Frank D. Eckardt

Mapping the iron oxide content of dune sands, Namib Sand Sea, Namibia, using landsat thematic mapper data

Abstract A linear mixture model was applied to Landsat Thematic Mapper data to map iron-oxide content over the northern part of the Namib Sand Sea, Namibia. Field samples were collected to calibrate the remotely sensed iron oxide proportions to dithionite extractable Fe in mg g−1, the in situ proportions correlating strongly with the remotely sensed estimates (r=0.91). The results reveal a region of high Fe-oxide concentration in the east, an area of low Fe-oxide concentration in the west, separated by a mixing zone. We interpret this to indicate that there is more than one sand source contributing to the sand sea.

Natural Chlorate in the Environment: Application of a New IC-ESI/MS/MS Method with a Cl18O3- Internal Standard

A new ion chromatography electrospray tandem mass spectrometry (IC-ESI/MS/MS) method has been developed for quantification and confirmation of chlorate (ClO₃⁻) in environmental samples. The method involves the electrochemical generation of isotopically labeled chlorate internal standard (Cl¹⁸O₃⁻) using ¹⁸O water (H₂¹⁸O) he standard was added to all samples prior to analysis thereby minimizing the matrix effects that are associated with common ions without the need for expensive sample pretreatments. The method detection limit (MDL) for ClO₃⁻ was 2 ng L⁻¹ for a 1 mL volume sample injection. The proposed method was successfully applied to analyze ClO₃⁻ in difficult environmental samples including soil and plant leachates. The IC-ESI/MS/MS method described here was also compared to established EPA method 317.0 for ClO₃⁻ analysis. Samples collected from a variety of environments previously shown to contain natural perchlorate (ClO₄⁻) occurrence were analyzed using the proposed method and ClO₃⁻ was found to co-occur with ClO₄⁻ at concentrations ranging from < 2 ng L⁻¹ in precipitation from Texas and Puerto Rico to >500 mg kg⁻¹ in caliche salt deposits from the Atacama Desert in Chile. Relatively low concentrations of ClO₃⁻ in some natural groundwater samples (0.1 µg L⁻¹) analyzed in this work may indicate lower stability when compared to ClO₄⁻ in the subsurface. The high concentrations ClO₃⁻ in caliches and soils (3-6 orders of magnitude greater) as compared to precipitation samples indicate that ClO₃⁻, like ClO₄⁻, may be atmospherically produced and deposited, then concentrated in dry soils, and is possibly a minor component in the biogeochemical cycle of chlorine.

Estimating aerodynamic roughness over complex surface terrain

[1] Surface roughness plays a key role in determining aerodynamic roughness length (zo) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While zo can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate zo to morphological roughness metrics. However, dust-emitting landscapes typically consist of complex small-scale surface roughness patterns and few metrics exist for these surfaces which can be used to predictzofor modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust-emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199mm, over which vertical wind velocity profiles were collected to enable estimation of zo. Our data suggest that, although a reasonable relationship (R 2 >0.79) is apparent between 3-D roughness density and zo, the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height (R 2 >0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger-scale isolated roughness elements is most important in determining zo. Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo. This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

The evolution of the morphological framework of the central Namib Desert, Namibia, since the early Cretaceous

The Central Namib Desert in Namibia is a hyper-arid area which was greatly affected by tectonic changes in the Early Cretaceous, associated with the opening up of the South Atlantic Ocean, continental fragmentation of West Gondwanaland and the movement of a major mantle plume (the Tristan Plume). These events led to the formation of a range of subvolcanic complexes – the so-called Damaraland Complexes – and to the deposition of flood basalts – the Etendeka Lavas. The Damaraland Complexes include some striking inselberg features of great size, including Erongo, Brandberg and Spitzkoppe. The Great Escarpment, which bounds the Central Namib to landward, is of uncertain age, but it appears to have experienced a substantial degree of erosion by the Late Cretaceous. The feature is rather less well developed and persistent in the Central Namib than elsewhere in southern Africa. It is probable that the Namib has been dry for much of the last 130 Ma, and there is evidence for aridity in the early Cretaceous and in the mid-Tertiary.

