SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Silt

170

We describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. The chamber was always in the dark zone, and not accessible to non-hominins. Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occurring during/after deposition. Hominins accumulated over time as older laminated mudstone units and sediment along the cave floor were eroded. Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date.

Concepts: Human, Sediment, Sedimentary rock, Erosion, Geology, Fossil, Silt, Taphonomy

154

Soil plays a key role in the global carbon © cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in microaggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation.

Concepts: Climate, Soil, Erosion, Atmosphere, Steppe, Silt, Subsoil, Topsoil

147

In the Loess Plateau, soil erosion has not only caused serious ecological and environmental problems but has also impacted downstream areas. Therefore, a model is needed to guide the comprehensive control of soil erosion. In this study, we introduced the WEPP model to simulate soil erosion both at the slope and watershed scales. Our analyses showed that: the simulated values at the slope scale were very close to the measured. However, both the runoff and soil erosion simulated values at the watershed scale were higher than the measured. At the slope scale, under different coverage, the simulated erosion was slightly higher than the measured. When the coverage is 40%, the simulated results of both runoff and erosion are the best. At the watershed scale, the actual annual runoff of the Liudaogou watershed is 83m3; sediment content is 0.097 t/m3, annual erosion sediment 8.057t and erosion intensity 0.288 t ha-1 yr-1. Both the simulated values of soil erosion and runoff are higher than the measured, especially the runoff. But the simulated erosion trend is relatively accurate after the farmland is returned to grassland. We concluded that the WEPP model can be used to establish a reasonable vegetation restoration model and guide the vegetation restoration of the Loess Plateau.

Concepts: Sediment, Soil, Erosion, Silt, Surface runoff, Geomorphology, Loess Plateau, Deforestation

140

The successful establishment of agricultural crops depends on sowing quality, machinery performance, soil type and conditions, among other factors. This study evaluates the operational quality of mechanized peanut sowing in three soil types (sand, silt, and clay) with variable moisture contents. The experiment was conducted in three locations in the state of São Paulo, Brazil. The track-sampling scheme was used for 80 sampling locations of each soil type. Descriptive statistics and statistical process control (SPC) were used to evaluate the quality indicators of mechanized peanut sowing. The variables had normal distributions and were stable from the viewpoint of SPC. The best performance for peanut sowing density, normal spacing, and the initial seedling growing stand was found for clayey soil followed by sandy soil and then silty soil. Sandy or clayey soils displayed similar results regarding sowing depth, which was deeper than in the silty soil. Overall, the texture and the moisture of clayey soil provided the best operational performance for mechanized peanut sowing.

Concepts: Soil, Erosion, Silt, Sand, Clay, Loess, Statistical process control, W. Edwards Deming

47

Sedimentary dispersal systems with fine-grained beds are common, yet the physics of sediment movement within them remains poorly constrained. We analyze sediment transport data for the best-documented, fine-grained river worldwide, the Huanghe (Yellow River) of China, where sediment flux is underpredicted by an order of magnitude according to well-accepted sediment transport relations. Our theoretical framework, bolstered by field observations, demonstrates that the Huanghe tends toward upper-stage plane bed, yielding minimal form drag, thus markedly enhancing sediment transport efficiency. We present a sediment transport formulation applicable to all river systems with silt to coarse-sand beds. This formulation demonstrates a remarkably sensitive dependence on grain size within a certain narrow range and therefore has special relevance to silt-sand fluvial systems, particularly those affected by dams.

Concepts: Sediment, River, Erosion, Silt, Yellow River, Sand, Sediment transport, Sedimentology

28

Soil degradation associated with soil erosion and land use is a critical problem in Iran and there is little or insufficient scientific information in assessing soil quality indicator. In this study, factor analysis (FA) and discriminant analysis (DA) were used to identify the most sensitive indicators of soil quality for evaluating land use and soil erosion within the Hiv catchment in Iran and subsequently compare soil quality assessment using expert opinion based on soil surface factors (SSF) form of Bureau of Land Management (BLM) method. Therefore, 19 soil physical, chemical, and biochemical properties were measured from 56 different sampling sites covering three land use/soil erosion categories (rangeland/surface erosion, orchard/surface erosion, and rangeland/stream bank erosion). FA identified four factors that explained for 82 % of the variation in soil properties. Three factors showed significant differences among the three land use/soil erosion categories. The results indicated that based upon backward-mode DA, dehydrogenase, silt, and manganese allowed more than 80 % of the samples to be correctly assigned to their land use and erosional status. Canonical scores of discriminant functions were significantly correlated to the six soil surface indices derived of BLM method. Stepwise linear regression revealed that soil surface indices: soil movement, surface litter, pedestalling, and sum of SSF were also positively related to the dehydrogenase and silt. This suggests that dehydrogenase and silt are most sensitive to land use and soil erosion.

Concepts: Statistics, Evaluation, Sediment, Soil, Factor analysis, Erosion, Silt, Geomorphology

28

The effects of monorhamnolipid (RL-F1) and dirhamnolipid (RL-F2) on the sorption and desorption of triclosan (TCS) in sediment-water system were investigated in this study. Results of the bath equilibrium experiments showed that RL-F2 provided much higher solubilization enhancement for TCS than RL-F1. Sorption of both rhamnolipids by the sediments was highly correlated with the sediment clay content. Moreover, the apparent distribution coefficients of TCS K(d)(∗) decreased with the increase of rhamnolipid concentration (0.05-7.5mM), and RL-F2 presented a larger distribution capacity of TCS into the aqueous phase at relatively higher concentrations (>2.5mM). Further results also indicated that the release of TCS from sediment could be enhanced by both rhamnolipids. RL-F2 was more efficient than RL-F1 in desorbing TCS from the sediment with low clay content. The TCS desorption percentages R(d)(∗) of RL-F2 (5mM) was 1.8-2.4 times that of RL-F1. These findings could provide useful guidelines for the application of rhamnolipid-enhanced remediation technologies for TCS contaminated sediment.

