Potential Acid Sulfate Soils Research Articles

LEACHING AND FLUSHING OF ACIDITY IN THE RECLAMATION OF ACID SULPHATE SOIL, KALIMANTAN, INDONESIA

ABSTRACTLowland reclamation for agricultural development was started 40 years ago in Indonesia. Part of the area is a tidal swamp that originated from marine sediment. Land reclamation by lowering the groundwater table promoted oxidation of acid sulphate soil that produced severe acidity. A tidal irrigation system that allows two‐way flow with a reservoir at the end of the channel was introduced at the beginning of development in order to maintain water movement and increase the volume of freshwater flow. After 40 years of reclamation, water and soil quality in several schemes indicate a slow improvement of acidity. After the dry season, acid water with pH 3 ~ 4 could be found in the canal, as well as potential acid sulphate soil still found in the shallow layer. Appropriate water management in the scheme should meet at least tree objectives, i.e. supplying enough water for leaching and diluting acid water, draining excess water during storms, and keeping the potential acid sulphate soil under reduced conditions in order to avoid excessive oxidation. Evaluation of the hydraulic performance of the existing main system indicates a need for upgrading of the channel to allow enough fresh water that could support the process of leaching and flushing. Copyright © 2013 John Wiley & Sons, Ltd.

Changes of Soil Chemical Properties During Rice Straw Decomposition in Different Types of Acid Sulphate Soils

Changes of Soil Chemical Properties During Rice Straw Decomposition in Different Types of Acid Sulphate Soils

The availability and mobility of arsenic and antimony in an acid sulfate soil pasture system

The Macleay floodplain on the north coast of New South Wales, Australia, has surface soil concentrations of up to 40mgkg−1 arsenic (As) and antimony (Sb), due to historical mining practices in the upper catchment. The floodplain also contains areas of active and potential acid sulfate soils (ASS). Some of these areas are purposely re-flooded to halt oxidation processes, but the effect of this management on the metalloid mobility and phytoavailability of the metalloids present is unknown. This study investigated the changes to soil solution As and Sb, associations of metalloids with soil solid phases, and uptake into two common pasture species following 20weeks of flooding in a controlled environment. The effect of an ASS subsoil was also investigated. The soil solution concentration and availability of the metalloids was in some instances higher in the floodplain soils than would generally be expected in soils with comparable contamination. There appeared to be few changes to soil solution concentrations or phase associations with flooding in this short term study, due to the high acid buffering and poise of the investigated soils. A strong relationship was found between the relative uptake of Sb into pastures and the oxalate extractable Fe in the soil, which was taken as a proxy for non-crystalline iron (Fe) hydroxides. This relationship was dependent on flooding and was absent for As. Further targeted investigations into metalloid speciation kinetics and the stability of soil solid phases with flooding management are recommended.

Microbial community potentially responsible for acid and metal release from an Ostrobothnian acid sulfate soil

Soils containing an approximately equal mixture of metastable iron sulfides and pyrite occur in the boreal Ostrobothnian coastal region of Finland, termed ‘potential acid sulfate soil materials’. If the iron sulfides are exposed to air, oxidation reactions result in acid and metal release to the environment that can cause severe damage. Despite that acidophilic microorganisms catalyze acid and metal release from sulfide minerals, the microbiology of acid sulfate soil (ASS) materials has been neglected. The molecular phylogeny of a depth profile through the plough and oxidized ASS layers identified several known acidophilic microorganisms and environmental clones previously identified from acid- and metal-contaminated environments. In addition, several of the 16S rRNA gene sequences were more similar to sequences previously identified from cold environments. Leaching of the metastable iron sulfides and pyrite with an ASS microbial enrichment culture incubated at low pH accelerated metal release, suggesting microorganisms capable of catalyzing metal sulfide oxidation were present. The 16S rRNA gene analysis showed the presence of species similar to Acidocella sp. and other clones identified from acid mine environments. These data support that acid and metal release from ASSs was catalyzed by indigenous microorganisms adapted to low pH.

