Spatial evaporation patterns within a small drainage basin in the Negev Desert

Sparsely vegetated bedrock slopes in deserts coincide with slope parameters, thus they have important implications on biological, chemical, hydrological and geomorphological processes. Spatial variations in these vegetation patterns, density and communities indicates on relatively humid habitats, which correspond with sinks for high runoff. Relations between the bedrock runoff generation and vegetation patterns may imply on the spatial locations of Byzantine – Early Muslim (400-1000 C.E.; 1600-1000 y BP) agriculture installations. These installations are widespread in the Negev Desert, Israel, utilized sophisticated runoff harvesting techniques by the ancient farmers. Applying a multi-disciplinary approach, we tested vegetation patterns as a precursor for runoff generation along bedrock slopes in the Negev Desert Highlands, and correlated them to the spatial distribution of the Byzantine – Early Muslim runoff agriculture installations. Integrating vegetation patterns, geological substrate data and bedrock-runoff generation data on a GIS model on a large scale (160 km2) of the Negev Highlands yields a synthetic potential runoff map. This map is a unique new product conducted for the first time during this study. Basing on it, runoff yield can be predicted for different scales, ranging from that of a single lithology slope to that of a basin of varying lithologies. Utilizing this methodology, we show that high correlation (80 %) exists between vegetation patterns and spatially located Byzantine – Early Muslim runoff-farming installations. This correlation turns the vegetation coverage as a reliable marker for predicting runoff yield in arid bedrock slopes and imply for stable arid climate in the past 1600 years in the Negev Desert.

Denitrification is the main process removing nitrate in river drainage basins and buffer input from agricultural land and limits aquatic ecosystem pollution. However, the identification of denitrification hotspots (for example, riparian zones), their role in a landscape context and the evolution of their overall removal capacity at the drainage basin scale are still challenging. The main approaches used (that is, mass balance method, denitrification proxies, and potential wetted areas) suffer from methodological drawbacks. We review these approaches and the key frameworks that have been proposed to date to formalize the understanding of the mechanisms driving denitrification: (i) Diffusion versus advection pathways of nitrate transfer, (ii) the biogeochemical hotspot, and (iii) the Damköhler ratio. Based on these frameworks, we propose to use high-resolution mapping of catchment topography and landscape pattern to define both potential denitrification sites and the dynamic hydrologic modeling at a similar spatial scale (<10 km2). It would allow the quantification of cumulative denitrification activity at the small catchment scale, using spatially distributed Damköhler and Peclet numbers and biogeochemical proxies. Integration of existing frameworks with new tools and methods offers the potential for significant breakthroughs in the quantification and modeling of denitrification in small drainage basins. This can provide a basis for improved protection and restoration of surface water and groundwater quality.

Morphometric parameters such as drainage density, stream magnitude, and relief ratio are practical measures of flood potential in small (&lt;100 mi2) drainage basins. Stereoscopic interpretation of low‐altitude aerial photographs provides the most accurate maps of basins for generating these parameters. Field surveys of a high‐density limestone basin in central Texas show that 1:24,000 scale topographic maps accurately portray the efficient stream channel system but fail to reveal numerous small gullies that may form portions of hillslope hydrologic systems. Flood potential in drainage basins can be defined by a regional index computed as the standard deviations of the logarithms of the annual maximum streamflows. High potential basins tend toward greater relief, greater drainage density, and thus greater ruggedness numbers than low–flash flood potential watersheds. For a given number of first‐order channels (basin magnitude), flash flood regions have greater ruggedness numbers, indicating higher drainage densities combined with steep hillslopes and stream channel gradients. Transient controls on flood response, such as differences between local rainstorm intensities, appear to be the major influences on hydrographs in areas of moderate dissection and relief. Morphometric parameters for low‐potential flash flood regions )Indiana and the Appalachian Plateau( are better estimators of frequent low‐magnitude runoff events (mean annual flood), while the same parameters correlate better with the maximum flood of record in high‐flood potential regions (central Texas, southern California, and north central Utah).

