Schwertmannite stability in acidified coastal environments

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.     

Release of arsenic associated with the reduction and transformation of iron oxides

The behaviour of trace amounts of arsenate coprecipitated with ferrihydrite, lepidocrocite and goethite was studied during reductive dissolution and phase transformation of the iron oxides using [⁵⁵Fe]- and [⁷³As]-labelled iron oxides. The As/Fe molar ratio ranged from 0 to 0.005 for ferrihydrite and lepidocrocite and from 0 to 0.001 for goethite. For ferrihydrite and lepidocrocite, all the arsenate remained associated with the surface, whereas for goethite only 30% of the arsenate was desorbable. The rate of reductive dissolution in 10 mM ascorbic acid was unaffected by the presence of arsenate for any of the iron oxides and the arsenate was not reduced to arsenite by ascorbic acid. During reductive dissolution of the iron oxides, arsenate was released incongruently with Fe²⁺ for all the iron oxides. For ferrihydrite and goethite, the arsenate remained adsorbed to the surface and was not released until the surface area became too small to adsorb all the arsenate. In contrast, arsenate preferentially desorbs from the surface of lepidocrocite. During Fe²⁺ catalysed transformation of ferrihydrite and lepidocrocite, arsenate became bound more strongly to the product phases. X-ray diffractograms showed that ferrihydrite was transformed into lepidocrocite, goethite and magnetite whereas lepidocrocite either remained untransformed or was transformed into magnetite. The rate of recrystallization of ferrihydrite was not affected by the presence of arsenate. The results presented here imply that during reductive dissolution of iron oxides in natural sediments there will be no simple correlation between the release of arsenate and Fe²⁺. Recrystallization of the more reactive iron oxides into more crystalline phases, induced by the appearance of Fe²⁺ in anoxic aquifers, may be an important trapping mechanism for arsenic.     

Sedimentary iron geochemistry in acidic waterways associated with coastal lowland acid sulfate soils

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 μM) surface water with low molar Cl:SO₄ 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 species). Subsurface sediments contained abundant pore-water HCO₃ (6-20 mM) and were reducing (Eh < −100 mV) with pH 6.0-6.5. The development of reducing conditions caused reductive dissolution of buried schwertmannite and goethite (formed via in situ transformation of schwertmannite). As a consequence, pore-water Fe^II concentrations were high (>2 mM) and were constrained by precipitation-dissolution of siderite. The near-neutral, reducing conditions also promoted SO₄-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. <0.1 μM) S^−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 (<300 μmol g⁻¹ as Fe) compared to disordered mackinawite (up to 590 μmol 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.     

落石堆积的结构特征与斜坡破坏型式之转换

在基岩山区和丘陵区，落石堆积的分布非常广泛、并可经长期积累而形成巨大规模。然而，因缺乏研究，它们(尤其是规模较大者)经常被误定成滑坡或崩塌堆积。为此，作者结合长江三峡工程和西部大开发的需要，采用天然模型勘测和岩相分析等多种方法对其进行了长期研究。结果认为：1．落石堆积(累积体)通常是在扩离-落石发育而崩塌、滑坡不发育的陡崖(坡)下形成，同时还需有较平坡面，便于落石停积而不易被重力和流水搬走的堆积场所；2．落石堆积的结构特征为：(1)前缘土体较密实且粒(块)径较小，后缘多大块石并常具架空结构；(2)不等粒系数普遍较大；(3)常有淤泥质和砂、卵石夹层或透镜体；(4)前缘可具向外陡倾的加积层理。基于此，水的潜蚀作用和地表水对前缘的集中冲刷常成为落石堆积变形破坏的主因；3．落石堆积的破坏型式为滑坡、泥石流或碎屑流；4．落石堆积的勘查应特别注意查明环境水文地质条件、储水结构及相关参数；其稳定性评价应首先分析不同工程活动影响下产生潜蚀的可能性；5．为防治斜坡失稳，首先应保护落石堆积的自稳结构和选用有防潜蚀功能的开放型措施；6．深入研究落石堆积，对沉积学和工程地质学也具有理论意义和实用价值。     

