Watershed vs in-lake alkalinity generation: A comparison of rates using input-output studies

As a means of assessing the relative contributions of watershed (terrestrial) and in-lake processes to overall lake/watershed alkalinity budgets, alkalinity production rates for watersheds and low alkalinity lakes were compiled from the literature and compared. Based on net alkalinity production data, derived using wet or bulk deposition data, mean and median alkalinity production for 20 watersheds in North America and Europe were 89 and 69 meq m^?2 yr^?1 (range 20 to 235 meq m^?2 yr^?1). For a subset of 10 watersheds with dry deposition data, terrestrial alkalinity production neutralized an additional 35 meq m^?2 yr^?1 of acidic deposition. For 11 lakes, mean and median in-lake alkalinity generation were 99 and 88 meq m^?2 yr^?1 (range 22 to 240 meq m^?2 yr^?1). Analysis of data indicates that for the low alkalinity systems described here, areal alkalinity production rates for watersheds and lakes are approximately equal. This relationship suggests that watershed area to lake area ratio can be used as a convenient estimator of the relative importance of watershed and in-lake sources of alkalinity for drainage lake systems. For precipitation-dominated seepage lakes and other systems where hydrology limits soil-water contact, hydrologic flow paths and residence times can be of overriding importance in determining alkalinity sources. For regions dominated by drainage lakes with high watershed area to lake area ratios (such as the Northeastern U.S.), however, alkalinity budgets are dominated by watershed processes. Omission of in-lake alkalinity consideration for most lakes in such regions would have little impact on computed alkalinity budgets or on predicted response to changes in acidic deposition loadings.     

Alkalinity generation by Fe(III) reduction versus sulfate reduction in wetlands constructed for acid mine drainage treatment

Despite the widespread use of wetlands for acid mine drainage (AMD) treatment, alkalinity generating mechanisms in wetlands and their abiotic and biotic controls are poorly understood. While both dissimilatory sulfate reduction and Fe(III) reduction are alkalinity-generating mechanisms, only the former has been considered as important in wetlands constructed for AMD treatment. This study was conducted to determine the extent to which Fe(III) reduction occurs and the extent to which sulfate reduction versus Fe(III) reduction contributes to alkalinity generation in 5 wetlands constructed with different organic substrates (Sphagnum peat with limestone and fertilizer, Sphagnum peat, sawdust, straw/ manure, mushroom compost) that had been exposed to the same quality and quantity of AMD for 18–22 months. These substrates had Fe oxyhydroxide concentrations of 250–810 μmol Fe g^?1 dry substrate. Flasks containing 100 g of wet substrate along with either 150 mL of wetland water or 130 mL of wetland water and 20 mL of 37 % formalin were incubated at 4 °C in January and 25 °C in May. On days 0, 2, 4, 8, 12 and 16, the slurry mixtures were analyzed for concentrations of H⁺, Fe²⁺ and SO₄ ^2?. The bulk of the evidence indicates that for all except the mushroom compost wetland, especially at 25 °C, biologically-mediated Fe(II) reduction occurred and generated alkalinity. However, in none of the wetlands, regardless of incubation temperature, was there evidence to support net biological sulfate reduction or its attendant alkalinity generation. Sulfate reduction and concurrent Fe(III) oxyhydroxide accumulation may be important in the initial stages of wetland treatment of AMD, both contributing to effective Fe retention. However, as Fe(III) oxyhydroxides accumulate over time, Fe(III) reduction could lead not only to decreased Fe retention, but also to the potential net release of Fe from the wetland.     

Modeling fate and transport of sulfate and alkalinity in an acidified lake

Acid mine drainage from Contrary Creek flows into an entire arm of Lake Anna. Much of the acid inflow is neutralized by bacterial sulfate reduction in the lake sediments. We developed a simple model to track the seasonal fate and mass transport of sulfate and alkalinity along the acidified arm. The loss of sulfate from the water column was characterized by a first-order decay reaction. A gain in alkalinity due to sulfate removal was also incorporated in the model. In addition, CO₂ acidity and pH in the water column were calculated. The model was calibrated with data collected in 1983 and 1984. Model sensitivity runs were conducted to demonstrate the importance of sulfate reduction in the system.     

综述: 酸性硫酸盐土壤的环境风险评价分析方法

Assessment of acid sulfate soil risk is an important step for acid sulfate soil management and its reliability depens very much on the suitability and ccuracy of various analytical methods for estimating sulfide-derived potential acidity,actual acidity and-neutralizing capacity in acid sulfate soils.This paper cirtically reviews various nalytical methods that are currently used for determination of the above parameters,as well as their implications for environmental risk assessment of acid sulfate soils.     

