Subaqueous Soils Research Articles

Subaqueous soil sequence in marine waters of the Strunjan Bay

Soil research focuses mainly on soils on land, but the process of soil formation also takes place in shallow waters. Subaqueous soils form below the water surface, mainly on the bottom of shallow, stagnant waters such as bogs, swamps, lakes, and shoals in the sea. Three subaquatic soil profiles were investigated in the Strunjan Bay to study them in detail. The sites for the soil investigation were selected after observing the movement of seawater and thus its possible influence on subaquatic soils. All the soils studied are permanently and year-round under water. Therefore, all soil samples were collected under water using drainage pipes and by excavation. The samples were slowly drained in the pipes to prevent mixing of the material and to keep the horizons as intact as possible. Visual observations and standard analyses were carried out in the laboratory according to the identified horizons. During the investigation, we found that apart from water properties and movement, most soil-forming factors can be considered constant, so we investigated and presented a soil hydrosequence. According to the WRB classification, the subaqueous soils in the waters of the Strunjan Bay were divided into the reference groups Gleysols and Leptosols.

A subaqueous soil‐landscape conceptual model to guide soil survey in Chesapeake Bay subestuaries

AbstractRhodeRiver, a subestuary on the western shore of Chesapeake Bay, contains a diverse array of subaqueous soils that range from submerged paleosols to fine‐textured fluid soils and organic soils. A subaqueous soil survey was completed for the Rhode River subestuary by collecting bathymetric data, delineating landforms, and sampling and describing soils across the submerged landscape. Soil map units were developed by correlating soil properties and taxonomic classification with delineated landforms, resulting in the development of seven proposed soil series corresponding to new soil map units. Geologic maps and other supporting information about the dominant factors of soil formation in this landscape were used with the soil survey of Rhode River to develop a conceptual subaqueous soil‐landscape model of soil genesis to explain the origin and distribution of soils in Rhode River. This is the first time that a subaqueous soil‐landscape model has been developed for the flooded river valley geomorphic setting of Chesapeake Bay, and it will assist subaqueous soil surveys in other western shore Chesapeake Bay subestuaries and similar environmental settings where upland environments have been or are currently submerging.

Methylmercury in lake bed soils during re-flooding of an Appalachian reservoir in the northeastern USA

Mercury methylation, where inorganic mercury (Hg) is converted to methylmercury (MeHg), can increase in soils when flooded. While effects of the initial flooding of soils on MeHg production have been well studied, less is known about impacts of re-flooding on MeHg production. Lake Perez, an impounded recreational reservoir in the Appalachian Highlands, was completely drained then re-filled 7 years later. We use a combination of chemical, soil physical, and microbial data to quantify changes in MeHg before and after re-flooding of the lakebed. Portions that were transiently saturated due to pluvial flooding had the highest pre-flooded MeHg concentrations. When the lake was re-flooded, concentrations of MeHg in subaqueous soils increased by a factor of 2.74 (+174%) on average. Substantial variability was observed among the sampling sites, with smaller increases in MeHg at sites subjected to seasonal flooding during periods when the reservoir was drained. The increase of soil MeHg after re-flooding was lower in this study compared to studies that evaluated soil MeHg after initial flooding, indicating that re-flooding of a former lake bed caused a smaller response in MeHg production compared to initial flooding of terrestrial land. This study advances understanding of the environmental impact of impounded reservoirs.

A simplified distillation-based sulfur speciation method for sulfidic soil materials

Speciation of inorganic sulfur species, mainly pyrite and metastable iron sulfides by operationally defined methods, is widely used for risk assessment of acid sulfate soils by quantifying the acidity producing elements, as well as for general characterisation of marine sediments and subaqueous soils. “Traditional” sulfur speciation methods commonly use highly specialised glassware which can be cumbersome for the operator, or, require long reaction times which limit the usability of the method. We present a simplified method which has a sufficiently low limit of detection (0.002%) and quantitation (0.006%) required for the analysis of sulfidic sulfur in acid sulfate soil materials. Commercially available sulfide reagents were used for determining reproducibility and the method was assessed on natural sulfidic soil materials, including fine to coarse grained soil materials as well as sulfide bearing peat, with a large variation of metastable sulfide and pyrite content.