전황함량과 순산발생능력의 상관관계를 통한 잠재특이산성토양 기준 설정

황철석 (Pyrite, FeS2)을 함유한 잠재특이산성토는 강하류 삼각지 토양, 간척지 등의 해성토뿐만 아니라, 영일만과 같은 융기해성토 지대, 내륙의 선상지하단 유기물이 많은 암흑색 토층이 있을 때에 존재하는 수가 있다. 또한 안산암 지역의 열수작용에 의해 생성되어 암맥을 따라 형성된 황철석이 광산개발이나 도로건설로 절취사면에서 노출되어 산화되면 매우 강한 산성을 띠는 특이산성토층을 형성하여 주변농경지에 피해를 주고 있다. 현재 잠재특이산성토양의 판정은 현장에서는 과산화수소로 반응 시 수증기발생 정도로 판단하거나 실내실험에서는 전황 (Total-S)성분의 함량으로 판단한다. 하지만 이들 방법은 시군농업기술센터 및 현장 진단 시 적용이 용이하지 않다. 산발생 능력평가 중 순산 발생능력실험 (Net Acid Generation, NAG pH)은 대상지역의 산성발생 가능성에 대한 예측을 정량적 계산으로 가능하다. 순산발생능력실험을 이용하여 전황함량과 NAG pH와의 상호관계를 통해 특이산성토양 판정을 제안하기 위해 화산기원의 잠재특이산성 토양과 사양질 토양을 일정비율로 혼합된 토양과 특이산성토양인 김해통과 해척통 토양에 대해 실험을 수행하였다. 전황의 함량이 0.75% 이상인 시료의 NAG pH가 2.5이며 0.75-0.50%의 중간 특이산성토양은 NAG pH 3.0으로 측정되었다. 그리고 전황 함량이 0.5-15% 약한 특이산성 토양은 NAG pH 3.8로 측정되었다. 따라서 순산발생량은 NAG pH를 이용하여 토양 내 황철석을 모두 산화시키고 pH를 측정하여 pH 3.8이하인 토양은 특이산성토양으로 구분하는 것이 타당할 것으로 판단되었다. Acid sulfate soil (ASS) and potential acid sulfate soil (PASS) are distribution in worldwide and originate from sedimentary process, volcanic activity, or metamorphism and are problematic in agriculture and environmental due to their present and potential acidity developed by the oxidation. The PASS was defined as soil materials that had sulfidic layer more than 20 cm thick within 4 m of the soil profile and contained more than 0.15% of total-sulfur (T-S). A tentative interpretative soil classification system was proposed weak potential acid sulfate (T-S, 0.15-0.5%), moderate potential acid sulfate (T-S, 0.5-0.75%) and strong potential acid sulfate (T-S, more than 0.75%). PASS due to excess of pyrite over soil neutralizing capacity are formed. It provides no information on the kinetic rates of acid generation or neutralization; therefore, the test procedures used in acid base account (ABA) are referred to as static procedures. The net acid generation (NAG) test is a direct method to measure the ability of the sample to produce acid through sulfide oxidation and also provides and indication. The NAG test can evaluated easily whether the soils is PASS. The samples are mixed sandy loam and the PAS from the hydrothermal altered andesite (1:3, 1:8, 1:16, 1:20, 1:40, 1:80 and 1:200 ratios) in this study. We could find out that the NAG pH of the soil containing 0.75% of T-S was 2.5, and that of the soil has 0.15% of T-S was 3.8. NAG pH test can be proposed as soil classification criteria for the potential acid sulfate soils. The strong type has NAG pH of 2.5, the moderate one has NAG pH of 3.0, and the weak one has NAG pH of 3.5.

Nutrient Removal by Rice Cultivated in Newly Opened Wetland Rice in Bulungan District, East Kalimantan

