Iron and sulfate reduction in the sediments of acidic mine lake 116 (Brandenburg,Germany): Rates and geochemical evaluation

A combination of rate measurements of iron(III)oxide and sulfate reduction, thermodynamic data, and pore-water and solid phase analyses was used to evaluate the relative significance of iron and sulfate reduction in the sediments of an acidic strip mining lake (Lake 116, Brandenburg, Germany). The rate of sulfate reduction was determined using a 35S-radiotracer method. Rates of iron turnover were quantified by mass balances based on pore-water concentration profiles. The differences in Gibbs free energy yield from reduction of iron and sulfate and from methanogenesis were calculated from individual redox couples and concentrations of reactants to account for the influence of high Fe2+ concentrations and differing mineral phases. Integrated (O-20 cm) mean rates of sulfate reduction were 1.2 (pelagial), respectively 5.2 (littoral) mmol (m2d)-1. Based on electron equivalents, the estimated iron reduction rates reached between about 50 % (pelagial) and 75 % (littoral) of the sulfate reduction rates. Compared to conditions usually assumed in the literature, in the sediments Gibbs free energy advantage of iron reduction over sulfate reduction was reduced frmm +11 KJeq-1 to a range of about +7 KJeq-1 (ferrihydrite, "reactive iron") to -6 KJeq-1 (goethite). This indicates that iron reduction was thermodynamically favored to sulfate reduction only if amorphous iron(III)oxides were available and is in accordance to the high competitiveness of sulfate reducers in the sediment. While total iron concentration in the sediments was high (up to 80% of the dryweight), reactive iron only accounted for 11-38% and was absolutely and relatively diminished in the zone of iron reduction. Pore-water concentration gradients and 137CS profiles indicated that little or no bioturbation occurred in the sediments, probably inhibiting the renewal of reactive iron. We further hypothesize that the reactivity of the iron oxide surfaces was reduced due to adsorption of DOM, suggested by IR spectra of the DOM and by a surface coverage estimate using literature data. Pelagial and littoral sediments displayed different dynamics. At the littoral relative iron reduction rate estimates were higher, iron sulfides were not accumulated and residence times of iron oxides were short compared to the pelagial. At the littoral site reoxidation of iron sulfides probably resulted in the renewal of reactive iron(III)oxides, possibly allowing for higher relative rates of iron reduction.     

Phosphorus Retention Mechanisms in the Sediment of an Eutrophic Mining Lake

A small, highly eutrophic mining lake (Golpa IV) in eastern Germany with a continuous input of nutrients and metals was used to study the mechanisms of phosphorus (P) fixation in the sediment. The sediment (0-15 cm) is characterised by high contents of iron (96 mg g-1 DW), aluminium (37.3 mg g-1 DW) and sulphur (54.3 mg g-1 DW) and an extreme accumulation of some trace metals. Despite oxygen free conditions in the hypolimnion and intensive sulphate reduction in the sediment, high P retention rates could be calculated from dated sediment cores (1986-1995: 11 g P m-2 a-1). The lake has shown a rapid response to reduction of P loading. In some sediment layers unusually high total sediment P concentrations with more than 24 mg P g-1 DW were observed. More than 80% of total sediment P was bound in the BD-SRP and NaOH-SRP fractions (extraction scheme according to Psenner et al., 1984) which indicates that a substantial portion of deposited P is immobilised in an Fe or Al bound form. This corresponds well with the presence of oxidised Fe species at all sediment depths. Furthermore thermodynamic calculations indicate that vivianite precipitation is favourable in deeper anoxic sediment layers. The inventory or input of Fe or Al seems to be more important for the permanent P immobilisation in the sediment of the investigated mining lake than redox forced mobilisation processes (e.g. iron or sulphate reduction).     