Determination of sulfate in soils by reduction with tin and phosphoric acid

Abstract

A rapid and precise method for determination of SO₄ ^2‐‐S in soils is described. It involves the extraction of SO₄ ^2‐ from soils and its reduction to H₂S by a reagent containing Sn and H₃PO₄ and subsequent determination as methylene blue. The results agreed closely with those obtained by reduction with the a reagent containing HI, H₃PO₂, and HCOOH and by ion chromatrography. Tests indicated that, in addition to SO₄ ^2‐, the Sn‐H₃PO₄ reagent reduces certain organic S and reduced inorganic S compounds, but these S compounds are not present in extracts of agricultural soils. By using a bank of 10 distillation units, a single operator can perform 60 analyses in a normal working day.     

Ferric reduction by geum urbanum: A kinetic study

The reduction capacity for ferric chelates of Geum urbanum L. showed a marked increase when plants were grown under conditions of iron‐shortage. Ferric ethylenediaminetetraacetate (FeEDTA) was reduced with a pH optimum between 5 and 6. The reaction exhibited a low substrate affinity with a K_m much higher than the expected concentration range of soluble iron in the soil. Analysis of the saturation plots conform to Michaelis‐Menten kinetics. Both V_max and K_m values varied to a broad extent with changing assay and plant culturing conditions. Ferricyanide was reduced at significantly higher rates than FeEDTA and inhibited the reduction of FeEDTA compete‐tively. The kinetic characteristics of iron reduction by plants will be discussed in terms of ecological significance as part of an adaptation to the soil conditions.     

The influence of gleyzation and sulfate reduction in different rocks on the lysimetric water from them: A model experiment

The model experiments showed that, under the influence of gleyzation and sulfate reduction, deep changes occurred both in the solid and liquid phases of the soil-forming rocks (soils). The results of an experiment with three widespread soil-forming rocks—river clayey alluvium, loess-like clayey alluvium, and lacustrine calcareous loamy-clayey alluvium—demonstrated that, under the stagnant-percolative water regime and periodic gleyzation, the liquid phase was drastically acidified (by 2–4 pH units) and the redox potential of the lysimetric water was significantly lowered. A significant increase in the input of iron (by 80 to 100 times compared to the control), calcium (10 times), and silicon (1.5–2.0 times) to the lysimetric waters was observed. The sulfate reduction retarded the removal of iron from the substrates to the lysimetric runoff.     

Adsorption of sulfate ions by soils (A Review)

The literature data on the adsorption of sulfates by soils were reviewed. Factors affecting the adsorption of sulfates and the major mechanisms of sulfate adsorption were considered, including the most important of them: the ligand exchange with the formation of surface outer-and innersphere complexes and the Coulomb interaction with the surface of mineral particles. Equations describing the adsorption isotherms of sulfates are given; some methods for the mathematical simulation of sulfate ion behavior in the “soil solid phase-soil solution” system are discussed.     

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.     

An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique

Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH₄⁺-N. With the addition of up to 100 ppm nitrogen as (NH₄)₂SO₄ to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.     

Enhanced iron reduction by iron supplement: A strategy to reduce methane emission from paddies

As an option for mitigating methane emissions from rice paddies the effects of ferrihydrite application to an experimental field plot at the beginning of the growth season was studied. Methane emissions during the vegetation period of rice were significantly lower (50%) in the fertilized plot compared to the non-supplemented control plot. Although toxic effects of iron are known to occur with wetland plants including rice, our field experiment showed no deterioration of agrophysiological data. Grain yield, harvest index, and iron content of grains were not different in the two plots. Therefore, we propose that iron application is a suitable strategy to reduce methane emission from rice paddies.     

联合国全球千年生态系统评估——荒漠化状况评估概要

 在联合国全球千年生态系统评价中,干旱生态系统和土地退化、荒漠化是其主要内容。在千年生态系统评价基础上,分别介绍如何正确理解荒漠化、荒漠化成因、荒漠化影响范围、荒漠化对生态系统及其人类社会影响、荒漠化与全球气候变化及生物多样性损失的关系、未来不同发展途径对荒漠化影响以及如何防治荒漠化等问题。     

沿海酸性硫酸盐土中气态N损失的短期研究

NO x and N 2 O emissions from coastal acid sulfate soils (CASS) cultivated for sugarcane production were investigated on the coastal lowlands of northern New South Wales,Australia.Two series of short-term measurements were made using chambers and micrometeorological techniques.Series 1 occurred during the wet season,the water-filled pore space (WFPS) was between 60%-80% and the site flooded during the measurements.Measurements were made directly after the harvest of soybean crop,which fixed an estimated 100 kg N ha-1,and the emission amounted to 3.2 kg NO x-N ha-1 (12 d) and 1.8 kg N 2 O-N ha-1 (5 d).Series 2 was made towards the end of the dry season when the WFPS was less than 60%.In Series 2,after an application of 50 kg N ha 1,emissions were markedly less,amounting to 0.9 kg N ha-1 over 10 d.During both series when the soil was moist,emissions of NO x were larger than those of N 2 O.The emission of NO x appeared to be haphazard,with little time dependence,but there was a clear diurnal cycle for N 2 O,emphasising the need for continuous measurement procedures for both gases.These results suggest that agricultural production on CASS could be important sources of greenhouse gases and nitrogen practices will need to be optimised to reduce the offsite effects of atmospheric warming,acidification or nitrification.Many questions still remain unanswered such as the emissions during the soybean bean filling stage and crop residue decomposition,the longer-term losses following the fertiliser application and emissions from CASS under different land uses.     