Highly weathered Indonesian soils and potential acid sulphate soils are mainly granted for developing newlyopened wetland rice field to meet rice growing demand in Indonesia. Nutrient removal by rice harvest product ofCiliwung variety planted in newly opened wetland rice was studied in Bulungan District, in 2009. The aims were toexamine the nutrient taken out by rice harvest product and to properly manage its fertility status to sustain ricefarming. Six treatments were studied including T0: farmers practices, T1: farmer practices + compost + dolomite, T2:NPK recommended rate, N and K were split two times, T3: NPK recommended rate, N and K were split three times,T4: NPK recommended rate, N and K were split three times + compost + dolomite and T5: NPK recommended rate,N and K were split two times + compost + dolomite. The results indicated that the highest concentrations of N, P,and K in rice grain and rice straw were observed at NPK with recommendation rate in which N and K were split threetimes + straw compost + dolomite (T4). The T4 (NPK with recommendation rate in which N and K were split threetimes + straw compost + dolomite) also showed the highest nutrient removal by harvest product. Depending on thetreatments, total nutrients removal through rice grains and rice straw varied from 61.81 to 101.71 kg N, 4.31 to13.69 kg P and from 95.77 to 171.16 kg K ha-1 season-1, meaning that at least about 137 to 225 kg urea, 50 to 160kg SP-36 and 190 to 339 kg KCl ha-1 season-1 should be given to replace nutrient removed by harvest product andto avoid any nutrients depletion. When all rice straws were returned to the field as compost, about 55 to 133 kg urea,25 to 110 kg SP-36 and 10 to 19 kg KCl ha-1 season-1 should be added to substitute nutrient removed by rice grain.[How to Cite: Sukristiyonubowo, K Nugroho and T Vadari. 2012. Nutrient Removal by Rice Cultivated in Newly Opened Wetland Rice in Bulungan District, East Kalimantan. J Trop Soils 17: 115-120. Doi: 10.5400/jts.2012.17.2.115] [Permalink/DOI: www.dx.doi.org/10.5400/jts.2012.17.2.115]

Effects of sulphide oxidation on selected soil properties

This study covered soils containing sulphides (Potential Acid Sulphate Soils - PASS), located on Karsiborska Kepa Island (NW Poland). The aim was to analyse changes in some soil properties caused by the oxidation of sulphides to sulphates for developing a new methodology. Soil samples taken from one representative pedon were oxidized under laboratory conditions for 8 weeks (incubation method). During this period the concentration of sulphates and pH in the soil extract was measured at multi-day intervals. Soil organic horizons characterized by a relatively high content of total sulphur (> 0.75%) showed no decrease in pH below 4 due to the oxidation. The opposite was observed in the case of sandy horizons, poor in sulphur. The rate of pH decline during incubation was the highest in the initial period of oxidation, which justifies the need to perform some soil analyses in samples of fresh /wet soil within 48 hours of sampling. The results enabled us to propose a procedure for soils containing sulphides, which included both field and laboratory tests, with special care taken to preserve as much as possible the natural reducing environment.

Soil cover and landscape evolution in the Senegal floodplain: a review and synthesis of processes and interactions during the late Holocene

The aim of this paper is to summarize the successive biological, pedological, hydrodynamic, geomorphological and geochemical processes that have occurred in the Senegal valley, and to describe how their interactions during the late Holocene conditioned soil cover formation and landscape evolution. Potential acidity accumulated as pyrite in the floodplain sediment during the last marine transgressions, and was expressed during the following regressions because of oxidation. Soil acidification was mitigated by the soil buffer capacity and by the interaction with the slightly alkaline continental freshwater of the river. Two pedogenetic transformation processes that resulted from the succession of acidic and neutral conditions, transformed unripe muds with pyrite (potential Acid Sulphate soil) to actual Acid Sulphate soils, and then to Vertisols. Geochemical modelling with PHREEQC quantitatively confirmed the feasibility of the processes involved. These two pedogenetic processes also controlled two independent salt accumulation processes: (i) the transformation of shell accumulation beds into gypsum layers and (ii) aeolian deflation and formation of clay dunes. The study shows that pedogenetic effects on alluvial material can lead to contrasting horizons that cannot be explained stratigraphically. It also shows that the presence of saline areas in the Senegal middle valley results from much more complex processes than a simple salt deposition during transgressions.

Estuarine infill and formation of Deltaic Plains, Shoalhaven River.