Phosphorus Removal by Sediment in Streams Contaminated with Acid Mine Drainage

Acid mine drainage (AMD) affects thousands of stream miles in the Appalachian region of the USA and results in elevated concentrations of iron and aluminum in the stream water and sediments and wide ranging pH values. It was hypothesized that these conditions would lead to increased P buffering capacity of the sediments which in turn would cause a decrease in dissolved reactive phosphorus (DRP) in the water column. In the lab fresh Fe, Al, and Mn oxide precipitates all adsorbed DRP strongly but over different pH ranges. Sulfate and calcium ions inhibited adsorption of DRP with Fe oxides but the effect was less apparent with Al oxides. In the field DRP concentration was reduced 54–90% just downstream of an AMD input compared to upstream of the input. In addition the sediment buffering capacity increased and equilibrium phosphate concentration decreased dramatically downstream of the AMD inputs. The strength of the effect and the widespread occurrence of AMD suggest that AMD could be altering the P dynamics of streams and rivers throughout the Appalachian region.     

A sediment exchange experiment to assess the limiting factors of microbial sulfate reduction in acidic mine pit lakes

Purpose

Microbial sulfate reduction is an alkalinity-producing process and potentially supports the neutralization of acidic mine pit lakes. In many acidic lakes the process does not occur. Sulfate-reducing bacteria are known to be pH sensitive. There are, however, several reports of sulfate reduction occurring in the sediment of acidic lakes. To find out why sulfate reduction occurs in some acidic lakes but not in others, we conducted a field experiment.

Materials and methods

Surface sediment from lake ML111 (pH?2.6, no sulfate reduction), in the Koyne-Plessa lignite mining district of Lusatia in Germany, was incubated in the less-acidic lake ML117 (pH?3.4, sulfate reduction) and vice versa. After 19?weeks of incubation, the sediments were sampled and analyzed for microbial sulfate reduction rates, bacterial numbers, and geochemical composition.

Results and discussion

Incubation of ML117 sediment in ML111 resulted in a partial inhibition of sulfate reduction while incubation of ML111 sediment in ML117 did not initiate sulfate reduction. We observed a linear relationship between sediment pH and sulfate reduction, while there was no relation with sedimentary iron content. Sulfate reduction was not only affected by the water quality but also by the experimental treatment. Homogenization of the sediment prior to incubation stimulated microbial sulfate and iron reduction. Due to the low pH, incubation in ML111 resulted in the dissolution of reduced inorganic sulfur.

Conclusions

We conclude that the water pH is the major regulator of sulfate reduction in the surface sediment of acidic lakes. The rate of sulfate reduction in the sediment of acidic lakes depends on a fragile equilibrium between proton flux between water and sediment, and buffering reactions in the sediment.     

ATP-sulphurylase: An enzymatic marker for biological sulphate reduction?

Adenosine triphosphate-sulphurylase (ATPS) plays a major role in dissimilatory sulphate reduction. In this study, the level of ATPS activity was monitored in a time course study using a biosulphidogenic batch bioreactor system. A coincident decrease in ATPS activity with a decline in sulphate concentration and an increase in sulphide concentration as biosulphidogenesis proceeded was observed. Flask studies further showed sulphate to be stimulatory to ATPS, while sulphide proved to be inhibitory. The effect of ions (Ca²⁺, Cl⁻, Fe²⁺ and Zn²⁺) on the ATPS activity was also investigated. Most of the ions studied (Ca²⁺, Cl⁻ and Fe²⁺) were stimulatory at lower concentrations (40-120 mg/l) but proved toxic at higher concentrations (>120 mg/l). In contrast, Zn²⁺ was inhibitory even at low concentrations (?40 mg/l). ATPS may potentially be used as an enzymatic marker for biological sulphate reduction in sulphate-rich wastewaters and natural environments (anaerobic systems such as soils and sediments found in freshwater and marine systems), providing all residual sulphide and interfering ions are removed using a simple preparative step.     