Even relatively pristine drainage basins in industrial countries would appear to have received anthropogenic inputs of heavy metals. Investigation of floodplain surface soils in the Lahn River drainage basin, west-central Germany, indicates that the Cu concentration is 1.5 times the pre-industrial level, Pb and Zn contents twice the pre-industrial level; Cd, Co, and Cr concentrations are nearly equal to background metal values. Based on contamination standards developed for the Lahn River, floodplain soils are moderately contaminated with Pb and Zn, slightly contaminated with Cu. Metal contents are uniform across the floodplain, with the exception of a peak immediately adjacent to the Lahn River. Floodplain surface soil metal contents are less in the Lahn River basin than in larger drainage systems of Germany. Although Lahn River metalliferous sediments are presently immobile, they would, if eroded, contribute to downstream heavy metal concentrations. Consequently, metal storage in smaller drainage basins such as the Lahn should be considered in predictions of future metal loads in major river systems, for aggregate small basins could serve as significant metal contributors.

Rock slabs were placed from 1991 through 2006 at the bottom of a north- (NFS) and a south-facing (SFS) slope of a first order drainage basin in the Negev Desert Highlands, Israel (P = 95 mm) where natural cobbles have >95% cover of endolithic and epilithic lichens. Periodic measurements of rain, dew and chlorophyll content took place. Lichen cover and the regeneration time were aspect-dependent. Lichen cover was 98% and 61% at NFS and SFS, respectively, while the lichen's recovery time was respectively ∼45 and ∼80 years. The fast regeneration time may have important implications regarding weathering and soil formation.

Watershed management and headwater reconstruction programmes require a reliable knowledge of sediment source dynamics. GIS techniques are a powerful tool for the assessment of active erosion areas in drainage basins. These analyses were conducted in two small drainage basins in the Italian Alps for which a DEM and detailed inventory maps of sediment sources are available. Field surveys found that active sediment sources (bare slopes, overgrazed areas, shallow landslides, eroding stream banks and debris flow channels) covered 1.1% of Cordevole Torrent basin and 5.2% of the Rio Cordon basin. The GIS techniques involve simple statistical analyses of thematic information, the use of indicators including basin topography and channel network, and the physically based modelling of shallow landslides. The model reproduces the observed distribution of landslide locations consistently and more than 80% of the observed landslide area is predicted to be unstable or to fail with low rainfall. Some 69% of the unconditionally unstable areas and 65% of the slopes predicted to become unstable with low-intensity steady-state rainfall (<_ 50 mm/day1) were identified. Avalanche sources areas and active scree slopes were closely correlated

Land use, precipitation, streamflow, and sediment discharge data were collected from nine small drainage basins in Montgomery County, Maryland, to evaluate runoff and sediment response to sediment-control practices in areas undergoing urban development. Drainage basins ranged in size from 0.35 to 21.1 sq mi and land use ranged from rural to 60 percent urban. Urbanization did not affect low and medium flows, but it did result in increased storm runoff and peak flows. Suspended sediment transported from one of the basins that underwent urban development, the 21.1 sq mi Anacostia River basin, averaged 15 ,400 tons/yr between 1962 and 1974. Bedload was estimated as 5 to 11 percent of the total load. Cropland, urban land, and construction sites were the major sources of sediment. Average annual sediment yields ranged from 065 to 4.3 tons/acre for cropland, 3.7 tons/acre for urban land, and 7 to 100 tons/acre for urban construction sites. The magnitude of the yields from construction sites was significantly affected by (1) the slope of the sites, (2) the proximity of stream channels, (3) buffer zones of natural vegetation, and (4) sediment-control measures. Sediment controls, particularly those enforced under a 1971 sediment-control ordinance, apparently decreased construction-site sediment yields by 60 to 80 percent.