Concepts: Concentration, Chemistry, Erosion, Aqueous solution, Silt, Phase diagram, Parts-per notation, Sediments

16

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide. Mechanical destruction of seagrass habitats may also trigger the erosion of sedimentary organic carbon (Corg) stocks, which may contribute to increasing atmospheric CO2. This study presents the first estimates of loss of Corg stocks in seagrass meadows due to mooring activities in Rottnest Island, Western Australia. Sediment cores were sampled from seagrass meadows and from bare but previously vegetated sediments underneath moorings. The Corg stores have been compromised by the mooring deployment from 1930s onwards, which involved both the erosion of existing sedimentary Corg stores and the lack of further accumulation of Corg. On average, undisturbed meadows had accumulated ~6.4 Kg Corg m(-2) in the upper 50 cm-thick deposits at a rate of 34 g Corg m(-2) yr(-1). The comparison of Corg stores between meadows and mooring scars allows us to estimate a loss of 4.8 kg Corg m(-2) in the 50 cm-thick deposits accumulated over ca. 200 yr as a result of mooring deployments. These results provide key data for the implementation of Corg storage credit offset policies to avoid the conversion of seagrass ecosystems and contribute to their preservation.

Concepts: Carbon dioxide, Sediment, Sedimentary rock, Ecosystem, Erosion, Silt, Gravel, Rottnest Island

15

Soil degradation due to erosion is connected to two serious environmental impacts: (i) on-site soil loss and (ii) off-site effects of sediment transfer through the landscape. The potential impact of soil erosion processes on biogeochemical cycles has received increasing attention in the last two decades. Properly designed modelling assumptions on effective soil loss are a key pre-requisite to improve our understanding of the magnitude of nutrients that are mobilized through soil erosion and the resultant effects. The aim of this study is to quantify the potential spatial displacement and transport of soil sediments due to water erosion at European scale. We computed long-term averages of annual soil loss and deposition rates by means of the extensively tested spatially distributed WaTEM/SEDEM model. Our findings indicate that soil loss from Europe in the riverine systems is about 15% of the estimated gross on-site erosion. The estimated sediment yield totals 0.164 ± 0.013Pgyr-1 (which corresponds to 4.62 ± 0.37Mgha-1yr-1 in the erosion area). The greatest amount of gross on-site erosion as well as soil loss to rivers occurs in the agricultural land (93.5%). By contrast, forestland and other semi-natural vegetation areas experience an overall surplus of sediments which is driven by a re-deposition of sediments eroded from agricultural land. Combining the predicted soil loss rates with the European soil organic carbon (SOC) stock, we estimate a SOC displacement by water erosion of 14.5Tg yr-1. The SOC potentially transferred to the riverine system equals to 2.2Tgyr-1 (~15%). Integrated sediment delivery-biogeochemical models need to answer the question on how carbon mineralization during detachment and transport might be balanced or even off-set by carbon sequestration due to dynamic replacement and sediment burial.

Concepts: Sediment, Soil, Erosion, Silt, Surface runoff, Gravel, Geomorphology, Sediment transport

10

Successful recruitment in corals is important for the sustenance of coral reefs, and is considered a demographic bottleneck in the recovery of reef populations following disturbance events. Yet several factors influence larval settlement behaviour, and here we quantified thresholds associated with light attenuation and accumulated sediments on settlement substrates. Sediments deposited on calcareous red algae (CRA) directly and indirectly impacted coral settlement patterns. Although not avoiding direct contact, Acropora millepora larvae were very reluctant to settle on surfaces layered with sediments, progressively shifting their settlement preference from upward to downward facing (sediment-free) surfaces under increasing levels of deposited sediment. When only upward-facing surfaces were presented, 10% of settlement was inhibited at thresholds from 0.9 to 16mgcm(-2) (EC10), regardless of sediment type (carbonate and siliciclastic) or particle size (fine and coarse silt). These levels equate to a very thin (<150μm) veneer of sediment that occurs within background levels on reefs. Grooves within settlement surfaces slightly improved options for settlement on sediment-coated surfaces (EC10: 29mgcm(-2)), but were quickly infilled at higher deposited sediment levels. CRA that was temporarily smothered by sediment for 6d became bleached (53% surface area), and inhibited settlement at ~7mgcm(-2) (EC10). A minor decrease in settlement was observed at high and very low light intensities when using suboptimal concentrations of a settlement inducer (CRA extract); however, no inhibition was observed when natural CRA surfaces along with more realistic diel-light patterns were applied. The low deposited sediment thresholds indicate that even a thin veneer of sediment can have consequences for larval settlement due to a reduction of optimal substrate. And while grooves and overhangs provide more settlement options in high deposition areas, recruits settling at these locations may be subject to ongoing stress from shading, competition, and sediment infilling.

Concepts: Algae, Sediment, Coral, Coral reef, Scleractinia, Sedimentary rock, Silt, Settling