sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

enrichment and fractionation of rare earth elements in fes and organic rich estuarine sediments receiving acid sulfate soil drainage abstract an understanding of processes controlling the behaviour of rare earth elements rees within estuarine sediments is essential for the effective use of rees as tracers of environmental conditions this study investigates the enrichment and fractionation of rees in sediments with abundant iron monosulfides fes measured as acid volatile sulfide median 156 mol g and organic carbon median 3 2 mmol g we examined sediments collected from a eutrophic estuary in western australia which comprised several sedimentary environments including sites receiving drainage from acid sulfate soils ass in general sediment bound rees were highly soluble in hcl with 1 mol l hcl extractable ree concentrations amounting to 80 of corresponding total concentrations in approximately 70 of samples a mid ree mree enrichment was consistently apparent in all sediment samples with a median mree enrichment value of 1 30 range 1 13 1 50 for the total ree concentrations and 1 26 range 1 17 1 44 in the 1 mol l hcl extractions also a ce anomaly was consistently observed in the sediments examined here with a median value of 1 11 range 0 79 1 58 for the total ree concentrations and 1 19 range 1 04 1 71 in the 1 mol l hcl extracts in general a minor depletion of heavy rees hrees relative to light rees lrees was also apparent in many of the sediments yb la

formation of siderite mg calcite iron sulphide concretions in intertidal marsh and sandflat sediments north norfolk england concretions cemented mainly by siderite mg calcite and iron monosulphide are common in late holocene marsh and sandflat sediments on parts of the north norfolk coast field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate reducing bacteria are active 13c values ranging from 3 to 11 8 mean 5 9 0 suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter 18o values ranged from 6 4 to 0 8 mean 1 0 suggesting that carbonate precipitated in porewaters ranging from pure sea water to sea water diluted with meteoric water chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation some concretions have formed around fragments of wood or metal but others contain no apparent nucleus in field experiments siderite fes and mg calcite were precipitated around several different nuclei within a period of six months we suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron

sulfur iron and carbon cycling following hydrological restoration of acidic freshwater wetlands abstract freshwater re flooding is a relatively novel approach to remediate drained acid sulfate soil ass wetlands this study documents the geochemical consequences of restoring freshwater re flooding for contemporary reduced inorganic sulfur ris and iron species in two coastal floodplain ass wetlands re flooding has established predominantly reducing suboxic conditions and encouraged organic carbon accumulation in surface sediments 20 30 the ph of former sulfuric horizons has increased by 2 3 units partly in response to alkalinity generation from anaerobic metabolism of organic carbon coupled with fe iii and so 4 2 reduction despite considerable sulfidisation reactive fe fe r sum of 1 m hcl and citrate dithionite extracts and non sulfidic fe ii remain abundant in both wetlands high concentrations of fe 2 up to 5 mm in wetland porewaters represent a considerable pool of labile net acidity and is partly a result of insufficient s ii to sequester excess fe 2 accumulation of iron sulfides appears to be constrained more by so 4 2 and carbon availability rather than fe r reformation and accumulation of ris species is greatest in organic rich surface horizons 40 500 mol g 1 where time integrated ris accumulation rates approximate 10 100 nmol g 1 d 1 while pyrite is the dominant ris species to have formed since re flooding there is anomalous accumulation of s 0 up to 80 mol g 1 accounting for 50 of the ris pool in some samples greigite fe 3 s 4 has formed in near surface sediments and while avs s is a minor component of the ris pool overall at some locations maximum concentrations exceed 300 mol g 1 contemporary near surface pyrite is characterised by abundant small 200 300 nm crystals in contrast to relic sedimentary pyrite of estuarine origin that is dominated by larger crystals with diverse habit although fe and so 4 2 reduction are partly responsible for wetland scale recovery from acute acidification the resultant accumulation of diverse ris species in surficial sediments indicates an oxidative component to the s cycle and represents a hysteresis in s cycling that contrasts markedly with the drained conditions existing before remediation analysis of seasonal climate fluctuations suggests that near surface sediments containing contemporary ris are vulnerable to oxidation and possible temporary re acidification during future drought episodes this study underscores the long term legacy of ass wetland drainage and highlights the need for both considered hydrological management of re flooded wetlands and further study to quantify possible re acidification risks associated with seasonal drought