Tertiary evolution of the coastal lowlands and the Clyde River palaeovalley in southeast New South Wales

Fluvial sediments, here assigned to the Bergalia Formation, adjacent to the middle reaches of the Clyde River near Batemans Bay on the New South Wales south coast were deposited prior to a basalt valley flow with K–Ar ages averaging 27.7 ± 0.3 Ma. Similar Bergalia Formation sediments are preserved near Mogo, south of Batemans Bay, and suggest that the Clyde River flowed south through the Mogo area prior to diversion to the east. The diversion resulted from local‐scale neotectonic movements or sea‐level changes after the mid‐Oligocene. The previously undescribed deposits at these two locations provide evidence that relief comparable to or greater than the present existed in the Clyde River valley by this time. The basalt and sediments in the Clyde River valley indicate that the coastal lowlands in southeast New South Wales were developed prior to the mid‐Tertiary period.     

Arsenic, iron and sulfur co-diagenesis in lake sediments

Profiles of porewater pH and dissolved As, Fe, Mn, sulfate, total sulfide (ΣS^−II), total zero-valent sulfur (ΣS⁰), organic carbon and major ion concentrations, as well as those of solid As, acid-volatile sulfide (AVS), total S, Fe, Mn, Al, organic C, ²¹⁰Pb and ¹³⁷Cs were determined in the sediment of four lakes spanning a range of redox and geochemical conditions. An inverse modeling approach, based on a one-dimensional transport-reaction equation assuming steady-state, was applied to the porewater As profiles and used to constrain the net rates of reactions involving As (). The model defines depth intervals where As is either released to (positive ) or removed from (negative ) the porewaters.At two of the sites, whose bottom water were oxygenated at sampling time, a production zone ( = 12 × 10⁻¹⁸ mol cm⁻³ s⁻¹-71 × 10⁻¹⁸ mol cm⁻³ s⁻¹) is inferred a few cm below the sediment-water interface, coincident with sharp porewater As and Fe peaks that indicate an intense coupled recycling of As and Fe. This process is confirmed by solid As and Fe maxima just below the sediment surface. In these two lakes a zone of As consumption ( = −5 × 10⁻¹⁸ mol cm⁻³ s⁻¹ to −53 × 10⁻¹⁸ mol cm⁻³ s⁻¹), attributed to the slow adsorption of As to authigenic Fe oxyhydroxides, occurs just above the production zone. A second-order rate constant of 0.12 ± 0.03 cm³ mol⁻¹ s⁻¹ is estimated for this adsorption reaction.Such features in the porewater and solid profiles were absent from the two other lakes that develop a seasonally anoxic hypolimnion. Thermodynamic calculations indicate that the porewaters of the four lakes, when sulfidic (i.e., ΣS^−II ? 0.1 μM), were undersaturated with respect to all known solid As sulfides; the calculation also predicts the presence of As^V oxythioanions in the sulfidic waters, as suggested by a recent study. In the sulfidic waters, the removal of As ( = −1 × 10⁻¹⁸ mol cm⁻³ s⁻¹ to −23 × 10⁻¹⁸ mol cm⁻³ s⁻¹) consistently occurred when saturation, with respect to FeS_(s), was reached and when As^V oxythioanions were predicted to be significant components of total dissolved As. This finding has potential implications for As transport in other anoxic waters and should be tested in a wider variety of natural environments.     