Proposed methodology for georeferencing and mosaicking Corona photographs

A practically based user‐friendly methodology to accurately georeference and colour balance Corona photographs for large area coverages without compromising information content by downgrading their high spatial resolution is presented. Tapping on a range of techniques provided in the Erdas Imagine environment, the procedures laid out in this paper go a step further than normal software guidelines by providing improvised techniques that are graphically illustrated by reference to a study area (the Okavango Delta in northern Botswana) covering about 65 000 km2 to allow the reader to assimilate the sequence of steps involved. With self evident usable results in the form of a 2 m‐resolution seamless mosaic providing blanket coverage for the above stated area on 15 September 1967, it is apparent that similar initiatives elsewhere can take advantage of our proposed methodology in putting together what is retrievable from the archives by building databases that extend time horizons into the historical past for use in long‐term environmental monitoring.

The use of step-wise density slicing in classifying high-resolution panchromatic photographs

The present paper provides an improvised, simple and easy‐to‐follow methodology in which step‐wise density slicing was used to classify high‐resolution panchromatic photographs to levels of spatial detail and accuracy that offer end products comparable with what is obtainable from conventional signature‐based classification of multispectral images. By tapping on a range of manipulative remote sensing and GIS techniques, we provide an illustrated example that takes the reader from on‐screen image display to final compilation and accuracy assessment of a classified map output. Comprising digital classification by image segmentation and visually‐guided grey scale coding, the methodology we offer was practically tested in a change detection investigation around the Okavango Delta in northern Botswana. We conveniently selected one site from this broad study and sampled results over four time‐slices for illustrative purposes. With this improvisation giving results with an accuracy level of 69%, we suggest that this methodology may be used for detailed classification of high‐resolution panchromatic images.

The Present Day Drainage Patterns of the Congo River System and their Neogene Evolution

Whilst the Congo Basin contains one of the world’s largest fluvial systems, little is known about the basin’s geomorphic evolution during the Cenozoic. The basin’s drainage patterns may provide insights into its geomorphic development during the Neogene. The juxtaposition of differing drainage patterns can be explained by the multi-stage evolution of the Congo Basin. The drainage pattern is influenced by several controls, such as lithology and tectonics, which dominate in some regions, with zones of overlap were controls inter-act. The evaluation of the drainage patterns in the context of the basin’s long wavelength geomorphology reveals a relative chronology of events. However, timings of key events are poorly known but evidence obtained using geoecodynamics constrains the ages of major river emplacements. The combination of geologic, geomorphic and phylogenetic data sheds light on the Neogene evolution of the Congo River System.

The dynamism of salt crust patterns on playas

Playas are common in arid environments and can be major sources of mineral dust that can influence global climate. These landforms typically form crusts that limit evaporation and dust emission, modify surface erosivity and erodibility, and can lead to over prediction or underprediction of (1) dust-emission potential and (2) water and heat fluxes in energybalance modeling. Through terrestrial laser scanning measurements of part of the Makgadikgadi Pans of Botswana (a Southern Hemisphere playa that emits significant amounts of dust), we show that over weeks, months, and a year, the shapes of these surfaces change considerably (ridge thrusting of >30 mm/week) and can switch among continuous, ridged, and degraded patterns. Ridged pattern development changes the measured aerodynamic roughness of the surface (as much as 3 mm/week). The dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models.

The Surface Geology and Geomorphology Around Gobabeb, Namib Desert, Namibia

Abstract This paper serves as a brief review and overview of the surface geology and geomorphology around obabeb in the entral amib esert. It introduces the major lithologies associated with the amara rogen of Precambrian and ambrian age, followed by ertiary sandstones and conglomerates and uaternary uiseb valley conglomerates, silts and gravels. To celebrate the 50th anniversary of the obabeb research station and the recent designation of the amib and ea as a world heritage site, we are presenting a map to inform and guide future research and educational activities around obabeb. The contrast between an ancient gravel plain to the north, a dynamic aeolian sand sea to the south and ephemeral river environments in between become apparent. These natural laboratories have attracted investigations of contemporary sand dune movement, hyper saline waters, evaporites and duricrusts and ephemeral flooding and recharge processes as well as environmental change and human impacts.

Hypergame analysis and hydroconflicts in the Okavango drainage basin

Abstract This article provides a game theory based approach to the analysis of interstate conflict between Angola, Botswana and Namibia over the Okavango Rivers shared water resources and tries to offer strategies that can be employed to harmonize incongruent interests. This is done by providing a compressed scenario in which interstate conflicts revolve around lack of adequate mechanisms to satisfactorily distribute shared water resources. The basic premise of the analysis is the following: if relevant data are available, the mathematical inclination of game theoretic modelling provides an objective framework for working out sharing arrangements that minimize conflict. We illustrate this claim on the basis of a hypothetical game where riparian states involved make compensatory sacrifices in order to offset the losses incurred by other partners. We cautiously provide suggestions for the way forward without pretending that these are exhaustive.