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Soil properties in and around acid sulfate soil scalds in the coastal floodplains of New South Wales, Australia.

Introduction

Acid sulfate soil (ASS) scalds are persistently bare areas of land associated with pyrite oxidation and ASS formation in drained coastal floodplains. In Australia, ASS scalds have not previously been a main focus of research and have been considered part of a wider problem. Yet their seemingly intractable nature reflects their significance as chronic contributors to problems surrounding actual ASS formation and its consequences, including environmental (e.g. water quality, fish kills), economic (e.g. public/private infrastructure, rural productivity, land prices, tourism values), and social effects (e.g. catchment health, visual amenity, conflict between disparate stakeholders).

Pyritic sediments are common along the now highly populated New South Wales (NSW) coastline of eastern Australia (White and Melville 1993). Various thicknesses of fluvial sediments have overlain these estuarine sediments, which are thickest at the main levees and thinnest in the backswamps, resulting in their low elevation (Lin and Melville 1993; Lin et al. 1995). Coastal wetlands and swamps in NSW have been progressively drained over the last 100 years or more (Davies and Mumby 1999; Tulau 1999; Tulau and Naylor 1999), accelerating oxidation of pyritic sediments. More than 400 000 ha of coastal land is considered at high risk of actual ASS degradation in NSW (Atkinson 1993). Toxic oxidation products such as soluble acidity, salinity, and iron (Fe) and aluminium (Al) compounds are formed and transported into drains and waterways. Pyrite oxidation causes environmental, economic, and social damage not only in Australia but also in other countries around the world (Dent and Pons 1995).

ASS formation is characterised by irreversible sediment shrinkage, cracking, and drying (Pons 1972). These effects increase oxygen incursion into the sulfidic layers, allowing accelerated pyrite oxidation. Where pyritic sediments are close to the soil surface and are allowed to oxidise, persistently bare areas can result (White et al. 1997). These areas are called 'ASS scalds'. Toxic oxidation products accumulate near the soil surface in these areas, and these soil layers can become so acidic (and often highly saline) that vegetation dies and can be chronically excluded (Mulvey 1993). Further environmental and economic damage can occur when acidity and soluble metals in ASS scald surface layers are transported into drains and released into creeks and estuaries, either in solution during runoff events, or through wind and water erosion of surface soil materials. ASS scalds are regarded as environmentally damaging, economically useless, and requiring urgent management attention (White et al. 1997).

Revegetation of ASS scalds is essential for the remediation of the wider backswamp areas in which they occur. In order to devise successful long-term revegetation strategies of ASS scalds it is necessary to understand the main chemical properties and processes occurring in these areas. The sulfide (pyrite) and pH profiles in 10 ASS scalds, and in adjacent non-scalded paddocks at 5 of these scalds, were examined for this study. The total carbon and the soluble sulfate and iron contents of the surface soil layers at each of these sites were also examined due to their importance in the sulfide formation process. The sulfide content is important because it is the basic cause of ASS-related degradation. Particular emphasis is placed on the likely re-formation of pyrite within surface soil layers (top 40 cm). Although neo-formed iron sulfide formation (including pyrite) has been reported elsewhere (Giblin 1988; Portnoy and Giblin 1997; Bush et al. 2000), it has not been previously described as occurring in the surface soils of coastal ASS backswamps that are used consistently for agricultural production. The pH of the soil profiles was also examined because, as well as affecting the rate of further oxidation of ASS, it is a major constraint to the successful revegetation of these areas.

Materials and methods

Site location and characteristics

Duplicate scald cores were collected in ASS scalds at various locations, including the Richmond (Site 1), Clarence (Site 2), Nambucca (Site 3), Macleay (Site 4 and 5), Camden-Haven (Site 6), Manning (Site 7), Hawkesbury (Site 8 and 9), and Shoalhaven (Site 10) catchments (Fig. 1). At 5 of the sites (Sites 4, 5, 7, 8, and 10), duplicate cores were also taken in adjacent areas with vegetative cover. The suffixes S (scald) and V (vegetated) will henceforth be used after relevant site numbers to distinguish between the different cores at the same site (e.g. 4S and 4V).