Distribution of Trace Elements in Sediments and Biota of Songkhla Lake, Southern Thailand

The concentrations of Co, Ni, Cu, Zn, Cd, Pb, As, Fe, Mn, and Al were determined in sediments and biota of Songkhla Lake, a shallow coastal lagoon located in southern Thailand. In June 2006, surface sediments were sampled in 44 stations in the three sections of the lake (inner-, middle-, and outer sections). Sediment cores were also sampled in 13 stations in three cross-sections of the lake. In surface sediments, trace and major elements, organic matter, sediment grain size analysis, and sulfides were determined, and in the sediment cores, redox profiles were made. Soil samples were also collected at garbage dumping sites in the vicinity of the lake. In addition, the metal accumulation in two catfish species (Arius maculatus and Osteogeneiosus militaris) and the crustacean (Apseudes sapensis) was also investigated. Trace element concentrations in sediments of Songkhla Lake show that, especially the Outer section of the lake, in particular the sediments at the mouths of the Phawong, U-Taphao, and Samrong Canals are significantly enriched with trace elements due to municipal, agricultural, and industrial discharges entering the lake through the canals. Aluminum-normalized enrichment factors throughout the lake vary from 0.4 to 1.7 for Ni, 0.3 to 3.3 for Cu, 0.2 to 7 for Zn, 0.1 to 14 for As, 1 to 24 for Cd, 0.7 to 6.8 for Pb, and 0.1 to 7.8 for Mn. Correlations between the elements and sediment characteristics show that Cu, Zn, Cd, and Pb are essentially associated with the sulfide fraction; that Ni and Co are predominantly bound to the clay minerals and iron oxy-hydroxides, and that As is principally bound to iron oxy-hydroxides. The accumulation of trace elements between muscle tissue and liver and eggs of A. maculatus and O. militaris is element-specific, but concentrations of trace elements in fish muscle tissue are well within the limits for human consumption.     

Observations on mineral transformations and potential environmental consequences during the oxidation of iron sulphide‐rich materials in incubation experiments

This paper attempts to acquire a good understanding of the formation and evolution of acid sulphate soils (ASS), as well as to assess the consequent environmental impacts. An incubation experiment to simulate the development of ASS under various weathering scenarios was set up. Fresh monosulphidic black ooze (MBO) material was divided into three parts and each was subjected to different drying and rewetting regimes by controlling an artificial water table in an incubation cell. The observations focused on the changes in mineralogy of the material and reflectance spectral changes during the oxidation process, and the ionic composition and chemical status of the solutions generated. Mineralogical investigations with hyperspectral and XRD analysis showed that frequent inundation produced extensive surface oxidation and a change from iron sulphide minerals to stable end members such as goethite. For the material experiencing moderate or occasional inundation, oxidation was less advanced and a different secondary mineral suite, with iron sulphate minerals such as jarosite, was present. Solutions generated from all the incubation cells were generally acidic with pH around 3.5, indicating that sulphide oxidation occurred rapidly in all cells. Sulphate concentrations in solutions from the different cells were calculated from the measurements of SO₄^2? and other anions in solutions and may approximate the rates of sulphide oxidation. Potential environmental impacts were illustrated in terms of soil acidity, salinity and trace metal release, and the effects of the different wetting/drying regimes on the oxidative process also provided insight into potential weathering effects in a changing climate.     

Contaminant Metal Behaviour During Re-suspension of Sulphidic Estuarine Sediments

Sediment re-suspension experiments have been conducted to predict contaminants release from sediments to the water column, during dredging operations. In this context, polluted, anoxic estuarine sediments from Rio de Janeiro, SE Brazil, were suspended in oxygenated estuarine water, in laboratory experiments intended to simulate their dispersion by flood flow or dredging operations, in order to measure any release into solution of heavy metals originally present as sulphides that might suffer oxidation. Oxidation of sulphides to sulphate acidified the waters but only after at least 5 h of suspension. Furthermore, the oxidation of acid volatile sulphide (AVS) to sulphate was more rapid and only proceded to completion within 5 days, when large quantities of sulphide forming metals other than Fe were not present. In sediment heavily polluted with zinc, oxidation of AVS was slower and incomplete, resulting in soluble release of a much smaller fraction of the Zn present in the sediment and a maximum dissolved zinc concentration that was much lower than that resulting from less contaminated sediment. The maximum percentages of sulphide-bound metals appearing in solution at any time during re-suspension were low, less than 46% in all cases and typically less than 10%. These maxima were manifested only after acidification by sulphate formation. Appreciable metal dissolution would not occur in an estuary if dilution and dispersion separated the sediment from acid generated or if dredged material settled before acidification occurred.     