legacy impacts of acid sulfate soil runoff on mangrove sediments reactive iron accumulation altered sulfur cycling and trace metal enrichment abstract the off site impacts of iron rich acidic runoff from drained acid sulfate soils ass on the geochemistry of estuarine sediments are relatively poorly constrained in this study we examine the geochemistry of intertidal zone mangrove sediments and porewaters from an estuarine tributary that received 15 20 years of acute ass drainage compared to adjacent control sites mixing of acidic iron rich ass drainage waters with circumneutral ph estuarine waters drove precipitation of fe iii floc and has led to significant localized accumulation of reactive fe species fer 1 m hcl and citrate buffered dithionite extracts up to 4200 mol g 1 as well as significantly elevated porewater fe2 1000 m in ass impacted sediments x ray diffraction indicates that goethite lepidocrocite and ferrihydrite are important fe iii minerals in surficial sediments at ass impacted sites the abundant fer is shifting the equilibrium of reduced inorganic sulfur ris mineral formation pathways towards accumulation of s 0 and acid volatile sulfide avs species and is buffering porewater s ii to low concentrations in contrast ris speciation at the control sites is dominated by pyrite scr and porewater s ii is present some porewater metals i e al mn cu cr are significantly elevated at sites proximal to the source of ass drainage compared to control sites abundant fer also provides a substrate for sorption and accumulation of metals and correspondingly there is significant relative enrichment of reactive metal fractions 1 m hcl extractable in sediments at the ass impacted sites with al mn u cu cr ni this study demonstrates that ass drainage which causes accumulation of reactive fe in mangrove environments can substantially influence sediment biogeochemistry by altering reduced inorganic sulfur cycling and enhancing the availability of some trace metals

stability of schwertmannite and jarosite in an acidic landscape prolonged field incubation abstract schwertmannite and jarosite are two of the main secondary iron iii minerals commonly found in acidic iron and sulfate rich environments such as acid mine drainage and coastal acid sulfate soils cass both minerals exert major influence on the water and soil quality in these environments while there are many studies conducted on the stability of these two minerals under controlled laboratory conditions the behaviour of schwertmannite and jarosite under field conditions and the factors influencing their behaviour have not been investigated directly in the present study we examined the net transformation of introduced schwertmannite and jarosite samples incubated in a typical acidic cass environment pure synthetic schwertmannite and jarosite samples were exposed to two main chemical regimes 1 aerobic acidic water column and 2 anaerobic neutral sediment in a cass environment changes in mineralogy micromorphology and composition of schwertmannite and jarosite samples were monitored over a period of 12 months schwertmannite suspended in the water column and buried in sediments transformed to goethite by the end of 12 months but more quickly in anoxic reducing sediments however schwertmannite incubated in the acidic water column transformed at a much faster rate than those reported for acidic and aerobic conditions in the laboratory jarosite incubated in both the water column and sediments was also transformed to goethite but at a much slower rate than schwertmannite dissimilatory microbial reduction and fe 2 catalysed transformation likely played a major role in accelerating the transformation of both minerals to goethite in sediments the transformation of both minerals in the water column was sensitive to the hydrological conditions and fluctuations in the water column in relation to antecedent rainfall in comparison the sediment s geochemistry was relatively stable and consequently the rate of transformation and dissolution of both schwertmannite and jarosite in this environment was not appreciably affected by variable hydrology

impact of isostatic land uplift and artificial drainage on oxidation of brackish water sediments rich in metastable iron sulfide this study examines the dynamics of sulfur and trace elements as co mo ni ti and zn when brackish water sediments unusually rich in metastable iron sulfide probably a mixture of mackinawite