[FIGURE 1 OMITTED]

Most of the sites were sampled between July 1998 and March 1999; Site 5 was sampled in July 2000 and Site 8 was sampled February 2000. Additionally, a transect of 10 surface samples (10 cm deep) was taken at Site 5, between the edge and the middle of an inundated ASS scald. The transect was effectively in a V-shape. Values progressively increased with distance from the edge, and water depth. Transect samples 1-7 were from the edge of the scald to where the water depth overlying the scald was 40 cm, whereas the last 3 samples (i.e. samples 8-10) were taken on a direct but different route back to the edge of the scald.

Preliminary analyses of some soil samples from these sites have been published (Rosicky et al. 2000, 2002; Lin et al. 200l). The bare surface soils of the study sites had extremely high concentrations of soluble and exchangeable acidity and aluminium (Rosicky et al. 2002). The ASS scalds were found to have extremely low levels of available phosphorous, and locally high levels of soluble manganese (Lin et al. 2001). The ASS scalds examined were usually relatively small areas of <10 ha located in low-elevation backswamps (1 m AHD or less) of coastal floodplains, but have occasionally affected larger areas of up to 200 ha (Rosicky et al. 2000). These former wetland sites have been extensively drained (>2 m deep) and are now used mainly for grazing beef cattle, except for Site 3 (housing allotment formerly used for grazing), Site 6 (dairy cattle grazing), and Site 9 (a tidal mangrove area recently cleared for intended grazing). ASS scald surfaces were routinely lower than surrounding vegetated surfaces, probably due to a combination of soil-profile desiccation, peat loss, and vegetation loss, which has led to soil-profile shrinkage and surface erosion.

Soil sampling

Duplicate cores were taken, using a 200-cm Dormer tapered gouge auger, from each scalded site and from vegetated sites adjacent to 5 of the scalds. Cores in the vegetated areas were taken at least 20 m from the scald edge. The duplicate cores were taken about 1 m apart. The cores were shaved to eliminate the risk of contamination of the samples. They were divided into 20-cm segments, except for the first 2 segments, which were in 10-cm increments. Each sample was placed into a plastic bag, the air expelled by twisting the bag tightly around the sample, and tied securely. They were placed on ice and returned to the laboratory, where the samples were oven-dried to 70[degrees]C.

After crushing for 10-15 s in a Labtechnics LMI Lab mill, a 1 : 5 soil : water solution was prepared for determination of pH. The soluble sulfate (S[O.sub.4]), soluble iron (Fe), and total carbon (C) were determined for surface samples (top 40 cm): these properties were obtained using a Lachat Flow Injection Analyser, an ICP-OES, and a Leco CNS Analyser, respectively. The soluble S[O.sub.4] and Fe were expressed in mg/g oven-dry (105[degrees] C) soil, and total C was expressed as a percentage of the oven-dry soil.

The amount of sulfide was determined using the chromium-reducible sulfur (CRS) method (Sullivan et al. 1998) and a sample weight of 300-500 mg. The results arc expressed as %[S.sub.CR]. All duplicate core segments were tested separately. Results were interpreted with reference to action criteria that are used in NSW for environmental risk assessment of different-textured materials (0.1% [S.sub.CR] in fine-, 0.06% in medium-, and 0.03% in coarse-textured materials or in amounts > 1000 t) (Ahem et al. 1998).

All laboratory testing was undertaken at the Environmental Analysis Laboratory, Southern Cross University, except for soluble Fe and organic C determinations, which were done through The University of New South Wales Department of Geography laboratories as part of a separate investigation (Lin et al. 2001).