Microbial production of sulphate and sulphide in some Australian soils

Fifty-six Australian soils were examined for their ability to produce sulphate from sulphur and sulphide from added sulphur, sulphate and cystine. Selective liquid media were used to obtain initial counts and progressive activities of some of the principal organisms involved. Attempts were made to correlate soil properties, initial microbial counts, classes of micro-organisms detected and metabolic activities.Almost half of the soils oxidized sulphur very slowly or not at all, most probably due to absence of thiobacilli, particularly Th. thiooxidans. Even soils which oxidized sulphur rapidly never gave initial counts greater than 10⁴ cells/g. The majority of soils produced sulphide from sulphur, between one-half and two-thirds of them formed sulphide from cystine but sulphate reduction was very rare. Sulphide escaped more readily from aerobic than from waterlogged soils. Numerous genera were isolated including Desulfovibrio and Desulfatomaculum capable of reducing sulphur, both aerobically and anaerobically, particularly sporing and non-sporing mesophiles which were sometimes present at 10⁶ cells/g of soil. Sulphate reduction by the genus Desulfovibrio was uncommon, and by the genus Desulfatomaculum extremely rare. Many genera of sporing and non-sporing mesophiles seemed capable of producing sulphide from cystine when first isolated, but they quickly lost this ability on subculturing. Initial counts of 10⁶ cells/g of soil were occasionally found but usually much lower.No significant correlations, only trends, were found suggesting that any soil properties measured affected the occurrence or activities of organisms capable of producing sulphate or sulphide.     

Biogeochemistry of Iron and Sulfur in Sediments of an Acidic Mining Lake in Lusatia,Germany

Chemical, microbiological and stable isotope analyses of sediments from an acidic mining lake were used to evaluate whether biogeochemical processes, such as iron and sulfate reduction, are extant, because such processes can potentially generate alkalinity. Sediment cores were sliced in cm intervals to achieve a high resolution for spatial distribution of organic and inorganic components. Iron, sulfur, carbon, nitrogen and phosphorus as well as the most probable number (MPN) of iron reducing bacteria, the amount of lipid phosphate and the stable isotope compositions of various sedimentary sulfur compounds were measured. Accumulation of degradable organic material, reduced mass fractions of iron, enhanced concentrations of lipid phosphate, high concentrations of DOC and ferrous iron in the pore water and a drastic change of sulfur isotope ratios in the upper 3 cm of the sediment all indicated a highly reactive zone of biogeochemical transformations. The data provide clear evidence for iron and sulfate reducing processes in the sediments that result in an increase of pH with depth.     

Testing In Situ Sulfate Reduction by H2 injection in a Bench-Scale Column Experiment

Autotrophic microbial sulfate reduction was tested in a fixed-bed bench-scale column experiment to lower sulfate and iron loads in acid-mine-drainage-influenced groundwater. The microbial process was enhanced by injecting H₂ gas as electron donor into the silicate bed. The experiments were performed at 2.5 atm and 10°C. Complete iron removal (3.8?±?0.3 mM) and partial sulfate removal from 17 to 9 mM were achieved at rates of about 0.004–0.019 mmol SO₄ per liter per hour and at hydraulic retention times of 51.5–19.8 days. The tests showed that most microbial activity took place in immobile zones. These zones create stable environmental conditions for the microorganisms leading to constant reduction rate despite possibly unfavorable conditions prevailing in the mobile phase. Diffusion between mobile and the immobile zones was not found to be the limiting factor for sulfate reduction. Rather, low H_2(aq) concentrations due to low H₂ solubility combined with the inhomogeneous distribution of H₂ gas in the pore space limited sulfate reduction. H_2(aq) concentrations in some parts of the sediment body were insufficient to maintain H_2(aq) concentrations in the immobile zones above the level of substrate limitation. Fe and S precipitated mostly as iron monosulfide and accumulated in regions with high H_2(aq) availability. Calculations showed that the deposition of iron sulfide in the pore space does not affect the pore volume significantly.     