formation of awaruite in the system ni fe mg si o h s and olivine hydration with naoh solution an experimental study the serpentinization of mg fe ni olivine by naoh solution at very low sulfur fugacity and in a sulfur free system has been investigated experimentally below the stability field of the assemblage olivine water at 350 degrees or 5 degrees c and 2 000 or 50 bars serpentinization at very low sulfur fugacity produces the opaque mineral assemblage of heazlewoodite ni poor magnetite ni poor awaruite while in the sulfur free system an opaque mineral assemblage of ni rich magnetite ni rich awaruite is formed the serpentine minerals antigorite and chrysotile obtained during the serpentinization process contain some ni and fe with an ni fe ratio of 0 4 2 4 the composition of the minerals produced is dependent on the composition of the original olivine oxygen and sulfur fugacities

exafs analysis of iron cycling in mangrove sediments downstream a lateritized ultramafic watershed vavouto bay new caledonia mangrove forests are the dominant intertidal ecosystem of tropical coastlines in new caledonia mangroves act as a buffer zone between massive fe lateritic deposits and a lagoon partly registered by unesco as a world heritage site the new caledonian mangroves are characterized by a botanical gradient composed of three main vegetal stands i e rhizophora spp avicennia marina and salt flat which relies on the duration of tidal immersion that imposes gradients of pore water salinity oxygenation and organic content in the sediment in the present study we have determined the distribution and speciation of fe in mangrove sediments along this botanical gradient by using x ray absorption spectroscopy xas at the fe k edge both xanes and exafs results show that iron speciation strongly follows the redox boundaries marking the intertidal and depth zonations fe bearing minerals eroded from lateritic outcrops mainly goethite a feooh and phyllosilicates serpentine and talc are the major fe hosts in the upward horizons these mineral species progressively disappear with increasing depth where pyrite fes2 forms in the hydromorphic rhizophora and avicennia zones sulfate reduction is not observed in the drier salt flat zone in addition to these reduction processes intense re oxidation of aqueous fe ii and pyrite leads to the formation of poorly ordered ferrihydrite lepidocrocite c feooh and likely goethite in the upper sediments beneath avicennia and rhizophora stands the relative proportion of the newly formed poorly ordered ferrihydrite and lepidocrocite is found to be higher in the rhizophora mangrove stand which is the closest to the shore tidal fluctuations may thus be a major cause for continuous fe reduction oxidation cycles in the vegetated mangrove stands which could significantly affect the iron mass balance in mangrove systems

divergent drivers of carbon dioxide and methane dynamics in an agricultural coastal floodplain post flood hydrological and biological drivers many coastal floodplains have been artificially drained for agriculture altering hydrological connectivity and the delivery of groundwater derived solutes including carbon dioxide co2 and methane ch4 to surface waters here we investigated the drivers of co2 and ch4 within the artificial drains of a coastal floodplain under sugarcane plantation and quantify the contribution of groundwater discharge to co2 and ch4 dynamics over a flood event 290 mm of rainfall high temporal resolution in situ observations of dissolved co2 and ch4 carbon stable isotopes of ch4 delta c 13 ch4 and the natural groundwater tracer radon rn 222 allowed us to quantify co2 ch4 and groundwater dynamics during the rapid recession of a flood over a five day period extreme super saturation of free co2 co2 up to 2 951 mu m 25 480 of atmospheric equilibrium was driven by large groundwater input into the drains maximum 87 cm day 1 caused by a steep hydraulic head in the adjacent water table groundwater input sustained between 95 and 124 of the surface co2 flux during the flood recession by delivering high carbonate alkalinity groundwater dic 10 533 mu m similar to ph 7 05 to acidic surface water ph 4 consequently transforming all groundwater derived dic to co2 in contrast groundwater was not a major direct driver of ch4 contributing only 14 of total ch4 fluxes a progressive increase in ch4 concentrations of up to similar to 2400 nm day 1 occurred as a combination of increased substrate availability delivered by post flood drainage water and longer residence times which allowed for a biogenic ch4 signal to develop the progressive enrichment in delta c 13 ch4 values 70 to 48 and increase in ch4 concentrations 46 2460 nm support coupled production oxidation with concentrations and delta c 13 values remaining higher 2 798 nm and 47 than pre flood conditions 534 nm and 55 parts per thousand three weeks after the flood our findings demonstrate how separate processes can drive the aquatic co2 and ch4 response to a flood event in a drained coastal floodplain and the key role groundwater had in post flood co2 evasion to the atmosphere but not ch4 c 2016 elsevier b v all rights reserved