Results

[S.sub.CR] profiles

The sulfide concentration profiles in the top 200 cm of the tested sites are shown in Table 1. In all cases (except Site 3), there was a zone of high sulfide concentration (> 0.1% [S.sub.CR]) underlying an upper zone with low sulfide concentration. At all sites, the zone of greatest [S.sub.CR] concentration coincided with the occurrence of fine-grained unconsolidated, blue/grey gel-like sediments. In NSW, these sediments typically accumulated in sheltered estuarine environments such as mangroves, saltmarsh, and backswamps (Bush et al. 2001) and their sulfide mineralogy was dominantly pyrite (Bush and Sullivan 2002). The soil layers overlying the pyritic gels were composed of medium- to fine-textured soil materials, often with yellow jarosite infillings in the soil matrix and root holes above the sulfide layer, and red/orange iron oxide/hydroxide segregations within the soil matrix and on the soil structural surfaces.

The depth to the underlying pyritic gels (usually >0.5% [S.sub.CR] content) in the ASS scalds varied from being within 10 cm of the surface at Site 9 to >200 cm depth at Site 3, with others at 50-100 cm depth. The vegetated paddock sites had sulfide profiles of similar concentration to their scalded counterparts. However, the uppermost boundary of the subsurface pyritic gels within the vegetated cores always started 20-40 cm further down from the soil surface than those of the adjacent scald cores (Table 1).

Sulfide concentrations in surface soil layers

At all sites examined (except Sites 8 and 9 where the pyritic zones were very close to the soil surface), the top 10-40 cm of the soil profiles had higher %[S.sub.CR] contents than the immediately underlying soil layers. Although the sulfide concentrations in these surface layers were much less than those of the underlying pyritic gels, for several surface layers these sulfide concentrations were considerably higher than the action criteria mentioned above (i.e. [greater than or equal to] 0.03%) (Ahem et al. 1998). In contrast to the underlying pyritic gels, which have a very soft light clay texture, the texture of these sulfidic surface layers was much coarser, being composed of materials with textures ranging from sandy loam to clay loam. At most of the 5 vegetated sites, the surface sulfide concentrations were greater than, or equal to, those for the adjacent ASS scalds (Table 1).

pH profiles

The pH (1 : 5 soil : water) for all sites (except Site 5V and the surface layer of 8V) was <4.5 in the top 1 m of the soil profile (Fig. 2), with most soil layers in the top 1 m having pH 3.0-4.0. Although for most sites the soil pH increased at depths >100 cm, low pH values (<4.5) extended into the unoxidised (as evidenced by a lack of iron segregations) pyritic gels for 20-40 cm at Sites 4S, 4V, 7S, 7V, 10S, and 10V. For Sites 1, 2, 5S, and 9, the top 60-80 cm of the unoxidised pyritic gels had a pH <4.5. At Sites 6, 8S, and 8V, the top 160, 150, and 120 cm (respectively) of the unoxidised pyritic gels had a pH <4.5. Similar pH concentrations were found in scalded and adjacent vegetated cores, again offset 20-40 cm deeper in the vegetated cores (Fig. 2b, c).

[FIGURE 2b, 2c OMITTED]

Surface pyrite in an inundated ASS seam

The transect through the inundated ASS scald at Site 5 (Fig. 3) shows that [S.sub.CR] concentration increased with both the distance from the scald edge and the depth of inundation. SCR concentration ranged from 0.03% at the edge of the inundated scald, to 0.27% closer to the centre where the water depth was >40 cm.

[FIGURE 3 OMITTED]

Surface soluble sulfate, soluble iron and carbon content in the top 10 cm of soil, soluble S[O.sub.4] values ranged between 0.5 and 12.4 mg/g oven-dry soil, soluble Fe between 0.001 and 0.464 mg/g soil, and total C between 3.9 and 24.9% (Table 2). There were higher values for all the above components in the 30 cm of soil immediately below the 10-cm surface zone.

Discussion

[S.sub.CR] profiles

At 7 of the 10 scalded sites, underlying pyritic gels, with SCR contents >0.5%, were within 80 cm of the soil surface. The remainder of the ASS scald and paddock sites (except Site 3) had underlying pyritic gels within 150 cm of the soil surface (Table 1). Site 3 was the exception to this relationship, with no subsurface pyrite zone in the top 2 m, although it demonstrated other characteristics of the ASS scalding process (Rosicky et al. 2002). A pyritic layer at about 2.5-3.0 m depth was found during an earlier study near Site 3 (Kemsley 1997). The considerable variation in depth to pyritic layers beneath the scalds investigated here indicates that the close proximity of pyritic materials to the soil surface is not essential for ASS scald formation.

