Evaluation of Jordanian zeolite tuff as a controlled slow-release fertilizer for NH4 +

 The exchange and release properties of the natural phillipsite tuff from the Aritain area in Jordan were evaluated by studying the exchange properties of this natural zeolite in the NH₄ ⁺–Na⁺ system. Exchange isotherms at 18, 35, and 50  °C showed that phillipsite exchanged NH₄ ⁺ preferably over Na⁺ at all temperatures. However, the selectivity coefficient for NH₄ ⁺ decreased with decreasing temperature. The release of NH₄ ⁺ from phillipsite saturated with ammonium sulfate took place in two stages characterized by different SO₄ ^2– : NH₄ ⁺ ratios. Aritain phillipsite from NE Jordan could be processed and used as NH₄ ⁺ slow-release fertilizers. The use of NH₄ ⁺-phillipsite tuff offers an option to the widely used soluble NH₄-fertilizers in agciculture to avoid environmental problems associated with nitrogen contamination of surface water and groundwater. Received: 19 December 1996 · Accepted: 13 May 1997     

Experimental study of igneous and sedimentary apatite dissolution: Control of pH, distance from equilibrium, and temperature on dissolution rates

Apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of pH, temperature, solution saturation state, and on non-carbonated and carbonated apatite compositions: igneous fluorapatite (FAP) and sedimentary carbonate fluorapatite (CFA), respectively. From 2 <pH <6, the rate of release from dissolution of all apatite components [calcium (Ca), phosphorus (P), and fluoride (F)] increased with decreasing pH for FAP. From 6 < pH < 8.5, the FAP dissolution rate is pH independent. Measuring apatite dissolution rates at pH > 8.5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of FAP. For the CFA compositions studied, the dissolution rate decreased with increasing pH from 4 < pH < 7. During early stages of the dissolution reaction for both FAP and CFA, mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P and Ca:F being greater than mineral stoichiometric ratios, suggesting that Ca was preferentially released compared to P and F from the mineral structure during the early stages of dissolution. An increase in reacted solution pH accompanies this early elevated release of Ca. As the dissolution reaction proceeded to steady state, dissolution became congruent. When normalized to BET measured surface area, FAP dissolved faster from 4 < pH < 7 compared to CFA. The apparent Arrhenius activation energy (E_a) of FAP dissolution over the temperature range of 25-55°C at pH = 3.0, I = 0.1, and pCO₂ = 0 is 8.3 ± 0.2 kcal mol⁻¹. Both the apparent exchange of solution H⁺ for solid-bound Ca at low pH in the early stage of dissolution and the E_a of dissolution suggest a surface and not a diffusion controlled dissolution reaction for FAP and CFA. The degree of undersaturation of the solution, ΔG_R, with respect to FAP was important in determining the dissolution rate. At pH = 3.0, I = 0.1, and pCO₂ = 0, the dissolution rate of FAP was ∼ 5× greater in the far-from-equilibrium region compared to the near-equilibrium slope region.A simple apatite weathering model incorporating the experimental results from this study was constructed, and numerical calculations suggest that during the Phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the P weathering flux from apatite dissolution. It is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early- to mid-Paleozoic resulted in elevated P weathering fluxes, which along with climatic evolutionary pressures of the Neoproterozoic, facilitated the radiation of multicellular organisms, large-scale phosphorite deposition, and abundance of calcium phosphate shelled organisms during the early Cambrian.     

Nutrient transport in a riverine-influenced,tidal freshwater bayou in Louisiana

Transport of ammonium (NH₄ ⁺), nitrate + nitrite (NO₃ ^?), total Kjeldahl nitrogen (TKN), soluble reactive phosphate (SRP), and total suspended solids (TSS) was measured in a freshwater tidal bayou located in a marsh system near the mouth of the Atchafalaya River in Louisiana. Sampling was conducted six times over one year and was timed to assess effects of seasonal variation in river flow and mean sea level of the Gulf of Mexico on material fluxes. Net fluxes of all materials were large and ebb directed in all seasons except fall, when net transport was 2 to 3 orders-of-magnitude smaller than in any other season. These results demonstrate that riverine forcing was the primary influence on materials transport in all seasons except fall when tidal forcing was most important. The range of net fluxes (g s^?1) for each nutrient was as follows (a negative sign indicates a net export toward the Gulf): NO₃ ^?, ?0.006 to ?6.69; TKN, 0.09 to ?10.41; NH₄ ⁺, ?0.02 to ?1.36; SRP, ?0.001 to ?0.53; TSS, ?2 to ?81. Analysis of nutrient concentrations indicated the marsh/aquatic system removed NO₃ ^?, SRP, and TSS from the water column from late spring through early fall and released NH₄ ⁺ and TKN in summer. The results of this study show that net materials export per unit cross section channel area increased as riverine influence increased.     

