Top Meter Research Articles

Region‐specific drivers cause low organic carbon stocks and sequestration rates in the saltmarsh soils of southern Scandinavia

AbstractSaltmarshes are known for their ability to act as effective sinks of organic carbon (OC) and their protection and restoration could potentially slow down the pace of global warming. However, regional estimates of saltmarsh OC storage are often missing, including for the Nordic region. To address this knowledge gap, we assessed OC storage and accumulation rates in 17 saltmarshes distributed along the Danish coasts and investigated the main drivers of soil OC storage. Danish saltmarshes store a median of 10 kg OC m−2 (interquartile range, IQR: 13.5–7.6) in the top meter and sequester 31.5 g OC m−2 yr−1 (IQR: 41.6–15.7). In a global context, these values are comparatively low. Soils with abundant clay (> 20%), older and stable saltmarshes in mesohaline settings, and with low proportion of algal organic material showed higher OC densities, stocks, and accumulation rates. Grazing led to significantly higher OC stocks than neighboring ungrazed locations, likely due to trampling modifying soil abiotic conditions (higher erosion‐resistance and higher clay content) that slow carbon decay. Scaling up, Danish saltmarsh soils, comprising about 1% of the country's area, have the potential to yearly capture up to 0.1% of Denmark's annual consumption‐based CO2 emissions. Our research expands the baseline data needed to advance blue carbon research and management in the Nordic region while highlighting the need for a more comprehensive approach to saltmarsh management that considers the full range of services of these ecosystems and does not only focus on climate benefits.

The influence of long-term dynamics of groundwater levels on the winter redistribution of moisture in arable soils of the Ishim steppe

The aim of the study was to establish the influence of long-term dynamics of the groundwater level on the winter redistribution of moisture in arable soils of the Ishim steppe. Location and time of the study. The Ishim-Irtysh steppe interfluve (Ishim steppe, Russia), 1986–1989 and 2002–2024. Methods. Soil samples were collected during soil-hydrological field observations from the reference pits of arable soils. The soil and subsoil moisture content was determined by thermostat-weighing /in samples collected in the pre-winter period (the second - third decades of October) and at the end of the winter season (the third decade of March). The depth of the groundwater table was measured in the hand-drilled simultaneous with soil sampling for moisture measurement. The layer of cryogenic accumulation and the freezing moisture volume were determined by comparing moisture profiles in mid-October and in the third decade of March. Snow surveying was carried out in the third decade of March. The penetration depth of 0°C temperature was determined using exhaust thermometers. Results. Within the upland areas, during the second half of the 20th century the aquifer rose from various depths to the levels above the critical level. The economic activity was the main reason for the rise. In the early decades of the 21th century, as the groundwater table was above the critical depth, the groundwater level in summer and autumn began to be predetermined by the amounts of precipitation over the previous cold season of the year. The peculiarities of the winter redistribution of moisture in arable soils were found to be largely determined by the depth of groundwater in the autumn season. If in the upland soils the groundwater table was located in autumn at a depth of more than 4 m, which was typical for the 1980s, a layer of cryogenic moisture accumulation was formed below the horizons of intense and complete desuctive drying for spring grain crops, from a depth of 0.8 m. The moisture freezing volume did not exceed 30 mm. Migrated moisture practically did not participate in replenishing the post-vegetation moisture deficit in the upper 1-meter-thick layer of soil. If the groundwater in the second and third decades of October was detected at a depth of less than 4 m, which is typical for upland areas in the 21st century, a layer of cryogenic accumulation can be traced from a depth of 0.4–0.8 m, the volume of freezing moisture can reach 50 mm, and 25 mm in the top 1-meter layer. The frozen moisture in the top meter layer helps reducing the post-vegetation deficit, but promotes conditions for anaerobiosis in the second half-meter soil layer and acts as an “island of cold,” delaying the soil warming in spring to active temperatures. In soils with negative relief forms, the groundwater level during the period of field survey exceeded the critical level. Therefore, specifics of winter moisture profile redistribution in were similar to the established characteristics of this phenomenon in upland soils during the current millennium. Conclusions. The groundwater level in the soil and subsoils of the Ishim steppe uplands showed long-term dynamics under the influence of anthropogenic as well as natural factors over the past twenty years. The autumn depth of the groundwater table determines specifics of winter moisture redistribution in the arable soils of plakors: the higher the level, the greater the amount of moisture freezing is fixed, and the closer the cryogenic accumulation layer is located to the daytime surface.