The vegetated paddock SCR profiles were of a similar concentration and pattern to those of their adjacent scalds, except they were consistently displaced 20-40 cm deeper than their scalded counterparts. This displacement was physically expressed at each scalded site by a prominent 'step down' from the vegetated paddock onto the scald surface, usually [greater than or equal to] 20 cm. The lower elevations of the scald surfaces compared with the surrounding vegetated paddocks are most likely caused by a combination of soil shrinkage, erosion, and loss of peat and/or vegetative cover from the scalded sites. Essentially, the top 20-40 cm of the vegetated paddock cores (composed largely of living and dead plant material) has been removed from the scalded areas.

The maximum [S.sub.CR] concentrations in the pyritic gels underlying each ASS scald ranged between about 1% and 4%. The [S.sub.CR] concentrations close to these maxima were reached abruptly and maintained down the profile to the 200 cm maximum sampling depth. The lowest maximum [S.sub.CR] value was found at Site 4S in the Macleay catchment. Despite this, the ASS scald at this site was once >200 ha, by far the largest observed so far in NSW (it is now much smaller due to drainage manipulation and other management activities). Additionally, pyritic gels with similar characteristics underlie both the ASS scalds and their adjacent vegetated area at all sites tested. These 2 facts indicate the potential for pyrite oxidation to scald much larger areas of ASS landscapes, given the necessary conditions to instigate the scalding process (a combination of factors including drainage, land management, soil type, vegetation type, and climatic conditions).

Other noteworthy profiles are Site 8S and 9, where the pyritic materials essentially start at the soil surface (Table 1). Site 8 is a former saltmarsh area and Site 9 is a former mangrove area, located 2 km apart on the same creek system. Both areas experienced waterlogging and seawater influence to varying degrees in the recent past, and both would have been accumulating pyrite until the time they were cleared and drained. These sites have been isolated from saltwater influence in the recent past (last 30 years) by the construction of bunds with the aim of establishing productive pasture.

pH profiles

The acidic nature of the uppermost part of each of the soil profiles has resulted from the effects of the pyrite oxidation dynamics and hydrology at each ASS scald. The acidity responsible for creating these pH profiles is derived from either the oxidation of sulfides lower in the profile or, given the low-lying location of these sites, from acidity transported laterally across the landscape to these sites.

The soils beneath the vegetated paddock sites had slightly higher pH values in the top 40 cm and then, as for the [S.sub.CR] profiles, essentially mimicked their scalded counterparts (allowing for 20-40 cm of extra surface material in the vegetated sites). Thus, the same conditions exist below ASS scalds and adjoining vegetated paddocks, and vegetation build-up impedes acid accumulation at the soil surface (Fig. 2b, c).

Acidic unoxidised pyritic layers

In most ASS profiles along the NSW coastline, it would be expected that the unoxidised pyritic gels underlying the oxidised zones would be of either neutral or alkaline pH (Bush et al. 2001). However, all of the scald soil profiles in this study have thick, acidic, but evidently unoxidised pyritic gels immediately underlying the oxidised zones. Given the absence of oxidation products such as iron segregations and the high [S.sub.CR] contents in these acidic gel layers, it is unlikely that the low pH in these zones is due to oxidation of pyrite in situ. The cause of the severe acidification of these unoxidised pyritic gels can be attributed to the downward diffusion of acidity either produced in overlying oxidised zones or, for scalds located in backswamps, transported laterally across the landscape to these low-lying areas.

Thick, acidified, unoxidised pyritic zones appear to be characteristic of soil profiles in and around ASS scalds along the NSW coastline. The drainage activities at Site 8S (a former salt marsh) and Site 9 (a former mangrove) have only occurred recently (i.e. within the past 30 years) yet the thickness of the acidified, unoxidised pyritic zones at these sites was 150 cm and 70 cm, respectively. It is clear that deep acidification of the pyritic gels can be relatively rapid, most likely due to diffusion of the acidic oxidation products of pyrite oxidation resulting from drainage activities.

