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Chemical characteristics of dissolved organic matter (DOM) extracted from an ombrotrophic bog in northern Minnesota by two methods – XAD-8 and DEAE-cellulose – were compared using 13C NMR spectroscopy, excitation–emission matrix fluorescence spectroscopy (EEMS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM extracted with XAD-8, a relatively hydrophobic sorbent, had a larger 13C NMR signal in the aromatic carbon region, but DOM extracted by DEAE-cellulose, a weak anion exchanger, had a larger signal in the carboxylic carbon region. DOM extracts prepared by the two methods were similar in their overall chemical characteristics that serve as proxies for organic matter sources. For example, only small differences were observed in the fluorescence index (FI) values of the extracts, and all values were within the range expected for terrestrially-derived DOM. EEMS spectra of both extracts had “humic-like” peak A areas smaller than that of standard reference Suwannee River fulvic acid. Of 2801 distinct chemical formulas assigned during FT-ICR MS analysis of the two extracts, 66% were present in both; 15% were unique to the XAD-8 extract, and 19% were unique to the DEAE-cellulose extract. Van Krevelen plots showed that the DEAE-cellulose extract had more tannin-like and condensed aromatic entities and formulas with higher O/C ratios, whereas the XAD-8 extract had more lignin-like material and formulas with higher H/C ratios. Overall, differences in chemical characteristics of the extracts reflect the mechanisms by which the extractants operate.

Lake Pepin, a natural impoundment on the Upper Mississippi River, has water quality problems of high sedimentation rates and elevated phosphorus (P) levels. The majority of sediments in Lake Pepin come from river banks consisting of fine tills in the Minnesota River Basin. Since 1850, inorganic P concentrations in lake sediments have continuously increased. This study explored whether the increase in inorganic P concentrations can be explained through selective transport of fine particles combined with in-stream P adsorption. The measurements included total P (TP) content, P adsorption/desorption isotherms, and the solution equilibrium P concentration at zero adsorption (EPC) for various bank materials. Results showed that till bank materials are inherently high in TP (>400 mg kg), have strong P binding ability, and have low EPC (

Root and microbial respiration is considered to be the main source of CO2 production in soil; however, calcite dissolution in calcareous soils may contribute to the emitted CO2. The major aim of this research was to quantify the contribution of CaCO3 dissolution to CO2 emission from a soil with and without the addition of an organic residue. Emissions of CO2 and its δ13C from incubated noncalcareous (Golan Heights [GH], −26.23‰) and calcareous (Bet She'an [BS], −11.47‰) soils with and without the addition of a pasteurized chicken manure (PCM, −23.2‰) were determined. During 56 d of incubation, 445 and 1804 mg kg−1 CO2–C emitted from BS and GH soils, and PCM application caused additional emission of 2430 and 1884 mg kg−1 CO2–C, respectively. The NO3−–N concentrations in the control BS and GH soils were 46 and 133 mg kg−1 and PCM application increased it to 508 and 577 mg kg−1, respectively. The emitted CO2–δ13C from BS and GH soils were −20.0 ± 0.2‰ and −27.2 ± 0.09‰ and application of PCM changed it to −20.6 ± 0.42‰ and −23.7 ± 0.16‰, respectively. Consequently, the contributions of the inorganic source to CO2–C emission from BS without and with PCM and from GH with PCM were 113.4, 417.5, and 176 mg kg−1 (26.5, 14.5, and 5% of the total), respectively. We suggest that oxidation of organic matter, mineralization of organic N, NH4 nitrification, oxidation of organic S, and production of organic acids caused chemical dissolution of calcite and CO2 emission. Ignoring this process will result in overestimation of the respired C.

