Salt Encrustations Research Articles

Evolution of Alkaline Mine Drainage and Unique Biodiversity on Soil-Free Mine Substrates, Southern New Zealand

Relatively impermeable soil-free substrates (clay-rich outcrops and sediments) exposed at eight abandoned placer gold mines generate alkaline mine drainage through evaporation and minor interaction between water and rock in a semi-arid rain shadow climate. Original mine sluicing a century ago created drainage channels over the land surface that still control the flow of ephemeral surface waters, with localised construction of erosional outwash pans. Ephemeral surface waters and associated evaporitic salts are dominated by halite derived from marine aerosols in rain, yielding circumneutral pH and electrical conductivity (EC) values locally exceeding 50 mS/cm. Weakly altered schist basement rocks and Miocene mudstone exposed at the surface contain abundant calcite, and surface waters are supersaturated with respect to Ca-carbonate minerals with a pH of ≈ 8 and an EC of ≈ 1 mS/cm. Water interaction with albite increases the dissolved Na/Cl molar ratio to > 1, and evaporative formation of Na-carbonate precipitates can raise the pH to > 10. Pyrite oxidation does not offset the alkaline pH in any of these processes, although dissolved sulfate can rise to high levels (> 2000 mg/L; EC ≈ 5 mS/cm), forming evaporative sulfate minerals. Ephemeral waters drain down outcrops and the relatively impermeable erosional pans, leaving salt encrustations with variable mineralogy and associated waters with pH and EC values that are partially controlled by rates of dissolution and reprecipitation of the minerals in the salts. The saline alkaline chemistry of the pans excludes most vegetation and has allowed development of salt-tolerant ecosystems with rare endemic halophytic plants. Maintenance of soil-free halophytic surfaces has potential applications in dryland mine sites around the world, especially as climate change enhances and extends aridity.

Geological controls on evolution of evaporative precipitates on soil-free substrates and ecosystems, southern New Zealand

Soil-free bare substrates have formed by natural and human-induced processes in a semi-arid rain shadow, in the lee of actively rising mountains. These substrates have developed evaporative salt encrustations with a wide range of minerals controlled by local substrate permeability and mineralogy. Many of these small (hectare scale) sites also host endemic salt-tolerant ecosystems that are currently endangered by weed incursion. This study characterises the differing mineralogy and geochemistry of these rare ecosystem-hosting substrates. Impermeable substrates, especially clay-rich schist basement, are dominated by NaCl from marine aerosols in rain. The high Na at these sites further enhances impermeability of substrates by promoting surficial clay mobility, so that even Pleistocene-Recent sediments derived from schist basement develop evaporative crusts. The Na/Cl ratio of some of these substrates, especially sediments, has been increased by alteration of albite. However, mineralogically similar greywacke-derived sediments do not develop saline encrustations. Penetration of rainwater into substrates facilitates water-rock interaction reactions that yield entirely different evaporative salt mineralogy, as the NaCl component is overshadowed by constituents dissolved from the rocks. Schist basement and limestone-rich substrates develop carbonate-dominated evaporites, especially calcite, and associated waters are typically supersaturated with respect to carbonate minerals. Some sulphate-rich evaporites form where rock pyrite has been oxidised. Hydrothermally altered schist basement is locally enriched in Mg-bearing carbonates, sulphides and gold. Bare substrates on these sites are variably permeable and develop evaporative salts with carbonates, sulphates, ferric oxyhydroxide (some arsenic-bearing), and minor brucite, after extensive water-rock interaction. Most of the sites are alkaline, and pH locally exceeds 10, as a result of the combinations of evaporative processes and water-rock interactions. The specialist plants have evolved to tolerate the relatively high salinities and pH of these chemically distinctive sites.

Contrasting geology and mineralogy of evaporative encrustations in salt-tolerant ecosystems, Maniototo basin, Central Otago, New Zealand

ABSTRACT Evaporative mineral encrustations have formed on bare substrates at three different sites in the Maniototo basin. Two sites, at Patearoa and Belmont have salts derived primarily from marine aerosols. The Patearoa site has developed on clay-rich pans formed on a terrace eroded by the Taieri River into clay-altered schist basement, and dissolution of albite from altered schist has resulted in precipitation of sodium carbonate with halite, at pH∼10. The Belmont site lies on the flat distal part of an active alluvial fan, and halite-dominated salt encrustations develop on thin dry crusts through capillary action from below. At the nearby Hamiltons historic placer gold mine, excavations exposed clay-altered schist basement beneath Eocene auriferous sediments. Highly fractured and hydrothermally altered fault zones dominate basement, with secondary ankeritic carbonate and pyrite. Water-rock interaction of shallow groundwater in the basement leads to enrichment in dissolved Mg and sulphate that overshadows the marine aerosol components, and evaporative encrustations are dominated by Mg-rich minerals including brucite and epsomite. The halite-dominated sites host rare halophyte ecosystems, but progressive colonisation by adventive species will eventually cover the bare saline substrates. Similar colonisation at the Hamiltons site will result in natural rehabilitation of the abandoned mine site.