The pH of the soil profiles may also reflect the environmental hazard of a particular site. At pH 7, pyrite oxidation proceeds relatively slowly. Low pH values (<4.5) greatly enhance pyrite oxidation by bacterial activity, reaching a maximum rate at around pH 3.2. Additionally, soluble ferric iron ([Fe.sup.3+]) is the most efficient pyrite oxidant, but only small amounts are usually available in the soil solution. Below pH 3.5, however, [Fe.sup.3+] increasingly remains in solution (Evangelou and Zhang 1995). The pyrite oxidation rate is then greatly increased, and as long as [Fe.sup.3+] stays in solution, oxidation can continue after waterlogged (anaerobic) conditions are re-introduced. Consequently, pyritic layers with low pH values (3.5-4.5) should be considered a greater environmental threat than those with neutral pH values.

Sulfidic surface layers

The SCR data in Table 1 show that sulfides (most likely pyrite) are concentrated in the surface layers of most of the ASS scalds and adjacent vegetated paddocks. Table 2 shows that formation requirements of pyrite (organic C, soluble S[O.sub.4], and Fe) are available in and around ASS scalds. The high levels of soluble S[O.sub.4] and Fe are derived from pyrite oxidation in the underlying pyritic layers and from ASS in the surrounding areas.

A reducing environment is also required to create the conditions necessary for pyrite re-formation. Although extensively drained, the NSW backswamps where ASS scalds develop are often at 0-1 m AHD (Davies and Mumby 1999; Tulau 1999; Tulau and Naylor 1999). These low elevations impede efficient drainage, and profile shrinkage in backswamps further hinders drainage efficiency. While each site has its own individual inundation regime, watertables at the time of sampling were all close to the soil surface, while rainfall recordings were around average for the 12 months previous to sampling (Rosicky et al. 2002). Site 4 and 5 were inundated with 3 cm and 15 cm of water, respectively. Most of the other sites had watertables located 35 cm, or less, below the soil surface. Only Sites 8 and 10 had deeper watertables of around 85 and 95 cm depth, respectively. Such shallow watertables during times of average rainfall suggest that the backswamps are generally prone to inundation. Personal observations (by the authors and local residents) attest that these backswamp areas do stay inundated and then waterlogged for 6-9 months in wet periods. Black monosulfidic accumulations, a precursor to pyrite formation, have been observed by the authors on the surface of waterlogged paddocks and in the root-zone at Sites 1, 4, 6, and elsewhere. Surface-soil sulfide contents were usually greater in the cores from adjacent vegetated soil than in the scalds and coincided with generally higher total C in the soils under vegetation than in the scalds (Table 2). More available C would encourage sulfide formation.

[S.sub.CR] content in the surface layer of an inundated ASS scald

The transect taken at Site 5 shows that conditions were evidently more conducive to pyrite formation in the deeper parts of the inundated scald (Fig. 3). This ASS scald was formerly covered with freshwater-induced pasture vegetation until it was inadvertently flooded with brackish water. The vegetation consequently died and more organic matter accumulated in the deeper parts of the flooded ASS scald.

Management implications

These data, showing sulfide accumulation in the soil surface layers and the presence of conditions conducive to pyrite formation, indicate that surface pyrite is being formed contemporaneously at these sites. The neo-formation of pyrite has been observed elsewhere. Giblin (1988) found significant pyrite re-formation in the top 10 cm of tidally inundated marsh soil cores, which were previously leached of pyrite. Portnoy and Giblin (1997) showed monosulfide formation in a drained ASS wetland to which tidal inundation was reinstated and monitored for 21 months. Bush et al. (2000), using sulfur isotope analysis, found neo-formed iron monosulfide and pyrite at the oxidation front of a drained freshwater-wetland area. This present study indicates that surface pyrite re-formation is a common occurrence in coastal ASS backswamp landscapes of NSW, which are used for constant primary production.