Restoration of wetland hydrology can produce ecological benefits but may have unintended consequences. We examined effects of altered water level on release of dissolved reactive phosphorus (DRP) and greenhouse gases (GHG) in soil cores from a marsh being evaluated for restoration. We also measured field concentrations of DRP and other constituents in wetland porewater. Intact cores from a sampling location with higher Fe and lower calcium carbonate (CaCO(3)) contents released more DRP than another location, and displayed higher DRP under completely saturated compared to partly drained conditions. Porewater samples collected from the high-Fe location also contained higher DRP levels. Chemical data suggest that redox-driven reactions largely controlled DRP levels at the high-Fe site, while CaCO(3) adsorption was more important at the low-Fe site. Over the long term, water table elevation may attenuate P draining from the wetland due to decreased mineralization. However, such measures may increase P release in the short term. Raising the water level in soil cores resulted in decreased nitrous oxide (N(2)O) emissions, increased methane (CH(4)) emissions, and an overall increase in total global warming potential (GWP). The proportion of total GWP contributed by N(2)O decreased from 14% to < or = 1% as water level was raised, while the proportion contributed by CH(4) increased from 10 to 20% to 60 to 80%. Restoration of hydrology in the Rice Lake wetland has the potential to affect both local water quality and global air quality. These combined effects complicate the cost-to-benefit analysis of such wetland restoration efforts.

We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to determine the coordination, geometry, and strength of methyl mercury, CH3Hg (II), bonding in soil and stream organic matter. Samples of organic soil (OS), potentially soluble organic substances (PSOS) from the soil, and organic substances from a stream (SOS) draining the soil were taken along a short “hydrological transect.” We determined the sum of concentrations of highly reduced organic S groups (designated Org-SRED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-SRED varied between 27% and 64% of total S in our samples. Hg LIII-edge EXAFS analysis were determined on samples added CH3Hg (II) to yield CH3Hg (II)/Org-SRED ratios in the range 0.01–1.62. At low ratios, Hg was associated to one C atom (the methyl group) at an average distance of 2.03 ± 0.02 A and to one S atom at an average distance of 2.34 ± 0.03 A, in the first coordination shell. At calculated CH3Hg(II)/Org-SRED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the organic S sites were saturated by CH3Hg+, and O (and/or N) atoms were found in the first coordination shell of Hg at an average distance of 2.09 ± 0.01 A. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH3Hg+, whereas RSSR and RSR groups do not, approximately 17% of total organic S consisted of RSH (+ RSSH) functionalities in the organic soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, respectively. Competitive complexation of CH3Hg+ by halide ions was used to determine the average binding strength of native concentrations of CH3Hg (II) in the OS sample. Using data for Org-SRED, calculated surface complexation constants were in the range from 1016.3 to 1016.7 for a model RSH site having an acidity constant of mercaptoacetic acid. These values compare favorably with identically defined stability constants (log K1) for the binding of methyl mercury to thiol groups in well-defined organic compounds.

Chelator-buffering methods with N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid (HEDTA) are used to elucidate Poaceae growth response to micronutrient metal activities including (Zn 2+ ), but reliable hydroponic methods that maintain stable (Zn 2+ ) for evaluating Zn deficiency in rice (Oryza sativa L.) have not been reported. The objective was to develop a chelator-buffered method that gauges rice growth response to (Zn 2+ ) in an otherwise chemically stable environment. Using GEOCHEM-PC to estimate solution activities, an aerobic HEDTA-nitrilotriacetic acid (NTA) dual-chelator method was developed that imposed five (Zn 2+ ) levels on cv. IR-36 seedlings for 21 d after transplanting (DAT) in a growth chamber. Control of pH 5.50 ± 0.05 using 3.0 mM2-(4-morpholino)-ethanesulfonic acid (MES) combined with periodic adjustment was critical to preserving target (Zn 2+ ). Solution treatments ranged from Zn deficient, where (Zn 2+ ) = 10 -10.0 M (0.25 μM total chelated Zn), to fully Zn sufficient where (Zn 2+ ) = 10 -8.8 M (4.00 μM total chelated Zn). Using 200.0 μM total chelated Fe(III), adequate Fe was maintained at (Fe 3+ ) = 10 -14.3 M. Phosphorous supply was controlled to prevent toxic P accumulation at low (Zn 2+ ). With increasing (Zn 2+ ), total biomass at 21 d ranged from 0.94 to 1.90 g plant -1 . Shoot Zn responded to (Zn 2+ ), not total chelated Zn 2+ , and roots responded similarly. Critical (Zn 2+ ) for normal growth was 10 -9.1 M, and leaf Zn-deficiency symptoms were observed at (Zn 2+ ) ≤10 -9.4 M (≤28 mg Zn kg -1 shoot). The HEDTA-NTA method provides a rapid and reliable means for evaluating Zn deficiency tolerance in IR-36 via diagnostic visual and physical symptoms in response to a range of (Zn 2+ ) levels.

