Rain impact soil crust. I. Formation on a granite derived soil

Soil Research ◽  
1991 ◽  
Vol 29 (2) ◽  
pp. 271 ◽  
Author(s):  
AJ Moss
Keyword(s):  
Optical Microscopy ◽  
Stress Waves ◽  
Bed Load ◽  
Soil Crust ◽  
Rigid Surface ◽  
Soil Crusts ◽  
Loose Packing ◽  
Underlying Soil ◽  
Silt Layer

The formation of soil crusts caused by raindrops (rain-impact soil crusts), on a granite-derived aqualf, was studied experimentally with the aid of optical microscopy. Crust development was initiated when rigid 10-50 pm particles were concentrated on the surface by preferential removal of both coarser and finer material in the airsplashing environment. The resulting silt concentrate was spread over the surface by lateral outflow sheets from the drops, forming a closely packed, dilatant, bed-load layer about 0-5 mm thick. This layer strongly resisted deformation by raindrop impacts and also suppressed hydraulic penetration, which tends to enhance loose packing. Compaction of the underlying soil, to a depth of about 5 mm, followed the establishment of the silt layer. This compaction was attributed to the action of stress waves, notably primary waves, propagated when drops impacted the effectively near-rigid surface of the silt layer.

Rain impact soil crust. IV. Packing of sand and silt fractions by raindrops

Soil Research ◽  
1991 ◽  
Vol 29 (2) ◽  
pp. 331 ◽  
Author(s):  
AJ Moss
Keyword(s):  
Void Ratio ◽  
Packed Bed ◽  
Stress Waves ◽  
Soil Crust ◽  
Structural Element ◽  
Loose Packing ◽  
Impact Events ◽  
Underlying Soil ◽  
Silt Layer ◽  
Critical Void

Comparison of resistance to fast and slow deformation by rain-packed and artificially prepared sand and silt fractions showed that, whereas sands are left in loosely packed states after accrual under rain impact, silts are left more densely packed, i.e. below critical void ratio. This contrast is attributed mainly to the declining importance of hydraulic penetration with pore size. Rain-packed silt is dilatant and cannot deform without expansion which, in turn, requires water entry at a rate compatible with the required deformation. In the short duration of rain-impact events, hydrodynamic time lagging occurs because water can move only slowly through the small silt pores. Consequently, densely packed silt remains essentially rigid. However, drop-outflow sheets are able to entrain silt and distribute it over the surface as densely packed bed-load deposits, thus maintaining its dilatancy. Sand, its larger pores invaded by hydraulic penetration jets which maintain loose packing, cannot behave in this manner. Relative stability of the silt layer on soil surfaces, and its suppression of hydraulic penetration, allow transmission of drop-generated stress waves which cause the immediately underlying soil to become compacted into the main structural element of the rain-impact soil crust.

scholarly journals Relationships between Soil Crust Development and Soil Properties in the Desert Region of North China

2017 ◽  
Author(s):  
Jiping Niu ◽  
Kai Yang ◽  
Zejun Tang ◽  
Yitong Wang
Keyword(s):  
Organic Matter ◽  
Microbial Biomass ◽  
Soil Properties ◽  
Enzyme Activities ◽  
North China ◽  
Organic Matter Content ◽  
Matter Content ◽  
Soil Crust ◽  
Soil Crusts ◽  
Underlying Soil

This study investigated the effects of soil crust development on the underlying soil properties. The field sampling work was conducted in June 2016 in the Hobq Desert in Inner Mongolia, North China. Soil crust samples and 0–6, 6–12, 12–18, 18–24, 24–30 cm deep underlying soil samples were taken from five representative areas of different soil crust development stages. All samples were analyzed for physicochemical properties including water content, bulk density, aggregate content, organic matter content, enzyme activities, and microbial biomass carbon and nitrogen. The results showed that the thickness, water content, macroaggregate (>250 μm) content, organic matter content, microbial biomass and enzyme activities of the soil crusts gradually increased along the soil crust development gradient, while the bulk density of the soil crusts decreased. Meanwhile, the physicochemical and biological properties of the soils below the algal and moss crusts were significantly ameliorated when compared with the physical crust. Moreover, the amelioration effects were significant in the upper horizons (approx. 0–12 cm deep) and diminished quickly in the deeper soil layers.