The distribution of depth, volume, and basin shape for lakes in the conterminous United States

AbstractDepth regulates many attributes of aquatic ecosystems, but relatively few lakes are measured, and existing datasets are biased toward large lakes. To address this, we used a large dataset of maximum (Zmax; n = 16,831) and mean (Zmean; n = 5,881) depth observations to create new depth models, focusing on lakes < 1,000 ha. We then used the models to characterize patterns in lake basin shape and volume. We included terrain metrics, water temperature and reflectance, polygon attributes, and other predictors in a random forest model. Our final models generally outperformed existing models (Zmax ; root mean square error [RMSE] = 8.0 m and Zmean ; RMSE = 3.0 m). Our models show that lake depth followed a Pareto distribution, with 2.8 orders of magnitude fewer lakes for an order of magnitude increase in depth. In addition, despite orders of magnitude variation in surface area, most size classes had a modal maximum depth of ~ 5 m. Concave (bowl‐shaped) lake basins represented 79% of all lakes, but lakes were more convex (funnel‐shaped) as surface area increased. Across the conterminous United States, 9.8% of all lake water was within the top meter of the water column, and 48% in the top 10 m. Excluding the Laurentian Great Lakes, we estimate the total volume in the conterminous United States is 1,057–1,294 km3, depending on whether Zmax or Zmean was modeled. Lake volume also exhibited substantial geographic variation, with high volumes in the upper Midwest, Northeast, and Florida and low volumes in the southwestern United States.

Converting croplands into perennials may contribute to the deep soil nitrogen (N) accumulation in N‐limited region: Evidence from the arid and semi‐arid Chinese Loess Plateau

AbstractConverting degraded croplands into perennials has been proposed as an effective method of soil N sequestration, however, the dynamics of deep soil N (>100 cm) following cropland conversion are not well understood. In this study, we synthesized 3049 observations to detect the changes in deep soil N content following cropland conversion on the arid and semiarid Loess Plateau. Our results showed that converting croplands into perennials significantly increased the soil N content by an average of 57.4%, 23.1%, and 29.5% in the surface (0–20 cm), subsurface (20–100 cm), and deep (100–200 cm) layers, respectively. The extent of the increase was influenced significantly by the land‐use conversion types and tree species. Specifically, the conversion of croplands into deep‐rooted forests or shrubs, particularly Robinia pseudoacacia and Caragana microphylla, exhibited higher advantages in deep soil N sequestration. Moreover, deep soil N sequestration increased significantly with time since cropland conversion (p < 0.001), and the rates in deep soils were approximately 26.1% and 66.7% of that in 0–20 and 20–100 cm soils, respectively. In the long term, converting croplands into forests and shrubs showed higher potential for deep soil N sequestration. Linear regression analysis showed that the changes of deep soil N sequestration were influenced significantly by initial soil N content (p < 0.001) and humidity index (p < 0.001), with the slopes in >100 cm layers being 2 to 3 times than that in the top meter, indicating higher sensitivity in deep soils. Overall, this study provides evidence that converting degraded croplands into perennials may contribute to deep soil N accumulation in N‐limited regions, which could potentially alleviate N limitation and sustain long‐term ecosystem carbon sequestration.