Microbial dissolution of calcite at T = 28 °C and ambient pCO2

This study used batch reactors to quantify the mechanisms and rates of calcite dissolution in the presence and absence of a single heterotrophic bacterial species (Burkholderia fungorum). Experiments were conducted at T = 28°C and ambient pCO₂ over time periods spanning either 21 or 35 days. Bacteria were supplied with minimal growth media containing either glucose or lactate as a C source, NH₄⁺ as an N source, and H₂PO₄⁻ as a P source. Combining stoichiometric equations for microbial growth with an equilibrium mass-balance model of the H₂O-CO₂-CaCO₃ system demonstrates that B. fungorum affected calcite dissolution by modifying pH and alkalinity during utilization of ionic N and C species. Uptake of NH₄⁺ decreased pH and alkalinity, whereas utilization of lactate, a negatively charged organic anion, increased pH and alkalinity. Calcite in biotic glucose-bearing reactors dissolved by simultaneous reaction with H₂CO₃ generated by dissolution of atmospheric CO₂ (H₂CO₃ + CaCO₃ → Ca²⁺ + 2HCO₃⁻) and H⁺ released during NH₄⁺ uptake (H⁺ + CaCO₃ → Ca²⁺ + HCO₃⁻). Reaction with H₂CO₃ and H⁺ supplied ∼45% and 55% of the total Ca²⁺ and ∼60% and 40% of the total HCO₃⁻, respectively. The net rate of microbial calcite dissolution in the presence of glucose and NH₄⁺ was ∼2-fold higher than that observed for abiotic control experiments where calcite dissolved only by reaction with H₂CO₃. In lactate bearing reactors, most H⁺ generated by NH₄⁺ uptake reacted with HCO₃⁻ produced by lactate oxidation to yield CO₂ and H₂O. Hence, calcite in biotic lactate-bearing reactors dissolved by reaction with H₂CO₃ at a net rate equivalent to that calculated for abiotic control experiments. This study suggests that conventional carbonate equilibria models can satisfactorily predict the bulk fluid chemistry resulting from microbe-calcite interactions, provided that the ionic forms and extent of utilization of N and C sources can be constrained. Because the solubility and dissolution rate of calcite inversely correlate with pH, heterotrophic microbial growth in the presence of nonionic organic matter and NH₄⁺ appears to have the greatest potential for enhancing calcite weathering relative to abiotic conditions.     

Quantifying Sediment Nitrogen Releases Associated with Estuarine Dredging

Experimental studies of sediment pore water NH₄ ⁺ chemistry, adsorbed NH₄ ⁺ concentrations, sediment?Cwater NH₄ ⁺ exchange and N₂?CN flux were carried out to quantify the mass of labile N that can be released during large-scale dredging activities. Pore water NH₄ ⁺ concentrations below 0.5-m sediment depth averaged 5 ± 2 mmol L^?1 with average adsorbed NH₄ ⁺ concentrations of 11 ??mol g^?1. Elevated NH₄ ⁺ concentrations found in rapidly accreting dredge channels are partly a result of the rapid advective burial of both reactive organic matter and pore water. Elutriate tests, a dilution of sediment with site water, yielded adsorbed NH₄ ⁺ concentrations very similar to those using the more typical KCl extraction. Intact deep sediment sections exposed to overlying water, used to simulate postdredging conditions, showed high initial fluxes of ammonium and no development of coupled nitrification?Cdenitrification under the cold incubation conditions. Despite high concentrations and effluxes of NH₄ ⁺ during dredging, the amount of NH₄ ⁺ release during dredging was <0.5% of northern Chesapeake Bay sediment fluxes. The likelihood of large environmental effects of nitrogen release during the dredging of navigational channels in the Chesapeake Bay is low.     

Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district,Andhra Pradesh,India

A survey on quality of groundwater was carried out for assessing the geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district, Andhra Pradesh, India, where the area is underlain by Peninsular Gneissic Complex. The results of the groundwater chemistry show a variation in pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^? and F^?. The chemical composition of groundwater is mainly characterized by Na⁺?HCO₃ ^? facies. Hydrogeochemical type transits from Na⁺–Cl^?–HCO₃ ^? to Na⁺–HCO₃ ^?–Cl^? along the flow path. Graphical and binary diagrams, correlation coefficients and saturation indices clearly explain that the chemical composition of groundwater is mainly controlled by geogenic processes (rock weathering, mineral dissolution, ion exchange and evaporation) and anthropogenic sources (irrigation return flow, wastewater, agrochemicals and constructional activities). The principal component (PC) analysis transforms the chemical variables into four PCs, which account for 87% of the total variance of the groundwater chemistry. The PC I has high positive loadings of pH, HCO₃ ^?, NO₃ ^?, K⁺, Mg²⁺ and F^?, attributing to mineral weathering and dissolution, and agrochemicals (nitrogen, phosphate and potash fertilizers). The PC II loadings are highly positive for Na⁺, TDS, Cl^? and F^?, representing the rock weathering, mineral dissolution, ion exchange, evaporation, irrigation return flow and phosphate fertilizers. The PC III shows high loading of Ca²⁺, which is caused by mineral weathering and dissolution, and constructional activities. The PC IV has high positive loading of Mg²⁺ and SO₄ ^2?, measuring the mineral weathering and dissolution, and soil amendments. The spatial distribution of PC scores explains that the geogenic processes are the primary contributors and man-made activities are the secondary factors responsible for modifications of groundwater chemistry. Further, geochemical modeling of groundwater also clearly confirms the water–rock interactions with respect to the phases of calcite, dolomite, fluorite, halite, gypsum, K-feldspar, albite and CO₂, which are the prime factors controlling the chemistry of groundwater, while the rate of reaction and intensity are influenced by climate and anthropogenic activities. The study helps as baseline information to assess the sources of factors controlling the chemical composition of groundwater and also in enhancing the groundwater quality management.     

Quantification of Cl,Br and I in Geological Materials by NH4F Digestion: Comparison with Rapid Acid Digestion

The lack of analytical techniques for halogens in geological materials is mainly due to the loss of analytes during sample preparation. This study describes a rapid bulk rock digestion method (NH₄F digestion) for determination of the abundances of Cl, Br and I in geological materials by SF-ICP-MS. During high temperature (200–240 °C) digestion, NH₃ released from the decomposition of molten NH₄F can effectively prevent the loss of halogens released from geological samples. Chlorine, Br and I were not lost during NH₄F digestion at 220 °C for 0.25–6 h. The limits of quantitation for NH₄F digestion were 2.8, 0.018 and 0.003 μg g^-1 Cl, Br and I, respectively. Most results for halogens in geological reference materials by NH₄F digestion were in agreement with their certified values, confirming that the high-performance rapid bulk rock NH₄F digestion has sufficient digestion capability to extract Cl, Br and I from rocks, sediments and soils. In comparison, results obtained following acid digestion showed that HNO₃ + HF digestion could effectively extract Br and I from soil and sediment samples, and that HNO₃ acid digestion is only suitable to use for the determination of Br and I in soil samples.     

Isotopic Approach to Determining the Fate of Ammonium Regenerated from Sediments in a Eutrophic Sub-estuary of Waquoit Bay,MA

We measured fluxes of NH₄⁺ and NO₃⁻ and δ¹⁵N of NH₄⁺, sediment, and porewater NH₄⁺ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH₄⁺ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not differ along the estuary. The δ¹⁵N of regenerated NH₄⁺ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰. Based on differences between the δ¹⁵N of regenerated NH₄⁺ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after remineralization of NH₄⁺. Differences between the δ¹⁵N of regenerated NH₄⁺ and the δ¹⁵N of porewater NH₄⁺ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH₄⁺ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification, NH₄⁺ flux released 1.4 mol N m⁻² year⁻¹ to the water column and could provide 42% of phytoplankton nitrogen requirements.     