Hornblende minerals are important in proton neutralization and base cation release processes in many soils. This study was conducted to determine the pH dependence of hornblende dissolution rates and the rate of proton consumption during weathering under laboratory conditions. Hornblende was crushed mechanically and purified by magnetic and density separation. The samples were initially weathered (22 days) in pH 4.0, 0.01mol/L HOAc-LiOAc buffer to minimize the effect of grinding on dissolution rates. The pH range investigated was from 3.4 to 4.6 at approximately 0.2 pH unit intervals. The hornblende dissolution experiment was conducted in a 0.01 mol/L HOAc-LiOAc buffer in batch-type reactors for 30 days. The rate of proton consumption was determined for both the initially weathered samples and for samples not initially weathered in 0.01 mol/L LiCl at pH near 4.0. The dissolution was nonstoichiometric during the study period, with preferential release of Al, Fe, and Mg relative to Si. Nearly linear kinetics were observed for the release of Si, but the release rates of Al, Fe, and Mg decreased with time. Hornblende dissolution rates in the pH range studied decreased as pH increased. The overall apparent linear reaction orders, with respect to solution pH, were found to be 0.71, 0.39, 0.42, and 0.79 for Al, Fe, Mg, and Si release, respectively. The reaction orders at pH values between 3.4 and 4.2 were lower than those between pH 4.2 and 4.6. The quantity of proton consumed was equivalent to the total charges of the cations released. The proton consumption rate of samples not initially weathered was five times higher than that of the initially weathered samples. Dissolution rates obtained in acetate buffer were 3 to 4 times higher than those obtained in unbuffered LiCl solution at comparable pH and ionic strengths. The rate of hornblende dissolution is a function of solution pH and concentration of organic ligand.

The dissolution rates of most primary and secondary minerals are promoted by the presence of proton- and complex-forming ligands. Effects on the rates of dissolution of hornblende by naturally occurring organic acids at concentrations commonly encountered in soil solutions s and surface waters was studied in a pH 4.0, 0.0 1M HOAc-LiOA c buffer. Crushed hornblende samples were purified by magnetic and density separation, followed by an initial period of weathering in a buffered aqueous solution for 39 d. After the initial weathering the rate of dissolution was measured at different concentrations of citric, oxalic, polygalacturonic, tannic, and fulvic acids at pH 4.0 for another 32 d in a batch-type reactor. Although nearly linear kinetics were observed for the release of Si, the release of At, Fe, and Mg decreased with time. The dissolution was nonstoichiometric during the study period with preferential release of At, Fe, and Mg relative to Si. All ligands studied were found to accelerate the dissolution process and the rates increased with solution concentrations of organic acids. The reaction orders with respect to dissolved organic C were generally low, ranging from near zero to 0.37 for different organic acids. At a concentration of 2.5 mM of dissolved C the relative effectiveness of these ligands on promoting dissolution was oxalic > citric > tannic > polygalacturonic > fulvic acid. The strengths of organic acids to promote dissolution is related to the quantity of phenolic and carboxylic functional groups present on the organic compounds, and it is related to the strength of the metal-ligand complex formed in solution or on the mineral surface.