Conversion of forest to cinnamon plantation depletes soil carbon stocks in the top metre of the tropical highlands of Kerinci Regency, Jambi Province, Indonesia

AbstractThis study aimed to investigate the effect of conversion from natural forest to cinnamon plantation on the top 1 m soil carbon stocks and soil characteristics. The project was conducted on Andosols of Kerinci Regency, Sumatera, Indonesia, sampling the soil profile under natural forests and a chronosequence of cinnamon plantations of different ages (1, 5 and 10 years). SOC stocks were quantified alongside physical properties (bulk density) and chemical properties (carbon, nitrogen, C/N ratio) to investigate the impact of land conversion. SOC stocks increased 1 year after conversion to cinnamon plantations, but then tended to decrease as the plantations got older. The initial increase was observed alongside decreasing bulk density 1 year after forest conversion to cinnamon plantation, likely as a result of the fresh input of (less dense) pyrogenic soil organic matter as a result of slash and burn practices and transport down the soil profile owing to leaching. In older plantations SOC stocks were lower, probably because organic matter had been decomposed or leached out of the profile. The free particulate organic matter (fPOM) was isolated from selected topsoil and subsoil layers and analysed for carbon, nitrogen, and FTIR analysis. FTIR analysis revealed that topsoil fPOM contained more aromatic functional groups than subsoils and had a higher degree of decomposition. Aromatic and carbohydrate functional groups were initially lower in recently converted cinnamon plantation, but the trend was reversed 10 years after conversion. The initial flush of fresh organic matter into soils after slash and burn provides fPOM with a lower degree of decomposition but is short‐lived and fPOM becomes more microbially processed as the cinnamon plantation ages. We conclude that, after a short term increase brought about by slash and burn, forest conversion to cinnamon plantation in Kerinci Regency depletes SOC stocks both in topsoils and subsoils.

Spatial variation of organic carbon storage and aggregate sizes in the sediment of the Zhangjiang mangrove ecosystem

Sediment organic carbon (SOC) in mangrove ecosystem, known as blue carbon, is a crucial component in estuarine carbon cycles. To get a deep insight into the mechanism of SOC accumulation, the sediment physicochemical properties, SOC density and aggregate sizes were investigated among mangrove (Kandelia obovata), saltmarsh (Spartina alterniflora) and mudflats at different elevations (upland mudflat, midland mudflat, lowland mudflat). The results showed that the higher SOC content was observed both in the 0–60 cm of mangrove and in the 0–40 cm of S. alterniflora compared with mudflats (P < 0.05). The SOC density in the top meter ranged from 99 to 202.7 Mg·ha−1 and had vertical difference at all sites. The highest SOC density were found in mangrove, while no difference was observed between S. alterniflora and mudflats. The mean weight diameter of aggregates was higher in the top 60 cm sediment of mangrove while S. alterniflora had no change indicating the capacity of aggregate formation. RDA analysis showed SOC storage could be more explained by the SOC content than bulk density, all sites in the top 40 cm could be well separated. The MWD had the 8.6 % individual effects on SOC content, reflecting the aggregated protection. The mangrove root system favored aggregates formation and physical protection, which facilitate the SOC accumulation. These findings revealed that mangroves restoration could effectively enhance SOC storage, and the mudflat is also significant SOC pool owning to the large bulk density and area. The invasive S. alterniflora did not enhance the SOC storage compared with mudflats and should be controlled in the future work.

