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Rehabilitation of gypsum-mined lands in the Indian desert

The economic importance of mining in the Indian Desert is second only to agriculture. Land disturbed by mining, however, has only recently been the focus of rehabilitation efforts. This research assesses the success of rehabilitation plans used to revegetate gypsum mine spoils within the environmental constraints of the north-west Indian hot-desert ecosystem. The rehabilitation plan first examined both mined and unmined areas and established assessments of existing vegetative cover and the quality of native soils and mine spoils. Tests were made on the effect of the use, and conservation, of available water through rainwater harvesting, amendment application (for physical and chemical spoil modification), plant establishment protocols, and the selection of appropriate germ plasm. Our results show that the resulting vegetative cover is capable of perpetuating itself under natural conditions while concurrently meeting the needs of farmers. Although the mine spoils are deficient in organic matter and phosphorus, they possess adequate amounts of all other nutrients. Total boron concentrations (>5.0 mg kg-1) in both the topsail and mine spoil indicate potentially phytotoxic conditions. Electrical conductance of mine spoil is 6-10 times higher than for topsail with a near-neutral pH. Populations of spoil fungi, Azotobactor, and nitrifying bacteria are low. The soil moisture storage in rainwater harvesting plots increased by 8% over the control and 48% over the unmined area. As a result of rehabilitation efforts, mine spoils show a steady buildup in organic carbon, and P and K due to the decomposition of farmyard manure and the contribution of nitrogen fixation by the established leguminous plant species. The rehabilitation protocol used at the site appears to have been successful. Following revegetation of the area with a mixture of trees, shrubs, and grasses, native implanted species have become established. Species diversity, measured in terms of species richness, increased after one year and then gradually declined over time; the decline was the result of the loss of annual species. The study not only develops methods of gypsum mine land rehabilitation but also helps in understanding processes of rehabilitation success in arid regions and emphasizes the importance of long-term monitoring of rehabilitation success. Copyright ?? 2001 Taylor & Francis.

Arid Soil Research and Rehabilitation

Hydraulic roughness of earth covers at a cold-desert waste burial site

A kinematic wave model of overland flow was used to calculate hydraulic roughness coefficients for earth covers and native hillslope surfaces at a waste burial site. Manning's n roughness coefficients were greater on earth cover plots planted to crested wheatgrass (n = 0.076) than on those planted to streambank wheatgrass (n = 0.030). Mound and intermound microtopography strongly influenced overland flow geometry on the bare native hillslope plots resulting in low apparent roughness values (n = 0.013). Time-related changes in hydraulic roughness appeared to be caused by development of a rain-induced crust on exposed soil surfaces that reduced infiltration and increased plot smoothness. -from Authors

Arid Soil Research and Rehabilitation

Surface disturbance of cryptobiotic soil crusts: nitrogenase activity, chlorophyll content, and chlorophyll degradation

Cryptobiotic soil crusts are an important component of semiarid and arid ecosystems. An important role of these crusts is the contribution of fixed nitrogen to cold‐desert ecosystems. This study examines the residual effects of various intensities and combinations of different surface disturbances (raking, scalping, and tracked vehicles) on nitrogenase activity, chlorophyll content, and chlorophyll degradation in these soil crusts. Nine months after disturbance chlorophyll content of disturbed soils was not statistically different from undisturbed controls, except in the scalped treatments, indicating recovery of this characteristic is fairly quick unless surface material is removed. Differences in chlorophyll degradation among treatments were not statistically significant. However, nitrogenase activity in all treatments showed tremendous reductions, ranging from 77–97%, when compared to the control, indicating this characteristic is slow to recover. Consequently, assessment of crustal recovery from disturbance must include not only visual and biomass characteristics but other physiological measurements as well. Areas dominated by these crusts should be managed conservatively until the implications of crustal disturbance is better understood.

Arid Soil Research and Rehabilitation

Temporal and abiotic fluctuations may be preventing successful rehabilitation of soil-stabilizing biocrust communities

Land degradation is a persistent ecological problem in many arid and semi-arid systems globally (drylands hereafter). Most instances of dryland degradation include some form of soil disturbance and/or soil erosion, which can hinder vegetation establishment and reduce ecosystem productivity. To combat soil erosion, researchers have identified a need for rehabilitation of biological soil crusts (biocrusts), a globally-relevant community of organisms aggregating the soil surface and building soil fertility. The impact of plant and biocrust cover was tested on soil erosion potential in the piñon-juniper woodlands of Bandelier National Monument, NM. Biocrusts were found to be similarly influential to vascular plants in reducing erosion, largely acting by promoting surface roughness. The potential to rehabilitate biocrusts within the Monument was also tested. In a full factorial design, plots were inoculated on eroding soils before the summer monsoon with greenhouse-cultured biocrusts, and administered the erosion intervention treatments of overland water flow barriers (flashing), slash placement, and seeding of vascular plants. Although significant and dynamic changes to soil stability, penetration resistance, and extractable soil nutrients were observed through time, no strong effects with the addition of inoculum, seeding, or erosion intervention treatments were seen. These results suggest possible ways forward to successfully rehabilitate biocrust, including varying the timing of biocrust application, amending inoculum application with different types of soil stabilization techniques, and adding nutrients to soils. The insights gleaned from the lack of response brings us closer to developing effective techniques to arrest soil loss in these important social-ecological dryland systems.