Preliminary Findings at a Late Old Kingdom Fort in South Sinai, Including the Pottery, from the 2008 Season

The 2008 excavations at Ras Budran continued exposing the late Old Kingdom fort’s courtyard, finding baking installations, deep hollows filled by ash and sand, and parts of an underlying occupation layer that may reflect earlier activity at the fort (which needs further clarification). The exploration of a suggestive “chamber” in the eastern enclosure wall revealed it to be a modern disturbance. The project also concentrated on the western “bastion,” tracing it for 20 meters and finding evidence for salt encrustations and potential storm activity along the fort’s western side; one preliminary conclusion is that the sealing of the fort’s original entryway, and the subsequent abandonment and dismantling of the fort, may have been encouraged by a poor placement of the fort too close to the Red Sea and/or possibly increasingly harsher (winter) weather ca. 2300–2200 B.C. The study also contains Rexine Hummel’s analysis of the fort’s pottery fabrics, forms, and functions.

Geoecology of ecosystem recovery at an inactive coal mine site, New Zealand

Ecological restoration of the Wangaloa coal mine in southern New Zealand is hindered by a range of geoecological factors. The site has some substrate acidification (down to pH 1) and acid rock drainage with discharge waters initially down to pH 4, although this has since risen to ca. pH 6. Surface and ground waters develop elevated sulfate (up to 700 mg/kg) during oxidation of pyrite in coal and quartz in waste rock. Coal has elevated boron content (up to 450 mg/kg) and surface waters on coal-rich waste rock have up to 6 mg/L dissolved boron. Evaporation causes formation of salt encrustations dominated by gypsum with minor boron salts. Boron is bioavailable and may be at toxic levels (>200 mg/kg) in some plants. Quartz-rich waste rock is readily eroded, and develops a cm-scale low-nutrient quartz pebble armouring layer with low water retention properties. All waste rocks including loess siltstone have low nutrient contents, and low moisture retention properties, that are barely sufficient for plant establishment. Native plants introduced to the site during rehabilitation have grown on loess substrate (up to fivefold increase in height over 3 years), with poor or no growth on coal-rich and quartz-rich substrates. In contrast, natural colonisation of manuka (Leptospermum scoparium) has been most effective at revegetation on even the most hostile substrates. This natural revegetation has been facilitated by islands of manuka established accidentally during 60 years of mining history. Manuka from local genetic stock is most viable for this revegetation, and introduced manuka seedlings have had a 70% mortality rate. Natural plant colonisation is the key step in overall ecosystem recovery, and invertebrates rapidly colonise beneath new shrubs irrespective of the nature of the substrate from vegetation islands that have high invertebrate numbers and species richness.

Elemental composition of the lichen Umbilicaria decussata

Total concentrations of major and trace elements were determined in thalli of the epilithic lichen Umbilicaria decussata from 37 habitats in Victoria Land (continental Antarctica). Average concentrations of Pb, Cu, Zn, Cr, Mn and Fe were among the lowest ever reported for lichens of genus Umbilicaria. On the contrary, Cd and Hg concentrations fell within the same range or were higher than those usually measured in samples from remote areas of the southern and northern hemispheres. No impact of local or remote human activities was detected. Comparison between average metal concentrations in U. decussata samples collected in 1989 and 1999 did not show significant variations, and this result was assumed to be indicative of negligible changes in the environmental biogeochemistry of Antarctic terrestrial ecosystems. The ad/absorption of soil and rock dust particles, atmospheric depositions, marine aerosols, guano of seabirds, and the uptake of soluble elements from widespread salt encrustations and/or rock minerals are the main sources of major and trace elements for epilithic lichens in continental Antarctica. Although the present results can be taken as baseline levels, further research is necessary in view of the expected effects of climatic changes on element bioavailability in ice‐free areas of Antarctica.

