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A chronosequence of rapid leaching of mixed podzol soil materials following sand mining
GEO1)EI~IA ELSEVIER
Geoderma 64 (1995) 297-308
A chronosequence of rapid leaching of mixed podzol soil materials following sand mining Ian P. Prosser*, Stuart J. Roseby School of Geography. University of New South Wales P.O. Box 1, Kensington, NSW 2033, Australia
(Received September 16, 1993;accepted after revisionFebruary9, 1994)
Abstract Pedogenesis was investigated on soils which were rehabilitated following mining of Late Pleistocene sand dunes at Tomago, on the east coast of Australia. The soils were rehabilitated by spreading stockpiled A1 horizon material over mixed A2 and B horizon materials from the original humus podzols. A four stage chronosequence of 1,5, 11, and 17 years since soil rehabilitation was established and changes in pH, organic carbon, and pyrophosphate and oxalate extractable Fe and A1 were investigated. An A2 horizon extending to at least the depth of the water table developed over the chronosequence by leaching of organic carbon and oxalate extractable Fe and A1. Eighty-one percent of the leaching occurred between 1 and 5 years after soil rehabilitation, at a mass loss rate of 3.0 t ha ~yr ~. Such rapid leaching led to thicker A2 horizons than before mining, which is attributed to physical destruction of the indurated B 1 horizon and its homogenisation with A2 and B2 material to form a permeable mass containing easily translocated forms of Fe and A1. Inorganic forms of Fe and AI were found to be more mobile than organic forms.
1. Introduction Late Quaternary sand dunes on the east coast of Australia have provided some of the best chronosequences of podzolisation studied, and show that several thousand years are reqtiired to develop mature profiles. Giant podzols, with A2 horizons 12 to 22 m thick, have resulted from remobilisation of sesquioxides and organic matter over periods of up to 700,000 years (Tejan-Kella et al., 1990). At the younger end of the time scale, the depth to the B horizon is 1.6 m or less on Holocene dunes and less than 50 cm on dunes deposited over the last 3000 years (Pye, 1981; Thom et al., 1981; Thompson, 1983; Bowman, 1989), which is consistent with rates of formation on similar parent materials elsewhere (Andriesse, 1969/ 1970; McBride and Wilson, 1991 ). The above soils developed in freely drained materials, *Correspondingauthor. 0016-7061/95/$09.50 © 1995 ElsevierScienceB.V. All rights reserved SSDIO016-7061 (94) 0001 I-X
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but in areas of low relief the water table can limit the depth of the A2 horizon and humus podzols will form, dominated by AI humates with Fe being lost under reducing conditions (Farmer et al., 1983b; Thompson and Bowman, 1984). There is limited evidence of initially more rapid podzolisation following soil disturbance or revegetation. A 1 to 2 cm thick A2 horizon, with pipes extending to 45 cm, developed in just 9 years after sand mining on the east coast of Australia ( Paton et al., 1976). A similar depth of A2 horizon, overlying an iron pan, developed within 100 years of the cessation of ploughing on Scottish podzols (Crompton, 1952) and a 5 cm deep A2 horizon formed within 50 years of dune stabilisation by planting pines (Gauld, 1981 ). None of the studies, however, involved a chronosequence of soils, thus the times suggested for formation of the various features are maximum times. In this paper we investigate the impact of sand mining on pedogenesis of replaced humus podzol materials. We use the history of sand mining at Tomago on the east coast of Australia to produce a four stage chronosequence of podzolisation spanning 17 years. The chronosequence shows very rapid development of an A2 horizon, and enables rates of leaching of Fe and Ai to be quantified. The study also demonstrates the potential impact of disturbances such as sand mining on pedogenesis.
2. Study site The Tomago sand beds are located 16 km north of Newcastle on the New South Wales central coast (Fig. 1 ). The Pleistocene marine sands were originally deposited as a coastal barrier at 120,000 BP, during the Last Interglacial, but were subsequently reworked by aeolian processes terminating at 12,000 BP (Thom et al., 1981). The sand beds are characterised by gently undulating ridge and swale relief of longitudinal and parabolic dunes less than 12 m high, separated from middle to late Holocene transgressive dunes by an interbarrier wetland. The mineralogy of the Pleistocene sands is strongly dominated by quartz with less than 5% of weatherable minerals, rock fragments, and silt and clay (Thorn et al., 1981 ). The dunes support dry sclerophyll forest dominated by Eucalyptus and Angophora species with a shrub understorey. Wetter swales contain Melaleuca with a sedge and Juncus understorey. The climate is humid temperate with a mean annual rainfall of 1200 mm evenly distributed over the year. An extensive aquifer underlies the dunes, with a water table depth ranging from 1 to 5 m depending upon topography (Resources Planning Pty Ltd, 1992). Podzols have developed in the dune sands since their stabilisation at 12,000 BP (Thom et al., 1981 ). The shallow depth to the water table has resulted in the dominance of humus podzols (Stace et al., 1968) also classified as hydromorphic humic podzols (Duchaufour, 1982), or Humods (Soil Survey Staff, 1975). Iron and humus-iron podzois are restricted to the higher, freely drained sites. The depth to the B horizon varies with that to the water table, ranging from 45 cm in the swamps to 300 cm on ridge crests (Resources Planning Pty Ltd, 1992). The B horizons are approximately 100 cm thick and can be strongly indurated resulting in seasonally perched water tables. Economically significant concentrations of rutile, ilmenite, and monazite have been mined from the sands over the last 20 years. Prior to mining, vegetation is removed and the A1
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I
I'.-)::::'.',':'.q
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LOCATION
Fig. 1. Location of study site at Tomago, and pattern of dunes in the Newcastle Bight. (Dunes from Thom et al., 1981 ).
horizon is stockpiled. The A2 and B horizons are then extracted to a depth of 4 to 7 m using a suction cutter dredge and heavy minerals are removed on site by gravity spiral concentrators. The sand mass is returned to the excavation site and when mining is completed the sand is reshaped to the original topography. The stockpiled A1 horizon is respread to a depth of 10 to 30 cm and the site revegetated using native species and fertiliser. The net results are relatively homogenised A2 and B horizons beneath a less disturbed A1 horizon. The progressive movement of mining across the sand beds has enabled a chronosequence of soils since rehabilitation to be established. Five sites were chosen, with ages of 0.5, 1, 5, 11 and 17 years since soil rehabilitation. Undisturbed soil was examined at a sixth site located in a dune swale. The mined sites differed in elevation by less than 2 m and were located on broad, low gradient flanks of barrier dunes. No vegetation had been planted on the 0.5 year site, and the 1 year site contained shrubs (1 m high and little litter. The 5 to 17 year sites were characterised by increasing tree and shrub height and an almost continuous layer of leaf litter. The 17 year site had similar vegetation structure and litter levels to undisturbed sites.