SELECTED CASES OF SUBAQUEOUS SOILS IN SLOVENIAN COASTAL WATERS

Selected cases of subaqueous soils in Slovenian coastal waters The soil is mainly on the mainland, but also in shallow waters, the so-called subaqueous soils. Subaqueous soils form under the water surface, mainly on the bottom of shallow, stagnant waters such as bogs, swamps, lakes, and sea shallows. In St. Bartholomew, three subaqueous soil profiles were studied to investigate them in detail. The sites for recording the soil profiles were selected at random, with the aim of finding a different type of vegetation at each site. We found that the soils were influenced by almost the same factors of subaqueous soil formation; thus, the same soil forming processes of different intensity took place. Therefore, the same, very similar types of subaqueous soils were developed at each site. All samples were collected underwater using drainage pipes and by excavation. The samples were drained in the pipes. In the laboratory, visual observations and standard analysis were performed according to the horizons determined. According to the WRB classification, subaqueous soils in Slovenian coastal waters were classified asreference groups Gleysols and, Arenosols.

Impacts of Oyster Aquaculture on Subaqueous Soils and Infauna

Oyster aquaculture maintains water quality via filter‐feeding processes; however, few studies have investigated the impacts of resulting biodeposits on the underlying soils. In this study, we investigated the impacts of oyster aquaculture by comparing biodeposition rates, physical and chemical properties of subaqueous soils, and infaunal communities among aquaculture and control sites in three coastal lagoons in Rhode Island. Aquaculture study sites ranged in age of use from 0 (control) to 21 yr. We applied biodeposits at an equivalent amount generated by as high as 2000 oysters m−2 wk−1 to control soils and did not observe significant enrichment, suggesting that soils and infauna can process considerable amounts of biodeposit‐derived N (5.4 g m−2 d−1) and C (44.3 g m−2 d−1) quickly. Although soils under aquaculture sites received significant biodeposits (67.8–346.47 g dry wt. m−2 d−1), soil N and C levels were only significantly higher at the 12‐yr site and at deeper depths (5–20 cm) in 50% of sites, suggesting considerable soil processing and/or mixing. Signs of detrimental impacts on the soil environment in aquaculture sites included elevated soil pore‐water sulfide levels, independent of time in aquaculture, and a shift in infaunal community structure, favoring higher populations of deposit feeders and opportunistic species indicative of environmental disturbance. Although our results suggest that biodeposit‐derived N and C additions are offset by infaunal processing, the changes in infaunal community structure and elevated pore‐water sulfides indicate that coastal managers should consider the possibility of a decrease in soil quality as a function of aquaculture‐related site disturbance.Core Ideas Oyster filter feeding expels N‐ and C‐rich biodeposits onto soils beneath aquaculture racks. Soils and infauna are capable of processing considerable amounts of oyster‐derived N and C inputs. Oyster aquaculture primarily affects infaunal communities and soil and pore‐water sulfide levels.

The forensic comparison of trace amounts of soil on a pyjama top with hypersulphidic subaqueous soil from a river as evidence in a homicide cold case

Abstract In a cold case investigation of a 1983 homicide, trace amounts of soil were identified on a 10-year-old victim's pyjama top. Swatch samples were cut from the pyjama top, specifically the hem, to determine the provenance of this questioned soil. A comparative study was undertaken of the questioned soil with control soils from the Onkaparinga estuary using morphological observations with the naked eye and scanning electron microscopy (SEM), chemistry, traditional laboratory X-ray diffraction (XRD) and synchrotron µ-XRD. Synchrotron µ-XRD with high-intensity X-rays provided greater sensitivity and resolution than the laboratory XRD source to identify pyrite and clay minerals on the pyjama top. SEM confirmed that these mineral particles are deeply impregnated in gaps between fibres of the fabric, which are likely to have originated under water with force being applied on the pyjama top – implying that the victim was pushed into the mud. This is substantiated by transference shaking experiments, where mineral particles are dominantly located on the surface of the fabric. The questioned soil samples have a moderately strong degree of comparability with the control hypersulphidic subaqueous soils containing pyrite in the Onkaparinga River estuary – providing evidence that the soils have similar origins. The accused was found guilty by a Supreme Court judge of murder.

