scholarly journals The hydrological role of biological topsoil crusts and water repellency in sandy dry-land areas

2018 ◽  
Vol 36 ◽  
pp. 33-44
Author(s):  
Aaron Yair ◽  
Ram Almog ◽  
Youval Arbel
Keyword(s):  
Water Regime ◽  
Water Repellency ◽  
Annual Rainfall ◽  
Striking Difference ◽  
Water Repellent ◽  
Runoff Generation ◽  
Rainfall Gradient ◽  
Large Trees ◽  
Average Annual Rainfall

Dryland areas are regarded as highly sensitive to climatic changes. A positive relationship between rainfall and environmental factors is often assumed for areas with an average annual rainfall of 100–300 mm. This assumption disregards the fact that a climate change in arid areas is not limited to climatic factors. It is often accompanied by a pronounced spatial variability in surface characteristics. The present work deals with the complex relationships among average annual rainfall, surface properties and the spatial redistribution of water resources in sandy areas located in the Northern Negev Desert. Two case studies are considered. The first deals with the hydrological effects of biological topsoil crusts on the water regime, along a rainfall gradient (86–170 mm). This study is based on five monitoring sites. Data obtained show a decrease in water availability with increasing annual rainfall. The findings are attributed to the decisive role played by the non-uniform properties of the topsoil crust along the rainfall gradient. The second case refers to the non-uniform development, and survival, of planted trees. Trees planted on steep dunes are well developed, with a high survival rate, whereas trees planted on low angle dunes are small. This study focused on the role of a water repellent layer on the water regime. Data obtained show a striking difference between steep and low dunes in all aspects studied, namely the degree of water repellency, frequency and magnitude of runoff events, infiltration depth and soil moisture. All variables monitored were found higher on steep than on low dunes. The large trees shed a substantial amount of leaves, whose decay developed a water repellent layer. Runoff generation over the repellent layer enhanced deep water penetration, through the process of subsurface flow. The lack of a water repellent layer over the low dunes prevented runoff generation, with its positive effects.

THE ROLE OF GRASSLAND IN MANAGEMENT

1968 ◽  
pp. 44-49
Author(s):  
B.K. Cameron
Keyword(s):  
Soil Temperature ◽  
Annual Rainfall ◽  
Silt Loam ◽  
Average Annual Rainfall ◽  
Very High ◽  
Wilting Point

THE PROPERTY to be discussed is a mixed sheep and cropping unit, situated ei ht a miles east of Ashburton and midway between the Ra aia and the Ashburton rivers. Average annual rainfall is 27 in., evenly spread, but there is very high summer evaporation and therefore frequent droughts. On average, the soil is below wilting point for 40 to 50 days each summer. Winters are cold with the soil temperature being below 48°F for about four months each year. The soil is a Lismore stony silt loam averaging 9 in. in depth over gravel.

Landscapes of sandy areas along a rainfall gradient (90-450 mm, average annual rainfall) in the south-eastern Mediterranean area, Israel

2021 ◽  
pp. 1-12
Author(s):  
Yair Aaron
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Environmental Variables ◽  
Eastern Mediterranean ◽  
Mediterranean Area ◽  
Annual Rainfall ◽  
Rainfall Gradient ◽  
Average Annual Rainfall ◽  
Eastern Mediterranean Area ◽  
Hydrological Effects

Dryland areas are regarded as highly sensitive to climatic changes. A positive relationship between average annual rainfall, and environmental factors (water availability, species diversity, etc.), is often assumed for areas with an average annual rainfall of 100-300 mm. However, the global climatological models fail to address an important issue. The above assumption disregards the fact that a climate change in some dry-land areas is not limited to climatic factors. It is often accompanied by a pronounced variability in surface properties, such as the deposition of loess in a wet climatic phase, and of sand during a dry climatic phase. Needless to say, the spatial variability of the new surface properties may have variable effects on water resources and related environmental variables. In addition, the climatic models, based on average annual rainfall, disregard the rainfall characteristics at the rain-shower level, which greatly influence the degree to which rainwater will percolate, or will be transformed into runoff, thereby significantly affecting the spatial redistribution of water resources. In other words, a climate change in dryland areas would be expected to have differential hydrological effects in a sandy area, a rocky area, or in a loess covered area. Differential spatial hydrological effects would be also expected within each of the areas listed above. The present manuscript deals with the complex relationships between average annual rainfall, and environmental variables in sandy areas, at three research sites, along a rainfall gradient of 90-450 mm, in the south eastern Mediterranean area, Israel. Data obtained clearly show that average annual rainfall is not a good indicator of water resources, and ecosystem structure, in each of the sites; and the controlling factors vary from one site to another.