3. Methods Soils were sampled by auger and bulked from two holes less than 20 m apart. The water table limited sampling depth to 130 cm at the 0.5 year site and to between 220 and 370 cm
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at other sites. Horizon boundaries, soil texture (Northcote, 1979) and Munsell colour were recorded in the field. Particle size analysis was performed on samples from 60 cm depth by sieving at 0.5~b intervals (~b= - l o g 2 d, where d is the particle diameter in mm). Soil pH was measured in 1:5 soil:water extracts and organic carbon was measured using dichromate digestion (McLeod, 1975). Organic complexes of Fe and AI were extracted from 1 g of soil using 100 ml of 0.1M sodium pyrophosphate and shaken overnight (Bascomb, 1968). Translocated Fe and AI were extracted from 1 g of soil using 60 ml of 0.2M ammonium oxalate adjusted to pH 3 and shaken in the dark for 4 hours (McKeague and Day, 1966). This procedure should extract both non-crystalline inorganic phases and organic complexed Fe and AI (Farmer et al., 1983a) although incomplete extraction of organic AI has been reported (Skjemstad et al., 1992). Concentrations of Fe and A1 were measured by atomic absorption spectrophotometry. Results from the 0.5 and 1 year sites were combined to form the 1 year site data because of the shallow depth to the water table in the 0.5 year site and because there were no significant differences between the two sites for all variables (Mann-Whitney U test, p)0.10).
4. Results 4.1. Undisturbed soil profile
The undisturbed soil profile has the following characteristics: 0-15 cm 15-40 cm 40-75 cm 75-145 cm 145 cm
A1 horizon; 10YR5/1, brownishgrey;loamysand; apedal; clear boundaryto A2 horizon; 10YR6/l, brownishgrey;mediumsand; apedal; clear boundaryto B1 horizon;7.5YR 3/4 dark brown;mediumsand; apedal indurated; gradual boundaryto B2 horizon;mottled 10YR8/2 (50%) light grey, 10YR5/4 (50%) yellowishbrown;medium sand, apedal; water table.
Laboratory results from the undisturbed profile are shown in Fig. 2. The A2 horizon has low concentrations of pyrophosphate and oxalate extractable Fe and A1 (Fepp, Feox, Alpp and Alox respectively), all below 0.08 g kg-~ and approximately 0.2% organic carbon (OC). Below this, in the B 1 horizon, the concentrations of OC, Fe and A1 sharply increase and A1 dominates over Fe, and pyrophosphate extractable A1 dominates over oxalate extractable AI. Most Fe, A1 and OC has accumulated in the top 40 cm of the B horizon, and concentrations decrease sharply in the B2 horizon. 4.2. Chronosequence
Field descriptions of the 0.5 and 1 year sites illustrate the direct effect of mining. The subsoil, that below the A1 horizon, shows no organisation into coherent horizons but has random layers of bleached sands, fragments of brownish black ( 10YR 2/2) indurated B1 horizon, and yellowish brown (10YR 5/3) layers containing a mixture of A2, B 1 and B2
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4
Depth
(5
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120
140
160
Fig. 2. Characteristics of the undisturbed humus podzol profile at Tomago. OC: orgamc carbon; Alox,Alpp, Fe.... Fepp: oxalate and pyrophosphateextracted AI and Fe respectively. horizon materials. No indurated B 1 material remains in the 5 year site and the sub-soil is more uniformly greyish yellow brown (10YR 4 / 2 ) in colour, with noticeable humate staining remaining on sand grains. Sand grains have less humate coatings at the 11 year site and colour value is higher (10YR 6 / 3 ) although 1 to 2 cm thick layers of fragments of previously indurated, humic B1 horizon material were found below 140 cm. The soil is 100
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.
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4 (0.064)
Fig. 3. Particle size distribution of samples taken from 60 cm depth in the undisturbed podzol and 1 to 17 years after rehabilitation following sand mining.
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pH 5
Depth (cm)
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150
200 25O
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35O
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Fig. 4. Depth trends of soil properties 1 to 17 years after rehabilitation. Soil properties are defined in Fig. 2 and in the text. The top sample in each profile was taken from the AI horizon, the remaining samples were from the homogenised A2 and B horizons.
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uniformly lighter in colour at the 17 year site ( 10YR 7/3), with only minor staining of sand grains evident. The undisturbed and rehabilitated soils have all developed on well sorted medium sands of similar particle size distribution (Fig. 3). Depth trends of soil chemical properties over the chronosequence are shown in Fig. 4. The top sample from each site was taken from the AI horizon, and the remaining samples were taken from the homogenised A2 and B horizons. Samples from A1 horizons show considerable variability and no coherent changes with time. Subsoil properties show little variation with depth, particularly in comparison with the undisturbed soil, and no systematic patterns to suggest the formation of soil horizons. A two way analysis of variance showed that no property varied significantly with depth but that all properties except Fepp varied significantly between sites. Consequently, subsoil values for each property were plotted against time (Fig. 5), and a regression analysis undertaken (Table 1). 0.5 O 7 O o
0.4
0 pH
%OC
45 ~
0.3 0.2 0.1
3
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5
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0 0
5
10 Time (y)
15
20
0
Fig. 5. Changes in soil properties over time for samples from 60-240 cm depth. Regression equations are given in Table 1. Soil properties are defined in Fig. 2 and in the text.