Improved prediction of soil exchangeable sodium percentage (ESP) using wavelet

In Australia, the soil is considered sodic when the top meter has an exchangeable sodium percentage (ESP) greater than six (6%). Sodicity is a natural feature of Queensland, particularly the case in northeast Queensland where sugarcane is grown. To ameliorate sodicity effectively, a digital soil mapping (DSM) approach with digital data (e.g. elevation, gamma-ray [γ-ray] spectrometry, and soil apparent electrical conductivity [(ECa)]) could be used. However, when a relationship between digital and soil data does not exist, wavelet transformation could be employed. Firstly, we aim to see if digital data, alone or in combination, can be used to predict topsoil (0–0.3 m) ESP using a linear mixed model (LMM). Secondly, we decompose the digital data using wavelet transform into components (i.e. detail [D] and approximate [A]) at different scales (i.e. 10, 20, 40, and 80 m). We then aim to develop an LMM to predict topsoil ESP using D or A or in combination. Results show that prediction of topsoil ESP by LMM using raw digital data either alone (Lin’s = 0.27) or in combination (0.37) was poor (Lin’s < 0.65). The prediction of topsoil ESP by LMM using D components alone was unsatisfactory at small scales, however, moderate agreement (0.65 < Lin’s < 0.8) was achieved at scales of 80 m (0.66). In combination with D and A, a moderate agreement was achieved at 40 m (0.71) and a good agreement at 80 m (0.85). When considering the decomposed digital data individually, and at the same scale, the prediction of topsoil ESP using decomposed ECa (0.56) was better than γ-ray (0.38). Interestingly, the decomposed elevation cannot be used individually to predict ESP. However, adding decomposed elevation to γ-ray (0.58) and ECa (0.67), the prediction of ESP was enhanced. The best prediction of ESP was achieved using all decomposed data at 80 m (0.85). However, further work in validation would be required to confirm topsoil ESP was non-sodic (<5 %) and where it was deemed to be strongly sodic (>20 %) as these were not measured. Nevertheless, the DSM offers the real prospect of applying the six-easy-steps ameliorant management guidelines (Schroeder et al., 2006) to apply suitable rates of gypsum, including 2 t/ha for sodic (ESP; 5–10 %), 4 t/ha for moderately (10–15 %) and 6 t/ha for strongly (>15 %) sodic topsoil.

Blue carbon stocks in southern Africa's Endangered seagrass Zostera capensis

Blue carbon research, although rapidly expanding, still requires site- and species-specific assessments to inform decision-making and policy formation. In this study, C stocks were assessed in the Endangered seagrass Zostera capensis. in the Knysna, Swartkops and Nxaxo estuaries, South Africa. Mean biomass C storage was 2.39 ± 1.42 Mg C ha−1 (similar to the global seagrass average), while 177.65 ± 122.29 Mg C ha−1 was estimated in the top meter of sediment. Sediment organic C content was 0.99 ± 0.45% — markedly lower than the seagrass global average but within the range reported for other Zostera species — and displayed significant spatial variability within and between estuaries. Sediment C was particularly high in the eutrophic Swartkops, likely due to excessive wastewater discharge introducing organic matter to the estuary's seagrass habitats. Based on the C stocks determine in this study, it is estimated that approximately 315 970 ± 217 111 Mg C could be stored in South Africa's 1755 ha of Z. capensis habitats. However, these important blue carbon habitats face multiple threats, particularly climatic events like droughts and floods, and anthropogenic eutrophication. This study has provided the first comprehensive C stock assessment for Z. capensis and contributes to global blue carbon datasets. Furthermore, this work has reinforced the importance of protecting the Endangered seagrass by highlighting the important ecosystem service it provides through climate change mitigation and adaptation.

An overlooked soil carbon pool in vegetated coastal ecosystems: National-scale assessment of soil organic carbon stocks in coastal shelter forests of China

Protection and restoration of vegetated coastal ecosystems provide opportunities to mitigate climate change. Coastal shelter forests as one of vegetated coastal ecosystems play vital role on sandy coasts protection, but less attention is paid on their soil organic carbon (OC) sequestration potential. Here, we provide the first national-scale assessment of the soil OC stocks, fractions, sources and accumulation rates from 48 sites of shelter forests and 74 sites of sandy beaches across 22° of latitude in China. We find that, compared with sandy beaches, shelter forest plantation achieves an average soil desalination rate of 92.0 % and reduces the soil pH by 1.3 units. The improved soil quality can facilitate OC sequestration leading to an increase of soil OC stock of 11.8 (0.60–64.2) MgC ha−1 in shelter forests. Particulate OC (POC) is a dominant OC fraction in both sandy beaches and shelter forests, but most sites are >80 % in shelter forests. The low δ13C values and higher C:N ratios, which are more regulated by climate and tree species, together with high POC proportions suggest a substantial contribution of plant-derived OC. Bayesian mixing model indicates that 71.8 (33.5–91.6)% of the soil OC is derived from local plant biomass. We estimate that soil OC stocks in Chinese shelter forests are 20.5 (7.44–79.7) MgC ha−1 and 4.53 ± 0.71 TgC in the top meter, with an accumulation rate of 45.0 (6.90 to 194.1) gC m−2 year−1 and 99.5 ± 44.9 GgC year−1. According to coastal shelter forest afforestation plan, additional 1.72 ± 0.27 TgC with a rate of 37.9 ± 17.1 GgC year−1 can be sequestrated in the future. Our findings suggest that construction of coastal shelter forests can be an effective solution to sequester more soil carbon in coastal ecosystems.