scholarly journals Biological soil crusts cause subcritical water repellency in a sand dune ecosystem located along a rainfall gradient in the NW Negev desert, Israel

2016 ◽  
Vol 64 (2) ◽  
pp. 133-140 ◽  
Author(s):  
Hannes Keck ◽  
Vincent John Martin Noah Linus Felde ◽  
Sylvie Laureen Drahorad ◽  
Peter Felix-Henningsen
Keyword(s):  
Subcritical Water ◽  
Water Drop ◽  
Water Repellency ◽  
Biological Soil Crusts ◽  
Water Repellent ◽  
Rainfall Gradient ◽  
Soil Crusts ◽  
Water Redistribution ◽  
Local Water ◽  
Wilhelmy Plate Method

AbstractThe biological soil crusts (BSCs) in the NW Negev cause local water redistribution by increasing surface runoff. The effects of pore clogging and swelling of organic and inorganic crust components were intensively investigated in earlier studies. However, the effect of water repellency (WR) was not addressed systematically yet. This study investigates subcritical WR of BSCs in three different study sites in the NW Negev. For this purpose, three common methods to determine soil WR were used: (i) the repellency index (RI) method (ii) the water drop penetration time (WDPT) test and (iii) the Wilhelmy plate method (WPM). Furthermore, the potential influence of WR on local water redistribution is discussed and the applied methods are compared. We found the BSC to be subcritically water repellent. The degree of WR may only affect water redistribution on a microscale and has little influence on the ecosystem as a whole. The RI method was clearly the most appropriate to use, whereas the WDPT and the WPM failed to detect subcritical WR.

Plant cover and composition in relation to density of Callitris glaucophylla (white cypress pine) along a rainfall gradient in eastern Australia

2005 ◽  
Vol 53 (6) ◽  
pp. 545 ◽  
Author(s):  
W. A. Thompson ◽  
D. J. Eldridge
Keyword(s):  
Plant Cover ◽  
Tree Cover ◽  
Annual Rainfall ◽  
Rainfall Gradient ◽  
Understorey Vegetation ◽  
Eastern Australia ◽  
Average Annual Rainfall ◽  
Callitris Glaucophylla ◽  
Understorey Plants ◽  
Cypress Pine

Despite the widespread distribution of Callitris glaucophylla J.Thompson & L.Johnson (white cypress pine) over large areas of eastern Australia, little is known about its impact on the diversity and cover of understorey plants. We examined C. glaucophylla woodlands to see whether stand density and land management influenced the cover and composition of the understorey vegetation. The cover and diversity of understorey plant communities were measured at 83 sites along a gradient in average annual rainfall (215–532 mm) in eastern Australia. The diversity and cover of understorey plants and the cover of trees increased, and the composition of the understorey community changed with increases in average annual rainfall. There were no clear relationships, however, between tree cover or density, and the cover or diversity of understorey plants. Sites that had not been logged contained significantly greater proportions of native and perennial vascular plants, and sites with extant eucalypts had a significantly higher proportion of shrubs than those sites without eucalypts. We attributed these differences to past forestry disturbance regimes which are correlated with the presence of mature eucalypts. Our results do not support the proposition that dense stands of C. glaucophylla suppress the understorey vegetation.

scholarly journals Peculiarities of Infiltration Measurements in Water-Repellent Forest Soil

Forests ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 472
Author(s):  
Tomáš Orfánus ◽  
Anton Zvala ◽  
Malvína Čierniková ◽  
Dagmar Stojkovová ◽  
Viliam Nagy ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Forest Soil ◽  
Forest Floor ◽  
Water Repellency ◽  
Water Infiltration ◽  
Water Repellent ◽  
Runoff Generation ◽  
Field Methods ◽  
Single Ring ◽  
Guelph Permeameter

The paper deals with measurements of water infiltration carried out on a well-developed forest floor formed by needle-leaf litter of Norway spruce. Three field methods (tension disk permeameter, single-ring infiltrometer and Guelph permeameter) were used to determine the soil hydraulic conductivity. The results were strongly influenced by the water repellency at the interface between the O- and A-horizons. This interface was severely water repellent during the hot and dry summer season, regardless of the generally humid mountain climate of the High Tatras foothill. The single-ring method paradoxically provided lower hydraulic conductivity (3.2 × 10−4 ± 1.3 × 10−4) compared to the tension disk permeameter (8.5 × 10−4 ± 3.3 × 10−4) due to the presence of the water-repellent O/A-interface. This effect was also observed with the Guelph permeameter method, which gave the lowest value (5.6 × 10−5 ± 4.3 × 10−5). Abrupt retardation of infiltration on the water-repellent interface may generate shallow subsurface runoff (as was proved by the irrigation experiment) or litter splash during extreme rainfall events and promote water flow to deeper soil horizons through preferential pathways. The observed effects of the forest floor on rainfall infiltration will depend on the seasonal variability of soil water repellency. Although the forest floor is a source of hydrophobic substances that cause water repellency at the O/A-interface and can trigger runoff generation, at the same time its cohesive duff layer protects the forest soil from erosion.

