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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 (

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.

Methylmercury cation (CH3Hg+) is known to have a strong affinity for organic matter in soil, sedimentary, and aquatic environments. The objective of this study is to determine the dominant ligands binding CH3Hg+ in humic acids by evaluating several CH3Hg+-ligand complexation models, using mercury LIII-edge extended X-ray absorption fine structure (EXAFS). The model CH3Hg+ binding ligands examined in this study include thiol (-SH), hydrogen polysulfide (-SSH or -SSSH), sulfide (-S-), disulfide (-SS-), carboxyl (-COOH), and amine (-NH2). Based on the atomic geometry around mercury in each model structure, we distinguished CH3Hg+-binding ligands in two different humic acids (soil and aquatic). We observed CH3Hg+ preferentially binds to thiol ligands. After saturating reactive thiol ligands, the majority of CH3Hg+ binds to carboxyl ligands rather than to amine or other reduced sulfur ligands than thiol. We found no evidence of significant CH3Hg+-sulfide/disulfide or CH3Hg+-hydrogen polysulfide complexes in any samples. When CH3Hg+ binds to a humic ligand, the C-Hg bond in CH3Hg+ remains intact. Some heavy atoms are proximately coordinated around the mercury atom in the sample containing the highest CH3Hg+ levels used in this study.

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.

Analysis of Hg(II) complexed by a soil humic acid (HA) using synchrotron-based X-ray absorption spectroscopy (XAS) revealed the importance of reduces sulfur functional groups (thiol (R-SH) and disulfide (R-SS-R)/disulfane (R-SSH)) in humic substances in the complexation of Hg(II). A two-coordinate binding environment with one oxygen atom and one sulfur atom at distances of 2.02 and 2.38 {angstrom}, respectively, was found in the first coordination shell of Hg(II) complexed by humic acid. Model calculations show that a second coordination sphere could contain one carbon atom and a second sulfur atom at 2.78 and 2.93 {angstrom}, respectively. This suggests that in addition to thiol S, disulfide/disulfane S may be involved with the complexation of Hg(II) in soil organic matter. The appearance of carbon atom in the second coordination shell suggests that one O-containing ligand such as carboxyl and phenol ligands rather than H{sub 2}O molecule is bound to the Hg(II). The involvement of oxygen ligand in addition to the reduced S ligands in the complexation of Hg(II) is due to the low density of reduced S ligands in humic substances. The XAS results from this experiment provided direct molecular level evidence for the preference of reduced S functional groups over oxygen ligandsmore » by Hg(II) in the complexation with humic substances.« less

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.

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.

A competitive-ligand, equilibrium-dialysis technique using bromide measured methylmercury (MeHg(+)) binding to Suwannee River fulvic acid (SRFA) and NOM from a lake and a bog in Minnesota. Distribution coefficients (K(OC)) and stability constants (K') varied only slightly over a range of [Br(-)] and ratios of MeHg(+) to reduced sulfur, S(re), the putative NOM binding site. For SRFA at pH 3.0, K(OC) ranged from 10(7.7) to 10(8.2) and K' ranged from 10(15.5) to 10(16.0) over MeHg(+):S(re) ratios from 1:1220 to 1:12 200 (well below S(re) saturation). The importance of pH depends on the calculation model for binding constants. Over pH 2.98-7.62, K(OC) had little pH dependence (slope = 0.2; r(2) = 0.4; range 10(7.7)-10(9.1)), but K' calculated using thiol ligands with pK(a) = 9.96 had an inverse relationship (slope = -0.8; r(2) = 0.9; range 10(15.6)-10(12.3)). A pH-independent model was obtained only with thiol pK(a) < or = approximately 4. The mean K'(4) for SRFA (K' with thiol pK(a) = 4.2) was 10(9.8) (range 10(9.11)-10(10.27)) and small slope (0.02). Similar values were found for Spring Lake NOM; bog S2 NOM had values one-tenth as large. These constants are generally similar to published values; differences reflect variations in methods, pH, types of NOM, and calculation models.

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

Aluminium is a pH-sensitive element that can cause acute toxicity symptoms in some organisms at aqueous activities of 10 µM or less1–3. Scientists working on agricultural systems have long been concerned with the deleterious effects of aluminium on crop roots4,5. More recently, environmental scientists have reported a potentially harmful biogeochemical link between acidic deposition onto forest soils and aluminium toxicity in forest and aquatic communities of northeastern North America and northern Europe6–8. Because of this general interest in aluminium toxicity as an environmental threat, there have been renewed efforts to model the chemistry and transport of aqueous aluminium in soils and surface waters. Here we propose that much of the spatial and temporal variability in aqueous aluminium chemistry can be accounted for by a two-component equilibrium model involving a solid-phase humic adsorbent and an aluminium trihydroxide mineral phase. Inputs for the model are solution pH, copper-extractable organic aluminium and the titratable carboxyl content of soil humus.

Honeylocust (Gleditsia triacanthos L.) seedlings were grown for 72 days in soil from a BC horizon of a Spodosol altered by adding four levels of AlCl3. Saturated paste extracts from controls to the highest AlCl3 treatment contained, respectively, 85 to 831 μM Al, 834 to 163 μM Ca and 316 to 35 μM Mg and had a pH of 4.4 to 4.0 Leaf, stem, and root concentrations of Al and P increased while those of Mg, Ca, and Zn decreased with increasing levels of Al. Growth decreased as Al, Al/Ca, and Al/Mg ratios in the extract increased. Growth was negatively related to tissue concentrations of Al, P, and Zn and positively related to tissue Mg and Ca. Growth was more closely correlated to elemental concentrations in the saturated paste extracts than in the SrCl2 extracts (1 part 0.01M SrCl2: 1 part moist soil).