Sulfur K-edge x-ray absorption near-edge structure spectroscopy (XANES) was used to identify multiple organic S oxidation states in aquatic and soil humic substances. The XANES results suggest that S in humic substances exists in four major oxidation groups similar to sulfate ester, sulfonate, sulfoxide, and thiol-sulfide. Thiol S cannot be separated from sulfide X and must be considered as a single thiol-sulfide peak. The second derivative spectra suggest the existence of thiophene and sulfone S. The relative quantities of each major S form in humic samples were estimated based on the integrated cross section of each s {r_arrow} p transition peak corresponding to different S oxidation states in the S K-edge XANES spectra. The XANES results of the four humic samples used in this study appear to reflect the environmental settings where the humic substances originally formed. The percentage of the most reduced organic S (thiol-sulfide and possibly thiophene) in humic substances follows the sequence:aquatic samples > organic soil sample > mineral soil sample. The percentage of most oxidized S (sulfate group) was the greatest in the humic substance from a mineral soil and the lowest in the aquatic humic substances.

The need to understand the biological reactivity of polymers has increased in response to the integration of biological waste treatment systems (e.g., composting and soil application) into waste management plans of communities worldwide. The purpose of this study was to evaluate the compostibility and fate of a commonly used, synthetic polymer that is present in most solid waste streams. This was accomplished using a laboratory-scale composting system, simulated solid waste, and crosslinked 14 C-polyacrylate. Commercial preparations were composed primarily of a high-molecular-weight fraction (>500 kDa) that was resistant to degradation. Only the unpolymerized monomers and low-molecular-weight oligomers (totaling about 8% of the commercial preparation) were readily degraded during composting. Polymer crosslinkages were also degraded rapidly. Degradation of the low-molecular-weight fractions was considered significant, because these fractions have demonstrated a greater mobility potential in soils. Molecular size distribution and infrared (IR) spectra of extractable organic fractions confirmed that the structural integrity of the polymer chains was maintained during composting. These residual, high-molecular-weight polyacrylates could improve soil structure, and should continue to degrade slowly leaving no toxic residues.

Boron is an essential plant nutrient having a narrow range between concentrations that cause deficiency or toxicity symptoms in plants. Boric acid (B[OH] 3 ) and silicic acid (Si[OH] 4 ) have many chemical similarities and both are thought to be associated with organic matter in soils. The objectives of this study were to investigate the variation in boric and silicic acid adsorption and desorption in low ash humic acid over a range of B and Si concentrations and pH values. Borate adsorption by humic acid increased significantly from pH 3.67 to 8.70. The data fit the Freundlich equation better than the Langmuir model at high pH ; however, both fit well at pH 10. The constant capacitance model predicted B adsorption and the pH maximum using catechol as the adsorbing ligand and published stability constants. The predicted adsorption envelope was narrower than experimental data. This could be due to variation in stability constants that result from variation in substitution on other sites on the aromatic ring. Inclusion of glucose and salicylate in the adsorption model would also broaden the adsorption envelope by increasing adsorption at pH > 9 and < 9, respectively. Desorption of B from humic acid appears to show hysteresis effects at pH 7.6 but not at pH 8.15 and 8.7. Generally, B will be easily released from HA as solution concentrations decrease. Silicic acid did not adsorb in humic acid. The stability constant of Si-catechol humate complexes is apparently too low for adsorption of Si to occur at the pH and solution concentrations used in this experiment.

Summary The mineralogies of ‘Tirs’ (Typic Pelloxererts), and ‘Debs’ (Typic Haploxerolls and Typic Xerochrepts) soils of the Gharb plain in north-western Morocco are investigated, with special attention given to the determination of the nature of the smectitic phase using the lithium test (Li test) and the alkylammonium method. The sand and silt mineralogy of Tirs soils is dominated by quartz with small amounts of feldspars and kaolinite. The sand and silt fractions of Dehs soils also contain significant amounts of mica, chlorite, and interstratified phyllosilicates. The clay minerals of Tirs soils are predominantly a high-charge smectite. The estimated interlayer charge for this phase is 0.61 mol(c)/O10(OH)2 and the fraction of tetrahedral charge varies from 38 to 44%. Although the percentage tetrahedral charge is less than 50%, the smectitic phase behaves as beidellite with the Li test. Dehs clays are more heterogeneous, consisting of smectite, vermiculite, illite, kaolinite, chlorite, and interstratified illite/smectite and illite/vermiculite. The Li test and the alkylammonium method demonstrate that a high-charge smectite or vermiculite is interstratified with illite. A low-charge montmorillonite is also present both in Tirs and in Dehs soils. The high-charge beidellitic phase is believed to be a transformation product of mica, whilst the low charge montmorillonite is thought to be inherited from the parent material.