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Table 1 Regression equations for changes in soil properties over time shown in Fig. 4 Equation
r~
pH = 1.31og(t) +4.2 OC = 0.39 - 0.019t Al,,x= 0.284- 0.195log(t) Alpv- 0.120 - 0.00465t Fe,,~= 0.257 - 0.153log(t) Fepp= 0.199
0.91 0.85 0.87 0.83 0.67 0.00
Probability {0.00l {0.00 I {0.00 I {0.00 I {0.001 0.92
t:time in years; OC: % organic carbon; Al,,x, Alpp, Fe,,~, Fevv: oxalate and pyrophosphate extracted AI and Fe respectively in g kg ~: r2: proportion of variance explained. Table 2 Mass loss rates of Fe and AI from 40-240 cm depth in rehabilitated podzols at Tomago, NSW Constituent
I-5 yr t ha ~yr i
5-11 yr t ha t yr i
Al,,, AIp~, Fe,,, Fepp Total
1.394 0.178 1.435 - 0.029 2.978
0.196 0.188 - 0.103 0.029 0.310
I 1-17 yr t ha lyr i 0.148 0.081 0.182 0.025 0.385
1-17 yr t ha l yr i 0.478 0.145 0.388 - 0.006 1.005
Al,,,, All,p, Fe,,~, Fep~,:oxalate and pyrophosphate extracted Al and Fe respectively. There is a net loss o f all constituents o v e r time, except Fepp which stays at a constant level equal to the mean concentration in the undisturbed soil. Changes o v e r time are highly significant and explain 67 to 91% of the variation in soil properties (Table 1 ). The amount of O C is initially similar to that expected from h o m o g e n i s a t i o n o f undisturbed soil, and declines linearly o v e r time to values comparable with the undisturbed A2 horizon. Values of Feox and Alox decline logarithmically o v e r time to the very low levels measured in the A2 horizon o f the undisturbed soil, but the Feox values are initially higher than expected from the undisturbed soil. There are very low concentrations of Alpp at all sites in comparison with the undisturbed soil, and there is only a slow decrease in concentration o v e r time. The rehabilitated soil is initially more acidic than the undisturbed profile but pH increases logarithmically o v e r time to be one pH unit less acidic than the undisturbed profile after 17 years. The rate of leaching of the rehabilitated soils can be calculated from concentrations of Fe and Al at each site. Using a soil bulk density of 1.6 g c m 3 (Stace et al., 1968), and mean extract concentrations b e t w e e n 40 and 240 cm depth, 1.0 t h a - 1 yr ~ of Fe and Al were lost on average o v e r the seventeen year period, 81% of which was lost in the first five years, and 86% of which was oxalate extractable Fe and AI ( T a b l e 2).
5. Discussion Analysis of soil c h r o n o s e q u e n c e s assumes that differences b e t w e e n sites are due to soil age and that variations in parent material, topography and other factors are relatively
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unimportant. In this study the uniform particle size, the dominance of quartz, and the homogenisation of soil during mining support the assumption. Topographic differences, however, may have caused some variation in soils between sites, particularly when comparing the undisturbed profile with the disturbed soils. Higher concentrations of Alpp and lower concentrations of Feox in the undisturbed soil can be attributed to its low topographic position and high water table facilitating the loss of Fe and precipitation of A1 from groundwater ( Farmer et al., 1983b). Disturbed profiles were from slightly higher elevations, where the water table is below 2 m depth, which together with topographic position suggest that A2 horizons extended to 150-250 cm depth (Resources Planning Pty Ltd, 1992). There is little variation in elevation between disturbed sites, however, and the depth of the original B horizons would have been well within the depth of mining. Hence, all of the disturbed profiles would have contained a mixture of A2 and B horizon materials following rehabilitation. The chronosequence shows very rapid development of a deep A2 horizon since soil rehabilitation. Much of this development took place within the first five years. Initially, concentrations of Feox, Alox, and OC are higher than in the undisturbed A2 horizon, but after only 5 years Feox and Al,,x values are similar, to a depth of at least 240 cm, to the low values of the undisturbed A2 horizon. Organic carbon falls uniformly below 0.2% after only 11 years, and soil colour value increases from 4 to 7 over the chronosequence, further indicating bleaching of the soil. Pyrophosphate extractable Fe is the only constituent that remains above levels in the undisturbed A2 horizon after 17 years. Processes of horizon development differ between the rehabilitated soils and the original podzols. In their original development, A2 horizons become thicker over time with progressively deeper leaching, together with an increasing contrast in Fe and A1 concentrations between horizons (Thompson and Bowman, 1984; Bowman, 1989; Thompson, 1992). The B horizons of humus podzols start to form near the seasonally average level of the water table and grow to up to 1 m above the water level (Farmer et al., 1983a; Thompson, 1992). In the rehabilitated soils there is uniform loss of Fe and A1 to at least the depth of the water table, and there is no evidence of B horizon development. The lowest sample from the 17 year site, at 370 cm depth, is 20 cm below the water table and well below the maximum depth of A2 horizons in the original soils, but has very low concentrations of Fe and A1. The lowest samples from other profiles are 0-10 cm above the water table, measured in late summer at seasonally low levels, and are well below the 150-250 cm depth of the A2/B horizon boundary in the original soils of dune flanks (Resources Planning Pty Ltd, 1992). Water tables have not been affected by mining, which is highly localised at any time, so the extended depth of A2 horizons cannot be attributed to changes in water table elevation. Such rapid development of deep A2 horizons has not been previously reported. The most comparable rate of pedogenesis is formation of a 1 cm thick A2 horizon nine years after mining of Holocene dunes at Myall Lakes 75 km north of Tomago (Paton et al., 1976). It would be incorrect, however, to compare either of these rates with natural podzolisation. Profile development following sand mining is essentially the redistribution of previous products of weathering, translocation and precipitation. The original profiles developed at much slower rates because of the time required for weathering of Fe and A1 from feldspars and sesquioxide coatings on quartz. Physical destruction of the impermeable, humate cemented B 1 horizon into a porous mass of humate coated grains positioned well above the
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water table would have further facilitated rapid movement of Fe and A1 in the rehabilitated soils. The slower rate of profile redevelopment at Myall Lakes can be attributed to the late Holocene parent material, which would contain less previously translocated Fe and A1. Furthermore, iron and iron-humus podzols dominate the Holocene dunes rather than the humus podzols of the Tomago sand beds. The relative mobility of particular forms of Fe and AI can be assessed by changes over the chronosequence. Oxalate should extract total translocated Fe and A1, including the organic complexes extracted by pyrophosphate (Farmer et al., 1983a). Concentrations of Fepp, however, are twice those of Feo× in the undisturbed profile and the 5 to 17 year old sites, probably a result of suspended Fe oxides in the Fepp extracts (Schuppli et al., 1983). It is likely then that the Fepp values are dominated by inorganic Fe that has been immobile since soil rehabilitation (Fig. 5). Concentrations of Alpp exceed those of Alox in the undisturbed soil, suggesting incomplete extraction of organic complexes of AI by oxalate (Skjemstad et al., 1992). Concentrations of Alox are 2.5 times higher than Alpp in the 1 year old site but have similar values in the 5 to 17 year old sites (Fig. 5). Therefore, most of the inorganic A1 is removed in the first five years, after which organic complexed AI dominates, regardless of the ability of oxalate to extract organic complexed A1. Similar trends are likely for Fe, assuming that the concentration of Feox sets an upper limit on the organic complexes of Fe in the Fepp extract. High rates of mass loss of Feox and Alox in comparison to Fevp and Alpp further illustrates mobility differences. The high mobility of inorganic A1 and relative stability of organic complexes of A1 support the recent shift away from fulvic acids to soluble inorganic complexes as the transporting agents for Fe and AI during podzolisation (Farmer et al., 1980; Anderson et al., 1982).