Sources and processes governing rainwater chemistry in New Delhi,India

Rainwater plays an important role in scavenging of aerosols and gases from atmosphere, and its chemistry helps to understand the relative contributions of atmospheric pollution sources. The present work is aimed to understand and explain the sources, seasonal patterns and the processes thereof affecting rainwater chemistry in an urban environment of Delhi, India. Rainwater samples (n = 111) collected throughout the year in New Delhi showed alkalinity in general. Eight rainwater samples, collected in late monsoon and winter season, had pH less than 5.6 indicating that Delhi continues to face the prospects of acid rain despite the introduction of compressed natural gas as the clean fuel in city transport. Organic acids could be the possible contributors of acidity in rainwater samples having the fractional acidity (FA) value of 0.174, which is greater than the annual average FA (0.011) and the (Ca²⁺ + Mg²⁺ + NH₄ ⁺)/(SO₄ ^2? + NO₃ ^?) ration of more than one. Average acid neutralization factors of cations decrease in the order Ca²⁺ (1.01) > NH₄ ⁺ (0.77) > Mg²⁺ (0.10). However, neutralization by Ca²⁺ dominates only in summer season as cation-rich dust is transported from the Great Indian Thar Desert to this region by strong summer S–SW winds, while NH₄ ⁺ dominates in rainwater of other three sampling seasons. Identified dominant sources for soluble ions in rainwater are (1) non-silicate crustal source for carbonates and sulfates of Ca and Mg, (2) emissions from catalytic convertor-fitted vehicles and agriculture fields for NH₃ and (3) mixed anthropogenic sources for SO₄ ^2?, NO₃ ^? and Cl^?. Rainwater chemistry showed significant seasonal variations. This could be due to the changes in relative proportions of natural and anthropogenic sources of soluble ions to rainwater. Dominance of anthropogenic sources over crustal sources can result in acidic rains, which can adversely affect the environment and human health in this region.     

Characterization of elemental release during microbe-granite interactions at T = 28 °C

This study used batch reactors to characterize the mechanisms and rates of elemental release (Al, Ca, K, Mg, Na, F, Fe, P, Sr, and Si) during interaction of a single bacterial species (Burkholderia fungorum) with granite at T = 28 °C for 35 days. The objective was to evaluate how actively metabolizing heterotrophic bacteria might influence granite weathering on the continents. We supplied glucose as a C source, either NH₄ or NO₃ as N sources, and either dissolved PO₄ or trace apatite in granite as P sources. Cell growth occurred under all experimental conditions. However, solution pH decreased from ∼7 to 4 in NH₄-bearing reactors, whereas pH remained near-neutral in NO₃-bearing reactors. Measurements of dissolved CO₂ and gluconate together with mass-balances for cell growth suggest that pH lowering in NH₄-bearing reactors resulted from gluconic acid release and H⁺ extrusion during NH₄ uptake. In NO₃-bearing reactors, B. fungormum likely produced gluconic acid and consumed H⁺ simultaneously during NO₃ utilization.Over the entire 35-day period, NH₄-bearing biotic reactors yielded the highest release rates for all elements considered. However, chemical analyses of biomass show that bacteria scavenged Na, P, and Sr during growth. Abiotic control reactors followed different reaction paths and experienced much lower elemental release rates compared to biotic reactors. Because release rates inversely correlate with pH, we conclude that proton-promoted dissolution was the dominant reaction mechanism. Solute speciation modeling indicates that formation of Al-F and Fe-F complexes in biotic reactors may have enhanced mineral solubilities and release rates by lowering Al and Fe activities. Mass-balances further reveal that Ca-bearing trace phases (calcite, fluorite, and fluorapatite) provided most of the dissolved Ca, whereas more abundant phases (plagioclase) contributed negligible amounts. Our findings imply that during the incipient stages of granite weathering, heterotrophic bacteria utilizing glucose and NH₄ only moderately elevate silicate weathering reactions that consume atmospheric CO₂. However, by enhancing the dissolution of non-silicate, Ca-bearing trace minerals, they could contribute to high Ca/Na ratios commonly observed in granitic watersheds.     

The abundance of ammonium in the granites of central Spain,and the behaviour of the ammonium ion during anatexis and fractional crystallization

Summary The granites of the Sistema Central Espanol are richer in ammonium than those of most other regions, and have a mean NH₄ ⁺ content of 84 ppm (range = 1–243 ppm). Among the possible causes for the high level of ammonium, a high proportion of organic-rich pelitic protolith and reducing conditions during anatexis are considered to be the most significant. The behaviour of the ammonium ion during magmatic differentiation is discussed by reference to its distribution in the Pedrobernardo layered intrusion: ammonium is depleted in the final liquid fraction, but there is no relative fractionation of NH₄ ⁺ and K⁺. The depletion of the melt in NH₄ ⁺ during crystallization is attributed to its removal by biotite and to a lesser extent by K-feldspar. The behaviour of the ammonium ion during anatexis is discussed with reference to the Peña Negra migmatite complex. It is shown that large amounts of NH₄ ⁺ are present in these high grade metamorphic rocks, and that NH₄ ⁺ is preferentially partitioned into the restite fraction during partial melting. These relationships are attributed to the preferential incorporation of NH₄ ⁺ into potassic host minerals in the order: biotite > muscovite > K-feldspar.