Unraveling the link between sediment acoustics and organic carbon

The top meter of marine sediments is estimated to store a total of 2322 Pg of carbon [Atwood et al., 2020. Front. Mar. Sci., vol. 7 p.165], which is twice that of terrestrial soils. Physical disturbance and remineralization of these carbon stocks could further accelerate climate change. Rapid and accurate quantification of sediment carbon stocks can (1) better inform carbon budgets and management of human activities in the ocean to minimize carbon remineralization and (2) monitor changes in sediment carbon stocks due to anthropogenic and natural disturbances. Sediment acoustics, which have been linked with sediment total organic carbon/content in mud banks, seagrass beds, and estuarine environments, can be measured in situ and offer a scalable solution toward rapid estimation of carbon stocks. However, before this modality can be applied broadly, a fundamental understanding between sediment acoustic properties and sediment organic/inorganic constituents must be realized. Here, direct ex situ measurements of sediment acoustic properties, sediment organic carbon, and grain size distribution will be compiled and compared across a variety of sediment types and locations from our own measurements and from published datasets. The development of a non-site-specific constitutive-based relationship will be discussed. [Work supported in part by ONR.]

Responses of Vegetation, Soil, and Microbes and Carbon and Nitrogen Pools to Semiarid Grassland Land-Use Patterns in Duolun, Inner Mongolia, China

Previous studies have observed that increased precipitation positively affects primary production in semiarid grasslands in Inner Mongolia, while soil carbon (C) and nitrogen (N) strongly influence how ecosystems respond to precipitation as well as anthropogenic disturbances under different management strategies. Therefore, in this study, we investigated the storage of organic C and N in four grassland sites with similar flora and landforms but with different grazing intensities to characterize how the storage and concentrations of C and N respond to relief from grazing pressure and precipitation. The concentrations of soil organic carbon (SOC), soil total nitrogen (STN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN), as well as the contents of soil bacteria and fungi in the 0–50 cm soil layers, were measured. The results showed that SOC, STN, MBC, and MBN storage varied greatly among the four grassland sites (p &lt; 0.05), with all decreasing significantly with grassland degradation and increasing greatly with the exclusion of grazing, i.e., the establishment of natural grassland (NG). More than 90% of C and 95% of N stored in the soil were lost due to heavy grazing, but the losses were smaller in other nutrient pools (including the aboveground biomass, litter, and roots). Interestingly, the proportion of the particle size fractions (clay, silt, and sand) had a stronger effect on limiting the soil and microbial nutrient pools compared to precipitation. The limited range of C and N storage found in these grassland soils indicated that enclosed fencing was a valuable management tool with a high potential to sequester C in the top meter of the soil, showing a stronger effect than precipitation. This study provides a theoretical basis for improving grassland recovery in semiarid areas that have been heavily grazed.