intense pyrite formation under low sulfate conditions in the achterwasser lagoon sw baltic sea in comparison to similar low sulfate coastal environments with anoxic sulfidic sediments the achterwasser lagoon which is part of the oder estuary in the sw baltic sea reveals unexpectedly high pyrite concentrations of up to 7 5 wt pyrite occurs mainly as framboidal grains variable in size with diameters between 1 and 20 m pyritization is not uniform down to the investigated sediment depth of 50 cm the consumption of reactive fe is most efficient in the upper 20 cm of the sediment column leading to degrees of pyritization dop as high as 80 to 95 sediment accumulation in the achterwasser takes place in high productivity waters the content of organic carbon reaches values of up to 10 wt indicating that pyrite formation is not limited by the availability of organic matter although dissolved sulfate concentration is relatively low 2 mmol l in the achterwasser the presence of h2s in the pore water suggests that sulfate is unlikely to limit pyrite authigenesis the lack of free fe ii in the pore waters combined with the possibility of a very efficient transformation of fe monosulfides to pyrite near the sediment water interface suggests that pyrite formation is rather controlled by i the availability of reactive fe which limits the fes formation and by ii the availability of an oxidant which limits the transformation of fes into pyrite the ultimate source for reactive fe is the river oder which provides a high portion of reactive fe 65 of the total fe in the form of suspended particulate matter the surficial sediments of the achterwasser are reduced but are subject to oxidation from the overlying water by resuspension oxidation of the sediments produces sulfur species with oxidation states intermediate between sulfide and sulfate e g thiosulfate and polysulfides which transform fes to fes2 at a significant rate this process of fes recycling is suggested to be responsible for the formation of pyrite in high concentrations near the sediment surface with dop values between 80 and 95 even under low sulfate conditions a postdepositional sulfidization takes place in the deeper part of the sediment column at 22 cm depth where the downward diffusion of h2s is balanced by the upward migration of fe ii the vertical fluctuation of the diffusion front intensifies the pyritization of sediments we suggest that the processes described may occur preferentially in shallow water lagoons with average net sedimentation rates close to zero such environments are prone to surficial sediment resuspension initiating oxidation of fe sulfides near the sediment water interface subsequent fes2 formation as well as postdepositional sulfidization leads to a major pyrite spike at depth within the sediment profile

sedimentary iron geochemistry in acidic waterways associated with coastal lowland acid sulfate soils abstract we examined the solubility mineralogy and geochemical transformations of sedimentary fe in waterways associated with coastal lowland acid sulfate soils class the waterways contained acidic ph 3 26 3 54 fe iii rich 27 138 m surface water with low molar cl so 4 ratios 0 086 5 73 the surficial benthic sediments had high concentrations of oxalate extractable fe iii due to schwertmannite precipitation kinetically favoured by 28 30 of aqueous surface water fe being present as the fe iii so 4 species subsurface sediments contained abundant pore water hco 3 6 20 mm and were reducing eh ii concentrations were high 2 mm and were constrained by precipitation dissolution of siderite the near neutral reducing conditions also promoted so 4 reduction and the formation of acid volatile sulfide avs the results show for the first time for class associated waterways that sedimentary avs consisted mainly of disordered mackinawite in the presence of abundant pore water fe ii precipitation dissolution of disordered mackinawite maintained very low i e ii concentrations such low concentrations of s ii caused slow rates for conversion of disordered mackinawite to pyrite thereby resulting in relatively low concentrations of pyrite 1 as fe compared to disordered mackinawite up to 590 mol g 1 as fe this study shows that interactions between schwertmannite goethite siderite disordered mackinawite and pyrite control the geochemical behaviour of sedimentary fe in class associated waterways