The presence of pyritic surface layers at most of the ASS scalds and adjacent paddocks has important management implications. Current recommendations for ASS scalds, and areas with pyritic zones close to the surface, are to impede drainage to maintain these sites in a waterlogged state. This would limit the current cycles of excessive drainage-induced rise and fall of the watertable, and associated surface and off-site delivery of soluble oxidation products. Waterlogging would dilute surface acidity and salinity, and encourage vegetation growth. Under these conditions surface pyrite formation can proceed, beneficially consuming acidity, raising pH, and immobilising soluble Al. However, as these backswamp sites inevitably drain and dry out during extended dry periods, surface pyritic zones would oxidise as soon as the watertable falls below the soil surface. This would create a source of acidity and toxic oxidation products in the most biologically important region of the soil profile, affecting farm productivity as well as causing on-site and off-site environmental damage during even short dry periods. The resulting oxidation products would need to be treated, or at least managed, to avoid flushes of acidity across large areas of ASS backswamp. This could explain vegetation die-off phenomena (reported by landowners and observed by the authors) where, in backswamp areas of ASS, small areas of dead grass appear and expand quickly in size after the onset of dry weather.

Conclusions

This study has found that:

(1) At the scalded sites, the depth from the soil surface to the main pyritic zone varied from being at the surface to >200 cm depth indicating that this variable is not critical to acid sulfate soil scald formation.

(2) A characteristic feature of the soil profiles at these sites was the presence of thick (i.e. up to 160 cm thick), acidic (i.e. pH <4.5), yet apparently unoxidised pyritic gel-like sediments beneath the oxidised zone of each scald. These thick, acidified, unoxidised pyritic zones can be attributed to the downward diffusion of acidity either produced in overlying oxidised zones, or transported laterally across the landscape to these low-lying areas. Acidified unoxidised pyritic zones up to 150 cm thick can form in these soils after several decades of drainage disturbance.

(3) For most of the sites examined the [S.sub.CR] contents in the surface soil layers were appreciably higher than those in the immediately underlying soil layers. Vegetated areas often had a higher [S.sub.CR] concentration than their adjacent ASS scald. The conditions necessary for pyrite formation (i.e. adequate supplies of organic matter, soluble iron, sulfate, and waterlogging) were found to exist at all sites and the pyrite accumulations in these surface soil layers are considered to be neo-formed.

(4) The practice of constant waterlogging or inundation of the whole soil profile, as is being currently recommended for these sites, will encourage surface pyrite re-formation creating a high risk of acidification if the inundated or waterlogged conditions cannot be maintained.

(5) the vegetated soil profiles were very similar to their scalded counterparts except that they had an extra 20-40 cm layer of vegetation and mulch which was missing from the scalded profiles, indicating that there is considerable potential for more extensive scalding in these ASS areas.
Table 1. Sulfide concentration and depth occurrence in the top 2 m of
10 ASS scalds, and at 5 sites in adjacent vegetated paddocks

Suffix S denotes scalded; suffix V denotes paddock with vegetation
cover

Depth Site Site Site Site Site Site Site Site Site
(cm) 1 2 3 4S 4V 5S 5V 6 7S

 0-10 0.14 0.03 0.07 0.03 0.11 0.05 0.05 0.11 0.06
 10-20 0.11 0.01 0.02 0.03 0.09 0.03 0.04 0.03 0.05
 20-40 0.05 0.01 0.01 0.02 0.08 0.02 0.01 0.03 0.02
 40-60 0.01 0.04 0.00 0.02 0.01 0.07 0.02 1.02 0.01
 60-80 0.02 0.05 0.00 0.80 0.02 1.08 0.01 2.59 1.08
 80-100 0.03 0.46 0.00 1.02 0.00 1.18 0.09 2.84 1.69
100-120 3.04 1.58 0.00 0.75 0.30 0.81 1.28 2.95 1.19
120-140 3.68 1.56 0.00 0.86 1.04 0.97 1.28 2.97 1.23
140-160 4.03 1.87 0.00 1.00 0.89 1.02 0.91 2.69 1.83
160-180 2.70 2.07 0.00 0.77 0.64 1.03 0.97 2.52 1.53
180-200 4.00 2.25 0.00 0.69 0.71 0.96 1.03 2.82 1.72