6. Conclusions
An A2 horizon extending to a depth of at least 3.7 m has formed in the 17 years since mining of podzols at Tomago. Leaching of Fe and A1 resulted in a mean mass loss of 1.0 t ha ~ yr-~ over the 17 year period, and 3.0 t ha ] yr t over the first five years. This unprecedented rate of pedogenesis can be attributed to the high permeability of the sands, the low silt and clay content, the previously advanced stage of weathering and pedogenesis, and the homogenisation of soil during mining. Inorganic translocated Fe and A1 are more easily leached than organic complexes of Fe and A1, and the rate of leaching is uniform with depth. Before sand mining, well developed B horizons occurred up to a metre above the water table, but there is now no evidence of B horizon formation to at least seasonally low levels of the water table. Sand mining has thus had a considerable impact on profile morphology with consequent impacts on soil hydrology. Prior to mining, water would perch seasonally above the impermeable B horizon and may have been important for plant growth given the low water holding capacity of sands. Organic matter accumulation in the B horizon may also have been important for nutrient supply, but there is now little possibility of nutrient or water storage below the A1 horizon in the rehabilitated soils.
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Acknowledgements We thank John Simpson of Rutile Zircon Mining Pty Ltd for information concerning sand mining operations and site rehabilitation, and Chris Myers and Stephanie Fikkers for assistance with laboratory analyses and field work.
References Anderson, H.A., Berrow, M.L., Farmer, V.C., Hepburn, A., Russell, J.D. and Walker, A.D., 1982. A reassessment of podzol formation processes. J. Soil Sci., 33: 125-136. Andriesse, J.P., 1969/1970. The development of the podzol morphology in the tropical lowlands of Sarawak (Malaysia). Geoderma, 3: 261-279. Bascomb, C.L., 1968. Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups. J. Soil Sci., 19: 251-268. Bowman, G.M., 1989. Podzol development in a Holocene chronosequence. I. Mornya Heads, New South Wales. Aust. J. Soil Res., 27: 607-628. Crompton, E., 1952. Some morphological features associated with poor soil drainage. J. Soil Sci., 3: 277-289. Duchaufour, P., 1982. Pedology, Pedogenesis and Classification (Translated by T.R. Paton). George Allen and Unwin, London, 448 pp. Farmer, V.C., Russell, J.D. and Berrow, M.L., 1980. Imogolite and proto-imogolite allophane in spodic horizons: evidence for a mobile aluminium silicate complex in podzol formation. J. Soil Sci., 31: 673-684. Farmer, V.C., Russell, J.D., Smith, F.L., 1983a. Extraction of inorganic forms of translocated AI, Fe and Si from a podzol Bs horizon. J. Soil Sci., 34: 571-576. Farmer, V.C., Skjemstad, J.O. and Thompson. C.H., 1983b. Genesis of humus B horizons in hydromorphic humus podzols. Nature, 304: 342-344. Gauld, J.H., 1981. The soils of Culbin Forest, Morayshire: their evolution and morphology, with reference to their forestry potential. Appl. Geogr., 1: 199-212. McBride, N. and Wilson, P., 1991. Characteristics and development of soils at Magilligan Foreland, Northern Ireland, with emphasis on dune and beach sand soils. Catena, 18: 367-378. McKeague, J.A. and Day, J.H., 1966. Dithionite and oxalate extractable Fe and AI as aids in differentiating various classes of soils. Can. J. Soil Sci., 46: 13-22. McLeod, S., 1975. Studies in wet oxidation procedures for the determination of "organic C'" in soil. In: Notes on Soil Techniques. CSIRO Aust. Div. of Soils, Adelaide, pp. 73-79. Northcote, K.H., 1979. A Factual Key for the Recognition of Australian Soils. Rellim, Adelaide, 124 pp. Paton, T.R., Mitchell, P.B., Adamson, D., Buchanan, R.A., Fox, M.D. and Bowman, G.M., 1976. Speed of podzolisation. Nature, 260: 601-602. Pye, K., 1981. Rate of dune reddening in a humid tropical climate. Nature, 290: 582-584. Resources Planning Pty Ltd, 1992. Environmental Impact Statement for Extension of Titanium Mineral Mining in the Richardson Road Area, Port Stephens Shire. Report prepared for Rutile Zircon Mines Ltd, Newcastle. Schuppli, P.A., Ross, G.J. and McKeague, J.A., 1983. The effective removal of suspended materials from pyrophosphate extracts of soils from tropical and temperate regions. Soil Sci. Soc. Am. J., 47: 1026-1032. Skjemstad, J.O., Fitzpatrick, R.W., Zarcinas, B.A. and Thompson, C.H., 1992. Genesis of podzols on coastal dunes in southern Queensland. II. Geochemistry and forms of elements as deduced from various chemical extraction procedures. Aust. J. Soil Res., 30: 615-644. Soil Survey Staff, 1975. Soil Taxonomy: a Basic System of Soil Classification for Making and Interpreting Soil Surveys. USDA Handbook 436. Govt. Print. Office, Washington, DC. Stace, H.C.T., Hubble, G.D., Brewer, R., Northcote, K.H., Sleeman, J.R., Mulcahy, M.S. and Hallsworth, E.G., 1968. A Handbook of Australian Soils. Rellim, Adelaide, 433 pp. Tejan-Kella, M.S., Chittleborough, D.J., Fitzpatrick, R.W. Thompson, C.H., Prescott, J.R. and Hutton, J.T., 1990. Thermoluminescence dating of coastal sand dunes at Cooloola and North Stradbroke Island, Australia. Aust. J. Soil Res., 28: 465---481.
