Stabilization of copper mine wastes in a semi-arid environment with perennial grasses

Journal of Arid Environments (1982) 5, 285-290

Stabilization of copper mine wastes in a semi-arid environment with perennial grasses*

A. D. Dayt & K. L. Ludeke] Accepted 17 September 1981 Experiments were conducted in Arizona to study the effects of four soil materials (desert soil, copper overburden, overburden plus copper mine tailings, and tailings) on germination, seedling establishment and growth of six perennial grass species. Perennial ryegrass (Lolium perenne L.), crested wheatgrass (Agropyron crista tum (L.) Gaertn.), Lehmann lovegrass (Eragrostis lehmanniana Nees.), weeping lovegrass (Eragrostis curvula (Schrad.) Nees.), Weiman lovegrass (Eragrostis superba Peyr.) and blue panicgrass (Panicum antidotale Retz.) were broadcast planted on each substrate. Plant growth indicated that desert soil had the highest productivity, followed by overburden, overburden plus tailings and tailings, in decreasing order. All species produced taller plants, more vegetation and more ground cover during their second year of growth than they did during the first year. Planting a variety of grasses on copper mine wastes increases the chances of obtaining successful revegetation and helps blend the disturbed areas into the surrounding environment.

Introduction Effective stabilization and revegetation of mining wastes may reduce or eliminate pollution problems associated with the mining industry. Disturbed land reclamation through revegetation has been accomplished successfully in many parts of the world. In the course of copper mining in the southwestern United States, unwanted materials are discarded adjacent to mining operations and usually consist of four materials: (a) desert soils, (b) copper mine overburden, (c) overburden plus copper mine tailings, and (d) pure tailings. Each material has a distinctive combination of physical and chemical characteristics which must be assessed before effective stabilization and revegetation can be implemented. Revegetation with perennial plant species has been most successful when organic matter was incorporated into the substrate.

Literature review The ultimate goal of vegetative stabilization of mining wastes is to produce a plant cover which will exist under local conditions without assistance (Dean, 1971). Replanting of tailings and overburden results in stabilization of the slopes and control of wind and • Contribution from the Arizona Agricultural Experiment Station, University of Arizona, Tucson, Arizona 85721, U.S.A.; and Cyprus Pima Mining Co., Tucson, Arizona 85713, U.S.A. Approved for publication as Arizona Agricultural Experiment Station Research Contribution No. 3070. t Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, U.S.A. t Cyprus Pima Mining Co., Tucson, Arizona 85713, U.S.A. 0140-1963/82/030285 +06 $03.00/0

© 1982 Academic Press Inc. (London) Limited

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A. D. DAY & K. L. LUDEKE

water erosion (Ludeke, Day et al., 1974). Jones, Armiger et al. (1975) showed that by using fast-growing plant species, such as small grains or summer annuals, disturbed areas of surface mine spoils could be stabilized quickly and that the vegetative growth from plant species could be used as a mulch in the establishment of perennial grasses. Mulch was applied to mine spoils to conserve moisture, reduce surface temperature and control erosion (Barth, 1977). Plass (1978) stated that annuals can be used as a temporary cover to protect disturbed sites until perennials can be established. Murray & Moffett (1977) reported that for effective tailings revegetation grasses should produce high yields and thick ground covers. In addition to providing an economical, quick ground cover, forages aid in the restoration of spoil material to a productive soil (Bennett, 1977). Day, Ludeke et al, (1976) suggested that forage for livestock grazing may be produced by growing spring barley (Hordeum vulgare L.) on copper mining wastes in Arizona. Environmental studies should be conducted to determine potential plant species compatible with the climate (Powell & Barnhisel, 1977). Day & Ludeke (1978) found that it was possible to select specific barley genotypes adapted for growing on tailings material. Preliminary revegetation research of mining wastes indicated that some overburden materials supported vegetation as well as the existing undisturbed soil materials (Payne, 1978). The objectives of this experiment were to study effective germination (emergence), seedling establishment, growth and ground cover from six perennial grasses grown on four materials associated with copper mines in Arizona.

