed Asymmetric Multiscale Convolution (AMC) structure is proposed in this paper. The whole network is composed of two parts: semantic part and depth completion part. The semantic part is constructed by an image-Lidar joint segmentation sub-network which produces semantic masks (ground or object) to the following network. The depth completion part is composed of a series of AMC convolution structure. By combining the semantic masks and treating the ground and non-ground objects separately, the proposed AMC structure can well fit the depth distribution pattern implied in road scene. The experiments carried on both synthesized and real datasets demonstrate that our method can effectively improve the accuracy of depth completion results.

Population structure and movement patterns of blackbelly rosefish in the NE Atlantic Ocean (Azores archipelago)

AbstractBlackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809) is one of the most important species of the demersal/deep‐water assemblages fished in the NE Atlantic Ocean (Azores archipelago). However, there is insufficient information about the stock structure of this species to support analytical resource assessments and it is currently managed with a precautionary approach. Here, we examine the depth and temporal distribution, size composition, sex, and movement patterns of blackbelly rosefish in order to test the hypothesis that the stock structure in the Azores region comprises different local management units (MUs). We also evaluate annual abundance indices and size composition from scientific surveys and commercial landings over the past c. 25 years for an assessment of the species' vulnerability to bottom longline fishing pressure. The greatest abundance occurred in seamount areas at 350–800 m depth. Larger individuals were mainly found in deeper waters, and no sexual segregation by depth was observed. Tagging results indicated a strongly sedentary behavior and an intraregional separation among populations. Although the abundance pattern and size composition were very similar over time, this species is particularly vulnerable to overfishing due to its biological characteristics (long life, large size, late maturity, slow growth, and low mortality rate). Proper monitoring and management of its exploitation should be a priority. Exploratory analysis for analytical assessment should be performed under the assumption of local MUs. Further oceanographic research is needed to understand larval transport and mixing of populations.

Application of 3D Euler Deconvolution and 2D inverse modelling to basin depth estimation, the case of the Keta basin, Ghana

ABSTRACT 3D Located Euler Deconvolution and 2D Inverse Modelling have been applied to aero-magnetic and gravity data, respectively, to estimate depth to the basement across the Keta-basin, South-eastern Ghana, West Africa. The Euler deconvolution estimated relative depths, illustrated by depth solutions across the entire basin while the inverse modelling estimated the absolute depth at various positions in the basin. To improve and provide more accurate depth solutions, we applied the Located 3D Euler Deconvolution Method instead of the Standard Euler Deconvolution. The Located Euler depth estimate were obtained by calculating an analytic signal grid, finding peaks in the grid, then using the peak locations for located 3D Euler deconvolution. This method produced far lesser solutions than the Standard 3D Euler deconvolution. To estimate absolute depths across the basin, 2D inverse models were created along with five profiles constructed across strike on the gravity bouguer anomaly map. An Iterative Least Squares Inversion Method which is a non-linear inversion technique was applied to automatically calculate the model parameter (depths) in each step of the iteration process. The inversion procedure can easily be integrated with geologically realistic models. Comparatively, both methods produced similar depth estimates. The study showed higher depths to the south and east of the study area (>2 km) as the shallower depth occurs to the north (<2 km). The relative thickness of sedimentary succession was inferred from the depth distribution patterns as observed from Euler depth solutions. The highest depth estimated was 3.57 km which occur further south of the basin.

Resolving Small‐Scale Forest Snow Patterns Using an Energy Balance Snow Model With a One‐Layer Canopy

AbstractModeling spatiotemporal dynamics of snow in forests is challenging, as involved processes are strongly dependent on small‐scale canopy properties. In this study, we explore how local canopy structure information can be integrated in a medium‐complexity energy balance snow model to replicate observed snow patterns at very high spatial resolutions. Snow depth distributions simulated with the Flexible Snow Model (FSM2) were tested against extensive experimental data acquired in discontinuous subalpine forest stands in Eastern Switzerland over three winters. While the default canopy implementation in FSM2 fails to capture the observed snow depth variability, performance is considerably improved when local canopy cover fraction and hemispherical sky view fraction are additionally accounted for (30% reduction in root mean square error). However, realistic snow depth distribution patterns throughout the season are only achieved if effective temperatures of near and distant canopy elements are discerned and if a mechanism to mimic preferential deposition of snow in canopy gaps is included. We demonstrate that by diversifying the canopy structure input in order to reflect respective portions of the canopy relevant to different processes, even a simple model based on widely used process parameterizations and canopy metrics can be applied for high‐resolution simulations of the sub‐canopy snow cover with just a few modifications. The presented approaches could be implemented in commonly used land surface models, allowing upscaling experiments and development of sub‐grid parameterizations without necessitating complex high‐resolution models.