The Shoalhaven River is an example of a mature, infilled estuary on a wave-dominated coast. The river presently flows between prominent levees towards the coast, periodically exiting at Shoalhaven Heads, but having much of its flow artificially diverted to exit at Crookhaven Heads. The alluvial plains east of Nowra are the result of estuarine infilling behind a sand barrier, represented by Comerong Island, a southern continuation of the Seven Mile Beach beach-ridge plain. Drilli has revealed marine sands adjacent to this eastern sand barrier, and extensive muds deposited in a barrier estuary beneath most of the plains. The molluscan composition of these sediments indicates deposition in brackish water conditions, with Notospisula trigonella especially widespread. Estuarine infill occurred progressively around deltaic channels, isolating smaller basins which accreted subsequently. Most of the estuarine sedimentation occurred 5500 – 3500 radiocarbon years BP. Brackish-water muds grade upwards into fresh-water alluvial muds deposited from fluvial overbank flows, and the transition is indicated from analysis of the diatoms within sediments in an augerhole near Jaspers Brush. Levees overlie these estuarine sediments in places and indicate natural changes in river channel location. There is an extensive potential acid sulphate soil hazard throughout the plains as a result of the occurrence of pyrite-rich estuarine muds up to an elevation close to mean sea level beneath most of the plains.

Assessment of the impacts of dredging and drainage on the mangrove soils from selected rivers in the niger delta, nigeria

This study assessed the impact of dredging and drainage on mangrove soils of the Niger Delta, Nigeria. Samples from intact/un-drained mangroves and dredged/drained soils were collected from selected rivers in the Niger Delta and analysed. The rivers included Benin, Escravos, Warri, and Gbaraun and Sego Creeks. The field pH of the dredged soil was in the range of 3.7 – 3.9. On the other hand, the intact soil under mangrove vegetation and tidal cover had field pH in the neutral range (7.0 – 7.2). Upon peroxide oxidation, the pHs of the drained and un-drained soils were in the ranges of 1.5 -1.6 and 1.3 – 2.9 respectively. The results therefore indicated that the un-drained soils are potential acid sulphate soils (PASS), while the drained soil, which are already undergoing acidification are actual acid sulphate soils (AASS). Indications of acidification include field pH, peroxide oxidation pH, dried sample pH, and the presence of sulphur oxidizing bacteria and sulphate reducing bacteria. The study concludes that mangrove soil disturbance through dredging, drainage and exposure to air cause acidification. Keywords : Acidification, dredging, pH, mangrove, Niger Delta, oil exploration

Schwertmannite stability in acidified coastal environments

Abstract A combination of analytical and field measurements has been used to probe the speciation and cycling of iron in coastal lowland acid sulfate soils. Iron K-edge EXAFS spectroscopy demonstrated that schwertmannite dominated (43–77%) secondary iron mineralization throughout the oxidized and acidified soil profile, while pyrite and illite were the major iron-bearing minerals in the reduced potential acid sulfate soil layers. Analyses of contemporary precipitates from shallow acid sulfate soil groundwaters indicated that 2-line ferrihydrite, in addition to schwertmannite, is presently controlling secondary Fe(III) mineralization. Although aqueous pH values and concentrations of Fe(II) were seasonally high, no evidence was obtained for the Fe(II)-catalyzed crystallization of either mineral to goethite. The results of this study indicate that: (a) schwertmannite is likely to persist in coastal lowland acid sulfate soils on a much longer time-scale than predicted by laboratory experiments; (b) this mineral is less reactive in these types of soils due to surface-site coverage by components such as silicate and possibly, to a lesser extent, natural organic matter and phosphate and; (c) active water table management to promote oxic/anoxic cycles around the Fe(II)–Fe(III) redox couple, or reflooding of these soils, will be ineffective in promoting the Fe(II)-catalyzed transformation of either schwertmannite or 2-line ferrihydrite to crystalline iron oxyhydroxides.