Blue carbon effects of mangrove restoration in subtropics where Spartina alterniflora invaded

Mangrove swamps and salt marshes are noted for their large carbon sequestration and storage capacity. In southeastern China, mangrove transplantation is conducted as ecological restoration where exotic Spartina alterniflora (hereafter Spartina) is removed. This study aimed to evaluate the effectiveness of mangrove transplantation on carbon sink potential. We analyzed chronological sediment accretion, soil carbon sequestration, and carbon storage of mangroves and Spartina on Maoyan and Ximen islands. Results showed that on both islands mangroves and invasive Spartina stored 12.7%–31.4% more carbon than bare mudflats over top meter soils, with Spartina outperforming restored mangroves. Both restored mangroves and invasive Spartina enhanced sediment accretion, but this enhancement was minimal in high sediment supply areas like Maoyan. Spartina invasion improved carbon sequestration capacity compared to bare mudflats in Maoyan, but mangrove restoration failed. In low sediment supply areas like Ximen, restored mangroves have outperformed Spartina invasion on carbon sequestration enhancement since >5 years of planting. Thus, carbon sink potential of mangrove restoration depended on sediment supply and time, with sediment supply being more important. We suggested that it was preferable to conduct mangrove restoration with Spartina eradication in low sediment supply areas in subtropics.

No-Till Mitigates SOC Losses after Grassland Renovation and Conversion to Silage Maize

Many studies recommend no-till (NT) to increase soil organic carbon (SOC) in the topsoil (&lt;30 cm) of arable land to counterbalance greenhouse gas emissions. Its potential use to mitigate SOC losses during conversion and renovation of grassland ecosystems in the top meter soil is yet to be determined. The SOC dynamics of a 10-year-old grassland converted to silage maize (CM) and renovated and seeded (GR) using either conventional tillage (CT) or NT were compared to an undisturbed grassland control (GC) for 7 years, across three fixed soil depth increments (0–30, 30–60, 60–90 cm). The annual C inputs (Cinput) from crop residues were further analyzed. The systems were either non-fertilized (N0) or fertilized with mineral N (N1) according to a demand of 180 and 380 kg N ha−1 year−1 in the silage maize and grassland systems, respectively. For the 7-year period, the renovated grassland using NT ensured maintenance of the initial SOC in the topsoil, while a conversion toward arable cropping resulted in SOC losses, regardless of the tillage method. The use of NT during conversion significantly reduced these losses from 2.5 Mg ha−1 year−1 to 1.8 Mg ha−1 year−1, for a 28% reduction compared to CT. In the subsoil (30–90 cm), SOC remained stable and was not affected by the cropping systems nor by the tillage method. Reduced annual Cinput was found as the main factor affecting SOC losses after grassland removal, regardless of the tillage method. Our findings highlight the potential of NT to mitigate annual SOC losses after grassland conversion if annual Cinput remains high.

Natural infrastructure in dryland streams (NIDS) can establish regenerative wetland sinks that reverse desertification and strengthen climate resilience

In this article we describe the natural hydrogeomorphological and biogeochemical cycles of dryland fluvial ecosystems that make them unique, yet vulnerable to land use activities and climate change. We introduce Natural Infrastructure in Dryland Streams (NIDS), which are structures naturally or anthropogenically created from earth, wood, debris, or rock that can restore implicit function of these systems. This manuscript further discusses the capability of and functional similarities between beaver dams and anthropogenic NIDS, documented by decades of scientific study. In addition, we present the novel, evidence-based finding that NIDS can create wetlands in water-scarce riparian zones, with soil organic carbon stock as much as 200 to 1400 Mg C/ha in the top meter of soil. We identify the key restorative action of NIDS, which is to slow the drainage of water from the landscape such that more of it can infiltrate and be used to facilitate natural physical, chemical, and biological processes in fluvial environments. Specifically, we assert that the rapid drainage of water from such environments can be reversed through the restoration of natural infrastructure that once existed. We then explore how NIDS can be used to restore the natural biogeochemical feedback loops in these systems. We provide examples of how NIDS have been used to restore such feedback loops, the lessons learned from installation of NIDS in the dryland streams of the southwestern United States, how such efforts might be scaled up, and what the implications are for mitigating climate change effects. Our synthesis portrays how restoration using NIDS can support adaptation to and protection from climate-related disturbances and stressors such as drought, water shortages, flooding, heatwaves, dust storms, wildfire, biodiversity losses, and food insecurity.

