Subaqueous Soils Research Articles

Regional distribution trends and properties of acid sulfate soils during severe drought in wetlands along the lower River Murray, South Australia: Supporting hazard assessment

Acid sulfate soil materials, if disturbed or influenced by lowering of water levels, can have serious environmental impacts, that include harm to ecosystems and leaching of acidity and metals into water bodies. Low river flows from 2007 to 2010 due to an unprecedented drought, resulted in 71 wetlands along 210km of the River Murray below Lock 1 in South Australia becoming dry, exposing the normally subaqueous soils in wetlands and, in some instances, causing severe soil acidification. The aim of this study was to provide an understanding of the nature and distribution of acid sulfate soils for hazard assessment and to guide management. Substantial soil survey and acid sulfate soil data from multiple studies were consolidated, interpreted, and described in a regional and local context. Pedological, soil chemical and geomorphology data showed that acid sulfate soils with hypersulfidic (potential to acidify to pH≤4) and sulfuric (pH<4) materials with higher acidification hazard were more dominant in downstream wetlands. A trend observed in the chromium reducible sulfur data was likely linked to regional fluvial erosion and deposition processes because the transition coincides with the river landscape changing from a linear gorge valley upstream to downstream open floodplain areas.

Mapping the Subaqueous Soils of Lake Champlain’s Missisquoi Bay Using Ground-Penetrating Radar, Digital Soil Mapping and Field Measurements

Eutrophication associated with high concentrations of phosphorus in Missisquoi Bay has raised concerns about its influence on submersed aquatic vegetation. Subaqueous soils could play an important role in nutrient cycling, algae blooms, the spread of invasive aquatic vegetation, and water quality. The objectives of this study were to (a) characterize some of the morphological, physical and chemical properties of subaqueous soils in Missisquoi Bay based on ground-penetrating radar and soil analysis; and (b) assess relationships among the subaqueous soil landscapes, radar facies, and submersed aquatic vegetation. Coarse Stratified Sediments and Lacustrine Silt radar facies associated with Delta/Nearshore and Lakebed/Bay Bottom subaqueous soil-landscape units covered 90 percent of the study area. The Lacustrine Silt radar facies occurred in relatively deep, low-energy, depositional areas and had the highest P concentrations. The majority of the submersed aquatic vegetation was associated with Delta/Nearshore and Fringing Peatland subaqueous soil landscapes under shallow water.

Mapping Soils under Water

Mapping Soils under Water

Genesis of freshwater subaqueous soils following flooding of a subaerial landscape

The majority of research on subaqueous soils has so far occurred in estuarine environments where their pedogenic concepts were first explored. We investigated subaqueous soils in a 91ha freshwater impoundment, which prior to flooding were subaerial. Five landscape units across the lake were delineated based on water depth, slope, landscape shape, and depositional environment. Soils were sampled and analyzed for bulk density, particle size distribution, rock fragments, pH, electrical conductivity (EC), organic C and sulfidic materials. Given these soils did not classify as subaqueous under current criteria in Soil Taxonomy, we determined current subaerial classifications and propose new subaqueous classifications: Histic Frasiwassept (subaerial: Typic Humaquept); Typic Frasiwassept (subaerial: Typic Endoaquept); and Fragic Frasiwassept (subaerial: Typic Endoaquept). Lake main channel units have water depths that exceed 2.5m, and thus exceed water depths where subaqueous soils are found. Across Lake channel bank deposits a Fragic Frassiwassept–Typic Frassiwassept complex is found with equal proportions of each soil. Across Lake bottom deposits Fragic Frassiwassepts are mapped. Lake cove deposits consist of a Fragic Frasiwassept–Histic Frasiwassept complex with equal proportions of each soil, and Lake shoals are comprised of Histic Frasiwassepts. Following impoundment creation, additions of mineral and organic material (likely erosional siltation) have resulted in soils with unique morphologic, physical, and chemical characteristics different from subaerial, shoreline soils but expressing a welded morphology that is a product of impoundment creation. These characteristics are identifiable across landforms, indicative of specific processes to soils, and can be reliably mapped in order to support aquatic ecosystem management.