Effect of waterlogging on soil biochemical properties and organic matter quality in different salt marsh systems

This study investigated the effects of hydroperiod on soil organic matter quality in three different salt marshes in the Baiona lagoon (N Italy) representing terrestrial, intertidal and subaqueous ecosystems in the area. The study specifically aimed to gain some insight into how soil waterlogging (hydroperiod) affects the chemical and biological properties of soils as well as the quality and structure of the soil organic matter (SOM). Total contents of selected nutrients, total organic carbon and carbon stable isotope (δ13C) were measured in all soil profiles. The results of these analyses enabled us to define the different origin of the SOM by discriminating between terrestrial and aquatic SOM sources. The findings also show that accumulation of nutrients and SOM is significantly magnified in intertidal systems, in which pedoturbation effects induced by water movements are particularly strong. In addition, DRIFT spectra of humic acids revealed the changes in the main functional groups in relation to increased waterlogging, highlighting the lower aromaticity and complexity in subaqueous soils (SASs), which is possibly due to the effect of the soil water saturation on the chemical and biological SOM transformation processes. Microbial biomass carbon (MBC), microbial quotient (Qmic) and the activities of some soil enzymes were measured to estimate soil metabolic activity in the systems and to evaluate how the microbial pool contributes to transforming the SOM. In all systems, the enzymatic activities were generally higher in subsurface horizons than in the surface horizon. This unexpected behaviour can be explained by the combined effect of water movement, erosion processes and preservation of SOM under anaerobic conditions. This study represents an attempt to investigate and understand the ongoing degradation processes in salt marsh ecosystems. The findings emphasize the strong influence of water flow and erosional processes associated with soil waterlogging on chemical and biological reactions in intertidal and subaqueous systems.

Mapping Freshwater Subaqueous Soil Resources: Examples from Southern New England

Core Ideas Soil series were developed for Humaquepts, Frasiwassists, and Psammentic and Aeric Frasiwassents. GPR technology provided accurate analysis of water depth, substrate type, and organic thickness. We identified five soil‐landscape units: lakebed, shoals, shoreline, coves, and deepwater. Subaqueous soils are those that occur under permanently flooded or ponded environments. Few studies have investigated freshwater subaqueous soil systems. In this study, we used traditional and modified soil survey techniques to investigate subaqueous soils in three created (impoundments) and three natural freshwater lakes in southern New England. The objectives were to test the effectiveness of bathymetric maps and ground‐penetrating radar (GPR) for establishing soil–landscape relationships in freshwater subaqueous systems, compare soil types between natural and impounded systems, and investigate the genesis of these soils. Bathymetric data were collected with a fathometer to create topographic maps of the lake bottoms to delineate subaqueous landscapes. Ground penetrating radar transects were run across landscape units to test the effectiveness of this technology to identify soil properties that could be used to separate mapping units. The primary landscape units identified included lakeshores, coves, lakebeds, and shoals. Lakebed and lakeshore units comprised 71 to 90% of the landscape regardless of whether the water bodies were natural or impounded. Ground penetrating radar was effective at identifying the presence of stones and boulders at the soil surface, stratified mineral layers, and the thickness of organic soil materials. Eighty‐one pedons were characterized and classified as Frasiwassists (34), Frasiwassents (32), and Humaquepts (18). All three great groups were identified in both natural and impounded systems with Frasiwassists the dominant soil type in all of the impounded sites. The primary soil processes included melanization resulting in umbric epipedons and organic matter accumulation resulting in histic epipedons in impounded sites with dense invasive vegetation. Frassiwassists were likely developed prior to submergence in both the natural and impounded systems.

Pedological Studies of Subaqueous Soils as a Contribution to the Protection of Seagrass Meadows in Brazil

ABSTRACT: Seagrass meadows are considered one of the most important and valuable ecosystems on the planet, but also one of the most threatened. Missing knowledge about their existence and their subtidal nature are the main reasons for the lack of information about seagrass soils, especially in Brazil and other tropical areas. This study discussed the paradoxical lack of information about subaqueous soils, with a view to stimulate research on soil properties of seagrass meadows. This short communication provides information about [...]