Relationship between Metals Leached and Soil Type from Potential Acid Sulphate Soils under Acidic and Neutral Conditions in Western Australia

Metal contaminants are likely to be mobilised from soil when in contact with acidic drainage. Soils containing sulphide are often associated with significant quantities of trace metals. Understanding the source of metal pollution is of significant concern for management because sulphide-containing soils are found in close proximity to estuaries, lowland rivers and lakes. This study focuses on Western Australian soils, which are typically sandy and well weathered. Two leachate trials, a batch and a column method, investigated the possibility of characteristic leachate signatures with respect to future traceability of metal contamination from soil drainage. Leaching signatures were assessed for four soil types (grey sand (GS), iron-rich sand (FeRS), silty sand (SS) and peat) found coastally between Perth and Albany, in Western Australia. Trace metals leached from the four soil types showed significant differences for both the metals leached and the concentrations for the column leaching trial. No nickel (<1.0 µgL−1) but relatively high concentrations of arsenic were leached from the peat site. The FeRS leachates contained chromium, copper, high aluminium and relatively high iron. The GS leached extremely high iron and relatively high manganese concentrations. In comparison, only small concentrations of nickel, iron, aluminium, arsenic and manganese leached from the SS columns. Selenium did not leach above reporting limits (<1.0 µg L−1) from any of the soil types. This work suggests that leachate signatures from different soil types exist and that soil type should be considered when determining the risk of aquatic impact associated with acidic drainage.

Pengaruh Bahan Amelioran terhadap Pertumbuhan dan Hasil Tiga Varietas Buncis di atas Sistem Surjan pada Lahan Sulfat Masam Potential

High soil acidity is one of the problems causing low snap bean yield on potential acid sulphate soils. Using tolerant variety and applying ameliorant were several efforts to increase snap bean yield on potential acid sulphate soils. The objective of this research was to evaluate the effect of ameliorant application on plant growth, and yield of three snap bean varieties on potential acid sulphate soils. This research was conducted on potential acid sulphate soil on surjan system at Experimental Station Belandean in Barito Kuala regency of South Kalimantan province in the dry season of 2005. The experiment was arranged in split-plot design with three replications. The main plots were ameliorant application, i.e. control, liming 1 t.ha -1 + manure 2.5 t.ha -1 , and liming 2 t.ha -1 + manure 5 t.ha -1 , and the sub plots were three snap bean varieties, i.e. Lebat, Perkasa and Bravo. The result showed that the plant growth and yield of snap bean were affected by ameliorant application. Liming with dosages of 1.0 t.ha + manure 2.5 t.ha -1 increased yield 2 581 kg.ha -1 or 81.5 % higher than control. All varieties showed the same yield on acid sulphate soil. Key words: Ameliorant, snap bean, potential acid sulphate soil

Evaluation Of Management Properties Of Wetland Soils Of Akwa Ibom State, Nigeria For Sustainable Crop Production

Management properties of soils of three wetland types in Akwa Ibom State were investigated. The wetland types are Inland Valley, Flood plain and Mangrove. The soils had silt/clay ratios above 0.15 and 0.25 indicating that they are of young soils. The pH of the wet soils was very slightly acidic (>6.4) while that of the air-dried samples was extremely acidic (>3.5). This suggests that the soils are potential acid sulphate soils. Organic matter content values were high with mean of 12.59, 60.01, and 3.20 percent for Inland valley, Flood plain and mangrove soils respectively. Effective cation exchange capacity (ECEC) was below the >20 cmol/kg reported by FAO (1976) as indicative of high suitability of soil for crop production. There was negative and significant correlation between ECEC and pH in Flood plain soils (r= -0.76) and positive but non-significant correlation between ECEC and organic matter in all the wetland types. The soil had low base saturation (

Sulfur dynamics in boreal acid sulfate soils rich in metastable iron sulfide—The role of artificial drainage

The sulfur dynamics of boreal brackish-water sediments rich in metastable iron sulfide (average elemental composition of FeS 1.1), which upon oxidation have a huge impact on stream-water chemistry, were studied. Two cores, extending from the upper oxidized layer (acid sulfate soil) into the underlying iron sulfide-bearing sediment (potential acid sulfate soil) were collected at a site close to the sea level and at another site about 40 m above the latter in a region of current isostatic land uplift (Finland). The data clearly show, in contrast to what is often argued, that these notorious acidic soils are formed not as a result of the natural uplift but because of extensive ditching of farmlands. Above the depth of artificial drainage, S and Ni are abundantly lost, while beneath that level pyrite is abundant and metastable iron sulfide is increasing with depth, and the Ni concentration is relatively stable. In the narrow zone between the reduced and oxidized layers, the processes are dynamic and result in preservation of elemental S at one of the locations. The sulfur isotopic composition for metastable iron sulfide and pyrite in the investigated acid sulfate soils were found to be distinctly bimodal and roughly corresponding to a similar distribution in stream-water sulfate earlier reported from the same region. This indicates that pyrite is the main source of sulfate and acidity in some affected drains, while in others it is metastable iron sulfide.