Estuarine Subaqueous Soil Temperature

Most biological and chemical processes related to soil function and formation are temperature dependent. To begin understanding soil temperature in estuarine subaqueous soils, this parameter was investigated in two shallow coastal lagoons in southern New England. Temperature loggers were placed in the soil at two depths (25 and 50 cm) on three subaqueous soil‐landscape types. Soil temperatures were compared among soil‐landscape types, and relative to overlying water temperature, ambient air temperature, and a tidal marsh soil. Subaqueous soil temperature varied slightly among soil‐landscape types, and appears to be primarily influenced by water temperature and depth. Mean annual water temperatures (11.5–12.4°C) were within 1°C of the associated soil temperatures regardless of water depth suggesting that mean annual water temperature would serve as an excellent surrogate for mean annual soil temperature. Soil temperatures at the 50‐cm depth showed less fluctuation than temperatures measured at 25 cm from the soil–water column interface. Mean annual soil temperatures measured at 50 cm were 12.3 and 12.6°C in washover fan and lagoon bottom soils, respectively. Subaqueous soil temperatures were noticeably warmer than the tidal marsh soil. Differences between mean summer and mean winter soil temperatures were &gt;10°C. Thus, these subaqueous soils classify within the mesic soil temperature regime; similar to subaerial soils of southern New England.

Subaqueous soils: their genesis and importance in ecosystem management

AbstractResearch by soil scientists examining estuarine aquatic substrates has identified pedogenic processes, resulting in the reclassification of these aquatic substrates (sediments) as subaqueous soils (SASs). Pedogenic processes in SASs are similar in concept to those occurring in subaerial soils, and thus SASs can be described and mapped based on pedogenic similarities using Jenny’s soil forming factors for interpreting soil genesis. The occurrence of SASs in estuarine and freshwater ecosystems places them at the centre of many ecosystem‐dependent processes supporting food webs linked directly to the human population and its economy. Early research on SASs has been driven by addressing fishery habitat support questions for US subaquatic vegetation populations (SAV), and for estimating the carbon sequestration potential of soils with SAV. New land use interpretations for SASs include bottom type, presence of sulphidic materials, potential for submerged aquatic vegetation restoration, limitations for moorings and species lists for plants and algae common to tidal areas. Subaquatic soils are a viable, exciting frontier of soil science research that will surely foster multi‐disciplinary collaborations. While their genesis is only beginning to be understood, it is clear that their importance in human‐dependent land management issues such as soil and water quality, food supply and human survival is great. However, the fragility of such soils for providing vital functions to support life on Earth suggests that they need to be investigated and monitored.

Avatar of Subaqueous Soils: 11th Edition

Avatar of Subaqueous Soils: 11th Edition

An acid sulfate perspective on landscape/seascape soil mineralogy in the U.S. Mid-Atlantic region

A conceptual framework is presented to portray how Fe, S and other elements (Ca, Si, K) are geologically and pedologically cycled between minerals that are formed and are stable in land-based aerobic environments and those that are formed and are stable in anaerobic sea-based environments. Foremost among the elements discussed are Fe and S, which cycle between Fe sulfides, formed by sulfidization in the anaerobic sea-based environments of tidal marsh and subaqueous soils and sediments, and Fe oxides and jarosite, formed by sulfuricization in upland soils upon the exposure of the sulfide-mineral bearing sediments to oxidizing conditions. Some results of previously conducted experiments are presented to demonstrate that Fe oxides placed in the sea-based anaerobic tidal marsh and subaqueous soils are rapidly transformed to Fe sulfides — apparently by the reduction of Fe 3+ by sulfide of H 2S, generated from sulfate of sea water with the oxidized form of S serving as the electron acceptor during the oxidation of organic matter. Documentation of rapid sulfuricization of sulfidic materials to form sulfuric horizons upon exposure to aerobic conditions is also presented. Ca from sea water, biologically precipitated as calcite and aragonite in shells of organisms that thrive in brackish sea-influenced environments is sometimes transformed temporarily, before dissolution and leaching of the Ca and sulfate, into gypsum by sulfuricization in uplands when the shells are present in exposed sulfidic materials. Silica is also released from silicate minerals during sulfuricization, which can reprecipitate as opal-CT, to cause cementation of soil materials into duripan-like formations. In the geologic past, opal (in the form of diatoms) and glauconite formed in Tertiary-age geologic sediments under marine conditions, to become part of the parent materials for upland active and post-active acid sulfate soils of the present time. Modern formation of glauconite in subaqueous soils and shallow sediments has not been found, but the topic needs further investigation.