Non-adhesive lotus and other hydrophobic materials

2008 ◽  
Vol 366 (1870) ◽  
pp. 1539-1556 ◽  
Author(s):  
David Quéré ◽  
Mathilde Reyssat
Keyword(s):  
Solid Surface ◽  
Room Temperature ◽  
Water Repellency ◽  
Short Review ◽  
Water Repellent ◽  
Practical Applications ◽  
Hydrophobic Materials ◽  
Volatile Liquid ◽  
Air Cushion ◽  
The Stability

Superhydrophobic materials recently attracted a lot of attention, owing to the potential practical applications of such surfaces—they literally repel water, which hardly sticks to them, bounces off after an impact and slips on them. In this short review, we describe how water repellency arises from the presence of hydrophobic microstructures at the solid surface. A drop deposited on such a substrate can float above the textures, mimicking at room temperature what happens on very hot plates; then, a vapour layer comes between the solid and the volatile liquid, as described long ago by Leidenfrost. We present several examples of superhydrophobic materials (either natural or synthetic), and stress more particularly the stability of the air cushion—the liquid could also penetrate the textures, inducing a very different wetting state, much more sticky, due to the possibility of pinning on the numerous defects. This description allows us to discuss (in quite a preliminary way) the optimal design to be given to a solid surface to make it robustly water repellent.

Variation in the morphology and flowering time of cluster clover (Trifolium glomeratum L.) and its relationship to distribution in southern Australia

1995 ◽  
Vol 46 (5) ◽  
pp. 1027 ◽  
Author(s):  
FP Smith ◽  
PS Cocks ◽  
MA Ewing
Keyword(s):  
Genetic Variation ◽  
Flowering Time ◽  
Seed Mass ◽  
Annual Rainfall ◽  
Strongly Correlated ◽  
Summer Maximum ◽  
Maximum Temperatures ◽  
Pattern Of Variation ◽  
Growth Habits

Cluster clover is a widely distributed and ecologically successful introduced legume in southern Australia. In an attempt to understand the role of genetic variation in this success, morphological and physiological traits were measured in 94 accessions from southern Australia and 6 from the Mediterranean basin. Flowering time ranged from 105 to 185 days after sowing, but was not strongly correlated with annual rainfall or length of growing season at the site of collection. Variation in other traits partitioned the populations into two morphs which, apart from flowering time and leaf marker, were largely homogeneous. The morphs differed significantly in floret number per inflorescence (22 v. 32-37) and seed mass (379 8g v. 523 8g), had different growth habits and strong within-morph associations between leaf markers and stipule and petal coloration. The morphs differed in their distributions within southern Australia and the pattern of distribution was related to summer maximum temperatures, winter minimum temperatures and spring rainfall. These results demonstrate that genetic variation has been important to the success of cluster clover and suggests that the variation is organized. The pattern of variation observed and its relationship to ecogeography is consistent with findings for other highly inbreeding species. A map of the species distribution in Western Australia is presented.

Wind blown sediment mass budget of Sahelian village land units in Niger

2001 ◽  
Vol 172 (5) ◽  
pp. 523-531 ◽  
Author(s):  
Jean-Louis Rajot
Keyword(s):  
Wind Erosion ◽  
Size Range ◽  
Arable Land ◽  
Annual Rainfall ◽  
Complete Disappearance ◽  
Mass Budget ◽  
Sediment Mass ◽  
Aeolian Sediments ◽  
Average Annual Rainfall ◽  
The Village

Abstract To assess the mass budget of aeolian sediments transported by wind (erosion vs. deposition) at the scale of village land units (25 kmX25 km), measurements were carried out during 3 years (from 1996 to 1998) in a cultivated field and in a fallow area simultaneously. These were located in the Sahelian zone of Niger with an average annual rainfall of 560 mm. The vertical upward fluxes of particles <20 mu m exported from the study area were estimated from the horizontal sediment fluxes measured using BSNE sand catchers. This mass of exported dust was compared with the vertical downward fluxes of particles of the same size range (<20 mu m) measured using passive CAPYR collectors. Values of deposition recorded in the field and in the fallow were similar. In the field, wind erosion reached its maximum in May and June when the vegetation cover was minimal. In the fallow area, wind erosion was always very low in comparison with the field. It occurred during the strongest storms when the grass cover was minimal. Nevertheless, the net balance between deposition and erosion was highly positive in the fallow areas. These results have been extrapolated at the scale of the village land units based on the current land use. At this scale, the balance was positive for the arable land, indicating a net deposition of aeolian sediments of +0.36 t ha (super -1) yr (super -1) . However, the complete disappearance of fallow land would result in a balanced budget for the arable land.