Soil taxonomy proposals for acid sulfate soils and subaqueous soils raised by the 8th International Acid Sulfate Soils Conference

The 8th International Acid Sulfate Soils Conference presented examples and discussions for classification of ‘acid sulfate soils’ and related issues for ‘subaqueous soils’. When these soils are disturbed or exposed, the sulfides (predominantly pyrite) react with oxygen to produce sulfuric acid; soil materials that do this to a great extent are recognised as ‘sulfidic materials’ in Soil Taxonomy. Soil Taxonomy describes physical and chemical properties and thresholds for incubation of sulfidic materials for acidification, and has developed definitions for features and materials commonly seen in these soils. However, based on discussions and examples from field tours the conference has several proposals to modify and add to existing definitions, such as adding new subgroups, defining sulfuric materials and editing the definition of the sulfuric horizon. These changes are centred on improving the interpretative value of taxa in Soil Taxonomy as well as use and management recommendations and their value in soil survey products.

Understanding sulfide distribution in subaqueous soil systems in southern New England, USA

Sulfidization is an important soil forming process in estuarine and marine soils. There has been considerable work done in intertidal and upland soils regarding sulfides, as well as a body of research on sulfides in marine sediments, but there has been little published on sulfide distribution in subaqueous soils in the context of the pedologic approach to studying and classifying these materials. Our objectives were to determine the distribution of sulfides in subaqueous soils and to evaluate sulfide levels (total reducible inorganic sulfur, TRIS; acid volatile sulfides, AVS; and chromium reducible sulfur, CRS) in relation to soil properties including carbon content, CaCO3 content, soil texture, oxidized pH, and conductivity. Sulfide analysis was completed on 52 representative samples collected from 17pedons in three shallow coastal embayments in southern New England, USA. TRIS, calculated as AVS plus CRS, ranged from 33 to 11,592μgg−1 with CRS representing nearly 100% of the sulfides. Sand content showed a strong negative correlation (r=−0.85) with TRIS. Thus, sandy subaqueous soils (Psammowassents) had the lowest sulfide levels. Although oxidized pH is often used to identify sulfidic materials, we found that the proportion of the variance in oxidized pH predicted from TRIS was very low (r=0.19). In contrast, the amount of salts extracted from samples after treatment with H2O2 (TSox) showed a strong relationship with TRIS (R2=0.70). We found that there was generally 5 to 10 times more CaCO3 by weight (the source of which is shell fragments) than sulfides, yet the pH often dropped below 4.0 upon moist incubation; suggesting that shell materials may not effectively neutralize acidity generated from oxidizing sulfides. Australian and World Reference Base (WRB) soil classification systems recognize both hyper (oxidized pH4.0 or below) and hypo (contain oxidizable sulfides, but pH doesn't drop as low as 4.0) sulfidic soil materials. Soil Taxonomy, however, only recognizes materials that result in a drop in pH below 4.0 as sulfidic (hypersulfidic). The recognition of hypersulfidic and hyposulfidic materials in Soil Taxonomy should be a consideration for future changes in this soil classification system.

Historical developments in the understanding of acid sulfate soils

Literature about the historical and current recognition of kinds, names and classification for, overall processes (sulfidization and sulfuricization) that form and conditions that induce the formation of potential, active and post-active acid sulfate soils are reviewed to set the stage for papers presented elsewhere in this special issue of Geoderma that contains some of the papers presented at the Eighth International Acid Sulfate Soils Conference held at the University of Maryland, College Park, MD, USA, July 17–23, 2016. Mention is made and examples cited of environmental problems such as AMD (acid mine drainage) and ARD (acid rock drainage), fish kills in waters receiving drainage from acid sulfate soils, even from ones considered post-active, and special land reclamation and management practices to produce crops on land disturbed (often deeply) by humans (including engineers poorly educated about acid sulfate soils) or by natural causes (sea level rise or fall, or extreme drought, such as the recent “Millennium Drought” in the Murray-Darling Basin of Australia. The global distribution of acid sulfate soils is considered, recognizing that post-active ones are extensive, with many likely currently unrecognized, although features in some of them, such as silcrete and ferricrete, likely owe their origin to acid sulfate weathering phenomena. Most coastal subaqueous soils are influenced by sulfidization and constitute sulfidic materials that if dredged and deposited in upland disposal areas become exposed to aerobic conditions and are likely to give rise to active acid sulfate soils with sulfuric horizons.