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

quantifying alkalinity generating processes in a tidally remediating acidic wetland abstract lime assisted tidal exchange late is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils cass however the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during late have not been quantified here we combine investigations of porewater and solid phase geochemistry from a remediating cass wetland to derive first order estimates of alkalinity generating processes and inputs after 6 years of late quantified inputs include marine derived hco 3 from tidal exchange hydrated lime additions and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate a progressive increase in tidal inundation led to the development of significant relationships 0 01 between topography and both non sulfidic solid phase fe ii and solid phase reduced inorganic sulfur species these topographic relationships were conjoined with a digital elevation model enabling up scaling of alkalinity estimates to a sub catchment level estimates indicate the relative order of importance of alkalinity generating processes and inputs is fe reduction 50 64 tidal exchange 25 42 sulfate reduction 7 13 hydrated lime addition 4 2 reduction was limited by an inability to distinguish between non sulfidic solid phase fe ii generated by microbial dissimilatory reduction of fe iii or chemical reduction of fe iii by h 2 s nevertheless the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74 of the total the majority 99 of net alkalinity generation was due to either tides or microbial metabolism this indicates that the late remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar cass landscapes provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine marine tidal hco 3 pool

the geochemistry during management of lake acidification caused by the rewetting of sulfuric ph 4 acid sulfate soils abstract understanding the geochemistry and kinetics of acidification events arising from acid sulfate soils is important to enable effective management and risk assessment large scale exposure and oxidation of acid sulfate soils occurred during a drought in the lower lakes murray darling basin of south australia we examined the geochemical changes that occurred in one region boggy lake that experienced surface water acidification and was subsequently neutralised via aerial limestone caco3 dosing and dilution via natural lake refill very low ph

glacier mass balance determination by remote sensing and high resolution modelling an indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice flow modelling is presented the method based on the mass continuity equation requires two datasets collected over the desired monitoring interval i the spatial pattern of glacier surface elevation change and ii the mass flux divergence field at haut glacier d arolla valais switzerland the mass balance distribution between september 1992 and september 1993 is calculated at 20 m resolution from the difference between the pattern of surface elevation change derived from analytical photogrammetry and the mass flux divergence field determined from three dimensional numerical flow modelling constrained by surface velocity measurements the resultant pattern of mass balance is almost totally negative showing a strong dependence on elevation but with large localized departures the computed distribution of mass balance compares well r 2 0 91 with mass balance measurements made at stakes installed along the glacier centre line over the same period despite the highly optimized nature of the flow modelling effort employed in this study the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal resolution estimates of mass balance

iron geochemical zonation in a tidally inundated acid sulfate soil wetland abstract tidal inundation is a new technique for remediating coastal acid sulfate soils cass here we examine the effects of this technique on the geochemical zonation and cycling of fe across a tidally inundated cass toposequence by investigating toposequence hydrology in situ porewater geochemistry solid phase fe fractions and fe mineralogy interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation redistribution and subsequent mineralogical transformations of fe within the landscape reductive dissolution of fe iii minerals including jarosite kfe3 so4 2 oh 6 resulted in elevated concentrations of porewater fe2 30 mmol l 1 in former sulfuric horizons in the upper intertidal zone tidal forcing generated oscillating hydraulic gradients driving upward advection of this fe2 enriched porewater along the intertidal slope subsequent oxidation of fe2 led to substantial accumulation of reactive fe iii fractions up to 8000 mol g 1 in redox interfacial tidal zone sediments these fe iii precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation schwertmannite fe8o8 oh 6so4 was the dominant fe mineral phase in the upper intertidal zone at mainly low ph 3 4 this was followed by increasing lepidocrocite feooh and goethite feooh at circumneutral ph within lower intertidal and subtidal zones relationships were evident between fe fractions and topography there was increasing precipitation of fe sulfide minerals and non sulfidic solid phase fe ii in the lower intertidal and subtidal zones precipitation of fe sulfide minerals was spatially co incident with decreases in porewater fe2 a conceptual model is presented to explain the observed landscape scale patterns of fe mineralisation and hydro geochemical zonation this study provides valuable insights into the hydro geochemical processes caused by saline tidal inundation of low lying cass landscapes regardless of whether inundation is an intentional strategy or due to sea level rise