Elemental sulfur in drain sediments associated with acid sulfate soils

This paper reports the abundance of elemental S in drain sediments associated with acid sulfate soils. The sediments exhibited near-neutral pH (5.97–7.27), high concentrations of pore-water Fe²⁺ (1.37–15.9 mM) and abundant oxalate-extractable Fe (up to 4300 μmol g⁻¹). Maximum acid-volatile sulfide (AVS) concentrations in each sediment profile were high (118–1019 μmol g⁻¹), with AVS often exceeding pyrite-S. Elemental S occurred at concentrations of 13–396 μmol g⁻¹, with the higher concentrations exceeding previous concentrations reported for other sedimentary systems. Up to 62% of reduced inorganic S near the sediment/water interface was present as elemental S, due to reaction between AVS and oxidants such as O₂ and Fe(III). Significant correlation (r = 0.74; P < 0.05) between elemental S and oxalate-extractable Fe(III) is indicative of elemental S formation by in situ oxidation of AVS. The results indicate that AVS oxidation in near-surface sediments is dynamic in acidified coastal floodplain drains, causing elemental S to be a quantitatively important intermediate S fraction. Transformations of elemental S may therefore strongly influence water quality in ASS landscapes.     

Climate drying and associated forest decline in the lowlands of northern Guatemala during the late Holocene

Palynological studies document forest disappearance during the late Holocene in the tropical Maya lowlands of northern Guatemala. The question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation, as previously suggested, or whether it was partly attributable to climate changes. We report multiple palaeoclimate and palaeoenvironment proxies (pollen, geochemical, sedimentological) from sediment cores collected in Lake Petén Itzá, northern Guatemala. Our data indicate that the earliest phase of late Holocene tropical forest reduction in this area started at ∼ 4500 cal yr BP, simultaneous with the onset of a circum-Caribbean drying trend that lasted for ∼ 1500 yr. This forest decline preceded the appearance of anthropogenically associated Zea mays pollen. We conclude that vegetation changes in Petén during the period from ∼ 4500 to ∼ 3000 cal yr BP were largely a consequence of dry climate conditions. Furthermore, palaeoclimate data from low latitudes in North Africa point to teleconnective linkages of this drying trend on both sides of the Atlantic Ocean.     

Geochemistry of trace metals associated with reduced sulfur in freshwater sediments

Porewater concentration profiles were determined for Fe, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn), sulfide, SO₄ and pH in two Canadian Shield lakes (Chevreuil and Clearwater). Profiles of pyrite, sedimentary trace elements associated with pyrite and AVS were also obtained at the same sites. Thermodynamic calculations are used, for the anoxic porewaters where sulfide was measured, to characterize diagenetic processes involving sulfide and trace elements and to illustrate the importance of sulfide, and possibly polysulfides and thiols, in binding trace elements. The ion activity products (IAP) of Fe sulfide agree with the solubility products (K_s) of greigite or mackinawite. For Co, Ni and Zn, IAP values are close to the K_S values of their sulfide precipitates; for Cu and Pb, IAP/K_s indicate large oversaturations, which can be explained by the presence of other ligands (not measured) such as polysulfides (Cu) and thiols (Pb). Cobalt, Cu, Ni and Zn porewater profiles generally display a decrease in concentration with increasing ΣH₂S, as expected for transition metals, whereas Cd, Pb and Zn show an increase (mobilisation). The results suggest that removal of trace elements from anoxic porewaters occurs by coprecipitation (As and Mn) with FeS(s) and/or adsorption (As and Mn) on FeS(s), and by formation of discrete solid sulfides (Cd, Cu, Ni, Pb, Zn and Co). Reactive Fe is extensively sulfidized (51–65%) in both lakes, mostly as pyrite, but also as AVS. Similarities between As, Co, Cu and Ni to Fe ratios in pyrite and their corresponding mean diffusive flux ratios suggest that pyrite is an important sink at depth for these trace elements. High molar ratios of trace elements to Fe in pyrite from Clearwater Lake correspond chronologically to the onset of smelting activities. AVS can be an important reservoir of reactive As, Cd and Ni and, to a lesser extent, of Co, Cu and Pb. Overall, the trace elements most extensively sulfidized were Ni, Cd and As (maximum of 100%, 81% and 49% of the reactive fraction, respectively), whereas Co, Cu, Mn, Pb and Zn were only moderately sulfidized (11–16%).     