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Thorn, B.G., Bowman, G.M. and Roy. P.S., 1981. Late Quaternary evolution of coastal sand barriers, Port Stephens Myall Lakes area, New South Wales, Australia. Quat. Res., 15:345 364. Thompson, C.H., 1983. Development and weathering of large parabolic dune systems along the subtropical coast of eastern Australia. Z. Geomorphol. Suppl., 45: 205-225. Thompson, C.H., 1992. Genesis of podzols on coastal dunes in southern Queensland. 1. Field relationships and profile morphology. Aust. J. Soil Res., 30:593-613. Thompson. C.H. and Bowman, GM., 1984. Subaerial denudation and weathering of vegetated coastal dunes in eastern Australia. ln: B.G. Thorn ( Editor), Coastal Geomorphology in Australia. Academic Press, Australia. pp. 263-290. -
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Geoderma 64 (1995) 297-308
A chronosequence of rapid leaching of mixed podzol soil materials following sand mining Ian P. Prosser*, Stuart J. Roseby School of Geography. University of New South Wales P.O. Box 1, Kensington, NSW 2033, Australia
(Received September 16, 1993;accepted after revisionFebruary9, 1994)
Abstract Pedogenesis was investigated on soils which were rehabilitated following mining of Late Pleistocene sand dunes at Tomago, on the east coast of Australia. The soils were rehabilitated by spreading stockpiled A1 horizon material over mixed A2 and B horizon materials from the original humus podzols. A four stage chronosequence of 1,5, 11, and 17 years since soil rehabilitation was established and changes in pH, organic carbon, and pyrophosphate and oxalate extractable Fe and A1 were investigated. An A2 horizon extending to at least the depth of the water table developed over the chronosequence by leaching of organic carbon and oxalate extractable Fe and A1. Eighty-one percent of the leaching occurred between 1 and 5 years after soil rehabilitation, at a mass loss rate of 3.0 t ha ~yr ~. Such rapid leaching led to thicker A2 horizons than before mining, which is attributed to physical destruction of the indurated B 1 horizon and its homogenisation with A2 and B2 material to form a permeable mass containing easily translocated forms of Fe and A1. Inorganic forms of Fe and AI were found to be more mobile than organic forms.
1. Introduction Late Quaternary sand dunes on the east coast of Australia have provided some of the best chronosequences of podzolisation studied, and show that several thousand years are reqtiired to develop mature profiles. Giant podzols, with A2 horizons 12 to 22 m thick, have resulted from remobilisation of sesquioxides and organic matter over periods of up to 700,000 years (Tejan-Kella et al., 1990). At the younger end of the time scale, the depth to the B horizon is 1.6 m or less on Holocene dunes and less than 50 cm on dunes deposited over the last 3000 years (Pye, 1981; Thom et al., 1981; Thompson, 1983; Bowman, 1989), which is consistent with rates of formation on similar parent materials elsewhere (Andriesse, 1969/ 1970; McBride and Wilson, 1991 ). The above soils developed in freely drained materials, *Correspondingauthor. 0016-7061/95/$09.50 © 1995 ElsevierScienceB.V. All rights reserved SSDIO016-7061 (94) 0001 I-X
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but in areas of low relief the water table can limit the depth of the A2 horizon and humus podzols will form, dominated by AI humates with Fe being lost under reducing conditions (Farmer et al., 1983b; Thompson and Bowman, 1984). There is limited evidence of initially more rapid podzolisation following soil disturbance or revegetation. A 1 to 2 cm thick A2 horizon, with pipes extending to 45 cm, developed in just 9 years after sand mining on the east coast of Australia ( Paton et al., 1976). A similar depth of A2 horizon, overlying an iron pan, developed within 100 years of the cessation of ploughing on Scottish podzols (Crompton, 1952) and a 5 cm deep A2 horizon formed within 50 years of dune stabilisation by planting pines (Gauld, 1981 ). None of the studies, however, involved a chronosequence of soils, thus the times suggested for formation of the various features are maximum times. In this paper we investigate the impact of sand mining on pedogenesis of replaced humus podzol materials. We use the history of sand mining at Tomago on the east coast of Australia to produce a four stage chronosequence of podzolisation spanning 17 years. The chronosequence shows very rapid development of an A2 horizon, and enables rates of leaching of Fe and Ai to be quantified. The study also demonstrates the potential impact of disturbances such as sand mining on pedogenesis.
2. Study site The Tomago sand beds are located 16 km north of Newcastle on the New South Wales central coast (Fig. 1 ). The Pleistocene marine sands were originally deposited as a coastal barrier at 120,000 BP, during the Last Interglacial, but were subsequently reworked by aeolian processes terminating at 12,000 BP (Thom et al., 1981). The sand beds are characterised by gently undulating ridge and swale relief of longitudinal and parabolic dunes less than 12 m high, separated from middle to late Holocene transgressive dunes by an interbarrier wetland. The mineralogy of the Pleistocene sands is strongly dominated by quartz with less than 5% of weatherable minerals, rock fragments, and silt and clay (Thorn et al., 1981 ). The dunes support dry sclerophyll forest dominated by Eucalyptus and Angophora species with a shrub understorey. Wetter swales contain Melaleuca with a sedge and Juncus understorey. The climate is humid temperate with a mean annual rainfall of 1200 mm evenly distributed over the year. An extensive aquifer underlies the dunes, with a water table depth ranging from 1 to 5 m depending upon topography (Resources Planning Pty Ltd, 1992). Podzols have developed in the dune sands since their stabilisation at 12,000 BP (Thom et al., 1981 ). The shallow depth to the water table has resulted in the dominance of humus podzols (Stace et al., 1968) also classified as hydromorphic humic podzols (Duchaufour, 1982), or Humods (Soil Survey Staff, 1975). Iron and humus-iron podzois are restricted to the higher, freely drained sites. The depth to the B horizon varies with that to the water table, ranging from 45 cm in the swamps to 300 cm on ridge crests (Resources Planning Pty Ltd, 1992). The B horizons are approximately 100 cm thick and can be strongly indurated resulting in seasonally perched water tables. Economically significant concentrations of rutile, ilmenite, and monazite have been mined from the sands over the last 20 years. Prior to mining, vegetation is removed and the A1
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I
I'.-)::::'.',':'.q
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LOCATION
Fig. 1. Location of study site at Tomago, and pattern of dunes in the Newcastle Bight. (Dunes from Thom et al., 1981 ).
horizon is stockpiled. The A2 and B horizons are then extracted to a depth of 4 to 7 m using a suction cutter dredge and heavy minerals are removed on site by gravity spiral concentrators. The sand mass is returned to the excavation site and when mining is completed the sand is reshaped to the original topography. The stockpiled A1 horizon is respread to a depth of 10 to 30 cm and the site revegetated using native species and fertiliser. The net results are relatively homogenised A2 and B horizons beneath a less disturbed A1 horizon. The progressive movement of mining across the sand beds has enabled a chronosequence of soils since rehabilitation to be established. Five sites were chosen, with ages of 0.5, 1, 5, 11 and 17 years since soil rehabilitation. Undisturbed soil was examined at a sixth site located in a dune swale. The mined sites differed in elevation by less than 2 m and were located on broad, low gradient flanks of barrier dunes. No vegetation had been planted on the 0.5 year site, and the 1 year site contained shrubs (1 m high and little litter. The 5 to 17 year sites were characterised by increasing tree and shrub height and an almost continuous layer of leaf litter. The 17 year site had similar vegetation structure and litter levels to undisturbed sites.