Scanning electron microscopy was used to assess the weathering status of plagioclase and alkali feldspar grains isolated from sandy outwash soils located under three vegetation communities: mixed red and white pine, maple-basswood, and white cedar. Feldspars were selected for this study because they were the most common weatherable minerals in these sandy soils. A morphological weathering index, based on the percent of the surface of the feldspar grains covered with etch pits, was used to evaluate weathering intensity. Results revealed that significant pedogenic weathering has occurred in the surface and subsurface horizons of these soils compared to the parent material. Plagioclases were found to be much more weathered than alkali feldspars. Within the plagioclase solid solution series, the weathering index increased linearly with increasing Ca content as determined by energy dispersive X-ray analysis. Comparisons among the three sites showed that weathering environments under the pine and maple-basswood communities were relatively similar, being only slightly more intense under pine. The most intense weathering occurred under the white cedar community, particularly in the E horizon. Linear regression analyses showed that the weathering index for alkali feldspars was significantly related to soil pH (r2 = 0.30, p < 0.001). In the case of plagioclases, multiple linear regression analyses showed that the weathering index was significantly dependent on both Ca(Ca + Na) molar ratio and pH (r2 = 0.83, p < 0.001) , with 64% weight effect due to Ca(Ca + Na) ratio, and 19% due to pH.

▪ Pollution control workers have proposed composting as a bioremediation method for the cleanup of contaminated soil and for the detoxification of hazardous organic chemicals. However, decomposition (mineralization to CO2 and H2O) may not always be enhanced by composting, and transformation products of unknown risk may accumulate during composting. This paper presents a scientifically based scheme to determine the ultimate fate of synthetic materials in a composting environment, and for studying factors that may control the degradation of specific chemicals including herbicides (e.g., substrate bioavailability, enzyme concentrations, environmental conditions).

A rapid batch method was developed for the analysis of Si, Ca, Mg, and K in a large number of plant tissue samples by fusion with lithium metaborate (LiBO3) in graphite crucibles with the use of a molybdenum blue spectrophotometric analysis of silicon and FAAS for Ca, Mg, and K. Our method was tested for whole plant analysis of mature wild rice (Zizania palustris L.). Analysis of Si in plant tissue with LiBO3 in graphite crucibles is reliable and fast. Thirty-six samples can be ashed overnight, fused in one hour the next day, and analyzed for Si within approximately two hours.

The use of organic residues as soil additives is increasing, but, depending on their composition and application methods, these organic amendments can stimulate the emissions of CO(2) and N(2)O. The objective of this study was to quantify the effects of management practices in irrigated sweet corn (Zea mays L.) on CO(2) and N(2)O emissions and to relate emissions to environmental factors. In a 3-yr study, corn residues (CR) and pasteurized chicken manure (PCM) were used as soil amendments compared with no residue (NR) under three management practices: shallow tillage (ST) and no tillage (NT) under consecutive corn crops and ST without crop. Tillage significantly increased (P < 0.05) CO(2) and N(2)O fluxes in residue-amended plots and in NR plots. Carbon dioxide and N(2)O fluxes were correlated with soil NH(4) concentrations and with days since tillage and days since seeding. Fluxes of CO(2) were correlated with soil water content, whereas N(2)O fluxes had higher correlation with air temperature. Annual CO(2) emissions were higher with PCM than with CR and NR (9.7, 2.9, and 2.3 Mg C ha(-1), respectively). Fluxes of N(2)O were 34.4, 0.94, and 0.77 kg N ha(-1) yr(-1) with PCM, CR, and NR, respectively. Annual amounts of CO(2)-C and N(2)O-N emissions from the PCM treatments were 64 and 3% of the applied C and N, respectively. Regardless of cultivation practices, elevated N(2)O emissions were recorded in the PCM treatment. These emissions could negate some of the beneficial effects of PCM on soil properties.