Soil/Landscape Relationships in a Mesotidal Maine Estuary

Submerged sediments represent an important component of near‐shore coastal systems. Soil scientists have begun to study subaqueous soils from a pedological perspective, and conceptualize these soils as organic or mineral materials, having the ability to support rooted plants, which are submerged by estuarine, marine, or lacustrine water for a period of time such that their pedogenesis reflects an environment dominated by submergence. The objective of this study was to describe and classify subaqueous soils of a shallow, mesotidal, Maine estuary and identify the relationship between soil properties and landscape position. A detailed bathymetric map was created for the study site using a fathometer, Global Positioning System (GPS), tide gauges, surveying equipment, and Geographic Information System (GIS) software. The bathymetric map was used to identify the slope for each landscape unit and the mean water depth above each landscape unit. Slopes in the study range from 1 to &gt;25%. Water depths above the soil surfaces are between 0.1 and 21.0 m at mean sea level (MSL). Soil samples were collected to depths between 1.0 and 5.5 m below the soil surface using a bucket auger, McCauley peat auger, or vibracoring device. Seven soil landscape units and 10 soil map units were differentiated from one another according slope class, geomorphic position, depositional environment, and soil characteristics. Most of the soil parent materials in the estuary are fine‐textured sediments. This work is the first estuary soil survey completed in Northern New England.

Landscape-level seagrass–sediment relations in a coastal lagoon

We investigated the relationships between sediment (subaqueous soil) properties and eelgrass ( Zostera marina L.) distribution to develop landscape-level soil-based strategies for choosing eelgrass restoration locations. Subaqueous soils were sampled and eelgrass cover determined for 14 soil-landscape units within a 116 ha area of Ninigret Pond, a coastal lagoon in Rhode Island, USA. Of the 14 soil-landscape units sampled for eelgrass cover, 52% had virtually no eelgrass cover (<10%), while 18% had high eelgrass cover (>90%). The Lagoon Bottom, Shallow Lagoon Bottom, Flood-tidal Delta Slope, and Barrier Cove subaqueous soil-landscape units had the highest eelgrass cover (66–100%). A weak relationship between eelgrass cover and water depths ( r 2 = 0.10) was observed suggesting that properties other than water depth may also control eelgrass distribution. Subaqueous soils on landscapes with >60% eelgrass cover had relatively high levels of acid-volatile sulfides (>90 μg/g), high soil salinity levels (34–44 ppt), fine textures (silt loam), and relatively high total nitrogen levels (>0.15%). Four principal components accounted for 81% of the variability in eelgrass cover. The first component reflected particle-size distribution (i.e. sand, silt, and clay contents) effects and accounted for 43% of the variability. The other components suggested that eelgrass cover is correlated to carbonaceous remains, non-calcareous rock fragments and soil salinity. These data suggest that the current distribution of eelgrass within the study area is strongly influenced by physical and chemical subaqueous soil characteristics. Soil survey techniques proved useful for the delineation of sediment characteristics (e.g. texture, salinity) that influence eelgrass distribution patterns at landscape-level scales.