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Ammonium in Zentralspanischen Graniten, und das Verhalten des Ammonium-Ions während Anatexis und fraktionierter Kristallisation

Zusammenfassung Die Granite des Sistema Central Espanol sind reicher an Ammonium als die der meisten anderen Regionen, und haben einen durchschnittlichen NH₄ ⁺ Gehalt von 84 ppm (von 1-243 ppm). Der hohe Ammoniumgehalt könme auf einen hohen Anteil peiitischer Ausgangsgesteine, die reich an organischen Material sind, and auf reduzierende Bedingungen während der Anatexis zurückgehen. Das Verhalten des Ammonium-Ions während magmatischer Differentiation wind in Hinblick seiner Verteilung in der geschichteten Intrusion von Pedrobernardo diskutiert: Ammonium ist in der finalen Schmelzfraktion angereichert, aber es gibt keine relative Fraktionierung von NH₄ ⁺ and K⁺. Die Verarmung der Schmelze an NH₄ ⁺ wahrend der Kristallisation geht darauf zurück, daß NH₄ ⁺ von Biotit and in einem geringen Ausmaß von K-Feldspat aufgenommen wird. Das Verhalten des Ammonium-Ions während der Anatexis wird am Peña Negra Migmatit-Komplex diskutiert. Es zeigt rich, daß große Mengen von NH₄ ⁺ in diesen hochgradig metamorphen Gesteinen vorkommen, and das NH₄ ⁺ während teilweiser Aufschmelzung vorzugsweise in der Restit-Fraktion angereichert wird. Diese Beziehungen gehen auf die vorzugsweise Aufnahme von NH₄ ⁺ in Kali-führenden Gastmineralen zurück, and zwar in folgender Ordnung: Biotit > Muskovit > K-Feldspat.

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With 5 Figures     

Controls on the chemical composition of groundwater from alluvial aquifers in the Wanaka and Wakatipu basins, Central Otago, New Zealand

 Groundwater in alluvial aquifers of the Wakatipu and Wanaka basins, Central Otago, New Zealand, has a composition expressed in equivalent units of Ca²⁺≫Mg²⁺≅Na⁺>K⁺ for cations, and HCO₃ ^–≫SO₄ ^2->NO₃ ^–≅Cl^– for anions. Ca²⁺ and HCO₃ ^– occur on a 1 : 1 equivalent basis and account for >80% of the ions in solution. However, some groundwater has increased proportions of Na⁺ and SO₄ ^2-, reflecting a different source for this water. The rock material of the alluvial aquifers of both basins is derived from the erosion and weathering of metamorphic Otago Schist (grey and green schists). Calcite is an accessory mineral in both the grey and green schists at <5% of the rock. Geological mapping of both basins indicates that dissolution of calcite from the schist is the only likely mechanism for producing groundwater with such a constant composition dominated by Ca²⁺ and HCO₃ ^– on a 1 : 1 equivalent basis. Groundwater with higher proportions of Na⁺ and SO₄ ^2- occurs near areas where the schist crops out at the surface, and this groundwater represents deeper and possibly older water derived from basement fluids. Anomalously high K⁺ in the Wakatipu basin and high NO₃ ^– concentrations in the Wanaka basin cannot be accounted for by interaction with basement lithologies, and these concentrations probably represent the influence of anthropogenic sources on groundwater composition. Received, June 1996 Revised, March 1997, July 1997 Accepted, July 1997     

Identifying the Sources of Solutes in Karst Groundwater in Chongqing,China: a Combined Sulfate and Strontium Isotope Approach

Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. In this paper, thirty?five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca?HCO3 type or Ca (Mg)?HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca?SO4 type (G25 site) or Ca?HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The δ34S?SO42? fell into a range of ?6.8‰?21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sul?de mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sul?de mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.     