Materials and methods A study of the stabilization of copper mine wastes with perennial grasses was conducted in Arizona at Cyprus Pima Mining Company in 1974 and 1975. Four materials associated with copper mining in Arizona were involved in the research: (a) desert soil (b) overburden, (c) overburden plus tailings and (d) tailings. Desert soil materiai (Anthony series) was the surface soil found in the semi-arid environment in southern Arizona. The Anthony series is a member of the coarse-loamy mixed (calcareous), thermic family of the Typic Torrifluvents. Overburden was the non-ore material located above copper ore deposits. Overburden plus tailings was a mixture of overburden and tailings. Tailings was the waste material from the milling of copper ore. Six species of grasses were grown in each of the four soil materials: (a) perennial ryegrass (Lolium perenne L.), (b) crested wheatgrass (Agropyron cristatum (L.) Gaertn.), (c) Lehmann lovegrass (Hragrostis lehmanniana Nees.), (d) weeping lovegrass (Eragrostis curvula (Schrad.) Nees.), (e) WeIman lovegrass (Eragrostis superba Peyr.) and (f) blue panicgrass (Panicum antidotale Retz.). The experimental design was a split plot with substrate materials as main plots and grass species as subplots with fOur replications. The replications were arranged horizontally along the berms containing each soil material so as to insure adequate sampling of each soil material. The subplot size was 48 m 2 . A smooth, loose seedbed was prepared on a 1·5: I berm slope in each Soil material using a 'sidewinder' and a 'sheepfoot roller'. Approximately 3 cm of irrigation water were sprinkled over the area prior to planting. Twenty-nine kg/ha of elemental nitrogen (N) were applied in the preplanting irrigation. In May of each year, seeds of the six grass species were broadcast planted by hand on each soil material at the following rates: (a) perennial ryegrass-56 kgjha (50 lbjacre), (b) crested wheatgrasec., 34 kg/ha (30 lbjacre), (c) Lehman lovegrass-39 kgjha (35 lb/acre), (d) weeping lovegrass-56 kg/ha (50 lb/acre), (e) WeIman lovegrass-56 kgjha (50 Ib/acre) and (f) blue panicgrass-87 kg/ha (60 Ib/acre). Immediately after planting, 11,200 kg/ha of barley (Hordeum vulgare L.) straw were applied to the experimental area. Following the straw application, 19 kgjha of N were applied in I em of irrigation water. In 1974 three and in 1975 five additional irrigation and fertilization applications were made throughout the growing seasons. During each subsequent irrigation, 1 cm of water and

STABILIZATION OF COPPER MINE WASTES

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50 kgjha of N were applied. Annual rainfalls during 1974 and 1975 were 26 and 23 em respectively. In 1974 the following data were recorded for each plot: (a) number of seeds germinated (emerged), (b) number of seedlings established, (c) number of stems produced, (d) plant height, (e) forage yield and (f) per cent ground cover. In 1975, the data collected from each plot included: (a) plant height, (b) forage yield and (c) per cent ground cover. All data were analysed using the standard analysis of variance and means were compared using Student-Newman-Keuls' test as described by Steel & Torrie (1960).

Results and discussion The average number of seeds germinated (emerged) per unit area differed between substrate materials (Table I). The highest number of seeds germinated in desert soil, followed by overburden, overburden plus tailings and tailings, in decreasing order. In desert soil, more seeds of Lehmann lovegrass germinated than all other species. There were no differences in germination rate between perennial ryegrass, weeping lovegrass and blue panicgrass or between crested wheatgrass and Weiman lovegrass. Lehmann lovegrass, weeping lovegrass and blue panicgrass had the highest germination rates in overburden. There were no differences in germination rate in overburden between perennial ryegrass, crested wheatgrass and Welman lovegrass. In overburden plus tailings, Lehmann lovegrass had the highest germination rate. There were no differences in germination rates for the other five grass species. In tailings, Lehmann lovegrass and blue panicgrass had the highest germination rates, followed by weeping and Weiman lovegrasses. There were no differences in germination rates between perennial ryegrass and crested wheatgrass. The number of seeds germinated per unit area is usually an indication of the amount of seedling establishment. The average number of seedlings established differed between materials (Table I). Seedlings established best in desert soil, followed by overburden, overburden plus tailings and tailings, in decreasing order. In desert soil, Lehmann lovegrass established the most seedlings per unit area. There were no differences in number of seedlings established between perennial ryegrass, weeping lovegrass and blue panicgrass or between crested wheatgrass and WeIman lovegrass. In overburden, Lehmann lovegrass and blue panicgrass established the most seedlings. There were no differences in seedling establishment between the other four species. Lehmann lovegrass established the highest number of seedlings in overburden plus tailings. The other five species established similar numbers of seedlings per unit area. In tailings, blue panicgrass had the highest seedling establishment. There were no differences between Lehmann, weeping and Weiman lovegrasses or between perennial ryegrass and crested wheatgrass in seedling establishment. High seedling establishment produces a more pleasing appearance for a disturbed area than does a low seedling establishment. The development of many separate roots resulting in a more compact root community below the soil surface accompanies high seedling establishment. A compact ~oot community stabilizes a disturbed area more effectively and makes it more resistant to the harmful effects of erosion and trampling by wildlife than does a sparse root system. The average number of stems produced per unit area differed between materials (Table 1). In desert soil, crested wheatgrass, Lehmann lovegrass and blue panicgrass produced the highest number of stems. There were no differences in number of stems produced between perennial ryegrass, weeping lovegrass and Weiman lovegrass. Crested wheatgrass and blue panicgrass produced the highest number of stems in overburden and in overburden plus tailings. There were no differences in stem production in overburden and in overburden plus tailings between Lehmann, weeping and Weiman lovegrasses. Perennial ryegrass had the lowest stem production in overburden and in overburden plus tailings. In tailings, blue panicgrass produced the highest number of stems followed by crested wheatgrass. There were no differences in