Simulated upland placement of estuarine dredged materials

Placement of estuarine dredged materials on the land surface can result in severe environmental issues if acid sulfate conditions develop. In this study, upland placement of marine dredged material was simulated using a mesocosm experiment. Dredged materials were sampled from eight low energy and high energy subaqueous soil-landscape units of four estuaries in Rhode Island. Soils were mapped in the low energy landscape units (i.e. coves and bottoms) as Sulfiwassents and in the high energy units (i.e. deltas and fans) as Psammowassents. Dredged materials were characterized for various physical and chemical properties, placed into mesocosms, and exposed to natural climatic conditions outside. In addition, high energy and low energy materials were mixed at ratios of 20:1, 10:1, 5:1, and 2.5:1 and placed in mesocosms. Mesocosm leachate was collected and analyzed for pH, conductivity, and sulfate content for over 2years (one year for the mixed mesocosms). Dredged materials ranged from sand to silt loam textures with the Sulfiwassents having finer textures and higher levels of carbon and calcium carbonates. Inorganic sulfide concentrations ranged from 56 to 3410μgg−1, with an average of 228μgg−1 for the Psammowassents and 2319μgg−1 for Sulfiwassents. Concentrations of Zn in the Sulfiwassent materials decreased by more than half after 2-years suggesting leaching of Zn during oxidation of the dredged materials. Leachate from low energy Sulfiwassents showed a large drop in pH (pH≤4.0) associated with sulfide oxidation and creation of acid sulfate conditions, while leachate from coarser textured Psammowassents increased in pH to >8.0, presumably from the formation of salts. These conditions generally persisted for the duration of the experiment. Salts washed out of the dredged material fairly quickly such that leachate conductivities reached <5dSm−1 in 10months. Sulfate content of the leachate varied for the first 18months with the Sulfiwassent materials having higher levels and taking longer to wash out. Leachate from mixing as little as 5% Sulfiwassent with Psammowassent materials resulted in acid sulfate leachate (pH<4) in less than a year. Our results suggest that developing soil interpretations for upland placement of dredged materials of estuarine subaqueous soils should be focused on limitations as the result of creation of acid sulfate conditions and leaching of metals for Sulfiwassents and potentially high pH values for Psammowassents.

Three new Penicillium species from marine subaqueous soils

During investigation of the mycobiota in the Sea of Okhotsk, three new Penicillium species were isolated from subaqueous soils collected in the Sakhalin Gulf and in the northeastern part of the Sakhalin shelf, near the Piltun Bay. According to Raper and Thom’s classification, the newly described species P. piltunense, P. ochotense, and P. attenuatum belong to subsection Divaricata. Two analyses were performed to reveal the phylogenetic relationships of the putative new species with other Penicillium species. Phylogenetically, the new species are related to the members of the P. canescens group and share some morphological and physiological features with them. However, they differ in having a larger colony diameter that makes them similar to P. atrovenetum, P. coralligerum, and P. antarcticum. A detailed analysis based on ITS, combined β-tubulin and calmodulin datasets, and morphological features revealed that the new species formed a distinct group inside the P. atrovenetum subclade. Moreover, P. attenuatum differs from the other two species macro- and micromorphologically and may represent a distinct phylogenetic lineage.

Extreme environments in the critical zone: Linking acidification hazard of acid sulfate soils in mound spring discharge zones to groundwater evolution and mantle degassing

A decrease in flow from the iconic travertine mound springs of the Great Artesian Basin in South Australia has led to the oxidation of hypersulfidic soils and extreme soil acidification, impacting their unique groundwater dependent ecosystems. The build-up of pyrite in these systems occurred over millennia by the discharge of deep artesian sulfate-containing groundwaters through organic-rich subaqueous soils. Rare iron and aluminium hydroxysulfate minerals form thick efflorescences due to high evaporation rates in this arid zone environment, and the oxidised soils pose a significant risk to local aquatic and terrestrial ecosystems. The distribution of extreme acidification hazard is controlled by regional variations in the hydrochemistry of groundwater. Geochemical processes fractionate acidity and alkalinity into separate parts of the discharge zone allowing potentially extreme environments to form locally. Differences in groundwater chemistry in the aquifer along flow pathways towards the spring discharge zone are related to a range of processes including mineral dissolution and redox reactions, which in turn are strongly influenced by degassing of the mantle along deep crustal fractures. There is thus a connection between shallow critical zone ecosystems and deep crustal/mantle processes which ultimately control the formation of hypersulfidic soils and the potential for extreme geochemical environments.