Intensive cropping of Italian ryegrass (Lolium multiforum L.) in pots was used to assess the contribution of non-exchangeable K to plant uptake. The soils used were: two soils high in mica (illite) developed on recent alluvium plus two smectitic (beidellitic) soils and a soil of mixed mineralogy rich in mica. Four K treatments were used (0, 28.6, 143, and 286 mg kg-1 soil) with 8 successive monthly cuttings. A response of plant K uptake to added K was observed in all soils. Both 1.0 M NH40Ac and 0.2 M CaCl2 extractable K were depleted to a minimum level specific for each soil. The minima were lower in the old upland soils compared to the young alluvial soils. Uptake of K by Italian ryegrass induced K release from the non-exchangeable K to replenish the plant available pool of K ions. The release of mica interlayer K in the alluvial and in the high K smectitic soil supplied sufficient K to plants even under intensive cropping. The rate of mobilization of interlayer K was low in the smectitic soil with lower K. The lowest release rate was in the old high mica soil. Iron coatings may have inhibited mobilization of interlayer K. The rates of mobilization cannot be predicted from mineralogical and K-extraction data only. The rates of K uptake and the rates of K release by ryegrass under intensive cropping are potential values which can be used for modelling K availability to plants in the soils studied.

The chemical composition of the soil solution provides used information on the feasibllity of amending agricultural land with municipal and industrial waste, because the soil solution is the medium for most soil chemical reactions, the mobile phase in soils, and the medium for mineral absorption by plant roots. The soil solutions studied in tits research were from plots in a 4-yr field experiment conducted to evaluate the effects of the trace metals and P in sewage-sludge incinerator ash. Treatments compared ash with equivalent P rates from triple-superphosphate fertilizer and a control receiving no P application. Ash and phosphate fertilizer were applied annually at rates of 35, 70, and 140 kg citrate-soluble P ha -1 . Cognitive ash applications during 4 yr amounted to 3.6, 7.2, and 14.4 Mg ash ha -1 . Soil solutions were obtained by centrifugation-immiscible liquid displacement using a fluorocarbon displacing agent. Following chemical analysis, a chemical speciation model was used to determine possible solubility-controlling minerals for trace metals and P, and correlations between solution composition and plant uptake were analyzed. Ash increased soil solution pH, Cd, and Zn, but bad no significant effect on solution concentrations of other trace metals. Ash increased soil solution P and S, but P increases were less than those from equivalent citrate-soluble P rates of phosphate fertilizer. Soil solution Ba appeared to be in equilibrium with barite (BaSO 4 ). Solubility data did not indicate that any discrete general phases controlled Cd, Zn, Cu, Ni, Pb, or P solubility. Soil solution P concentration was strongly correlated (r=0.92) with P accumulation in sweet corn (Zea mays L.) plants, but solution trace metal concentrations were either weakly correlated (r=0.49 for Zn and 0.36 for Cd) or not significantly correlated (r=0.09 for Ni and -0.25 for Cu) with plant accumulation

We planted three varieties of soybeans (Glycine max (L.) Merr.) with varying Fe‐ efficiency ratings (Swift, Hodgson, Anoka) across a high‐lime chlorotic spot in western Minnesota. Our objective was to determine the chemical components in soil solutions associated with chlorotic and nonchlorotic areas along transects through the chlorotic spot. We also measured soil temperature, soil moisture and bulk density along the transects. Chlorosis, determined by visual ratings and chlorophyll content, was associated with high CaCO3(s) and mobile ion (i.e. Mg2+, Na+, Cl‐) accumulations at the edge of the depressional area. High soil solution Mg2+ (≈10 mM) and high plant Mg (1.5%) were consistently associated with low chlorophyll content, suggesting a possible causative relationship in reducing Fe2+ uptake. High Mg/Ca ratios (?1.8) in chlorotic areas were related to the over‐saturation of the soil solutions with respect to calcite. High HCO‐ 3 activities (8 ?M) correlated with chlorosis for one transect, bu...