Biological and ecological aspects of the deep‐water red crab populations inhabiting isolated seamounts to the west of the Azores (Mid‐Atlantic Ridge)

AbstractSeamounts are common topographic features in the Mid‐Atlantic Ridge (MAR) including the Azores. However, the knowledge on the ecology of seamounts in this region remains scarce despite needs for assessment and management of seamount resources such as the developing fisheries for deep‐water crabs. We described here for the first time the biological characteristics of an unexploited virgin deep‐water red crab Chaceon affinis population on seamount areas of the MAR to test the hypothesis that its general life history characteristics are similar in different ecosystem types (coastal areas and seamounts) across Macaronesia. We used a randomly stratified design to prospect a layer between 600 and 900 m depth around the summit of two isolated seamounts off the Azores. Results were consistent with the literature information in relation to the patterns of depth distribution, size and sex structure, and reproductive aspects. On the other hand, seamounts showed higher abundances when compared to previously studied coastal areas. Abundance may be also different between seamount areas as a function of the suitable bottom type available and presence of hydrothermal vents. We recommend that the essential habitat of the species should be better mapped identifying vulnerable areas before the development of any fishery.

Depth distribution pattern of soil organic carbon in forest from Taowan basin of Funiu Mountain area.

Depth distribution pattern of soil organic carbon in forest from Taowan basin of Funiu Mountain area.

The Depth Distribution of Dominant Species of Macrophytes in the Northwestern Part of the Tatar Strait

This paper investigates the depth distribution patterns of bottom vegetation dominants in the western Tatar Strait (within Khabarovsk Krai). Materials were collected during SCUBA diving surveys performed by the Khabarovsk Branch of the Pacific Research Fisheries Center. The vegetation cover, in the presence of suitable bottom substrates, is formed to depths of 18–22 m and is replaced below by sparse settlements. The abundance indices of most of the dominant species remain relatively stable within depths of 2–20 m. Their ecological optima, as a rule, occur at depths of 2–6 m with increased hydrodynamics. A scheme of the vertical division of vegetation in the area is proposed that corresponds to the results of previous studies on phytal zoning. The location of vegetation horizons and strata is not different from those previously identified, while their boundaries are blurred and correspond to the continuous live cover distribution.

Biogeographic distributions of Cytheropteron species (Ostracoda) in Icelandic waters (sub-polar North Atlantic)

The ostracod genus Cytheropteron (Ostracoda: Crustacea) has been widely used for paleoenvironmental, paleoceanographic, and paleobiogeographic studies. But species-level data remain limited, especially for deepwater species. Here, we show the depth and spatial distribution patterns of 33 species of the ostracod genus Cytheropteron found in recent surface sediments of Icelandic waters. Species-specific depth ranges may serve as a useful tool in ostracod-based paleoenvironmental reconstruction. Biogeographic distributions of Cytheropteron species indicate the shallow Greenland-Iceland-Faroe Ridge as the major barrier for the distribution of deep-sea organisms.

An interaction between vertical and lateral movements of soil constituents by tillage in a steep-slope landscape

The interaction between vertical and lateral movements of soil constituents by tillage needs to be addressed to better understand the transfer processes of soil constituents on a hillslope. In this experiment, traditional tillage by consecutive hoeing during a few days and the cesium-137 (137Cs) tracing were performed in the Sichuan Basin, China to demonstrate direct effects of intensive tillage on the vertical redistribution of soil constituents and the interaction between vertical and lateral transfers of soil constituents. The changes in 137Cs residual rates showed that intensive downslope movement of soil by tillage occurred along the transect of slopes, and the lateral transfer of those soil constituents proceeded in the same direction as the soil movement by tillage. The vertical transfer patterns differed from one another for the upper, middle, and lower slope positions. At the upper slope positions, intensive tillage notably decreased the concentrations of soil organic carbon (SOC) and total nitrogen (TN) in the whole soil profile. At the middle and lower slope positions, SOC concentrations in the surface soil layer (0–15cm) markedly declined after intensive tillage, suggesting that the downslope movement of soil by tillage translocated the soil with low concentrations of SOC and TN derived from upslope towards the middle and lower slopes. The decreases in SOC and TN of the surface soil exerted an important impact on the underlying soil near the surface soil due to the vertical transfer of soil constituents by mixture effects of tillage. Significant changes in the depth distribution pattern of soil constituents by intensive tillage occurred close to the upslope and downslope boundaries of the field Our results revealed that the vertical movement of soil constituents interacted with their downslope movement under intensive tillage, which resulted in a chain transfer process of soil constituents: effects of the vertical transfer at all landscape positions on the lateral transfer along the transect of slopes, and conversely, effects of the lateral transfer on the vertical transfer.

Depth-distribution patterns and control of soil organic carbon in coastal salt marshes with different plant covers.

This study was carried out in three kinds of salt marshes according to the vegetation covers, including Phragmites australis salt marsh (PSM), Suaeda salus salt marsh (SSM) and Tamarix chinensis-Suaeda salus salt marsh (TSSM). We applied allometric function, exponential function and logistic function to model the depth distribution of the SOCv and SOCc for each salt marsh, respectively. The results showed that the exponential function fits the depth distribution of the SOCv more well than other two functions. The SOCc can be fitted very well by all three functions for three salt marsh (Adj. R2 > 0.99), of which the allometric function was the best one. The mean topsoil concentration factors (TCFs) of three salt marshes were beyond 0.1, which means the SOC enrichment in surface soils due to plant cycling, but TCFs in PSM were significantly higher than those in SSM (P < 0.05). Nearly 30% of SOC was concentrated in the top 20 cm soils. The results of general linear model (GLM) suggested that four soil properties (soil water content, pH, soil salt content and silt+clay) and their interactive effects explained about 80% of the total variation of SOC stock in the top 20 cm soils and the 20–100 cm soil layers.