Most of the waters in Serbia are drained to the Black Sea drainage basin (92.6% of its territory), while only a few percentages belong to the Adriatic and Aegean basins. The largest rivers in Serbia are international rivers such as Danube, Sava, Drina, Tisza which have water discharge of 5084 m3/s and the domestic waters contribute with only 481 m3/s. Spatial and temporal distribution of runoff is unequal due to different pluviometric and temperature regimes. The average specific runoff is about 6 l/s/km2 and vary from <1 l/s/km2 (northern parts of Serbia) to 40 l/s/km2 (Prokletije Mt., Šar-planina Mt.). High waters occur in spring, and low waters appear during summer-autumn period. The floods in large river valleys threaten about 18% of the territory of Serbia, while torrential floods occur in small drainage basins with great terrain slopes and erosion on the territory south of the Sava and the Danube. In Serbia, there are a relatively small number of natural lakes. Reservoirs have greater importance for water management. There are also various types of aquifers which are mostly used for the water supply system, while the thermal-mineral water has a recreational-therapeutic purpose.KeywordsHydrological characteristics GroundwaterRiver regimesFloodsHydrological droughtsLakes and reservoirsSerbia

Observed vertical sediment accumulation rates (n = 1031) were gathered from ~ 55 years of peer reviewed literature. Original methods of rate calculation include long-term isotope geochronology (14C, 210Pb, and 137Cs), pollen analysis, horizon markers, and box coring. These observations are used to create a database of global, contemporary vertical sediment accumulation rates. Rates were converted to cm year−1, paired with the observation’s longitude and latitude, and placed into a machine learning–based Global Predictive Seabed Model (GPSM). GPSM finds correlations between the data and established global “predictors” (quantities known or estimable everywhere, e.g., distance from coastline and river mouths). The result, using a k-nearest neighbor (k-NN) algorithm, is a 5-arc-minute global map of predicted benthic vertical sediment accumulation rates. The map generated provides a global reference for vertical sedimentation from coastal to abyssal depths. Areas of highest sedimentation, ~ 3–8 cm year−1, are generally river mouth proximal coastal zones draining relatively large areas with high maximum elevations and with wide, shallow continental shelves (e.g., the Gulf of Mexico and the Amazon Delta), with rates falling exponentially towards the deepest parts of the oceans. The exception is Oceania, which displays significant vertical sedimentation over a large area without draining the large drainage basins seen in other regions. Coastal zones with relatively small drainage basins and steep shelves display vertical sedimentation of ~ 1 cm year−1, which is limited to the near shore when compared with shallow, wide margins (e.g., the western coasts of North and South America). Abyssal depth rates are functionally zero at the time scale examined (~ 10−4 cm year−1) and increase one order of magnitude near the Mid-Atlantic Ridge and at the Galapagos Triple Junction.

Cyanobacteria are confined to dewless habitats within a dew desert: Implications for past and future climate change for lithic microorganisms

Source‐to‐sink studies typically utilize the sedimentary record preserved in basins to infer source area parameters such as estimates of drainage area and discharges of fluvial systems in the hinterland, the characterization of which remains elusive as few geomorphic elements of the hinterland are preserved. Clastic wedges within foreland basin settings often contain fluvial deposits, and the scale of fluvial architectural elements can be used to estimate drainage area and discharge within the accreted hinterland. This study uses thicknesses of fluvial architectural elements within the Late Ordovician Taconic, the Late Devonian‐Early Mississippian Acadian, and the Late Mississippian to Early and Middle Pennsylvanian Alleghanian clastic wedges, together with climatic conditions interpreted from palaeosol data, to estimate the drainage areas and discharges of the river systems which drained the hinterlands of the accreted Taconic and Acadian terrains and the Alleghanian suture of Laurentia and Gondwana. Published detrital zircon age spectra provide insight into ages of source areas of sediments as well as the timing of terrane accretion. The increase in hinterland drainage areas calculated for Late Devonian Acadian Orogeny river systems compared to Late Ordovician Taconic Orogeny river systems can be attributed to the increase in size of accreted terranes to the east of the foreland basins during that period of time. The decrease in hinterland drainage area from the Late Devonian Acadian Orogeny to the Middle to Late Pennsylvanian Alleghanian Orogeny is attributed to the westward migration of the drainage divide as the Alleghanian orogeny proceeded. It is inferred that the drainage divide migrated towards the drier leeward side of the mountain range and caused drainage basins to shrink and split into smaller drainage basins.