太湖北部沉积物中铁硫的地球化学特征研究

选择太湖北部柱状沉积物为研究对象,对沉积物及间隙水中铁硫的地球化学特征进行了研究。结果显示．间隙水中Fe^2＋的平均浓度是S^2-平均浓度的82倍,其值为9．6～270．5μmol／L。这说明沉积物中是以Fe^3＋的还原为主,而非SO4^2-。沉积物中还原性无机硫以黄铁矿为主,其次为AVS,最后为单质硫。沉积物中的Fe^2＋的浓度均高于其他形态的铁,约占总铁含量的30％～40％。活性铁的浓度为109．86～208．16μmol／g,仅占总铁的20％左右。沉积物各层中与硫结合的铁仅占总铁的0．12％～2．35％,占活性铁的0．39％～8．36％,通过分析铁硫之间的关系并结合蓝藻爆发的时间推断,铁硫化合物的生成不是PO4^3-释放的原因。太湖北部沉积物中Fe—S及P-S之间相互关系较弱。     

Hydrogeochemical processes of migration of sulfur and iron sulfides in fuel shales

Local hydrogeochemical regime of the Kashpirian bituminous shales is conducive to a significant mobilization of iron sulfide, e.g. by oxygen or by aggressive carbon dioxide, and to migration of iron in subsurface drainage, “downstream,” as well as to its accumulations a few hundred meters away from its source. Such accumulations may be taken as prospecting indications of the shales, under certain conditions. – IGR Staff.     

Carbon and sulfur isotopic fluctuations associated with the end-Guadalupian mass extinction in South China

Concentrations of total organic matter (TOC), carbon isotopic compositions of carbonate and organic matter (δ¹³C_carb, δ¹³C_org), and sulfur isotopic compositions of carbonate associated sulfate (δ³⁴S_sulfate) across the Guadalupian–Lopingian (G–L) boundary were analyzed from identical samples of Tieqiao section, Laibin, Guangxi province, South China. The δ¹³C_carb values show a positive excursion from − 0.45‰ to the peak of 3.80‰ in the Laibin limestone member of the Maokou Formation, followed by a drastic drop to − 2.60‰ in the lowest Heshan formation, then returned to about 1.58‰. Similar to the trends of the δ¹³C_carb values, Δ¹³C_carb–org values also show a positive excursion followed by a sharp negative shift. The onset of a major negative carbon isotope excursion postdates the end Guadalupian extinction that indicates subsequent severe disturbance of the ocean–atmosphere carbon cycle. The first biostratigraphic δ³⁴S_sulfate values during the G–L transition exhibit a remarkable fluctuation: a dramatic negative shift followed by a rapid positive shift, ranging from 36.88‰ to − 37.41‰. These sulfate isotopic records suggest that the ocean during the G–L transition was strongly stratified, forming an unstable chemocline separating oxic shallow water from anoxic/euxinic deep water. Chemocline excursions, together with subsequent rapid transgression and oceanic anoxia, were likely responsible for the massive diversity decline of the G–L biotic crisis.     

Cu and Fe associated with humic acids in sediments of a tropical coastal lagoon

The amount of Cu and Fe associated with humic acids was estimated in five sediment cores from a tropical coastal lagoon (Piratininga Lagoon, Rio de Janeiro, Brazil). Core samples were analysed for humic acid contents, total Fe and Cu content. Fe and Cu associated with humic acids were also measured. Results show amounts of humic acids ranging from 0.7 to 21.7% of the dry weight of sediment (average 4.6%, standard deviation 4.4%). Concentrations of Fe and Cu ranged from 0.3 to 6.0% (average 2.2%, S.D. 1.2%) and from <1.0 to 65.0 μg g⁻¹ (average 28.6 μg g⁻¹, S.D. 16.4 μg g⁻¹), respectively. The results of strongly bound metals show that while humic acids are the main carrier for Cu, Fe does not seems to be significantly associated with this organic matter.     