Rain impact soil crust. II. Some effects of surface slope, drop size and soil variation

Soil Research ◽  
1991 ◽  
Vol 29 (2) ◽  
pp. 291 ◽  
Author(s):  
AJ Moss
Keyword(s):  
Drop Size ◽  
Surface Zone ◽  
Special Role ◽  
Soil Crust ◽  
Surface Slope ◽  
Small Surface ◽  
Near Surface ◽  
Loose Packing ◽  
Soil Variation ◽  
Stable Particles

Formation and non-formation of the rain-impact soil crust were studied experimentally over ranges of surface-slope, drop-size and soil variation. In these contexts, the formative process was found to be very versatile. However, stable particles, of a size just movable on the soil surfaces by raindrops, appear to play a special role in preventing crust development. Becoming juxtaposed on the surface, these particles form clusters which allow hydraulic penetration of water from impacting drops, through their large pores. This maintains loose packing in the near-surface zone as opposed to the compaction associated with crust formation where only small surface pores exist. A method of soil modification, involving increasing the proportion of durable, barely rain-movable particles in soils, is suggested as a means of combating crusting on a long-term basis.

Heppia arenacea and Lempholemma polycarpum, two new species from southern Yemen and Socotra

2005 ◽  
Vol 37 (3) ◽  
pp. 227-235 ◽  
Author(s):  
M. SCHULTZ
Keyword(s):  
New Species ◽  
Calcareous Soil ◽  
Soil Crust ◽  
Soil Material ◽  
Diagnostic Characters ◽  
Basaltic Rocks ◽  
South Eastern ◽  
Soil Crusts ◽  
Two New Species

Heppia arenacea M. Schultz and Lempholemma polycarpum M. Schultz are described as new and placed in the Lichinaceae. Heppia arenacea occurs in soil-crust communities in southern Yemen and on Socotra. It colonizes both calcareous soil-crusts over limestone as well as soils originating from basaltic rocks. The sand-coloured, squamulose thallus, the erumpent, dark red apothecia and the incorporation of soil material into the thallus are diagnostic characters. Lempholemma polycarpum occurs on inclined limestone boulders in south-eastern Yemen. It is characterized by an umbilicate-lobate thallus with radiating, tongue-shaped, furcate lobes which bear numerous, small, immersed apothecia with punctiform discs.

Modes of Bed-Load Movement on a Smooth Rigid Surface

2011 ◽  
Vol 137 (10) ◽  
pp. 1283-1286 ◽  
Author(s):  
C. S. James ◽  
N. Bulovic ◽  
E. Naidoo
Keyword(s):  
Bed Load ◽  
Rigid Surface ◽  
Load Movement

Morphological diversity and abundance of biological soil crusts differ in relation to landscape setting and vegetation type

2008 ◽  
Vol 56 (3) ◽  
pp. 246 ◽  
Author(s):  
A. Briggs ◽  
J. W. Morgan
Keyword(s):  
Vascular Plants ◽  
Vegetation Type ◽  
Biological Soil Crust ◽  
Biological Soil Crusts ◽  
Annual Rainfall ◽  
Soil Crust ◽  
Vegetation Types ◽  
Bare Ground ◽  
Soil Crusts ◽  
Morphological Composition

Biological soil crusts are common in many arid and semi-arid regions of the world, including Australia. Crusts alter soil factors including water availability, nutrient content and erosion susceptibility and are likely to both directly and indirectly affect vascular plants. Despite emerging recognition as important ecosystem components, these soil communities are understudied. We describe the morphological composition and distribution of lichens and bryophytes in soil crusts from the northern riverine plains, Victoria, in relation to landscape setting and vegetation type. Sampling was conducted across a geomorphological gradient in three different vegetation types (Callitris glaucophylla woodland, Eucalyptus woodland and red-soil native tussock grassland) with an annual rainfall of ~400 mm. Mean cover of biological soil crust for the study area was 18%, with mosses and crustose and foliose lichens the most conspicuous components. Total cover of biological soil crust increased as bare ground and vascular plant cover increased, and litter cover decreased. As a consequence, cover and morphological composition of biological soil crusts differed in the three vegetation types, with mosses responding differently from lichens and liverworts in relation to the cover of litter, bare ground and vascular plants. Hence, biological soil crusts were a conspicuous component in vegetation where they had not previously been described and may play an important role in regulating the structure and function of these plant communities.

scholarly journals Microdiagnostics of initial pedogenesis on a phosphogypsum dump