Solution geochemistry and behaviour of major and trace elements during summer in a moss community at Edmonson Point, Victoria Land, Antarctica

Physical and chemical characteristics and solution geochemistry of major and trace elements were investigated in an area of volcanic soil colonized by mosses at Edmonson Point (central Victoria Land) during the international BIOTAS (Biological Investigations of Terrestrial Antarctic Systems) expedition (BIOTEX) in the 1995–96 summer. The broad objective was to study the environmental factors involved in plant colonisation and survival in terrestrial continental Antarctic ecosystems. The results showed that moss distribution and survival throughout the summer was closely dependent on water supply. In Antarctic coastal ecosystems the environmental biogeochemistry is largely dominated by ions of marine origin. At the drier end of a hydrological gradient the dry cushions of Hennediella heimii were encrusted with salts and showed much higher concentrations of soluble ions (Na+, Cl−, K+, Ca2+, Mg2+, SO42−, NO3−) than those in adhering soil particles or in other moss species from wetter parts of the transect. Although salt encrustations may partly derive from sublimation of surface snow, comparisons between concentrations of soluble ions in the dry moss and those in the < 2 mm fraction of surface and deep soil showed an upward migration along the soil profile of soluble ions as the substratum dried out, between December and January, and their accumulation mostly on mosses. At the wet end of the transect messes were less affected by salt encrustations and there was evidence of Ca2+ uptake and an active cycling of nutrients.

Baseline concentrations of elements in the antarctic macrolichen Umbilicaria decussata

Total concentrations of major and trace elements were determined in samples of the epilithic lichen Umbilicaria decussata from 24 ice-free areas in coastal Victoria Land (Antarctica). Overall average concentrations of trace elements except Cd were the lowest ever reported for lichens of the genus Umbilicaria. Specifically, the mean level of Pb in lichens from granitic rocks (0.46 ± 0.18 μg g −1 dry wt) was more than four times lower than the lowest record in Arctic lichens. No impact of local human activities was detected, but the elemental composition of U. decussata was affected by entrapment of soil or rock dust particles and probably by uptake of soluble elements from substrate. Relationships between elements and their distribution patterns in the study area indicated that the marine environment is the main source of major ions and perhaps of Cd in lichens. Accumulation of P was detected in samples from coastal sites frequented by seabirds. Although the present results can be taken as baseline levels of major and trace elements in Antarctic U. decussata from substrates with very different geochemical features, further research is necessary to evaluate the relative element contribution from each substrate with respect to those from snow, marine aerosol, salt encrustations and guano.

Application of satellite data for monitoring degradation of tidal wetlands of the Gulf of Kachchh, Western India

Tidal wetlands act as feeding, spawning and nursery grounds to marine fisheries. They also help in protecting the coast from the marine erosion. Thus there is a need to monitor the tidal wetlands periodically. Landsat MSS and TM data of period 1975–1986 is analysed for monitoring the tidal wetland areas of the Gulf of Kachchh, Western India. This area was declared as the Marine National Park in 1982. Various wetland categories like beach, mudflats, coral reefs, mangroves, marsh vegetation, algae, coastal dunes, salt pans and salt encrustations were delineated. The classification accuracy of these maps is 83% at 90% confidence level. The coral reefs and mangrove ecosystems in the area are in great danger. The total reef area has reduced from 217 to 123 sq km from 1975 to 1986. The degradation and destruction of the reefs is mainly due to high turbidity in the coastal waters and carbonate sand mining, for manufacture of cement in the area. The mangroves have severely degraded and reduced from 275 to 218 sq km in the part of Gulf of Kachchh and 138 to 33 sq km, in the core area of the Marine National Park, from 1975 to 1986. Near the mouth of the Gulf, the mangroves along with marsh vegetation have drastically reduced from 730 to 180 sq km from 1975 to 1982. The destruction is mainly because of their use as fuel and fodder, and the proliferation of the salt works. The analysis of the satellite data, thus helps in planning proper conservation measures and ultimately to its better management.

Friable Pigments and Ceramic Surfaces: A Case Study from SW Iran

The loss of friable pigments, as well as the ceramic surfaces to which they were applied, was researched in an attempt to stay the destructive processes affecting sherds recovered by survey in SW Iran. Prior to experimental treatment, the pigments and salt efflorescences were identified using optical and instrumental analyses. A technique for cleaning the calcareous encrustations from the pigment and ceramic surfaces without the use of acids was developed. This cleaning technique also solved a problem encountered in x-ray diffraction analysis when studying pigments applied to ceramics affected by salt encrustations. Several consolidant solutions were tested and applied to polychrome painted sherds recovered from one of the sites in the Deh Luran Plain. An acrylic resin was found to be acceptable as a consolidation agent. The authors feel that the experiments and results presented will serve as useful models for archaeologists and conservators facing similar problems.