Carbon stocks in southern England's intertidal seagrass meadows

This study analyses total carbon stock (Cstocks) from the Isle of Wight, Solent, and adjacent harbours in southern England, including organic carbon (Corg) stored in the sediment and plant. Results from this study contribute to global blue carbon research by reporting the first direct assessment of sediment Cstocks in the top metre of intertidal seagrass meadows from the Solent region, with significant Cstocks, on average 103.12 ± 71.45 MgC ha−1, comparable to other global regions. This study also compared sediment %Corg and percentage of organic matter (%OM) within seagrass meadows and adjacent, un-vegetated, sampling points, showing that un-vegetated mudflats had higher %Corg and %OM than seagrass for most sites, apart from Hayling Island. This study shows that %OM can be confidently used as a proxy to determine sediment %Corg values in intertidal seagrass meadows. These results support the inclusion of the region's seagrass meadows in conservation and restoration projects, aiming not only to conserve the C stored in their soils, but also increase their future C uptake potential.

Tidal Flats as a Significant Carbon Reservoir in Global Coastal Ecosystems

Tidal flats are widely distributed and provide a variety of ecosystem services. Nevertheless, the consequences of tidal flat loss and implications for services such as carbon (C) sequestration have not been assessed. In unvegetated tidal flat ecosystems, sediment is the most important carbon reservoir, similar to that of vegetated coastal wetlands (i.e., mangroves, salt marshes, and seagrass). We examined the C stocks and C accumulation rate (CAR) reported from 123 locations of tidal flat around the world and compared these results with data from mangroves, salt marshes, and seagrass meadows. The global average CAR of tidal flats is 129.8 g C m-2 yr-1, with the top-meter sediments containing on average 86.3 Mg C ha-1. Globally, tidal flat can bury 6.8 Tg C (24.9 Tg CO2) per year and can store 0.9 Pg C (3.3 Pg CO2) in the top meter sediment. Assuming the same rate of loss tidal flats as in the past three decades and that all disturbed sediment C is remineralized, 4.8 Tg C will be lost from tidal flat sediments every year, equivalent to an emission of 17.6 Tg CO2 to the water column and atmosphere.

Ocean bubbles under high wind conditions – Part 2: Bubble size distributions and implications for models of bubble dynamics

Abstract. Bubbles formed by breaking waves in the open ocean influence many surface processes but are poorly understood. We report here on detailed bubble size distributions measured during the High Wind Speed Gas Exchange Study (HiWinGS) in the North Atlantic, during four separate storms with hourly averaged wind speeds from 10–27 m s−1. The measurements focus on the deeper plumes formed by advection downwards (at 2 m depth and below), rather than the initial surface distributions. Our results suggest that bubbles reaching a depth of 2 m have already evolved to form a heterogeneous but statistically stable population in the top 1–2 m of the ocean. These shallow bubble populations are carried downwards by coherent near-surface circulations; bubble evolution at greater depths is consistent with control by local gas saturation, surfactant coatings and pressure. We find that at 2 m the maximum bubble radius observed has a very weak wind speed dependence and is too small to be explained by simple buoyancy arguments. For void fractions greater than 10−6, bubble size distributions at 2 m can be fitted by a two-slope power law (with slopes of −0.3 for bubbles of radius &lt;80 µm and −4.4 for larger sizes). If normalised by void fraction, these distributions collapse to a very narrow range, implying that the bubble population is relatively stable and the void fraction is determined by bubbles spreading out in space rather than changing their size over time. In regions with these relatively high void fractions we see no evidence for slow bubble dissolution. When void fractions are below 10−6, the peak volume of the bubble size distribution is more variable and can change systematically across a plume at lower wind speeds, tracking the void fraction. Relatively large bubbles (80 µm in radius) are observed to persist for several hours in some cases, following periods of very high wind. Our results suggest that local gas supersaturation around the bubble plume may have a strong influence on bubble lifetime, but significantly, the gas in the bubbles contained in the deep plumes cannot be responsible for this supersaturation. We propose that the supersaturation is predominately controlled by the dissolution of bubbles in the top metre of the ocean, and that this bulk water is then drawn downwards, surrounding the deep bubble plume and influencing its lifetime. In this scenario, oxygen uptake is associated with deep bubble plumes but is not driven directly by them. We suggest that as bubbles move to depths greater than 2 m, sudden collapse may be more significant as a bubble termination mechanism than slow dissolution, especially in regions of high void fraction. Finally, we present a proposal for the processes and timescales which form and control these deeper bubble plumes.