3. Methods Soils were sampled by auger and bulked from two holes less than 20 m apart. The water table limited sampling depth to 130 cm at the 0.5 year site and to between 220 and 370 cm
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at other sites. Horizon boundaries, soil texture (Northcote, 1979) and Munsell colour were recorded in the field. Particle size analysis was performed on samples from 60 cm depth by sieving at 0.5~b intervals (~b= - l o g 2 d, where d is the particle diameter in mm). Soil pH was measured in 1:5 soil:water extracts and organic carbon was measured using dichromate digestion (McLeod, 1975). Organic complexes of Fe and AI were extracted from 1 g of soil using 100 ml of 0.1M sodium pyrophosphate and shaken overnight (Bascomb, 1968). Translocated Fe and AI were extracted from 1 g of soil using 60 ml of 0.2M ammonium oxalate adjusted to pH 3 and shaken in the dark for 4 hours (McKeague and Day, 1966). This procedure should extract both non-crystalline inorganic phases and organic complexed Fe and AI (Farmer et al., 1983a) although incomplete extraction of organic AI has been reported (Skjemstad et al., 1992). Concentrations of Fe and A1 were measured by atomic absorption spectrophotometry. Results from the 0.5 and 1 year sites were combined to form the 1 year site data because of the shallow depth to the water table in the 0.5 year site and because there were no significant differences between the two sites for all variables (Mann-Whitney U test, p)0.10).
4. Results 4.1. Undisturbed soil profile
The undisturbed soil profile has the following characteristics: 0-15 cm 15-40 cm 40-75 cm 75-145 cm 145 cm
A1 horizon; 10YR5/1, brownishgrey;loamysand; apedal; clear boundaryto A2 horizon; 10YR6/l, brownishgrey;mediumsand; apedal; clear boundaryto B1 horizon;7.5YR 3/4 dark brown;mediumsand; apedal indurated; gradual boundaryto B2 horizon;mottled 10YR8/2 (50%) light grey, 10YR5/4 (50%) yellowishbrown;medium sand, apedal; water table.
Laboratory results from the undisturbed profile are shown in Fig. 2. The A2 horizon has low concentrations of pyrophosphate and oxalate extractable Fe and A1 (Fepp, Feox, Alpp and Alox respectively), all below 0.08 g kg-~ and approximately 0.2% organic carbon (OC). Below this, in the B 1 horizon, the concentrations of OC, Fe and A1 sharply increase and A1 dominates over Fe, and pyrophosphate extractable A1 dominates over oxalate extractable AI. Most Fe, A1 and OC has accumulated in the top 40 cm of the B horizon, and concentrations decrease sharply in the B2 horizon. 4.2. Chronosequence
Field descriptions of the 0.5 and 1 year sites illustrate the direct effect of mining. The subsoil, that below the A1 horizon, shows no organisation into coherent horizons but has random layers of bleached sands, fragments of brownish black ( 10YR 2/2) indurated B1 horizon, and yellowish brown (10YR 5/3) layers containing a mixture of A2, B 1 and B2
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4
Depth
(5
0
I
% OC 2
3
0.5
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0
(era)
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20
40
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Fepp, Alpp (mg/kg) 1 1.5 i
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2 i
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60
80
100 AIOx ---
FeOx
120
140
160
Fig. 2. Characteristics of the undisturbed humus podzol profile at Tomago. OC: orgamc carbon; Alox,Alpp, Fe.... Fepp: oxalate and pyrophosphateextracted AI and Fe respectively. horizon materials. No indurated B 1 material remains in the 5 year site and the sub-soil is more uniformly greyish yellow brown (10YR 4 / 2 ) in colour, with noticeable humate staining remaining on sand grains. Sand grains have less humate coatings at the 11 year site and colour value is higher (10YR 6 / 3 ) although 1 to 2 cm thick layers of fragments of previously indurated, humic B1 horizon material were found below 140 cm. The soil is 100
.///
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m
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30
20
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lo
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~
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3
3.5
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(0.5)
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.
2 (0.25)
Particlesize(~)
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(0.125)
4 (0.064)
Fig. 3. Particle size distribution of samples taken from 60 cm depth in the undisturbed podzol and 1 to 17 years after rehabilitation following sand mining.
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pH 5
Depth (cm)
Alox (g/kg)
%O.C. 6
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Feox (g/kg)
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Fepp (g/kg) 0.8
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0.4
0.6
0.8
0
5O 100
150
200 25O
3OO
35O
4OO
Fig. 4. Depth trends of soil properties 1 to 17 years after rehabilitation. Soil properties are defined in Fig. 2 and in the text. The top sample in each profile was taken from the AI horizon, the remaining samples were from the homogenised A2 and B horizons.
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uniformly lighter in colour at the 17 year site ( 10YR 7/3), with only minor staining of sand grains evident. The undisturbed and rehabilitated soils have all developed on well sorted medium sands of similar particle size distribution (Fig. 3). Depth trends of soil chemical properties over the chronosequence are shown in Fig. 4. The top sample from each site was taken from the AI horizon, and the remaining samples were taken from the homogenised A2 and B horizons. Samples from A1 horizons show considerable variability and no coherent changes with time. Subsoil properties show little variation with depth, particularly in comparison with the undisturbed soil, and no systematic patterns to suggest the formation of soil horizons. A two way analysis of variance showed that no property varied significantly with depth but that all properties except Fepp varied significantly between sites. Consequently, subsoil values for each property were plotted against time (Fig. 5), and a regression analysis undertaken (Table 1). 0.5 O 7 O o
0.4
0 pH
%OC
45 ~
0.3 0.2 0.1
3
0
0
5
10
15
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(g/kg) 0.2 o
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0.1
0
0 0
5
10 Time (y)
15
20
0
Fig. 5. Changes in soil properties over time for samples from 60-240 cm depth. Regression equations are given in Table 1. Soil properties are defined in Fig. 2 and in the text.