The effects of NaCl deicing salts on Sphagnum recurvum P. beauv.

In response to documented impacts of deicing salt runoff from a salt storage area along the Indiana Toll Road on the vegetation of Pinhook Bog, a study of the effects of NaCl on one of the prominent bryophytes of the bog was iniiated. Salt concentrations between 300 and 1500 mg/l as Cl significantly reduced growth in length of Sphagnum recurvum in laboratory cultures. Growth in biomass was also reduced at higher concentrations under certain treatment conditions. Chloride appeared to be a stronger growth inhibitor than sodium. In experiments in which water contact was reduced and evaporational plant surfaces increased, salt was deposited on plant tips through the evapotranspiration process, resulting in plant mortality at all NaCl concentrations tested. Washing of plants to simulate rainfall removed the salt encrustations, but they developed again quickly and produced similar lethal effects within 3 weeks of the last wash treatment. Since growth reduction and mortality of S. recurvum were shown at NaCl concentrations observed in Pinhook Bog, it is likely that deicing salts were responsible for the elimination of Sphagnum from the impacted area.

Properties of a chronosequence of ultraxerous soils in the trans-antarctic mountains

Cold desert soils were examined on 27 lateral moraines and on ground moraine in Arena Valley, Antarctica (77°50′S 161°E). The soils range in age from 200 000 to possibly 7–10 m.y. and have formed under virtually abiotic conditions, currently receiving less than 1 cm of water-equivalent precipitation per year. On 314 m2 circular plots, the frequency of surface boulders decreases and the frequencies of ventifacted boulders and pitted dolerite boulders increase with time. The desert pavement becomes more distinct with time, as manifested by an increase in rock types resistant to weathering, proximity of fragments greater than 15 mm, and number of coarse fragments which are stained and ventifacted. The thickness of solum and depth at which comminuted clasts occur increase with time. Whereas salt encrustations beneath clasts are prevalent in the youngest soils, the oldest soils contain a weakly cemented salt pan. Cracks measuring 1–5 cm intwidth, irregularly spaced at 15–50 cm intervals and extending to depths of 50 cm, occur primarily in older ultraxerous soils. Electrical conductivity and concentrations of sodium and nitrate in water extracts of the salt-enriched horizon increase with time. Concentrations of cations in water extracts are ranked: Na+ >Ca2+, Mg2+ ⪢ K+, whereas anions are ranked: NO3− >SO42− >Cl−. In the upper part of the solumn, the amount of gravel (76-2 mm) decreases and the amounts of silt (20-2 μm) and clay (< 2 μm) increase with time. The proportions of quartz and mica, the dominant minerals in the clay-size fraction, increase with time. Lesser amounts of vermiculite, montmorillonite and interstratified chlorite-vermiculite and mica-montmorillonite occur in the clay fraction.

Salinity Damage to Norfolk Island Pines Caused by Surfactants. I. The Nature of the Problem and Effect of Potassium, Sodium and Chloride Concentration on Uptake by Roots

As part of an investigation into the deterioration of Norfolk Island pine, Araucaria heterophylla (Salisb.) Franco, on the coast of eastern Australia, seedlings were grown in nutrient solutions in which sodium was substituted for potassium over the range 0.1 - 2.1 mM to give six treatments, each with four ratios of sulfate to chloride. Potassium was freely taken up and translocated to the shoots, the levels in the shoots being higher than those in the roots. However, the levels of potassium in both shoots and roots were significantly reduced in solutions in which sulfate predominated over chloride. Uptake and translocation of sodium was restricted, the ratio of sodium (shoots) to sodium (roots) being less than unity. The concentration of chloride in the shoots and roots generally increased with increasing solution chloride concentration but was significantly reduced at the lowest potassium-to-sodium ratio. In a second experiment the ratio of sodium to potassium was kept at 50:1, sodium and chloride in the solutions increasing from 2.5 to 460 mM and potassium from 0.05 to 9.2 mM. At the lower concentrations, uptake and translocation followed similar patterns to those found in the first experiment. However at solution concentrations of 20 mM sodium and above, levels of sodium in the shoots exceeded those of potassium and chloride. At sodium chloride concentrations of 260mM - 460mM, plants showed toxic symptoms with salt encrustations appearing on the stems. Analysis of the saturation extracts of soils taken from beneath affected seaside trees showed that the concentrations of sodium and chloride were not sufficiently high to account for the high levels of these elements found in the shoots of affected trees.