Depth Site Site Site Site Site Site
(cm) 7V 8S 8V 9 10S 10V

 0-10 0.08 0.04 0.02 0.77 0.02 0.04
 10-20 0.12 0.76 0.02 0.98 0.01 0.04
 20-40 0.05 2.16 0.07 1.44 0.01 0.05
 40-60 0.00 2.03 1.12 1.94 0.01 0.02
 60-80 0.00 1.77 2.11 1.97 0.81 0.02
 80-100 0.00 1.88 1.80 2.05 1.58 1.35
100-120 0.37 2.12 1.95 2.28 1.75 1.40
120-140 1.28 2.33 2.06 2.32 1.55 1.66
140-160 1.55 2.60 2.43 2.35 1.59 1.55
160-180 1.37 2.46 2.69 1.89 1.75 1.67
180-200 1.45 2.53 2.80 1.76 1.78 1.28

Table 2. Total carbon, soluble sulfate, and soluble iron in 10 ASS
scalds, and at 5 sites in adjacent vegetated paddocks

Suffix S denotes scald; suffix V denotes paddock with vegetation cover

Depth Site Site Site Site Site Site Site Site
(cm) 1 2 3 4S 4V 5S 5V 6

Total carbon (%C)

 0-10 20.8 3.9 14.7 10.9 24.9 NA NA 13.6
10-20 21.7 4.0 7.6 2.2 24.5 NA NA 4.3
20-40 24.9 4.5 0.5 1.2 22.5 NA NA 1.6

Soluble sulfate (mg/g S[O.sub.4])

 0-10 6.200 3.475 6.780 1.690 0.490 4.752 3.959 4.590
10-20 9.995 2.635 3.855 2.385 0.530 3.052 4.284 1.620
20-40 10.040 3.230 1.785 4.535 1.300 3.234 1.531 1.700

Soluble iron (mg/g Fe)

 0-10 0.061 0.007 0.003 0.013 0.006 0.008 0.012 0.046
10-20 0.070 0.005 0.003 0.011 0.043 0.013 0.003 0.045
20-40 0.010 0.005 0.002 0.014 0.003 0.009 0.001 0.063

Depth Site Site Site Site Site Site Site
(cm) 7S 7V 8S 8V 9 10S 10V

Total carbon (%C)

 0-10 13.2 17.3 11.1 13.1 13.7 5.3 13.5
10-20 15.6 12.6 6.8 6.6 16.1 3.9 19.2
20-40 2.7 1.0 4.9 6.0 16.7 2.2 10.9

Soluble sulfate (mg/g S[O.sub.4])

 0-10 6.900 0.760 12.392 4.155 3.790 4.545 2.350
10-20 3.615 1.070 16.011 4.135 5.610 5.285 3.520
20-40 3.135 1.370 17.041 4.741 12.210 4.250 7.890

Soluble iron (mg/g Fe)

 0-10 0.019 0.001 0.464 0.003 0.098 0.030 0.029
10-20 0.016 0.004 3.179 0.023 0.133 0.032 0.031
20-40 0.018 0.006 2.380 0.062 1.534 0.021 0.063


Acknowledgments

This research was funded by the Acid Sulfate Soil Program (ASSPRO), a NSW government initiative, and administered by the Acid Sulfate Soil Management Advisory Committee (ASSMAC).

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Mark A. Rosicky (A, C), Leigh A. Sullivan (A), Peter G. Slavich (B), and Mike Hughes (B)

(A) Centre for Acid Sulfate Soil Research, Southern Cross University, Lismore, NSW 2480, Australia.

(B) New South Wales Agriculture, Wollongbar Agricultural Institute, Bruxner Highway,

Wollongbar, NSW 2477, Australia.

(C) Corresponding author; email: mrosic10@scu.edu.au

Manuscript received 16 May 2003, accepted 10 May 2004
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Author:Rosicky, Mark A.; Sullivan, Leigh A.; Slavich, Peter G.; Hughes, Mike
Publication:Australian Journal of Soil Research
Geographic Code:8AUST
Date:Sep 1, 2004
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