Performance Study of Nano-TiO2 Modified Fabric

2012 ◽  
Vol 549 ◽  
pp. 733-736
Author(s):  
Xiao Mian Chen ◽  
Jing Jing Shi ◽  
Hong Sha Su ◽  
Chun Ting Lin ◽  
En Long Yang
Keyword(s):  
Titanium Dioxide ◽  
Catalytic Activity ◽  
Catalytic Properties ◽  
Antibacterial Property ◽  
Wear Behavior ◽  
Water Repellency ◽  
Innovative Technology ◽  
Water Repellent ◽  
High Catalytic Activity ◽  
Performance Study

The catalytic properties of nano-TiO2 modified fabric suits the demand for self-cleaning in recent years. In this paper, advanced and innovative technology were used to synthesize water sol of titanium dioxide photocatalyst with high catalytic activity for fabric finishing. The wear behavior, antibacterial property and water repellency of treated and untreated fabric were tested. Results indicate that finishing and washing of the titanium dioxide had no effect on wear behavior; finished and washed fabric has a certain antibacterial and water repellent properties.

scholarly journals Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

2009 ◽  
Vol 9 (5) ◽  
pp. 1579-1595 ◽  
Author(s):  
C. Galy-Lacaux ◽  
D. Laouali ◽  
L. Descroix ◽  
N. Gobron ◽  
C. Liousse
Keyword(s):  
Wet Deposition ◽  
Ph Value ◽  
Precipitation Chemistry ◽  
Annual Rainfall ◽  
Deposition Flux ◽  
Air Concentration ◽  
Ionic Charge ◽  
Rainfall Gradient ◽  
The Mean

Abstract. Long-term precipitation chemistry have been recorded in the rural area of Banizoumbou (Niger), representative of a semi-arid savanna ecosystem. A total of 305 rainfall samples ~90% of the total annual rainfall) were collected from June 1994 to September 2005. From ionic chromatography, pH major inorganic and organic ions were detected. Rainwater chemistry is controlled by soil/dust emissions associated with terrigeneous elements represented by SO42−, Ca2+, Carbonates, K+ and Mg2+. It is found that calcium and carbonates represent ~40% of the total ionic charge. The second highest contribution is nitrogenous, with annual Volume Weighed Mean (VWM) for NO3− and NH4+ concentrations of 11.6 and 18.1 μeq.l−1, respectively. This is the signature of ammonia sources from animals and NOx emissions from savannas soil-particles rain-induced. The mean annual NH3 and NO2 air concentration are of 6 ppbv and 2.6 ppbv, respectively. The annual VWM precipitation concentration of sodium and chloride are both of 8.7 μeq.l−1 which reflects the marine signature of monsoonal and humid air masses. The median pH value is of 6.05. Acidity is neutralized by mineral dust, mainly carbonates, and/or dissolved gases such NH3. High level of organic acidity with 8μeq.l−1 and 5.2 μeq.l−1 of formate and acetate were also found. The analysis of monthly Black Carbon emissions and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) values show that both biogenic emission from vegetation and biomass burning could explain the rainfall organic acidity content. The interannual variability of the VWM concentrations around the mean (1994–2005) is between ±5% and ±30% and mainly due to variations of sources strength and rainfall spatio-temporal distribution. From 1994 to 2005, the total mean wet deposition flux in the Sahelian region is of 60.1 mmol.m−2.yr−1 ±25%. Finally, Banizoumbou measurements are compared to other long-term measurements of precipitation chemistry in the wet savanna of Lamto (Côte d'Ivoire) and in the forested zone of Zoétélé (Cameroon). The total chemical loading presents a maximum in the dry savanna and a minimum in the forest (from 143.7, 100.2 to 86.6 μeq.l−1), associated with the gradient of terrigeneous sources. The wet deposition fluxes present an opposite trend, with 60.0 mmol.m−2.yr−1 in Banizoumbou, 108.6 mmol.m−2.yr−1 in Lamto and 162.9 mmol.m−2.yr−1 in Zoétélé, controlled by rainfall gradient along the ecosystems transect.

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