2018 ◽  
Vol 8 ◽  
Author(s):  
Victor Petrovich Belobrov ◽  
M. P. Lebedeva ◽  
K. N. Abrosimov ◽  
A. M. Grebennikov ◽  
E. L. Torochkov ◽  
...  
Keyword(s):  
Water Erosion ◽  
Morphological Features ◽  
Soil Crust ◽  
Thin Sections ◽  
Saratov Region ◽  
Structural Organisation ◽  
Soil Crusts ◽  
Dry Steppe ◽  
Bioclimatic Conditions ◽  
Pedogenic Processes

This paper presents the results of the study of initial pedogenesis on phosphogypsum dump rocks under dry steppe bioclimatic conditions (Balakovo, Saratov Region, Russia). It was shown that a soil crust about 3 cm thick was formed at the dump surface as a result of natural pedogenic processes over a period of 20-30 years. Such soil crusts act to cement the surface and protect the dump material from deflation and water erosion. The crust was shown to consist of two parts that can be distinguished by morphological features: an upper part (about 2 cm thick) of a more firmly bound material more grey in colour and a lower part (about 1 cm thick) with a looser consistency and lighter colour. The structural organisation is primarily determined by the presence of live roots of grasses and mosses, which is characteristic of a biogenic crust. The two parts of the crust were characterized at both macro- and micro-scales, by use of thin sections and tomographic imagery. The presence of humification features and porosity observed within the crust allowed for the diagnostics of initial pedogenesis.</p><p align="center"> </p><p align="center"> 

The lifestyle of lichens in soil crusts

2018 ◽  
Vol 50 (3) ◽  
pp. 397-410 ◽  
Author(s):  
T. G. Allan GREEN ◽  
Ana PINTADO ◽  
Jose RAGGIO ◽  
Leopoldo Garcia SANCHO
Keyword(s):  
Climate Extremes ◽  
Net Photosynthesis ◽  
Water Source ◽  
Soil Crust ◽  
Soil Crusts ◽  
The Usa ◽  
Additional Water ◽  
The Common ◽  
Open Nature ◽  
Thallus Water Content

AbstractLichens are one of the common dominant biota in biological soil crusts (biocrusts), a community that is one of the largest in extent in the world. Here we present a summary of the main features of the lifestyle of soil crust lichens, emphasizing their habitat, ecophysiology and versatility. The soil crust is exposed to full light, often to high temperatures and has an additional water source, the soil beneath the lichens. However, despite the open nature of the habitat the lichens are active under shady and cooler conditions and avoid climate extremes of high temperature and light. In temperate and alpine habitats they can also be active for long periods, several months in some cases. They show a mixture of physiological constancy (e.g. similar activity periods and net photosynthetic rates) but also adaptations to the habitat (e.g. the response of net photosynthesis to thallus water content can differ for the same lichen species in Europe and the USA and some species show extensive rhizomorph development). Despite recent increased research, aspects of soil crust ecology, for example under snow, remain little understood.

scholarly journals Diversity of algae and lichens in biological soil crusts of Ardley and King George islands, Antarctica

2017 ◽  
Vol 29 (3) ◽  
pp. 229-237 ◽  
Author(s):  
Nadine Borchhardt ◽  
Ulf Schiefelbein ◽  
Nelida Abarca ◽  
Jens Boy ◽  
Tatiana Mikhailyuk ◽  
...  
Keyword(s):  
Green Algae ◽  
Biological Soil Crust ◽  
Soil Crust ◽  
Antarctic Soil ◽  
Sources Of Information ◽  
Maritime Antarctic ◽  
Soil Crusts ◽  
Sampling Locations ◽  
High Species Richness ◽  
Layer Chromatography

AbstractIn the present study the biodiversity of the most abundant phototrophic organisms forming biological soil crust communities were determined, which included green algae, diatoms, yellow-green algae and lichens in samples collected on Ardley and King George islands, Maritime Antarctic. The species were identified by their morphology using light microscopy, and for lichen identification thin layer chromatography as also used to separate specific secondary metabolites. Several sources of information were summarized in an algae catalogue. The results revealed a high species-richness in Antarctic soil crust communities with 127 species in total. Of which, 106 taxa belonged to algae (41 Chlorophyta, nine Streptophyta, 56 Heterokontophyta) and 21 to lichens in 13 genera. Moreover, soil crust communities with different species compositions were determined for the various sampling locations, which might reflect microclimatic and pedological gradients.

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