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.     

Modern and paleolimnological evidence for accelerated leaching and metal accumulation in soils in New England,caused by atmospheric deposition

Empirical field evidence for changing chemical processes in soils caused by atmospheric deposition of pollutants consists of: (1) Long-term water quality data including total dissolved solids, concentrations of specific metals (e.g. Ca), and conductivity; (2) Cation exchange capacity and base saturation values for soils located on precipitation pH gradients; (3) Lysimeter studies; and (4) Chemical analysis of organic soils on precipitation pH and metal gradients. For well-drained organic soils, as precipitation pH decreases, metals are differentially leached at an accelerated rate (Mn>Ca>Mg≥Zn>Cd and Na>Al). Experimental field and laboratory lysimeter studies on soil columns yield similar results, with increases in leaching rates for soil solutions with pH=3 up to 100 × values for soil solutions with pH=5. Nearly 100% of the Pb from precipitation is accumulating in the organic soil layer or sediments. Zn is accumulating in soils and sediments where the pH's of precipitation, soil solutions, and surface waters are generally above 5 to 5.5. At lower pH values Zn and other chemically similar elements are desorbed/leached (net) at an accelerated rate. Chemical analyses of dated sediment cores from high and low altitude lakes, with drainage basins relatively undisturbed for the last 200+ yr, reveal that increased deposition of metals on a regional scale started in the northeastern United States as early as 1880, consistent with increased fossil fuel consumption. This suggests acidified precipitation as early as 1880. Cores from historically acidified lakes (pH<≈5.3 to 5.5) indicate that, as acidification of surface waters occurs (caused by acidic deposition), concentrations of Zn, Mn, and Ca decrease in the sediment. Apparently the metals are leached from the detritus prior to sedimentation. This conclusion results from data from experimental acidification of sediment cores and the general observation that precipitation pH is generally ≥0.5 pH units lower than lake water pH. Accelerated leaching of soil in New England dates to earlier than 1900.     

A rapid colorimetric method for analysis of nitrate nitrogen by reduction to nitrite

Abstract

A new method was developed for the determination of nitrate based on a soluble powder containing zinc and a bluish diazotizing solution. In this procedure about 10% of the nitrate content of the sample is converted to nitrite, but the intensity of the color developed is proportional to the nitrate content. The color changes from blue through green to yellow. The nitrate concentration can be estimated visually or determined spectrophotometerically at λ_max 400 nm in the range of 4–40 mg/L N. When the color change is very small, a coupling solution is added, and the violet color that develops can be measured colorimetrically at λ _max 545 nm in the range of 0.5–5 mg/L N. This simple method employs harmless chemicals and is especially suitable for use in agriculture. Reliable results are obtained in less than 10 minutes.     

A microassay technique for sulfate determination in plant samples

Abstract

A microassay for the measurement of sulfate sensitive to below 1 nmol is described. Accuracy and reproducibility were demonstrated with trichloroacetic acid clarified plant sample volumes of only 5 μl. The sensitivity of this assay enabled, for the first time, the measurement of sulfate in the medium of plant suspension cultures during its depletion down to the compensation point in a non‐disruptive manner. This was possible because very small volumes could be sampled from continuously growing cultures.     

Satellite remote sensing for water erosion assessment: A review

Water erosion creates negative impacts on agricultural production, infrastructure, and water quality across the world. Regional-scale water erosion assessment is important, but limited by data availability and quality. Satellite remote sensing can contribute through providing spatial data to such assessments. During the past 30 years many studies have been published that did this to a greater or lesser extent. The objective of this paper is to review methodologies applied for water erosion assessment using satellite remote sensing. First, studies on erosion detection are treated. This comprises the detection of erosion features and eroded areas, as well as the assessment of off-site impacts such as sediment deposition and water quality of inland lakes. Second, the assessment of erosion controlling factors is evaluated. Four types of factors are discussed: topography, soil properties, vegetation cover, and management practices. Then, erosion mapping techniques are described that integrate products derived from satellite remote sensing with additional data sources. These techniques include erosion models and qualitative methods. Finally, validation methods used to assess the accuracy of maps produced with satellite data are discussed. It is concluded that a general lack of validation data is a main concern. Validation is of utmost importance to achieve regional operational monitoring systems, and close collaboration between the remote sensing community and field-based erosion scientists is therefore required.     

农田磷的环境风险及评价研究进展

本文综述了农田磷环境风险及其评价研究进展。着重阐述了农田磷的迁移途径、农田土壤磷水平、土壤磷的吸附和解吸特性以及磷肥和有机肥用量等对农田磷地表径流流失和渗漏的影响;农田土壤磷环境风险评价方法及P-index评价方法的建立和应用等。提出了今后该领域的研究方向。