Phosphorus Availability in Soils Amended with Different Phosphate Fertilizers

Abstract

Accurate measurement and characterization of phosphate rock dissolution are important for a better understanding of phosphorus (P) availability in soils. An incubation study was carried out on two New Zealand topsoils (0–15 cm; high P buffering capacity Craigieburn and low P buffering capacity Templeton) amended with North Carolina phosphate rock (NCPR) and water‐soluble phosphate (WSP) at 218 mg P kg^?1 (equivalent to 60 kg P ha^?1). Isotopic exchange kinetics was carried out after 12 h and 28 days of incubation to characterize P availability. This study showed that sensitivity of capacity factors (r₁/R, n) to explain changes in E_1min values was affected by the P buffering capacity of the soils. The recovery of applied P in the E pool (Rec_inE%) with extended incubation time was similar from the NCPR and WSP treatments (3.1–3.3%) in the Craigieburn soil compared with the Templeton soil in which Rec_inE% values were greater in WSP (9%) than NCPR (1.3%) treatment. The higher values of P derived from the applied P fertilizers in the E pool (Pdff_inE%>80%) suggested that the NCPR application in both soils would be efficient for increasing P availability to plants.     

Enhancing Nitrogen Availability,Ammonium Adsorption-Desorption,and Soil pH Buffering Capacity using Composted Paddy Husk

Form of nitrogen present in soils is one of the factors that affect nitrogen loss. Nitrate is mobile in soils because it does not absorb on soil colloids, thus, causing it to be leached by rainfall to deeper soil layers or into the ground water. On the other hand, temporary retention and timely release of ammonium in soils regulate nitrogen availability for crops. In this study, composted paddy husk was used in studies of soil leaching, buffering capacity, and ammonium adsorption and desorption to determine the: (i) availability of exchangeable ammonium, available nitrate, and total nitrogen in an acid soil after leaching the soil for 30 days, (ii) soil buffering capacity, and (iii) ability of the composted paddy husk to adsorb and desorb ammonium from urea. Leaching of ammonium and nitrate were lower in all treatments with urea and composted paddy husk compared with urea alone. Higher retention of soil exchangeable ammonium, available nitrate, and total nitrogen of the soils with composted paddy husk were due to the high buffering capacity and cation exchange capacity of the amendment to adsorb ammonium thus, improving nitrogen availability through temporary retention on the exchange sites of the humic acids of the composted paddy husk. Nitrogen availability can be enhanced if urea is amended with composted paddy husk.     

Hypolimnetic Alkalinity Generation in Two Dilute, Oligotrophic Lakes in Ontario, Canada

It has been observed that the alkalinity concentrations in the hypolimnia of many thermally stratified lakes increase over the duration of the summer. We have quantified the processes, both redox and exchange, that contributed to the alkalinity increases measured in two lakes that are situated on the Precambrian Shield of Ontario, Canada by measuring hypolimnetic mass balances for all substances involved in alkalinity-generating or -consuming reactions. These include nitrate, ammonium base cations, iron, manganese, sulphate, organic anions, as well as alkalinity itself. In one lake, iron reduction was the dominant source of alkalinity; since this process is probably reversed at fall overturn when hypolimnetic waters mix with oxygenated surface waters, the alkalinity generated by this mechanism is likely temporary in nature. In the second lake, iron reduction and sulphate reduction were both important the latter should provide more permanent alkalinity.     