Plant species

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t t

391 b 374 c 506 a 401 b 324c 420b 329 b 340 b 448 a 341 b 310 b 388 a 312 b 323 b 414a 323 b 280b 344 b 161 c 86 c 228 b 202 b 194 b 269a

t t

404 b" 382 c 525 a 427 b 386 c 437 b 350 b 350 b 495 a 409 a 374 b 418 a 323 b 324 b 447 a 350 b 356 b 362 b 175 c 161 c 301 a 208 b 226 b 311 a

t t

t

t

t t

1864 b 487 c 2213 a 1880 b 1801 b 2223 a 1204c 470 d 1863 a 1609 b 1659 b 1886 a 1022 b 438 c 1239 a 1052 b 1086 b 1232 a 744 b 391 c 883 a 691 b 612 b 878 a 33 b 15 c 69 a 79 a 74 a 51 b 38 b 15 c 56 b 69 a 66 a 48 b 30 b 13 c 51 a 64a 58 a 38 b 25 b 10 c 46 a 51 a 51 a 30 b

Plant height (cm)

t

t t t t

t

2050 b 536 c 2434 a 2068 b 1981 b 2445 a 1324 c 517 d 2049 a 1770b 1825 b 2075 a 1124 b 482 c 1363 a 1157 b 1195 b 1355 a 818 b 430 c 971 a 760 b 673 b 966 a 36 b 17 c 76 a 87 a 81 a 56 b 42 b 17 c 62 b 76 a 73 a 53 b 33 b 14 c 56 a 70 a 64a 42 b 28 b II c 51 a 56 a 56 a 33 b

(em)

Plant height

t t

67 b 78 a 76 a 80 a 84 a 83 a 64b 72a 73 a 76 a 81 a 80 a 50 c 62 b 67 a 73 a 73 a 67 a 31 a 34 a 22 b 22 b 20 b 20 b

Forage yield (12 per cent Ground moisture) cover (kgjha) (per cent)

60b 70 a 68 a 71 a 75 a 74 a 57 b 64a 65 a 68 a 72a 71 a 45 c 55 b 60 a 65 a 65 a 60 a 28 a 30 a 20 b 20 b 18 b 18 b

Forage yield (12 per cent Ground moisture) cover (kgjha) (per cent)

Second year (1975)

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..Means followed by the same letter, within soil materials and between plant species, are not different at the 5% levelof significance using the Student-Newman-Keul's

Desert soil

Perennial ryegrass Crested wheatgrass Lehmann lovegrass Weeping lovegrass WeIman lovegrass Blue panicgrass Overburden Perennial ryegrass Crested wheatgrass Lehmann love grass Weeping lovegrass WeIman lovegrass Blue panicgrass Overburden Perennial ryegrass Crested wheatgrass plus Lehmann love grass tailings Weepinglovegrass Weiman lovegrass Blue panicgrass Tailings Perennial ryegrass Crested wheatgrass Lehmann love grass Weeping lovegrass We1man lovegrass Blue panicgrass Significance of differences: Between soil materials Between plant species

Soil materials

Seeds Seedlings Stems germinated established produced in 1 m 2 in 1m 2 in I m 2 (no.) (no.) (no.)