Ecological Applications

Rehabilitation of lands mined for limestone in the Indian desert

In the Indian desert, the economics of mining is second only to agriculture in importance. However, research on the rehabilitation of land disturbed by mining has only recently received serious attention. An attempt has been made to determine both the qualitative and quantitative success of rehabilitation plans used to revegetate limestone mine spoils in an area near Barna, northwest arid India. Rehabilitation success was achieved using a combination of rainwater harvesting techniques, soil amendment application approaches, plant establishment methods and the selection of appropriate germplasm material (trees, shrubs and grasses). It is expected that the resulting vegetative cover will be capable of self-perpetuation under natural conditions while at the same time meeting the land-use needs of the local people. The minespoils have adequate levels of the major nutrients (except P, Mo and Se) for proper plant and grazing animal health. Levels of organic matter are low whereas total B concentrations are exceptionally high. Also, the population of soil fungi, Azotobactor, and nitrifying bacteria is negligible. Enhanced plant growth was achieved in treated plots, compared to control plots, where spoil moisture storage was improved by 5-45 per cent. Due to the decomposition of farmyard manure and nitrogen fixation by planted leguminous plant species, the electrical conductance of treated mine spoils increased threefold, CaCO3 content decreased from 20??0 to 5??2 per cent, and organic carbon, P, K, and biological activity increased significantly. The rehabilitation protocol used at the site appears to have been successful because plant self-regeneration is occurring. The increased diversity of woody perennials resulted in 'dominance' being better shared among species and 'evenness' being increased within the plant community elements. The early to mid-successional trends are continuing for six years following initial rehabilitation. This study developed methods for the rehabilitation of lands mined for limestone and has also resulted in an understanding of rehabilitation processes in arid regions with an emphasis on the long-term monitoring of rehabilitation success. Copyright ?? 2000 John Wiley & Sons, Ltd.

Land Degradation and Development

Nutrient availability affects pigment production but not growth in lichens of biological soil crusts

Recent research suggests that micronutrients such as Mn may limit growth of slow-growing biological soil crusts (BSCs) in some of the drylands of the world. These soil surface communities contribute strongly to arid ecosystem function and are easily degraded, creating a need for new restoration tools. The possibility that Mn fertilization could be used as a restoration tool for BSCs has not been tested previously. We used microcosms in a controlled greenhouse setting to investigate the hypothesis that Mn may limit photosynthesis and consequently growth in Collema tenax, a dominant N-fixing lichen found in BSCs worldwide. We found no evidence to support our hypothesis; furthermore, addition of other nutrients (primarily P, K, and Zn) had a suppressive effect on gross photosynthesis (P = 0.05). We also monitored the growth and physiological status of our microcosms and found that other nutrients increased the production of scytonemin, an important sunscreen pigment, but only when not added with Mn (P = 0.01). A structural equation model indicated that this effect was independent of any photosynthesis-related variable. We propose two alternative hypotheses to account for this pattern: (1) Mn suppresses processes needed to produce scytonemin; and (2) Mn is required to suppress scytonemin production at low light, when it is an unnecessary photosynthate sink. Although Mn fertilization does not appear likely to increase photosynthesis or growth of Collema, it could have a role in survivorship during environmentally stressful periods due to modification of scytonemin production. Thus, Mn enrichment should be studied further for its potential to facilitate BSC rehabilitation. ?? 2008 Elsevier Ltd.

Soil Biology and Biochemistry

Rehabilitation of a lignite mine-disturbed area in the Indian Desert

Extensive lignite mining in the Indian (Thar) Desert commenced within the past decade. Accompanying extraction of this valuable resource there have been visible, important environmental impacts. The resultant land degradation has prompted concern from both public and regulatory bodies. This research assesses the success of rehabilitation plans implemented to revegetate a lignite mine-disturbed area, near the village of Giral in western Rajasthan State. Rehabilitation success was achieved within the environmental constraints of this northwest Indian hot-desert ecosystem using a combination of: (1) backfilling (abandoned pits) with minespoil and of covering the backfilled-surfaces with fresh topsoil to a thickness of about 0??30 m; (2) use of micro-catchment rainwater harvesting (MCWH) technique; (3) soil profile modification approaches; (4) plant establishment methodologies; and (5) the selection of appropriate germplasm material (trees, shrubs and grasses). Preliminary results indicate that the resulting vegetative cover will be capable of self-perpetuation under natural conditions while at the same time meeting the land-use requirements of the local people. The minespoil is alkaline in nature and has high electrical conductance. The average content of organic carbon, N, P and K is lower than in the regional topsoil. However, the concentration of Ca, Mg, Na and total S in the minespoil is much higher than in the topsoil. Further, the spoil material has no biological activity. Enhanced plant growth was achieved in MCWH plots, compared to control plots, where minespoil moisture storage was improved by 18-43 per cent. The rehabilitation protocol used at the site appears to have been successful because, in addition to the planted species, desirable native invasive species have become established. This study developed methods for the rehabilitation of lignite mine-disturbed areas and has also resulted in an understanding of rehabilitation processes in arid regions with an emphasis on the long-term monitoring of rehabilitation success. ?? 2004 John Wiley and Sons, Ltd.

Land Degradation and Development