Distribution and isotope composition of nitrogen in Bay of Quinte (Lake Ontario) sediments

The concentrations and isotopic compositions of the various forms of nitrogen in silty clay sediments from the Bay of Quinte (Lake Ontario) have been determined. The total organic-N content is high throughout the sediment profiles and generally decreases with depth. On the contrary, exchangeable NH⁺₄-N concentration is quite low and tends to increase with depth in two out of three sediment cores examined. The concentration of non-exchangeable NH⁺₄-N and the 6 N HCl hydrolyzable NH⁺₄-N are relatively constant with depth. Among the N fractions analyzed, the exchangeable NH⁺₄-is most enriched in ¹⁵N. In most cases, the δ ¹⁵ N values of the N fractions remain relatively constant with sediment depth. There is no apparent correlation of δ ¹⁵ N values with the N concentration for any of the individual N fractions. The observed ranges in the δ ¹⁵ N values are: exchangeable NH⁺₄, + 5–+10‰; 6 N HCl hydrolyzable total N and 6 N HCl hydrolyzable NH⁺₄-N, + 3.5–+5.5‰.     

Deep groundwater in the crystalline basement of the Black Forest region

Two major types of groundwater can be readily distinguished in the Variscian crystalline basement of the Black Forest in S–W Germany. Saline thermal water utilized in spas has its origin in 3–4 km deep reservoirs and developed its composition by 3 component mixing of surface freshwater, saltwater (of ultimately marine origin) and a water–rock reaction component. In contrast to the thermal water, CO₂-rich mineral water, tapped and bottled from many wells in the Black Forest, has low salinities but a TDS distribution similar to that of thermal water. It developed its chemical composition entirely by reaction of CO₂-rich water with the gneissic or granitic aquifer rock matrix. Particularly important is the contribution of various plagioclase dissolution and weathering reactions that may, at some locations, involve precipitation and dissolution of secondary calcite. Sodium/Ca ratios of water and of rock forming plagioclase in the basement rocks suggests that plagioclase weathering is strongly incongruent. Calcium is released to the water, whereas Na remains fixed to the albite feldspar component.The major element composition of 192 water samples used in this study also indicates a clear vertical stratification of the type of water chemistry; Ca–HCO₃ near the surface, Na–Ca–HCO₃–SO₄ at intermediate depth and Na–Ca–Cl at great depth.The mean permeability of Black Forest granite is about K=10⁻⁶ m/s; it is significantly lower in gneisses (gneiss: mean K=5×10⁻⁸ m/s) leading to focused flow through granite. Highly permeable fracture and fault zones, particularly in granite, are utilized by high-TDS saline deep groundwater as ascent channels and flow paths. Although spatially closely associated, the topography driven upwelling system of saline deep water and the near-surface flow system of CO₂-rich mineral waters are hydraulically and chemically unconnected.     

The effect of medium chemistry on the solubility and morphology of brushite crystals

An experimental study of the particulars of the solubility and crystallization of brushite Ca(HPO₄) · 2H₂O from aqueous solution in conditions of a variable pH (6.0–3.0) and the contents of impurity ions (K⁺, Na⁺, NH ₄ ⁺ , Mg²⁺, SO ₄ ^2? , CO ₃ ^2? ) has been conducted. It is established that brushite solubility markedly rises with a decrease in pH from 6 to 3 and slightly rises with an increase in Mg²⁺ and SO ₄ ^2? concentrations. The enrichment in K⁺, Na⁺, and NH ₄ ⁺ does not affect brushite solubility. The changeable chemistry of the medium results in variation of the synthetic crystal habit, from rhombic tabular to thickened prismatic crystals.     

Reversible ion-exchange fixation of cesium-137 leading to mobilization from reservoir sediments