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Table 1 Regression equations for changes in soil properties over time shown in Fig. 4 Equation
r~
pH = 1.31og(t) +4.2 OC = 0.39 - 0.019t Al,,x= 0.284- 0.195log(t) Alpv- 0.120 - 0.00465t Fe,,~= 0.257 - 0.153log(t) Fepp= 0.199
0.91 0.85 0.87 0.83 0.67 0.00
Probability {0.00l {0.00 I {0.00 I {0.00 I {0.001 0.92
t:time in years; OC: % organic carbon; Al,,x, Alpp, Fe,,~, Fevv: oxalate and pyrophosphate extracted AI and Fe respectively in g kg ~: r2: proportion of variance explained. Table 2 Mass loss rates of Fe and AI from 40-240 cm depth in rehabilitated podzols at Tomago, NSW Constituent
I-5 yr t ha ~yr i
5-11 yr t ha t yr i
Al,,, AIp~, Fe,,, Fepp Total
1.394 0.178 1.435 - 0.029 2.978
0.196 0.188 - 0.103 0.029 0.310
I 1-17 yr t ha lyr i 0.148 0.081 0.182 0.025 0.385
1-17 yr t ha l yr i 0.478 0.145 0.388 - 0.006 1.005
Al,,,, All,p, Fe,,~, Fep~,:oxalate and pyrophosphate extracted Al and Fe respectively. There is a net loss o f all constituents o v e r time, except Fepp which stays at a constant level equal to the mean concentration in the undisturbed soil. Changes o v e r time are highly significant and explain 67 to 91% of the variation in soil properties (Table 1 ). The amount of O C is initially similar to that expected from h o m o g e n i s a t i o n o f undisturbed soil, and declines linearly o v e r time to values comparable with the undisturbed A2 horizon. Values of Feox and Alox decline logarithmically o v e r time to the very low levels measured in the A2 horizon o f the undisturbed soil, but the Feox values are initially higher than expected from the undisturbed soil. There are very low concentrations of Alpp at all sites in comparison with the undisturbed soil, and there is only a slow decrease in concentration o v e r time. The rehabilitated soil is initially more acidic than the undisturbed profile but pH increases logarithmically o v e r time to be one pH unit less acidic than the undisturbed profile after 17 years. The rate of leaching of the rehabilitated soils can be calculated from concentrations of Fe and Al at each site. Using a soil bulk density of 1.6 g c m 3 (Stace et al., 1968), and mean extract concentrations b e t w e e n 40 and 240 cm depth, 1.0 t h a - 1 yr ~ of Fe and Al were lost on average o v e r the seventeen year period, 81% of which was lost in the first five years, and 86% of which was oxalate extractable Fe and AI ( T a b l e 2).
5. Discussion Analysis of soil c h r o n o s e q u e n c e s assumes that differences b e t w e e n sites are due to soil age and that variations in parent material, topography and other factors are relatively
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unimportant. In this study the uniform particle size, the dominance of quartz, and the homogenisation of soil during mining support the assumption. Topographic differences, however, may have caused some variation in soils between sites, particularly when comparing the undisturbed profile with the disturbed soils. Higher concentrations of Alpp and lower concentrations of Feox in the undisturbed soil can be attributed to its low topographic position and high water table facilitating the loss of Fe and precipitation of A1 from groundwater ( Farmer et al., 1983b). Disturbed profiles were from slightly higher elevations, where the water table is below 2 m depth, which together with topographic position suggest that A2 horizons extended to 150-250 cm depth (Resources Planning Pty Ltd, 1992). There is little variation in elevation between disturbed sites, however, and the depth of the original B horizons would have been well within the depth of mining. Hence, all of the disturbed profiles would have contained a mixture of A2 and B horizon materials following rehabilitation. The chronosequence shows very rapid development of a deep A2 horizon since soil rehabilitation. Much of this development took place within the first five years. Initially, concentrations of Feox, Alox, and OC are higher than in the undisturbed A2 horizon, but after only 5 years Feox and Al,,x values are similar, to a depth of at least 240 cm, to the low values of the undisturbed A2 horizon. Organic carbon falls uniformly below 0.2% after only 11 years, and soil colour value increases from 4 to 7 over the chronosequence, further indicating bleaching of the soil. Pyrophosphate extractable Fe is the only constituent that remains above levels in the undisturbed A2 horizon after 17 years. Processes of horizon development differ between the rehabilitated soils and the original podzols. In their original development, A2 horizons become thicker over time with progressively deeper leaching, together with an increasing contrast in Fe and A1 concentrations between horizons (Thompson and Bowman, 1984; Bowman, 1989; Thompson, 1992). The B horizons of humus podzols start to form near the seasonally average level of the water table and grow to up to 1 m above the water level (Farmer et al., 1983a; Thompson, 1992). In the rehabilitated soils there is uniform loss of Fe and A1 to at least the depth of the water table, and there is no evidence of B horizon development. The lowest sample from the 17 year site, at 370 cm depth, is 20 cm below the water table and well below the maximum depth of A2 horizons in the original soils, but has very low concentrations of Fe and A1. The lowest samples from other profiles are 0-10 cm above the water table, measured in late summer at seasonally low levels, and are well below the 150-250 cm depth of the A2/B horizon boundary in the original soils of dune flanks (Resources Planning Pty Ltd, 1992). Water tables have not been affected by mining, which is highly localised at any time, so the extended depth of A2 horizons cannot be attributed to changes in water table elevation. Such rapid development of deep A2 horizons has not been previously reported. The most comparable rate of pedogenesis is formation of a 1 cm thick A2 horizon nine years after mining of Holocene dunes at Myall Lakes 75 km north of Tomago (Paton et al., 1976). It would be incorrect, however, to compare either of these rates with natural podzolisation. Profile development following sand mining is essentially the redistribution of previous products of weathering, translocation and precipitation. The original profiles developed at much slower rates because of the time required for weathering of Fe and A1 from feldspars and sesquioxide coatings on quartz. Physical destruction of the impermeable, humate cemented B 1 horizon into a porous mass of humate coated grains positioned well above the
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water table would have further facilitated rapid movement of Fe and A1 in the rehabilitated soils. The slower rate of profile redevelopment at Myall Lakes can be attributed to the late Holocene parent material, which would contain less previously translocated Fe and A1. Furthermore, iron and iron-humus podzols dominate the Holocene dunes rather than the humus podzols of the Tomago sand beds. The relative mobility of particular forms of Fe and AI can be assessed by changes over the chronosequence. Oxalate should extract total translocated Fe and A1, including the organic complexes extracted by pyrophosphate (Farmer et al., 1983a). Concentrations of Fepp, however, are twice those of Feo× in the undisturbed profile and the 5 to 17 year old sites, probably a result of suspended Fe oxides in the Fepp extracts (Schuppli et al., 1983). It is likely then that the Fepp values are dominated by inorganic Fe that has been immobile since soil rehabilitation (Fig. 5). Concentrations of Alpp exceed those of Alox in the undisturbed soil, suggesting incomplete extraction of organic complexes of AI by oxalate (Skjemstad et al., 1992). Concentrations of Alox are 2.5 times higher than Alpp in the 1 year old site but have similar values in the 5 to 17 year old sites (Fig. 5). Therefore, most of the inorganic A1 is removed in the first five years, after which organic complexed AI dominates, regardless of the ability of oxalate to extract organic complexed A1. Similar trends are likely for Fe, assuming that the concentration of Feox sets an upper limit on the organic complexes of Fe in the Fepp extract. High rates of mass loss of Feox and Alox in comparison to Fevp and Alpp further illustrates mobility differences. The high mobility of inorganic A1 and relative stability of organic complexes of A1 support the recent shift away from fulvic acids to soluble inorganic complexes as the transporting agents for Fe and AI during podzolisation (Farmer et al., 1980; Anderson et al., 1982).