sulfur biogeochemical cycling and novel fe s mineralization pathways in a tidally re flooded wetland abstract sulfur biogeochemical cycling and associated fe s mineralization processes exert a major influence over acidity dynamics electron flow and contaminant mobility in wetlands benthic sediments and groundwater systems while s biogeochemical cycling has been studied intensively in many environmental settings relatively little direct information exists on s cycling in formerly drained wetlands that have been remediated via tidal re flooding this study focuses on a tidal wetland that was drained in the 1970s causing severe soil and water acidification and subsequently remediated by controlled re flooding in 2002 we examine so 4 2 reduction rates and fe s mineralization at the tidal fringe 7 years after the commencement of re flooding the initial drainage of the wetland examined here caused in situ pyrite fes2 oxidation resulting in the drained soil layers being highly acidic and rich in so 4 2 bearing fe iii minerals including jarosite kfe3 so4 2 oh 6 tidal re flooding has neutralized much of the previous acidity with the pore water ph now mostly spanning ph 5 7 the fastest rates of in situ so 4 2 reduction up to 300 nmol cm 3 day 1 occur within the inter tidal zone in the near surface soil layers to 60 cm below ground surface the so 4 2 reduction rates correlate with pore water dissolved organic c concentrations thereby suggesting that electron donor supply was the predominant rate determining factor elemental s was a major short term product of so 4 2 reduction comprising up to 69 of reduced inorganic s in the near surface soil layers this enrichment in elemental s can be partly attributed to interactions between biogenic h2s and jarosite a process that also contributed to enrichment in pore water fe2 up to 55 mm and so 4 2 up to 50 mm the iron sulfide thiospinel greigite fe3s4 was abundant in near surface soil layers within the inter to sub tidal zone where tidal water level fluctuations created oscillatory redox conditions there was evidence for relatively rapid pyrite re formation within the re flooded soil layers however the results indicate that pyrite re formation has occurred mainly in the lower formerly drained soil layers whereas the accumulation of elemental s and greigite has been confined towards the soil surface the discovery that pyrite formation was spatially decoupled from that of elemental s and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation in fact the results suggest that greigite and pyrite may represent distinct end points of divergent fe s mineralization pathways overall this study highlights novel aspects of fe s mineralization within tidal wetlands that have been drained and re flooded in contrast to normal undisturbed tidal wetlands as such the long term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re flooding cannot be predicted from the well studied behaviour of normal tidal wetlands

contemporary pedogenesis of severely degraded tropical acid sulfate soils after introduction of regular tidal inundation abstract marine tidal inundation was partially restored to a severely degraded tropical acid sulfate soil landscape after having been excluded for over 30 years the effects on soil acidity and iron sulfide mineral reformation were investigated by comparing the geochemistry of soils before and after five years of regular tidal inundation the soil ph increased by 2 3 units and titratable actual acidity taa decreased by 40 50 mol h g 1 within former sulfuric horizons relict acidity remained at depth 1 m in the underlying sulfidic horizons 34 s data indicate that tidal inundation caused exchange of marine solutes within former sulfuric horizons but not within underlying sulfidic material there was considerable reformation of pyrite within former sulfuric horizons after tidal inundation with reduced inorganic sulfur increasing by 60 mol g 1 acid volatile sulfide also accumulated but mainly near the soil surface up to 16 mol g 1 reduction of fe iii minerals strongly influences the geochemistry of the tidally inundated soils after tidal inundation the soil ph and eh closely followed the iron redox couple and there was non sulfidic solid phase fe ii up to 600 mol g 1 there was also substantial diagenetic enrichment of poorly crystalline fe oxides near the soil surface following tidal inundation with reactive fe spanning 400 1800 mol g 1 while the decreases in soil acidity documented here are likely due to a combination of marine alkalinity inputs and reduction of both fe and so 4 2 the relative importance of each process remains to be determined this study demonstrates that marine tidal inundation can be an effective landscape scale strategy for ameliorating severe acidity associated with drained acid sulfate soils

