Spatial Variation of Soil Salinity in the Mexicali Valley, Mexico: Application of a Practical Method for Agricultural Monitoring

The degradation of irrigated lands through the process of soil salinization, or the buildup of salts in the soil, has hampered recent increases in agricultural productivity and threatens the sustainability of large-scale cultivation in critical agricultural regions of the world. Rapid detection of soil salinity on a regional basis has been identified as key for effective mitigation of such land degradation. The ability to detect regional patterns of soil salinity at an accuracy sufficient for regional-scale resource management is demonstrated using Landsat 5 Thematic Mapper (TM) imagery. A case study of the Mexicali Valley of Baja California, Mexico was selected due to the region's agricultural significance and concern for future soil salinity increases. Surface soil salinity was mapped using georeferenced field measurements of electrical conductivity (EC), collected concurrently with Landsat 5 TM imagery. Correlations between EC measurements and common indices derived from the satellite imagery were used to produce a model of soil salinity through regression analysis. Landsat band 7, TNDVI, PCA 1, Tasseled Cap 3 and Tasseled Cap 5 were found to offer the most promising correlations with surface soil salinity. Generally low levels of soil salinity were detected, however, distinct areas of elevated surface salinity were detected at levels potentially impacting sensitive crops cultivated within the region. The difficulty detecting low levels of salinity and the mid-range spatial resolution of Landsat 5 TM imagery restrict the applicability of this methodology to the study of broad regional patterns of degradation most appropriate for use by regional resource managers.     

Chemical and colloidal analyses of natural seep water collected from the exploratory studies facility inside Yucca Mountain,Nevada, USA

Yucca Mountain is being considered as a geological repository for the USA’s spent nuclear fuel and high-level nuclear waste. Numerous groundwater seeps appeared during March 2005 within the exploratory studies facility (ESF), a tunnel excavated in the mountain. Because of the relevance to radionuclide transport and unsaturated zone-modeling studies, we analyzed the seep samples for major anions and cations, rare earth elements, and colloids. Major ion species and elemental concentrations in seep samples reflect interaction of the water with the volcanic rock and secondary calcites. Elemental fractograms from flow-injection field-flow fractionation ICP–MS scans detected Br, Ca, Cl, Cu, Fe, I, Mg, Si, Sr, W, and U at void fractions, suggesting they may be present in the form of dissolved anions. Colloids approximately 10 nm in hydrodynamic diameter, possibly calcite, were also present in the seepage samples. Geochemical calculations indicate, however, these may be an artifact (not present in the groundwater) which arose because of loss of CO₂ during sample collection and storage.     

Risks and opportunities for foreign investment in the mineral sectors of the Central Asian Republics: Kazakstan,Kyrgyzstan, Tajikistan and Uzbekistan

With the dissolution of the former Soviet Union in 1991, the nations of Central Asia gained independence and began the transition to market driven economies. Both the political and economic transformations of the Central Asian Republics (CARs) (Kazakstan, Kyrgyzstan, Tajikistan and Uzbekistan) have been difficult primarily because of a holdover of various centrally planned `command and control' approaches to national development. The extensive mapping and exploration of the CARs during the Soviet era (approximately 1921–1991) led to the discovery of several hundreds of mineral deposits that were subsequently evaluated, and it is this `pool' of known, but undeveloped, deposits which is of major interest to foreign and domestic companies. However, foreign investment in the mineral sectors of the CARs is at best quite modest and there are very few positive signs that foreign investment will increase dramatically in the near term. The major risks that the mining industry faces as it works in the CARs arise primarily from the fact that the nations are transitional economies which lack both a comprehensive legal framework and experience in dealing with foreign mining corporations and their practices. The major risks are political, economic, financial, infrastructure, contractual, environmental, social and cultural and workforce related. If all individual risk factors are weighted equally, the relative ranking of the countries (from least risk to most risk for mineral development) would be Kyrgyzstan, Kazakstan, Uzbekistan and Tajikistan respectively. However, such a classification scheme does not effectively weight the importance of mineral potential. If the risk criteria are weighted with respect to geologic potential, the ranking of the countries would be (from least risk to most risk) Kazakstan, Uzbekistan, Kyrgyzstan and Tajikistan, respectively.     

Dust dynamics in off-road vehicle trails: Measurements on 16 arid soil types, Nevada, USA

Soil analyses and measurements with the Portable In Situ Wind Erosion Laboratory (PI-SWERL) were conducted on 16 soil types in an area heavily affected by off-road vehicle (ORV) driving. Measurements were performed in ORV trails as well as on undisturbed terrain to investigate how ORV driving affects the vulnerability of a soil to emit PM10 (particles < 10 μm), during the driving as well as during episodes of wind erosion. Particular attention is paid to how the creation of a new trail affects those properties of the topsoil that determine its capability to emit PM10. Also, recommendations are given for adequate management of ORV-designed areas. The type of surface (sand, silt, gravel, drainage) is a key factor with respect to dust emission in an ORV trail. Trails in sand, defined in this study as the grain size fraction 63–2000 μm, show higher deflation thresholds (the critical wind condition at which wind erosion starts) than the surrounding undisturbed soil. Trails in silt (2–63 μm) and in drainages, on the other hand, have lower deflation thresholds than undisturbed soil. The increase in PM10 emission resulting from the creation of a new ORV trail is much higher for surfaces with silt than for surfaces with sand. Also, the creation of a new trail in silt decreases the supply limitation in the top layer: the capacity of the reservoir of emission-available PM10 increases. For sand the situation is reversed: the supply limitation increases, and the capacity of the PM10 reservoir decreases. Finally, ORV trails are characterized by a progressive coarsening of the top layer with time, but the speed of coarsening is much lower in trails in silt than in trails in sand or in drainages. The results of this study suggest that, to minimize emissions of PM10, new ORV fields should preferably be designed on sandy terrain rather than in silt areas or in drainages.