35S-sulphate reduction and transformation in peat

The incorporation of ³⁵S-labelled sulphate into reduced inorganic forms and into organic S has been studied in peat samples from two contrasting sites, a deep blanket peat and a shallow hill blanket peat. During anaerobic incubation, ³⁵S was rapidly incorporated into AVS (acid volatile sulphide), elemental S and Cr-reducible S but these pools showed evidence of rapid recycling. In the longer term, ³⁵S was found in the ester sulphate pool and in a residual S pool, taken to be principally C-bonded organic S. Incorporation was more rapid in the deep peat than in the hill peat, in peat from wet areas more than dry areas and in subsurface (10–20 cm) peat more than in surface (0–10 cm) peat. Incorporation in the hill peat under aerobic incubation into either reduced inorganic or organic forms was very limited. Mean sulphate reduction rates at the temperature of incubation (26°C) were estimated to be in the range 60–12,000 μg S kg⁻¹ wet weight peat d⁻¹ while mean turnover times of reduced S were 17 and 550 d for the deep and hill peats, respectively.     

Mercury methylation by sulphate-reducing bacteria from sediments of an acid stressed lake

The role of freshwater sulphate-reducing bacteria in McHg production was examined by adding specific microbial inhibitors to anoxic lake sediments spiked with ²⁰³HgCl₂ and measuring net methylation. The effect of increased sulphate (such as would arise from acid deposition in the area) on the activity of sulphate-reducing bacteria both in terms of sulphate reduction rate and methylation of Hg was examined by adding sulphate to ²⁰³HgCl₂ spiked sediments. Sodium molybdate (10 mM), a specific inhibitor for sulphate-reducing bacteria, reduced the amount of MeHg produced from anoxic lake sediments by 75% compared with controls over a 7 d period. In contrast, 2-bromoethane sulfonic acid (15 mM), a specific inhibitor for methanogenic bacteria, did not alter the amount of McHg produced. Additions of sulphate that were “realistic” in terms of the normal range of the area (5 to 30 mg.L^?), increased the sulphate reduction rate of sediment slurries. However, in the experimental system, these additions did not stimulate McHg production. In our study, methylation of Hg in sediments was primarily due to the activity of sulphate-reducing bacteria. However, the methylation rate does not appear to be sensitive to the concentration of sulphate over the range typical of softwater, Precambrian Shield lakes. This could be due to reduced availability of Hg due to the formation of insoluble HgS or to the fact that the overall activity of sulphate reducers not being stimulated even if sulphate reduction rate is, or both.     

Interactions Between Benthic Phosphorus Release and Sulfur Cycling in Lake Scharmützelsee (Germany)

Sulfur (S) conversions were determined during summer stratification in 1995/96 to assess the extent to which benthic release of phosphorus (P) is influenced by the S cycling in eutrophic, dimictic, sulfate-rich (61.33 ± 10.41 mg SO42- l-1) freshwater Lake Schamützelsee. Hypolimnetic SO42- reduction (4.56 ± 0.73 g (S) m-2 d-1) forming ΣH2S (44.71 ± 17.57 mg ΣH2S m-2 d-1), leading to iron sulfide precipitation (5.62 ± 1.72 mg FeS m-2 d-1) and dissolved iron depletion in the hypolimnion has a major influence on benthic P mobilization and release. The most important inorganic S pool is the CRS (FeS2 + S° + H2S; 15.1 % total S), being 1.3 to 6.6 times higher than the AVS (FeS + H2S) in the uppermost 0 - 8 cm sediment. This diminishes the ability of the sediment to bind P (indicated by 14.6 % loosely bound P (NH4Cl-P) and an exhaustion of the redox-sensitive P (BD-P)), leading to interstitial water P concentrations up to 10.8 mg l-1 and P release rates of 2.64 ± 0.56 mg P m-2 d-1. As a consequence the P content of the lake increased fourfold within 58 days.     