Influence of metal ions and pH on the hydraulic properties of potential acid sulfate soils

Summary Acid sulfate soils (ASS) cover extensive areas of east Australian coastal floodplains. Upon oxidation, these hydromorphic pyritic sediments produce large quantities of sulfuric acid. In addition, due to their geographic location, these soils may also come in contact with high ionic strength estuarine tidal waters. As a result, there is typically a large variation in acidity (pH) and cation concentrations in soil porewaters and adjacent aquatic systems (e.g., agricultural field drains, rivers, estuaries, etc.). Acid sulfate soils, especially from the unoxidized gelatinous deeper layers, contain a relatively high proportion of montmorillonite, which is wellknown for its shrink-swell properties. Variations in cation concentrations, including H3O+, can influence montmorillonite platelet interactions and may, thus, also significantly affect the hydraulic conductivity of materials containing this clay. In this paper we report on the effect of four common cations, at reasonable environmental concentrations, on the hydraulic properties of potential (unoxidized) acid sulfate soil materials. The natural system was simplified by examining individually the effects of each cation (H+, Ca2+, Fe2+ and Na+) on a soil–water suspension in a filtration cell unit. Moisture ratio, hydraulic conductivity and the consolidation coefficient of the deposited filter cakes were calculated using material coordinates theory. The results indicate that the hydraulic conductivity of potential acid sulfate soils increases at low pH and with cation concentration. Although an increase in the charge of amphoteric edge groups on montmorillonite clays may result in some aggregation between individual clay platelets, we conclude that the extent of these changes are unlikely to cause significant increases in the transportation of acidity (and contaminants) through potential acid sulfate soils as the hydraulic conductivity of these materials remain low (

Fertility status and management implications of wetland soils for sustainable crop production in Akwa Ibom State, Nigeria

Fertility status of soils of three wetland types in Akwa Ibom State, Nigeria, was investigated. The wetland types are Inland Valley (IV), Flood Plain (FP) and Mangrove (MG). The soils have silt-clay ratios above 0.15 and 0.25 indicating that they are of young parent materials with low degree of weathering and possible weatherable minerals for plant nutrition. The pH of the soils was near neutral (>6.4) when wet but extremely acid (>3.5) when dried indicating that the soils are potential acid sulphate soils. Organic matter content was high with mean values of 12.59, 6.03 and 3.20% for IV, FP and MG soils, respectively. Total N (nitrogen) was low except in IV soils where the value was above the 0.30% critical level. The C:N ratios were narrow with mean of 20.90, 12.17 and 12.12 for IV, FP and MG soils, respectively. The contents of basic cations [Calcium (Ca), Magnesium (Mg), Potasium (K) and Sodium (Na)] were low while acidic cations [Aluminium (Al) and Hydrogen (H)] were high. The Ca:Mg ratios were below the optimum range of 3:1 to 4:1 required for most crops. The Mg:K ratios were above 1.2, below which yields of crops like corn and soybean may be reduced. Effective cation exchange capacity (ECEC) was below the 20 cmol/kg. Percent base saturation was low (<38) indicating that the soils are potentially less fertile. Exchangeable Al and percent Al saturation were high, above 60% in IV and FP soils. Electrical conductivity was above the critical value of 2 dsm−1 while exchangeable sodium percentage was less than 15. Available Phosphorus (P) and low, <10 ppm and free Fe2O3/clay ratios were <0.15. Positive correlation existed between silt and ECEC, implying that silt contributed to nutrient status of the soils. Generally, fertility status of the soil is low and would require maintenance of adequate organic matter, application of lime and organic and inorganic fertilizers, drainage and irrigation if the land is to be used for intensive/sustainable crop production.