Subaqueous Soil‐Landscape Relationships in a Rhode Island Estuary

Subaqueous soils occur from the lower limit of the intertidal zone to a depth of &lt;2.5 m in protected estuarine coves, bays, inlets, and lagoons. These soils support a diverse floral and faunal assemblage and are a vital component of the estuarine ecosystem. Only recently have pedologists considered these substrates soil, thus, very few subaqueous soils have been characterized and relationships between subaqueous soils and associated subtidal landforms are unknown. In this study, we investigated shallow‐subtidal settings and associated subaqueous soils within a 116‐ha area of a Rhode Island estuary. Our objectives were to gain an understanding of soil distribution within a coastal lagoon and to elucidate subaqueous soil‐landscape relationships within differing geomorphic settings. Twelve submerged landscape units were delineated based on water depth, slope, landscape shape, and the depositional environment. Soils were sampled, described, and representative samples from each landscape unit were analyzed for pH, electrical conductivity, CaCO3, particle‐size distribution, and organic matter. The Lagoon Bottom landscape unit was mostly comprised of Typic Hydraquents (70%). These soils had the finest particle‐size distribution of all soils sampled (silt contents ranged from 23 to 64%; clay contents ranged from 16 to 30%). All the subaqueous soils found within the Storm‐surge Washover Fan Flat were classified as Typic Sulfaquents. Greater than 75% of the Barrier Submerged Beach, Mainland Submerged Beach, Shoal, and the Mid‐lagoon Channel landscape units contained Typic Endoaquents. Thapto‐histic Hydraquents were found in 60% of the Mainland Cove landscape units. These relationships suggest that landscape units can be used to model subaqueous soil distribution at the subgroup taxonomic level. Understanding of the distribution of these soils and the associated characteristics should prove valuable to coastal specialists managing these critical resources.

BEHAVIOR OF CHEMICAL SPECIES UNDER REDOX ENVIRONMENT USING

In order to understand the physical, chemical and biological processes of the chemical species in a subsurface environment, it is important to include the biochemical and cation exchange reactions in the solute transport model. In this study, a two-soil column experiment was carried out to examine the behavior of chemical species in sub-aqueous soils similar to paddy field. A solute transport model that predicts the behavior and transport of multicomponent chemical species in the subsurface environment was developed and applied. The biochemical reactions and cation exchange reactions are modeled in the transport equation as the sink/source terms. This model simulates solute transport and computes changes in concentration over time caused by the biochemical and cation exchange processes. The results of numerical simulation correlated fairly well with the measured concentration.

Factors of subaqueous soil formation: a system of quantitative pedology for submersed environments

The development and use of estuarine sediment maps for estuarine restoration efforts have been hindered by the lack of a formal classification system or comprehensive model that explains the distribution of sediments. To enhance the evaluation, understanding, and management of sediments in shallow water habitats, a new approach must be developed in order to provide a more holistic assessment and cartographic representation of the sediment column. Having demonstrated that shallow water sediments undergo pedogenic processes and are systematically distributed across the subaqueous landscape, we applied this new technique to the development of subaqueous soil resource inventories of Sinepuxent Bay, MD and Indian River Bay, DE. These efforts indicate that the present concept of sediment as unconsolidated geologic materials must give way to a new concept—the concept of subaqueous soils. In addition, our studies indicate the need to alter present methodologies for the acquisition and cartographic representation of sediment data through the utilization of the soil–landscape paradigm and a classification scheme (such as Soil Taxonomy) for the development of subaqueous soil resource inventories. Here we present the supporting rationale for the development of subaqueous soil resource inventories; and through a synthesis of geologic and pedologic principles and concepts, propose a new state factor equation to explain subaqueous soil genesis and distribution.

Subaqueous Soils Pedogenesis in a Submersed Environment

Proposals for the inclusion of permanently submersed materials in soil taxonomic systems have periodically been put forth since some time in the mid 1800s. The proposals were largely conceptual in nature, relying more on subjective reasoning rather than analytical and field data. Advances in computer and global positioning technology, and the continuing development of the discipline of pedology provided the opportunity to examine shallow water estuarine sediments within a pedological framework. Morphological and analytical data from 85 1.5‐ to 2.0‐m profiles from Sinepuxent Bay, Maryland, indicate that the four pedogenic processes of additions, losses, transformations, and transfers outlined in the generalized theory of soil genesis are active in a subaqueous environment. The evidence of pedogenic processes includes the addition of biogenic calcium carbonate (shells), organic fragments, and organic matter; the loss of organic matter and surficial material; the transfer of oxygen through diffusion and bioturbation processes; and the transformation of humic substances and sulfur (sulfidization). The change in the concept of estuarine substrates from sediment to soil has significant ramifications for pedologists, ecologists, estuarine researchers, and government agencies involved in soil resource inventory and estuarine restoration programs. Application of these concepts could help further our understanding of the relationships between subaqueous soil distribution and submersed aquatic vegetation (SAV); clam, scallop, and oyster habitat; and dredge sites with potential acid‐sulfate weathering. This work resulted in a change to the definition of soil in Soil Taxonomy to include subaqueous soils that are capable of or presently support rooted SAV.