mid proterozoic ferruginous conditions reflect postdepositional processes to evaluate the mechanics of mid proterozoic environmental iron transport and deposition we coupled microscale textural and bulk rock magnetic techniques to study the 1 4 ga lower belt group belt supergroup montana and idaho we identified a pyrrhotite siderite isograd that marks metamorphic iron bearing mineral reactions beginning in subgreenschist facies samples even in the best preserved parts of the basin secondary overprints were common including recrystallization of iron bearing sulfides base metal sulfides and nanophase pyrrhotite despite these overprints a record of redox chemistry was preserved in the early diagenetic framboidal pyrite and detrital iron oxides including trace nanoscale magnetite that remained after sulfidization in anoxic and sulfidic sedimentary pore fluids based on these results we interpret the belt basin as having oxic waters at least in shallow water environments with no indication of abundant ferrous iron in the water column this is consistent with the cooccurrence of early eukaryotic fossils within the same strata

seawater inundation of coastal floodplain sediments short term changes in surface water and sediment geochemistry abstract coastal floodplains are highly vulnerable to seawater inundation as a result of storm surge and sea level rise due to their low elevation and proximity to the coastline intact soil cores from a levee acid sulfate soil scald and four backswamp sites on a coastal floodplain in eastern australia were inundated with artificial seawater treatments 0 50 and 100 for 14 days to examine the short term consequences for surface water and floodplain sediment geochemistry all sites displayed an initial decrease in surface water ph following inundation with 50 and 100 seawater in addition higher concentrations of trace metals al fe mn ni and zn were observed in most sites inundated with 50 or 100 seawater this was generally attributed to competitive exchange and desorption of trace metals from sediments due to the higher ionic strength of the seawater solutions and upward diffusive flux of metals from the sediments to surface waters at one backswamp site reductive processes had established by day 7 which also resulted in elevated fe 2 concentrations in the overlying surface waters transmission electron microscopy tem identified the presence of poorly crystalline ferrihydrite and schwertmannite and goethite and jarosite these meta stable fe iii minerals can act as a source of metals for desorption and can also be readily reduced and act as a source of fe 2 to surface waters importantly inundation with either 50 or 100 seawater resulted in a similar magnitude of acidity and trace metal mobilisation the data suggest that an inundation event of 0 2 m depth with either 50 or 100 seawater could cause a pulse mobilisation of up to 64 8 and 9 1 kg ha 1 of fe and al respectively quantities of similar magnitude to previous estimates of annual drainage fluxes from similar backswamps this study suggests that the short term inundation of coastal floodplain sediments by either brackish water or seawater will result in rapid declines in surface water quality as a result of increased liberation of acidity and trace metals

reclamation influence and background geochemistry of neutral saline soils in the po river delta plain northern italy reclaimed neutral saline sulphate soils constitute a large part of the eastern part of po plain lowlands where intensive agricultural activities take place the knowledge of their geochemical features is essential to develop the best management practices capable to preserve this threatened environment with this aim three boreholes were drilled in an agricultural field and a typical reclaimed soil profile has been characterized for major and trace element ph electrical conductivity redox conditions and water soluble anions and ammonium statistical analysis cluster analysis and principal component analysis has been used to understand the relationship between elements and grain size the soil profile is characterized by high salinity and high organic matter contents responsible for high chloride sulphate and ammonium concentrations heavy metal content is naturally high since po plain sediments are the result of ultramafic rocks erosion in addition organic matter tends to concentrate heavy metals by adsorption mainly in peaty horizons as a consequence of chemical and zootechnical fertilization high no3 contents have been found in the top soil thus enhancing the risk of nitrate discharge in the water system especially in relation to extreme climatic events