The radioactive fission product, ¹³⁷Cs, has been observed to mobilize from bottom sediments of two South Carolina reservoirs during summer thermal stratification and hypolimnetic anoxia. Mobilization is attributed to ion-exchange displacement of ¹³⁷Cs from sediments by cations such as NH⁺₄, Fe⁺² and Mn⁺² released under anaerobic conditions.Three types of ¹³⁷Cs binding sites to sediment clay minerals are identified: 1) surface and planar sites from which ¹³⁷Cs is generally exchangeable by all cations studied (Na⁺, NH⁺₄, H⁺, Cs⁺, Ca⁺², Mg⁺², Fe⁺², and Mn⁺²); 2) wedge sites where ¹³⁷Cs exchange is sterically limited to cations of similar size and charge (NH⁺₄, Cs⁺, K⁺, and perhaps H₃O⁺); 3) interlayer sites from which ¹³⁷Cs is not readily exchanged. More than 15 years after final ¹³⁷Cs inputs, the reservoir sediments we studied showed the following percentage distribution of sites: 2 to 9% surface sites, 6 to 13% wedge sites, and 78 to 85% interlayer sites. In contrast, lake and stream sediments near Oak Ridge, Tennessee receiving ¹³⁷Cs inputs more than 20 years earlier had greater than 99% of their ¹³⁷Cs associated with non-exchangeable interlayer sites. The difference is attributed to the paucity in the South Carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites. Such interlayer deficient clays are dominant in the Atlantic and Gulf coastal plains of the United States and elsewhere. This suggests that ¹³⁷Cs will be physically and chemically more mobile in such areas as well as more biologically available. Mobility will be enhanced in regimes where cation inputs favoring ¹³⁷Cs exchange occur. Subsurface waste disposal sites where anaerobic conditions develop with NH⁺₄ production and Fe⁺² and Mn⁺² release might be such a regime.     

Assessment of hydrogeochemistry and contamination of Varamin deep aquifer,Tehran Province,Iran

The present study investigates the hydrogeochemistry and contamination of Varamin deep aquifer located in the southeast of Tehran province, Iran. The study also evaluates groundwater suitability for irrigation uses. The hydrogeochemical study was conducted by collecting and analyzing 154 groundwater samples seasonally during 2014. Based on evolutionary sequence of Chebotarev, the aquifer is in the stage of SO₄ + HCO₃ in the north half of the plain and it has evolved into SO₄ + Cl in the south half. The unusual increase in TDS and Cl^? toward the western boundaries of the aquifer indicates some anomalies. These anomalies have originated from discharge of untreated wastewater of Tehran city in these areas. The studied aquifer contains four dominant groundwater types including Na–Ca–SO₄ (55%), Na–Ca–HCO₃ (22%), Na–Cl (13%) and Ca–Cl (10%). The spatial distributions of Na–Cl and Ca–Cl water types coincide with observed anomalies. Ionic relationships of SO₄ ^2? versus Cl^? and Na⁺ versus Cl^? confirm that water–rock interaction and anthropogenic contribution are main sources of these ions in the groundwater. The main processes governing the chemistry of the groundwater are the dissolution of calcite, dolomite and gypsum along the flow path, and direct ion exchange. Reverse ion exchange controls the groundwater chemistry in the areas contaminated with untreated wastewater. Based on Na% and SAR, 10.3 and 27% of water samples are unsuitable for irrigation purposes, respectively. Regarding residual sodium carbonate, there is no treat for crop yields. Only 6% of water samples represent magnesium adsorption ratios more than 50% which are harmful and unsuitable for irrigation.     

A comparative study on the dissolution and solubility of hydroxylapatite and fluorapatite at 25 °C and 45 °C

Dissolution of the synthetic hydroxylapatite (HAP) and fluorapatite (FAP) in pure water was studied at 25 °C and 45 °C in a series of batch experiments. The XRD, FT-IR and SEM analyses indicated that the synthetic, microcrystalline HAP and FAP with apatite structure used in the experiments were found to have no obvious variation after dissolution except that the existence of OH groups in FT-IR spectra for FAP after 2880 h dissolution was observed. During the HAP dissolution (0–4320 h), the aqueous calcium and phosphate concentrations reached the maxima after 120 h and then decreased slowly with time. For the FAP dissolution in pure water, after a transient time of 1440 h (< 60 d), element concentrations and pH became constant suggesting attainment of a steady-state between the solution and solid. During early stages of the FAP dissolution reaction (< 72–120 h), mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P, Ca:F and P:F being lower than mineral stoichiometric ratios of Ca₅(PO₄)₃F, i.e., 1.67, 5.0 and 3.0, respectively. This indicated that F were preferentially released compared to Ca from the mineral structure. The mean K_sp values were calculated by using PHREEQC for HAP of 10^− 53.28 (10^− 53.02–10^− 53.51) and for FAP of 10^− 55.71 (10^− 55.18–10^− 56.13) at 25 °C, the free energies of formation ΔG_f^o[HAP] and ΔG_f^o[FAP] were calculated to be − 6282.82 kJ/mol and − 6415.87 kJ/mol, respectively.