6. Conclusions
An A2 horizon extending to a depth of at least 3.7 m has formed in the 17 years since mining of podzols at Tomago. Leaching of Fe and A1 resulted in a mean mass loss of 1.0 t ha ~ yr-~ over the 17 year period, and 3.0 t ha ] yr t over the first five years. This unprecedented rate of pedogenesis can be attributed to the high permeability of the sands, the low silt and clay content, the previously advanced stage of weathering and pedogenesis, and the homogenisation of soil during mining. Inorganic translocated Fe and A1 are more easily leached than organic complexes of Fe and A1, and the rate of leaching is uniform with depth. Before sand mining, well developed B horizons occurred up to a metre above the water table, but there is now no evidence of B horizon formation to at least seasonally low levels of the water table. Sand mining has thus had a considerable impact on profile morphology with consequent impacts on soil hydrology. Prior to mining, water would perch seasonally above the impermeable B horizon and may have been important for plant growth given the low water holding capacity of sands. Organic matter accumulation in the B horizon may also have been important for nutrient supply, but there is now little possibility of nutrient or water storage below the A1 horizon in the rehabilitated soils.
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Acknowledgements We thank John Simpson of Rutile Zircon Mining Pty Ltd for information concerning sand mining operations and site rehabilitation, and Chris Myers and Stephanie Fikkers for assistance with laboratory analyses and field work.
References Anderson, H.A., Berrow, M.L., Farmer, V.C., Hepburn, A., Russell, J.D. and Walker, A.D., 1982. A reassessment of podzol formation processes. J. Soil Sci., 33: 125-136. Andriesse, J.P., 1969/1970. The development of the podzol morphology in the tropical lowlands of Sarawak (Malaysia). Geoderma, 3: 261-279. Bascomb, C.L., 1968. Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups. J. Soil Sci., 19: 251-268. Bowman, G.M., 1989. Podzol development in a Holocene chronosequence. I. Mornya Heads, New South Wales. Aust. J. Soil Res., 27: 607-628. Crompton, E., 1952. Some morphological features associated with poor soil drainage. J. Soil Sci., 3: 277-289. Duchaufour, P., 1982. Pedology, Pedogenesis and Classification (Translated by T.R. Paton). George Allen and Unwin, London, 448 pp. Farmer, V.C., Russell, J.D. and Berrow, M.L., 1980. Imogolite and proto-imogolite allophane in spodic horizons: evidence for a mobile aluminium silicate complex in podzol formation. J. Soil Sci., 31: 673-684. Farmer, V.C., Russell, J.D., Smith, F.L., 1983a. Extraction of inorganic forms of translocated AI, Fe and Si from a podzol Bs horizon. J. Soil Sci., 34: 571-576. Farmer, V.C., Skjemstad, J.O. and Thompson. C.H., 1983b. Genesis of humus B horizons in hydromorphic humus podzols. Nature, 304: 342-344. Gauld, J.H., 1981. The soils of Culbin Forest, Morayshire: their evolution and morphology, with reference to their forestry potential. Appl. Geogr., 1: 199-212. McBride, N. and Wilson, P., 1991. Characteristics and development of soils at Magilligan Foreland, Northern Ireland, with emphasis on dune and beach sand soils. Catena, 18: 367-378. McKeague, J.A. and Day, J.H., 1966. Dithionite and oxalate extractable Fe and AI as aids in differentiating various classes of soils. Can. J. Soil Sci., 46: 13-22. McLeod, S., 1975. Studies in wet oxidation procedures for the determination of "organic C'" in soil. In: Notes on Soil Techniques. CSIRO Aust. Div. of Soils, Adelaide, pp. 73-79. Northcote, K.H., 1979. A Factual Key for the Recognition of Australian Soils. Rellim, Adelaide, 124 pp. Paton, T.R., Mitchell, P.B., Adamson, D., Buchanan, R.A., Fox, M.D. and Bowman, G.M., 1976. Speed of podzolisation. Nature, 260: 601-602. Pye, K., 1981. Rate of dune reddening in a humid tropical climate. Nature, 290: 582-584. Resources Planning Pty Ltd, 1992. Environmental Impact Statement for Extension of Titanium Mineral Mining in the Richardson Road Area, Port Stephens Shire. Report prepared for Rutile Zircon Mines Ltd, Newcastle. Schuppli, P.A., Ross, G.J. and McKeague, J.A., 1983. The effective removal of suspended materials from pyrophosphate extracts of soils from tropical and temperate regions. Soil Sci. Soc. Am. J., 47: 1026-1032. Skjemstad, J.O., Fitzpatrick, R.W., Zarcinas, B.A. and Thompson, C.H., 1992. Genesis of podzols on coastal dunes in southern Queensland. II. Geochemistry and forms of elements as deduced from various chemical extraction procedures. Aust. J. Soil Res., 30: 615-644. Soil Survey Staff, 1975. Soil Taxonomy: a Basic System of Soil Classification for Making and Interpreting Soil Surveys. USDA Handbook 436. Govt. Print. Office, Washington, DC. Stace, H.C.T., Hubble, G.D., Brewer, R., Northcote, K.H., Sleeman, J.R., Mulcahy, M.S. and Hallsworth, E.G., 1968. A Handbook of Australian Soils. Rellim, Adelaide, 433 pp. Tejan-Kella, M.S., Chittleborough, D.J., Fitzpatrick, R.W. Thompson, C.H., Prescott, J.R. and Hutton, J.T., 1990. Thermoluminescence dating of coastal sand dunes at Cooloola and North Stradbroke Island, Australia. Aust. J. Soil Res., 28: 465---481.
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Thorn, B.G., Bowman, G.M. and Roy. P.S., 1981. Late Quaternary evolution of coastal sand barriers, Port Stephens Myall Lakes area, New South Wales, Australia. Quat. Res., 15:345 364. Thompson, C.H., 1983. Development and weathering of large parabolic dune systems along the subtropical coast of eastern Australia. Z. Geomorphol. Suppl., 45: 205-225. Thompson, C.H., 1992. Genesis of podzols on coastal dunes in southern Queensland. 1. Field relationships and profile morphology. Aust. J. Soil Res., 30:593-613. Thompson. C.H. and Bowman, GM., 1984. Subaerial denudation and weathering of vegetated coastal dunes in eastern Australia. ln: B.G. Thorn ( Editor), Coastal Geomorphology in Australia. Academic Press, Australia. pp. 263-290. -
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