Making silica rock coatings in the lab: synthetic desert varnish

Application of field portable X-ray fluorescence to the analysis of desert varnish samples in areas affected by coal-fired power plants

Environmental Chemistry ◽

10.1071/en11139 ◽

2012 ◽

Vol 9 (4) ◽

pp. 379 ◽

Cited By ~ 7

Author(s):

Piotr Nowinski ◽

Vernon F. Hodge ◽

Shawn Gerstenberger

Keyword(s):

Air Pollution ◽

Power Plant ◽

Power Plants ◽

Tracer Concentration ◽

X Ray ◽

Desert Varnish ◽

Geographical Regions ◽

Rock Coatings ◽

Fluorescence Spectrometer ◽

Non Destructive

Environmental context Rock surfaces are often covered with a dark coating called desert varnish that can capture and retain air pollutants. A field portable X-ray fluorescence spectrometer was used for direct non-destructive analysis of varnished rocks in the fallout zones of two coal-fired power plants. At one power plant where tracer studies had been carried out, the highest concentration of elements including Cr, As, Pb and Zn in the rock varnish samples, coincides with the peak tracer concentration locations. AbstractDesert varnish samples were collected near two coal-fired power plants to determine if the varnish contained a record of recent air pollution. Samples were collected: (1) in the fallout patterns of the shuttered Mohave Power Plant (MPP), located in Laughlin, NV; and (2) near the operating Reid-Gardner Power Plant (RGPP), just east of Las Vegas, NV. Small pieces of varnished rocks were analysed by field portable X-ray fluorescence spectroscopy (FPXRF). Results were obtained for 15 elements: Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, Mo, Hg and Pb. The FPXRF data indicate that the elements commonly found in fly ash from coal-fired power plants (e.g. Cr, Zn, As and Pb) had significantly higher concentrations in the rock coatings in relation to the unvarnished substrate rock. For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the desert varnish coincided with the peak tracer concentration locations. Thus, these elements in desert varnish hold promise for identifying those geographical regions affected by nearby power plants. However, additional samples are required to demonstrate unequivocally that the power plants are indeed the sources of these elements. Overall, it is apparent that desert varnish can be utilised as a passive environmental monitor to investigate recent air pollution (past 20–30 years) and that FPXRF can be used as a surveying tool to obtain multi-element data from a large number of samples.

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Rock Coatings

10.1016/s0928-2025(98)x8001-6 ◽

1998 ◽

Keyword(s):

Rock Coatings

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Impact of Climatic Change on an Arid Watershed: Nahal Yael, Southern Israel

Quaternary Research ◽

10.1016/0033-5894(79)90001-2 ◽

1979 ◽

Vol 11 (2) ◽

pp. 153-171 ◽

Cited By ~ 54

Author(s):

William B. Bull ◽

Asher P. Schick

Keyword(s):

Climatic Change ◽

Sediment Yield ◽

Fracture Density ◽

Dense Networks ◽

Valley Fill ◽

Water And Sediment ◽

Desert Varnish ◽

Gravel Size ◽

Induced Changes ◽

Geomorphic Surfaces

The Nahal Yael basin is underlain chiefly by schist, amphibolite, and granite. Thin (generally <1 m thick), grussy colluvium which covered the lower portions of granitic hillslopes in the late Pleistocene has now been stripped completely, causing marked contrasts in outcrop morphologies, even where there is no contrast of fracture density or petrologic characteristics. Formerly mantled slopes are now smooth and crumbly, and lack desert varnish. Previously unmantled slopes are rough and craggy, and varnished but little weathered. Such stripping suggests a change from a semiarid to a drier and/or warmer climate. Slopes underlain by amphibolite responded similarly to the climatic change, but the amphibolite was more deeply weathered, and the colluvium was only partially stripped. The least stripping of colluvium occurred on schist hillslopes, partly because schist outcrops require more rain to generate runoff, and partly because angular blocks of schist require larger flows for transport, compared to other slope lithologies. The stream subsystem responded to the climatically induced changes in the discharge of water and sediment from the hillslopes. Increase in sediment yield caused valley alluviation in the early Holocene, and a decrease in sediment yield later in the Holocene caused entrenchment of the valley fill. More granite and amphibolite gravel-size particles are transported now than when the hillslopes were extensively mantled. Dense networks of trails are not common on Holocene geomorphic surfaces, but are present on remnants of Pleistocene surfaces.

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