Mineralogical Studies and Radioactivity of the Top Meter Depth of the Egyptian Black Sand, El-Dibeh, Port Said Governorate, Northern Coast of Egypt

Mineralogical Studies and Radioactivity of the Top Meter Depth of the Egyptian Black Sand, El-Dibeh, Port Said Governorate, Northern Coast of Egypt

Brazilian Mangroves: Blue Carbon Hotspots of National and Global Relevance to Natural Climate Solutions

Mangroves are known for large carbon stocks and high sequestration rates in biomass and soils, making these intertidal wetlands a cost-effective strategy for some nations to compensate for a portion of their carbon dioxide (CO2) emissions. However, few countries have the national-level inventories required to support the inclusion of mangroves into national carbon credit markets. This is the case for Brazil, home of the second largest mangrove area in the world but lacking an integrated mangrove carbon inventory that captures the diversity of coastline types and climatic zones in which mangroves are present. Here we reviewed published datasets to derive the first integrated assessment of carbon stocks, carbon sequestration rates and potential CO2eq emissions across Brazilian mangroves. We found that Brazilian mangroves hold 8.5% of the global mangrove carbon stocks (biomass and soils combined). When compared to other Brazilian vegetated biomes, mangroves store up to 4.3 times more carbon in the top meter of soil and are second in biomass carbon stocks only to the Amazon forest. Moreover, organic carbon sequestration rates in Brazilian mangroves soils are 15–30% higher than recent global estimates; and integrated over the country’s area, they account for 13.5% of the carbon buried in world’s mangroves annually. Carbon sequestration in Brazilian mangroves woody biomass is 10% of carbon accumulation in mangrove woody biomass globally. Our study identifies Brazilian mangroves as a major global blue carbon hotspot and suggest that their loss could potentially release substantial amounts of CO2. This research provides a robust baseline for the consideration of mangroves into strategies to meet Brazil’s intended Nationally Determined Contributions.

The Effect of Vegetation Restoration in Soil Organic Carbon Storage

This review paper has been made to assess the past studies reviewed regarding vegetation restoration and its impact on soil organic carbon content. A Vegetation Restoration is an influential technique that can be used to respond to these effects. As a response to the global biodiversity crisis, more restoration actions have been taken. The European Union Council’s results on kinds of diversity after 2010 highlight words like stopping biodiversity loss and the breakdown of ecological systems in the European Union. The United Nations Conference on Biological Diversity’s growth strategy for 2022, which includes restoring at least 15% of degraded ecosystems, has made this possible. Soil types are among the most vulnerable resources on the planet due to factors such as climate change, land degradation, and the reduction of biodiversity. Organic Carbon, the top meter of soil, could potentially store three times as much carbon as is found in the air and almost twice as much as in plants. For the systematic literature review, past papers on vegetation restoration have been extracted from the latest papers of 2013 and onwards to 2022. The summary of results included key findings of the papers, the interpretation of papers reviewed, and the relevant references. Thirty papers were reviewed and selected from authentic databases and assessed that vegetation restoration significantly affects soil organic carbon (SOC). The findings also exhibit that the primary sources of prediction for SOC dynamics include changes in soil properties, quality, the number of carbon inputs, and the composition of the C pool. Vegetation restoration also plays an important role in improving the services of ecosystems such as controlling the erosion of soil and increasing the carbon sequestration. Moreover, some papers concluded that vegetation restoration positively influences on the SOC. Moreover, to increase the generalizability of the study, implications and future research indications have also been included in the end.