Development of a protocol for recognizing sulfidic sediments (potential acid sulfate soils) in freshwater wetlands

Summary The presence of sulfidic sediments (potential acid sulfate soils) is an emerging problem in the management of inland wetlands. Using data from 81 wetlands in the Murray‐Darling Basin, a simple protocol was developed to assess whether a wetland will contain sulfidic sediments at levels that could cause ecological damage. Risk factors include whether or not the wetland receives municipal waste or irrigation return water, elevated salinity in the overlying water (&gt;1750 µS/cm) or sediment (400 µS/cm in a 1:5 soil : water extract) and high levels of sulfate in the water column (&gt;10 mg/L). Neutral or basic sediment pH indicates that, even if the sediment does contain sulfidic sediments, there is a reduced likelihood of acidification if the sediments are oxidized.

Sulfidic materials in dryland river wetlands

Due to a combination of river regulation, dryland salinity and irrigation return, lower River Murray floodplains (Australia) and associated wetlands are undergoing salinisation. It was hypothesised that salinisation would provide suitable conditions for the accumulation of sulfidic materials (soils and sediments enriched in sulfides, such as pyrite) in these wetlands. A survey of nine floodplain wetlands representing a salinity gradient from fresh to hypersaline determined that surface sediment sulfide concentrations varied from &lt;0.05% to ~1%. Saline and permanently flooded wetlands tended to have greater sulfide concentrations than freshwater ones or those with more regular wetting–drying regimes. The acidification risk associated with the sulfidic materials was evaluated using field peroxide oxidations tests and laboratory measurements of net acid generation potential. Although sulfide concentration was elevated in many wetlands, the acidification risk was low because of elevated carbonate concentration (up to 30% as CaCO3) in the sediments. One exception was Bottle Bend Lagoon (New South Wales), which had acidified during a draw-down event in 2002 and was found to have both actual and potential acid sulfate soils at the time of the survey (2003). Potential acid sulfate soils also occurred locally in the hypersaline Loveday Disposal Basin. The other environmental risks associated with sulfidic materials could not be reliably evaluated because no guideline exists to assess them. These include the deoxygenation risk following sediment resuspension and the generation of foul odours during drying events. The remediation of wetland salinity in the Murray–Darling Basin will require that the risks associated with disturbing sulfidic materials during management actions be evaluated.

Heavy-metal loadings related to urban contamination in the Kooloonbung Creek catchment, Port Macquarie, New South Wales

Urbanisation and industrial development lead to contamination of estuaries and streams with dispersed loadings of heavy metals and metalloids. Contributions of these elements also occur from natural sources. This study provides baseline geochemical data on the respective natural and anthropogenic inputs of Cu, Pb, Zn, Cd, As, Sb, Cr, Ni, Mn and S to estuarine, fluvial and wetland sediments, and adjacent soils, in the Kooloonbung Creek catchment that drains the Port Macquarie urban area in north coastal New South Wales. There have been anthropogenic additions of Cu, Pb, Zn and As from dispersed urban sources at Port Macquarie, but they are restricted to the local catchment and do not impact on the adjacent Hastings River estuary. The most contaminated sediments display enrichment factors up to 20 × for Cu and Pb, 9 × for Zn and 5 × for As relative to local background values. However, only one value (for Pb) exceeds National Water Quality Management Strategy interim sediment quality guideline (high) values. On the other hand, sediments and local soils are commonly strongly enriched in Cr, Ni and Mn, reflecting adjacent ultramafic and mafic rock substrate and lateritic regolith. Concentrations of Cr and Ni are commonly well above interim sediment quality guideline (high) values for sediments, but are in mineralogical forms that are not readily bioavailable. Sediment and soil quality guideline values consequently need to recognise natural enrichments and the mineralogical siting of heavy metals. Although dissolved concentrations of heavy metals in stream waters are commonly low, there is evidence for mobility of Cu, Zn, Fe and Al. Parts of the Kooloonbung Creek wetland area lie on sulfidic estuarine sediments (potential acid sulfate soils). Experimental oxidation of uncontaminated and contaminated sulfidic sediments leads to substantial dissolution of heavy metals under acid conditions, with subsequent aquatic mobility. The results warn about disturbance and oxidation of potential acid sulfate soils that have been contaminated by urban and natural heavy-metal sources.