Man and climate in the Maya lowlands

A 15-m sedimentary core from Lake Salpeten provides the first complete Holocene sequence for the lowlying Peten District, Guatemala. Today, Lake Salpeten is a brackish, calcium sulfate lake near saturation surrounded by tropical semievergreen forest. The basal pollen record depicts sparse juniper scrub surrounding a lake basin that held ephermal pools and halophytic marshes. The lake rapidly deepened to > 27 m in the early Holocene and may have been meromictic, because nearly 2 m of gypsum “mush” was deposited. Mesic forests were quickly established and persisted until the Maya entered the district 3000 yr ago and caused extensive deforestation. Any climatic information contained in the pollen record of the Maya period is thus masked, but a regional pollen sequence linked to the archaeological record is substantiated because environmental disturbance was pervasive. Local intensification of occupation and population growth are seen as an increased deposition of pollen of agricultural weeds and colluviation into the lake, while the Classic Maya collapse is marked by a temporary decline in Compositae pollen. Effects of perturbations induced by the Maya persist in the pollen and limnetic record 400 yr after the Spanish conquest.     

Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments

Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r² = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r² = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence.     

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Methylmercury can accumulate in fish to concentrations unhealthy for humans and other predatory mammals. Most sources of mercury (Hg) emit inorganic species to the environment. Therefore, ecological harm occurs when inorganic Hg is converted to methylmercury. Sulfate- and iron-reducing bacteria (SRB and FeRB) methylate Hg, but the effects of processes involving oxidized and reduced forms of sulfur and iron on the reactivity of Hg, including the propensity of inorganic Hg to be methylated, are poorly understood. Under abiotic conditions, using a laboratory flow reactor, bisulfide (HS⁻) was added at 40 to 250 μM h⁻¹ to 5 g L⁻¹ goethite (α-FeOOH) suspensions to which Hg(II) was adsorbed (30-100 nmol m⁻²) at pH 7.5. Dissolved Hg initially decreased from 10³ or 10⁴ nM (depending on initial conditions) to 10⁻¹ nM, during which the concentration of Hg(II) adsorbed to goethite decreased by 80% and metacinnabar (β-HgS_(s)) formed, based on identification using Hg L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The apparent coordination of oxygens surrounding Hg(II), measured with EXAFS spectroscopy, increased during one flow experiment, suggesting desorption of monodentate-bound Hg(II) while bidentate-bound Hg(II) persisted on the goethite surface. Further sulfidation increased dissolved Hg concentrations by one to two orders of magnitude (0.5 to 10 nM or 30 nM), suggesting that byproducts of bisulfide oxidation and Fe(III) reduction, primarily polysulfide and potentially Fe(II), enhanced the dissolution of β-HgS_(s) and/or desorption of Hg(II). Rapid accumulation of Fe(II) in the solid phase (up to 40 μmol g⁻¹) coincided with faster elevation of dissolved Hg concentrations. Fe(II) served as a proxy for elemental sulfur [S(0)], as S(0) was the dominant bisulfide oxidation product coupled to Fe(III) reduction, based on sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In one experiment, dissolved Hg concentrations tracked those of all sulfide species [S(-II)]. These results suggest that S(-II) reacted with S(0) to form polysulfide, which then caused the dissolution of β-HgS_(s). A secondary Fe-bearing phase resembling poorly formed green rust was observed in sulfidized solids with scanning electron microscopy, although there was no clear evidence that either surface-bound or mineralized Fe(II) strongly affected Hg speciation. Examination of interrelated processes involving S(-II) and Fe(III) revealed new modes of Hg solubilization previously not considered in Hg reactivity models.     