Subaqueous Soils: A Pedological Approach to the Study of Shallow-Water Habitats

Science-based management of shallow-water habitats is limited by information on the spatial distribution of properties of sediments. This limitation in part stems from the lack of an adequate model or system to classify and delineate subaqueous soil types (sediments). Present classification systems are inadequate because the existing paradigm does not actually consider them as “soils” but merely as “sediments”. Field observations suggest that these sediments could be better understood as “soils”, and the present paradigm could be modified to incorporate a new one—a pedological paradigm. We propose the application of a pedological paradigm for subqueous soils of subtidal habitats to develop ecological interpretations of subaqueous soil types and apply an inventory of subaqueous soil resources for management of estuarine shallow-water habitats. *** DIRECT SUPPORT *** A01BY074 00009

Geochemical dispersion in lake waters and sediments from massive sulphide mineralization, Agricola Lake area, Northwest Territories

Abstract The Agricola Lake area lies within the tundra and is underlain by continuous permafrost. Archean metavolcanic rocks are host to massive sulphide mineralization, which contains Zn, Cu, Pb, Ag, Au, As, Cd and Hg. This mineralization is being actively oxidized, producing acidic waters enriched in a number of metals. The elements Pb, Ag and Hg are immobile in the surface environment and are largely retained in the soils near the mineralization. Zn, Cd and Cu are mobile and are dispersed in quantity far along the lake-stream system draining the mineralization. Arsenic is relatively immobile, but it has so wide a primary distribution, particularly in metasedimentary rocks overlying the volcanics, that it too is anomalous in sediments throughout the drainage. Ni and Co, derived from these metasedimentary rocks, and as mobile as Zn and Cd, are also strongly anomalous in lake sediments. Fixing of the mobile elements in sediments appears to be determined by their adsorption on iron oxides, Cu being adsorbed at lower pH values and closer to the mineralized source, than Zn, Cd, Ni or Co. The use of nearshore and centre-lake sediments for reconnaissance-level geochemical exploration is compared. The latter are a more homogeneous, finer-grained sampling medium. Dispersion of mobile indicator elements from their source in centre-lake sediment is greater than for nearshore sediment. This is because nearshore sediments are essentially subaqueous soils, that are not produced by lacustrine sedimentation. Adsorption of metals on nearshore material takes place in situ, so that dispersion trains can be no longer than that of the waters in contact. In the case of centre-lake sediments, it is suggested that metals are adsorbed on fine-grained particulates, which travel downstream before settling in the centre-lake bottoms. Waters are the most convenient sampling medium for more detailed levels of exploration. Surface waters are homogeneous within any one lake and show only moderate variation in composition throughout the summer ice-free season. Lake waters that are not derived from mineralized areas are very pure, with dissolved solids contents of 10 ppm or less.

Nitrogen transformations in the former subaqueous soils of polders recently reclaimed from lake IJssel

Nitrogen transformations in the former subaqueous soils of polders recently reclaimed from lake IJssel

Nitrogen transformations in the former subaqueous soils of polders recently reclaimed from Lake Ijssel

Nitrogen transformations in the former subaqueous soils of polders recently reclaimed from Lake Ijssel

Nitrogen transformations in the former subaqueous soils of polders recently reclaimed from Lake Ijssel

In incubation experiments, carried out at 29°C with a calcareous loam soil which had been enriched with ammonium nitrogen and kept in shallow jars, losses of mineral nitrogen, due to denitrification of nitrates previously formed at a slow rate, were found to occur when the moisture content was 90 to 100 per cent of the water capacity (W.C.).