The rate of precipitation of calcite is an important geochemical process which can influence the saturation state of natural waters with respect to pure calcite. The present study was established to determine the influence of water-soluble soil organic ligands on the rate of calcite precipitation. A reproducible seeded growth method was used to measure the rate constant for calcite precipitation at pH = 8.4 and 25°C, in the presence of varying amounts of total soluble organic carbon (CTS) added as a water-soil extract (WSE) or Seward fulvic acid (FA). The rate equation which described the rate of calcite precipitation in the present experiments was: where R = rate of calcite precipitation (mol Ls), kf = precipitation rate constant (L molms), s = surface area of calcite seeds (mL), = divalent ion activity coefficient, brackets represent concentrations (mol L), and Ksp is the solubility of pure calcite at 25°C. Rate constants decreased to zero in the presence of 0.15 mM and 0.028 mM CTS added as the WSE and FA, respectively. The organic C surface coverage on the calcite seeds corresponding to complete inhibition of calcite precipitation was 90 and 30 atoms C nm 2 for the WSE and FA, respectively. The efficacy of inhibition of calcite precipitation in the presence of soluble soil organic matter explains why many natural waters, including soil solutions of Calciaquolls, are oversaturated with respect to pure calcite. Soluble polymeric carbon constituents which adsorb onto potential calcite seeds, render these surfaces inactive as sites for crystal growth. Additional Index Words: calcium carbonate, crystal growth, fulvic acid, calcite supersaturation. View complete article To view this complete article, insert Disc 4 then click button8

The bicarbonate ion has been implicated as a causative agent in iron chlorosis induced by high moisture in calcareous soils. Our studies have demonstrated a correlation between soil solution bicarbonate and chlorosis in soybeans in fields in western Minnesota and under growth chamber conditions. In the growth chamber studies, we found that the severity of chlorosis increases with increasing soil moisture to near the saturated water content. At high moisture, soil pores were filled with water and the partial pressure of CO2 in the soil air increased. Since the soil pH is strongly buffered by the high cation exchange capacity of the soils, soil pH remained constant and [HCO‐ 3] increased. In a system in which CaC03 is in equilibrium with the solution phase, the [HCO‐ 3] should be controlled by CaCO3 solubility. In soils, however, the soil solutions were as much as 20‐fold over‐saturated with respect to CaCO3 solubility and [HCO‐ 3] was much greater than predicted by solubility calculations.

A simple semiempirical model for the prediction of changes in soil pH and base saturation with acidic deposition was developed. In steady-state ecosystems acidic deposition results in losses of basic cations from exchange sites. In the model, depletion of exchangeable bases is calculated from the difference between input acidity and output of H/sup +/ and Al/sup 3 +/ in water percolating through the solum. A correction for the decrease in bicarbonate weathering is made but sulfate adsorption is not considered. Estimates including the effect of increased mineral weathering with decreased pH can be made if the natural weathering rate is known and if the order with respect to H/sup +/ is known for the rate expression for soil weathering. The model predicted laboratory data for the acidification of samples for three soil horizons. For a fourth horizon, that was formed in contact with bedrock and high in weatherable minerals, the model overestimated the effect of the acid. Model predictions using soil data showed a slow decrease in soil pH and base saturation until the pH region of Al buffering was attained and then a new steady-state was achieved. The pH and base saturation in the Al buffering region was similarmore » to that found in very acid soils under forest vegetation.« less