In a flat loess area in the Negev Desert of Israel, different amounts and distribution of irrigation were given to 48 squares of 0.25 m2 on 1 and 30 August, 1977. At this time evaporation rates were high and the range of temperatures near the soil surface between irrigation and seedling emergence was 15–53 °C. Of the species appearing in winter in the Negev, only 22 emerged, and only 3 appeared in substantial numbers. Seedlings of species that emerge during winter after about 10 mm of rain did not emerge after the first irrigation in squares receiving 60 mm of water, a few emerged after 90 and 120 mm, and only 57 after 150 mm. After the second irrigation, when evaporation rates and temperatures were lower, in the same squares, 154,334,534, and763 seedlings emerged after receiving90,120,150, and 200 mm, respectively. The highest number of seedlings emerged, but the lowest percentage survived, when the water was divided into equal daily irrigations during the first 9 days. As the daily water amounts decreased, the number of emerging seedlings also decreased, but the % survival increased. As the daily number of irrigations of 30 or 10 mm increased, the number of emerged seedlings and the % survival increased. However, there were significant differences among the species that emerged. The amounts and distribution of water evaporation rates and temperatures were found to be the important germination regulators in those plants which also inhabit regions receiving summer rains.

Flight paths of more than 40,000 nocturnal migrants were collected by tracking radars simultaneously at two sites in spring and autumn. Winds were similar in autumn and spring: i.e., typical, rather weak trade winds with northerly directions below about 1500 m above sea level and with southerly or westerly directions higher up. The tracks of the birds were concentrated around 190° (between S and SSW) in autumn and around 5° (nearly N) in spring. Slight differences between the directional distribution of birds above the Negev Highlands and the Arava Valley could be attributed mainly to local winds and topography. Reversed migration occurring in autumn was at the altitudes of the southwesterly winds. Tracks and headings of different wingbeat classes did not differ significantly, except that birds with low wingbeat frequency and passerine-type flight had more westerly directions in autumn and more easterly directions in spring. Mean groundspeed in autumn was nearly 50 km/h, most birds profiting from...

The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. Valley and channel widths are often estimated through a power-law scaling between width (W) and drainage area (A), and where lithologic variability or differential uplift rates dominate, width was suggested to scale with both slope (S) and drainage area, through the relation W = kb Ab Sc. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in widths that are disproportional to their drainage areas. Consequently, in such cases, the width-area-slope scaling is expected to deviate relative to drainages that did not experience reorganization. To explore the effect of reorganization on width-area-slope scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the drainage area exponent, b, differs between valley categories, and that reversed valleys are characterized by a negative b exponent, indicating valley narrowing with increasing drainage area. A detailed study of a reversed valley reveals that unlike the negative b exponent that links drainage area to valley width, the relation between drainage area and channel width is best fitted with a positive b exponent. This difference indicates that the timescale of channel width adjustment to post-reorganization drainage area distribution is faster than that of the valley width adjustment. We find that the difference in channel width across the divide causes a step change in unit stream power between the adjusted reserved channel and the unadjusted, beheaded channel. Gradients in width and unit stream power across the divide, lead to a width-feedback that promotes ongoing divide migration and reorganization. The identified distinct width-area-slope scaling of reorganized valleys could assist in recognizing and constraining the dynamics of landscapes influenced by drainage reorganization and likely has critical implications for the distribution of erosion rates in reorganized landscapes.

Land use effects on sediment yields and soil loss rates in small basins of Triassic sandstone near Sydney, NSW, Australia