Short‐term transformations of lead and cadmium compounds in soil after contamination

The behaviour and fate of trace metals, in particular lead and cadmium, when they contaminate the soil as atmospheric fall‐out are not well understood. To improve our understanding, we incorporated pure compounds of lead and cadmium into samples taken from surface horizons of three chemically contrasting soils and monitored the changes in their speciation by analysing the soil solution. In most instances the concentrations of trace metals in solution were maximal during the first few days after mixing the contaminants with the soil, and depended strongly on soil type. The exception was when the contaminant was added as sulphide particles. The initial speciation of metals also influenced their solubility, following a decreasing order which did not depend on the soil type:
Lead sulphide was progressively oxidized, but cadmium sulphide was hardly dissolved. When lead was added as sulphate, between 10 and 20% of lead particles dissolved, regardless of the soil type. For the other species, dissolution was enhanced at lower soil pH. Thermodynamic calculations with the WinHumic V program indicated that the solution was not saturated with respect to lead sulphate. We conclude that dissolution must be limited by the adsorption of inhibitors on reactive surfaces. The calculations also showed that precipitation of chloropyromorphite probably controls lead concentration in leachate from the acid organic soil. Finally, both soil type and initial speciation of contaminants control the behaviour of trace metals in soils for a time greater than a cropping season and must be considered for understanding their environmental impact.     

旱作褐土中氧化铁的厌氧还原与光合型亚铁氧化特征

土壤中铁的氧还过程与碳氮转化及自净能力关系密切,已还原亚铁的氧化受土壤性质的影响。采用室内恒温培养试验研究了旱作褐土中铁还原氧化过程、及其与水溶性碳、NO3-、SO42-的关系。结果表明旱作褐土中铁氧化物在厌氧光照条件下可先被还原后被再次氧化,其再氧化量介于1.46~3.00 mg g-1之间,平均2.09 mg g-1;再氧化速率常数介于0.23~0.80 d-1之间,平均0.48 d-1。再氧化量与土壤无定形铁、水溶性硫酸盐含量、阳离子交换量显著负相关,与土壤总氮、总磷显著正相关;再氧化速率常数与土壤有机碳显著负相关,与黏粒含量极显著正相关。厌氧光照培养可使旱作褐土水溶性无机碳平均降低52.74%,水溶性NO3-降低92.15%,水溶性SO42-增加55.38%。研究结果为深入理解旱作土壤潜在的微生物铁循环转化方式提供理论支持。     

近60年湘江流域水沙特性及其对人类活动的响应

湘江流域人类活动对湘江水沙变化具有显著影响。利用M-K次序法、Pettitt非参数检验法和双累积曲线法分析湘江干支流1953-2014年的年径流量、汛期径流量和非汛期径流量与输沙量的关系,并分析水土保持和水库建设等人类活动与水沙演变的关系。结果表明:1)湘江干支流水文站的年径流量、汛期径流量与输沙量的相关性强,且1990年后湘潭站径流量-输沙量的相关系数为0.83,而非汛期相关性较弱。1990年前,干流站点径流量和输沙量处于波动状态,1990年后干流站点径流量总体呈增加趋势,但输沙量呈减小趋势,且老埠头站的输沙量发生微幅突变。除个别站点之外,支流站点的径流量和输沙量发生突变的年份与变化规律均一致。2)水土保持以及水库建设对湘江流域的拦沙作用是输沙量减少的主要原因。相比支流,水土保持对湘江干流流域的输沙量减少影响更显著,水库建设与湘江干支流输沙量减少均密切相关。3)根据湘江流域输沙量突变点可划分A(1960-1987年)、B(1988-1996年)、C(1997-2013年)3个时期,在不考虑温度变化的影响下,以A时期1960-1987年为基准期,利用累积量斜率变化率比较法可知,相比基准期A时期,B、C时期水土保持和水库拦沙等人类活动对输沙量的减少的贡献率为88.58%和94.01%,人类活动为输沙量减小的主要因素。