Oxidation state of iron and extensive redistribution of sulfur in thermally modified Stardust particles

Two representative thermally modified Stardust samples were investigated by analytical transmission electron microscopy in order to decipher their iron oxidation state after the strong thermal episode due to the capture in aerogel. Their dominant microstructure consists of evenly distributed rounded Fe-Ni-S nano-droplets within a silica-rich glassy matrix. The mineralogy and associated redox state of iron is assessed using a Fe-Mg-S ternary diagram on which ferromagnesian silicates, sulfides and metal can be represented and potentially compared with any other extraterrestrial material. In this diagram, all the data (bulk and local analysis of silicates, sulfide + metal) scatter along a mixing line between the Mg corner and the average composition of the iron-sulfide. There is an obvious genetic relationship between the different phases observed in such samples, further supported by the very low concentration of iron in the glassy matrix. Silicate glasses contain a significant concentration of dissolved sulfur probably present as MgS complexes. This chemical signature is typical of highly reduced environments. These secondary microstructures were established during the high temperature stage of the capture. A significant part of the Fe-droplets formed in situ by reduction at high temperature of ferromagnesian silicates (olivine and pyroxenes) during the impact. At this stage, the indigenous sulfides destabilized and sulfur readily volatilized as S₂, diffused into molten materials and condensed later onto the Fe-precipitates that formed in the silicate melt. This scenario is supported by the structure of Fe-Ni-S beads with a metal core and a sulfide rim. It will be difficult to derive reliable information on the redox state of 81P/Wild 2 particles based on bulk analyses of whole tracks because particles found along the walls of tracks suffered strong reduction reactions, contrary to terminal particles that may have preserved their pristine redox state. The capture effect must be taken into account for comparison of Wild 2 particles with other chondritic material.     

Far-field impact and coastal sedimentation associated with the 2006 Java tsunami in West Australia

A detailed assessment of the impact of a far-field tsunami on the Australian coastline was carried out in the Steep Point region of Western Australia following the July 17 2006 Java tsunami. Tsunami inundation and run-up were mapped on the basis of eyewitness accounts, debris lines, vegetation damage and the occurrence of recently deposited fish, starfish, corals and sea urchins well above high-tide mark. A topographic survey using kinematic GPS with accuracies of 0.02 m in the horizontal and 0.04 m in the vertical recorded flow depths of between 1 and 2 m, inundation of up to 200 m inland, and a maximum recorded run-up of 7.9 m AHD (Australian Height Datum). The tsunami impacted the sparsely populated Steep Point coastline close to low tide. It caused widespread erosion in the littoral zone, extensive vegetation damage and destroyed several campsites. Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A sand sheet, up to 14 cm thick and tapering landwards over 200 m, was deposited over coastal dunes. The deposits are predominantly composed of moderately well-sorted, medium-grained carbonate sand with some gravel and organic debris. A basal unconformity defines the boundary between tsunami sediments and underlying aeolian dune sand. Evidence for up to three individual waves is preserved as normally graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Given the strong wind regimes in the area and the similarity of the underlying dune deposits to the tsunami sediments, it is likely that seasonal erosion will remove all traces of these sediment sheets within years to decades.     

Acidic deposition impacts mediated by sulfur cycling in a coastal plain forest ecosystem

Deposition in the New Jersey Pinelands was very acidic (pH=4.17) and contained high levels of SO₂ ⁻² based on bulk deposition measurementsfrom July 1984–July 1986. Streamwater over the same interval in undisturbed watersheds was less acidic (pH =4.52) and had proportionately less SO₄ ⁻². A preliminary alkalinity budget for undisturbed watersheds suggested that SO₄ ⁻² retention within Pinelands watersheds accounted for a large portion of the total alkalinity generated and thereby lessened the impact of acidic deposition on surface waters. The only process capable of explaining the retention of SO₄ ⁻² was microbial sulfate reduction in the extensive wetlands surrounding Pinelands streams which occurred at high rates.