First year (1974)

Table 1. Average germination, seedling establishment, number of stems produced, plant height,jorage yield and ground cover for six perennial grasses grown on four soil materials associated with copper mines near Tucson, Arizona in 1974 and 1975

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STABILIZATION OF COPPER MINE WASTES

289

stem production in tailings between weeping and Weiman lovegrasses or between perennial ryegrass and Lehmann lovegrass. The number of stems produced is an indication of vegetative cover and forage production. A high number of stems per unit area creates a favorable habitat and food supply for wildlife. In 1974 and 1975, there were differences between materials in average plant height (Table 1). Plants grown in desert soil were tallest, followed by overburden, overburden plus tailings, and tailings, in decreasing order. In desert soil, Lehmann, weeping and Weiman lovegrasses grew the tallest followed by perennial ryegrass, blue panicgrass and crested wheatgrass. Weeping and Weiman lovegrasses grew the tallest in overburden. There were no differences in plant height in overburden between perennial ryegrass, Lehmann lovegrass and blue panicgrass. Crested wheatgrass was the shortest in overburden. In overburden plus tailings and in tailings, Lehmann, weeping and Welman lovegrasses were the tallest, followed by perennial ryegrass and blue panicgrass. Crested wheatgrass was the shortest in overburden plus tailings and in tailings. In general, taller grasses have more eye-appeal and produce more vegetation per unit area than shorter grasses. Forage yields per unit area differed for the four materials in 1974 and 1975 (Table 1). Desert soil produced the most forage and tailings produced the least. Overburden and overburden plus tailings were intermediate in forage production. Lehmann lovegrass and blue panicgrass produced the highest yields of forage in desert soil and crested wheatgrass produced the lowest yields. There were no differences in forage yield between perennial ryegrass, weeping lovegrass and Welman lovegrass. In overburden, Lehmann lovegrass and blue panicgrass produced the most forage, followed by weeping and Weiman lovegrasses. Perennial ryegrass and crested wheatgrass produced the lowest yields of forage. In overburden plus tailings and in tailings, Lehmann lovegrass and blue panicgrass produced the most forage and crested wheatgrass produced the lowest yields. There were no differences in forage production between perennial ryegrass, weeping lovegrass and Weiman lovegrass. In 1974 and 1975, there were differences between materials in per cent ground cover (Table 1). Desert soil produced the highest ground cover followed by overburden, overburden plus tailings and tailings, in decreasing order. In both desert soil and overburden, perennial ryegrass produced less ground cover than the other five grass species. In overburden plus tailings, Lehmann, weeping and Weiman lovegrasses and blue panicgrass produced similar amounts of ground cover. Perennial ryegrass and crested wheatgrass produced less ground cover than did the other four species in overburden plus tailings. Perennial ryegrass and crested wheatgrass produced the most complete ground cover in tailings. There were no differences in ground cover production in tailings for the other four grass species. Complete ground cover increases the general eye appeal of an area and protects the soil surface against wind and water erosion. Replanting of copper mining wastes with grasses results in stabilization of the slopes and control of wind and water erosion. There was a variable response in emergence, establishment, tillering, forage yield and ground cover between species and between soil materials. When seeded on the most productive- wastes (desert soil and overburden), Lehmann lovegrass was superior in all categories evaluated. Perennial ryegrass and crested wheatgrass were generally the lowest yielding species; however, they did produce the most ground cover on the least productive waste material (tailings). The data from this research suggest that a specific plant species may be best adapted to a specific soil material. Using a variety of grass species increases the chances of obtaining successful overall revegetation and helps blend the disturbed area into the surrounding environment. The authors gratefully acknowledge the assistance of M. A. Norem with portions of the research involving this contribution.

290

A. D. DAY & K. L. LUDEKE

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Dean, K. C. (1971). USBM finds many routes to stabilizing mineral wastes. Mining Engineering,

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Jones, J. N., j r., Armiger, W. G. & Bennett, O. L. (1975). A two-step system for revegetation of surface mine spoils. Journal of Environmental Quality, 4(2): 233-235. Ludeke, K. L., Day,A. D., Stith, L. S. & Stroehlein, J. L. (1974). Pima studies tailings soil makeup as prelude to successful revegetation. Engineering and Mining Journal, 175: 72-74. Murray, D. & Moffett, D. (1977). Vegetating the uranium mine tailings at Elliott Lake, Ontario. Journal of Soil and Water Conservation, 32(7): 171-174. Payne, A. (ed.) (1978). Strip mine rehabilitation: the American approach. South African Mining Journal, 84(4137): 41--45. Plass, W. T. (1978). Reclamation of coal-mined land in Appalachia. Journal of Soil and Water Conservation, 33(2): 56-6l. Powell, J. L. & Barnhisel, R. 1. (1977). Reclaiming surface-mined land in west Kentucky. Mining Congress Journal, 63(12): 29-35. Steel, R. G. D. & Torrie, J. H. (1980). Principles and Procedures of Statistics. Tokyo: McGraw_ Hill. 632 pp.