Hydromorphic to subaqueous soils transitions in the central Grado lagoon (Northern Adriatic Sea, Italy)

The Grado lagoon is among the largest in the Mediterranean sea and is characterized by salt marshes, where tides influenced the development of a complex micromorphology coupled to a micromosaic of vegetation covers. This study represents the first contribution to the understanding of the main processes governing formation, development and spatial transitions between hydromorphic and subaqueous soils in an Adriatic lagoon ecosystem. Physicochemical characteristics and development of soils were investigated in three salt marshes differing for their proximity to the open sea, textural composition and age of formation. Soils of back barrier salt marshes had A/C profiles and were mostly characterized by a sandy coarse texture that allows rapid drainage and subsurface oxygen exchanges. Soil sequences from the inner salt marsh to its submerged border slope or to a brackish waterhole do not simply represent a hydrosequence, but also reflect erosion/sorting/accumulation processes.The soils in the central part of the lagoon have finer texture and in displayed transition or cambic horizons. Silty clay loam textures and low positions allowed the development of more severe anoxic conditions and accumulation of sulphides. The tide oscillation strongly contributed to formation of redoximorphic features, intensity of anaerobic conditions but also colonization by different plant communities. Discriminant analysis was performed to identify physicochemical properties which discriminate the different soils according to geo-morphological position and prevailing plants. It confirmed that differentiation of plant communities occurred according to distinct morphological and physicochemical soil properties, but also acted as a primary affecting factor of pedogenesis.

First observations on marine subaqueous soils in "Torre del Cerrano" marine protected area, Adriatic sea (Italy)

Subaqueous soils have to be studied with proper methodologies, according to a pedological approach and considering the key role of animal bioturbation. Morphological and chemical characteristics of submerged soils found in the MPA of Torre del Cerrano, Adriatic sea (Italy), have been studied in this way, and we conclude that submarine soils of the MPA are important examples of pedogenesis promoted by animals. Soils from the highly protected marine area hosted a major biodiversity than those from the sub- and non-protected areas, while no striking differences in terms of soil physical and chemical characteristics among protected, sub-protected and non-protected areas occurred.

Subaqueous Soils and Coastal Acidification: A Hydropedology Perspective with Implications for Calcifying Organisms

In the coastal zone, biological and biogeochemical processes, influenced by anthropogenic inputs, drive pH variability and contribute to coastal acidification. Spatial patterns of these processes across coastal estuaries are unknown. In this study, we used a hydropedological approach to assess the spatial variability of coastal acidification within two coastal lagoons and embayments in Rhode Island by measuring oyster shell dissolution, pH within the water column, and pore water pH within the upper 5 cm of the underlying subaqueous soils. Sampling and monitoring sites were stratified based on submerged soil-landscape types mapped at the Great Group level as Haplowassents, Sulfiwassents, and Psammowassents. We found that pore water pH varied significantly among soils and with depth. Median pore water pH was significantly greater in sandy, low organic matter content Psammowassents (7.97) than the finer textured, higher soil organic matter content Sulfiwassents (7.35), and the Haplowassents (6.57) that receive groundwater discharge from the surrounding subaerial soils. Juvenile calcifying organisms can experience acidic stress at pH values below 7.6; thus, current pH values within the upper few centimeters of Sulfiwassents and Haplowassents may be low enough to impact recently set juvenile calcifying organisms inhabiting these soils. Consequently, mean shell loss during a 4-wk period was significantly greater in the Sulfiwassents (1.54) than the Psammowassents (0.96%), with the greatest shell loss (18.62%) in one of our Haplowassent sites with groundwater discharge. Our research suggests that measures of pore water pH and shell dissolution may be helpful in developing soil interpretations regarding the effects of coastal acidification on calcifying organisms.

Underwater Soils: Classifying and studying subaqueous soils can provide huge benefits for conservation, restoration, ecosystem services, and infrastructure

Underwater Soils: Classifying and studying subaqueous soils can provide huge benefits for conservation, restoration, ecosystem services, and infrastructure