Beschreibung:    Calcium concentration and calcite supersaturation (Ω) needed for calcium carbonate nucleation and crystal growth in Pyramid Lake (PL) surface water were determined during August of 1997, 2000, and 2001. PL surface water has Ω values of 10–16. Notwithstanding high Ω, calcium carbonate growth did not occur on aragonite single crystals suspended PL surface water for several months. However, calcium solution addition to PL surface-water samples caused reproducible calcium carbonate mineral nucleation and crystal growth. Mean PL surface-water calcium concentration at nucleation was 2.33 mM ( n  = 10), a value about nine times higher than the ambient PL surface-water calcium concentration (0.26 mM); mean Ω at nucleation (109 with a standard deviation of 8) is about eight times the PL surface-water Ω. Calcium concentration and Ω regulated the calcium carbonate formation in PL nucleation experiments and surface water. Unfiltered samples nucleated at lower Ω than filtered samples. Calcium concentration and Ω at nucleation for experiments in the presence of added particles were within one standard deviation of the mean for all samples. Calcium carbonate formation rates followed a simple rate expression of the form, rate (mM/min) =  A (Ω) +  B . The best fit rate equation “Rate (Δ mM/Δ min) = −0.0026 Ω + 0.0175 ( r  = 0.904, n  = 10)” was statistically significant at greater than the 0.01 confidence level and gives, after rearrangement, Ω at zero rate of 6.7. Nucleation in PL surface water and morphology of calcium carbonate particles formed in PL nucleation experiments and in PL surface-water samples suggest crystal growth inhibition by multiple substances present in PL surface water mediates PL calcium carbonate formation, but there is insufficient information to determine the chemical nature of all inhibitors. Content Type Journal Article Category Original Paper Pages 1-19 DOI 10.1007/s10498-011-9150-3 Authors Michael M. Reddy, US Geological Survey (USGS), National Research Program (NRP), Central Branch (CB), Denver Federal Center, P.O. Box 25046, MS 403, Lakewood, CO 80225, USA Anthony Hoch, US Geological Survey (USGS), National Research Program (NRP), Central Branch (CB), Denver Federal Center, P.O. Box 25046, MS 403, Lakewood, CO 80225, USA Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165

Beschreibung:    Between 1990 and 2007, twenty-nine box cores were recovered within the Arctic Ocean spanning shelf, slope and basin locations, and analyzed for aluminum (Al), manganese (Mn), other inorganic components and organic carbon (C Org ). Using these core data together with literature values, we have constructed budgets for Al and Mn in the Arctic Ocean. Most of the Al and Mn entering the Arctic comes from rivers or coastal erosion, and almost all of these two elements is trapped within the Arctic. Total Mn distributions in sediments reflect the recycling and loss of much of the Mn from shelf sediments with ultimate burial over the slopes and in basins. Mn enrichments observed as bands in long cores from the basins appear to co-occur with inter-glacial periods. Our Mn budget suggests that change in sea level associated with the accumulation and melting of glaciers is a likely cause for the banding. The Arctic Ocean, which presently contains as much as 50% shelf area, loses most of that when global sea level falls by ~120 m during glacial maxima. With lower sea level, Mn input from rivers and coastal erosion declines, and inputs become stored in permafrost on the sub-aerial shelves or at the shelf margin. Sea-level rise re-establishes coastal erosion and large riverine inputs at the margin and initiates the remobilization of Mn stored on shelves by turning on algal productivity, which provides the C Org required to reduce sedimentary Mn oxyhydroxides. Content Type Journal Article Category Original Paper Pages 1-27 DOI 10.1007/s10498-011-9149-9 Authors Robie W. Macdonald, Department of Fisheries and Oceans, Institute of Ocean Sciences, PO Box 6000, Sidney, BC V8L 4B2, Canada Charles Gobeil, INRS-ETE, Université du Québec, 490 de la Couronne, Quebec, QC G1K 9A9, Canada Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165

Beschreibung:    Volcanic islands, being characterized by highly porous basaltic/andesitic lava flows and pyroclastic deposits, are subject to important chemical weathering by subsurface waters. Moreover, such subsurface weathering is impacted by hydrothermal springs in both active and non-active volcanic areas, thus increasing dissolved load concentrations. Here, we focus on the subsurface water chemistry in the volcanic islands of the Lesser Antilles and Réunion and on the origin of these subsurface flows. We are able, through the use of various isotopic tools (C, Sr, U–Th), to identify hydrothermal influences in river water. For example, Li concentrations show a positive correlation with temperature of hot and cold springs and also a relationship with δ 13 C; from this, we can show that several sources of hydrothermal activity influence the rivers of the Lesser Antilles and that some rivers also reveal an important organic influence. As much as 20% of the subsurface hydrothermal springs go to feed the rivers. The increasing temperatures result in more dissolved elements being mobilized and an increase in chemical weathering rates. In addition, using the ( 230 Th/ 238 U) isochron for the well and river dissolved loads in Martinique, Guadeloupe and Réunion, we can evaluate residence times in the river water, i.e. the average residence time in the water along the circulation path to the sampling point. Alteration takes longer when the water circulates through thick soil, for example, 400–5,000 years when circulating under an ash profile and 1,200–15,000 years when circulating through a collapse zone. It would appear that waters circulation is globally three times longer for subsurface water than for surficial water. The weathering regime in tropical volcanic environments seems to be controlled mainly by such subsurface circulation with high chemical concentration from hydrothermal inputs. The origin of these compositions is varied and not controlled by a single hydrothermal spring. Consequently, it is subsurface circulation that determines the weathering regime in tropical volcanic islands with the main controlling parameters being temperature and residence time. Content Type Journal Article Category Original Paper Pages 221-241 DOI 10.1007/s10498-011-9122-7 Authors Sétareh Rad, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, 75238 Paris Cedex 05, France Karine Rivé, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, 75238 Paris Cedex 05, France Claude Jean Allègre, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, 75238 Paris Cedex 05, France Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 3

Beschreibung:    Lake Kitagata, Uganda, is a hypersaline crater lake with Na–SO 4 –Cl–HCO 3 –CO 3 chemistry, high pH and relatively small amounts of SiO 2 . EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001 ), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments. Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi 7 O 13 (OH) 3 ·3H 2 O], burkeite [Na 6 (CO 3 )(SO 4 ) 2 ]) and as diagenetic intrasediment growths (mirabilite (Na 2 SO 4 ·10H 2 O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The dominant inflow water, groundwater, plays a significant role in driving the chemical evolution of Lake Kitagata water and mineral precipitation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO 2 concentrations than exist today. Content Type Journal Article Category Original Paper Pages 129-140 DOI 10.1007/s10498-010-9108-x Authors Lichun Ma, Institute of Mineral Resources, Chinese Academy of Geological Sciences, 100037 Beijing, China Tim K. Lowenstein, Department of Geological Sciences, State University of New York, Binghamton, NY 13902, USA James M. Russell, Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912, USA Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 2

Beschreibung:    Recent improvements to experiments and modelling of batch dissolution in a turbulent reactor, based upon the shrinking object model, are extended to middle loadings of gypsum, that is, in the region between low and high loadings, which lead, respectively, to high under-saturation or saturation with a great excess of solid left undissolved. Dissolved calcium sulphate concentration was monitored by change in electrical conductivity. This investigation uses an improved, ion-pair model for CaSO 4 0 to allow for the presence of calcium or sulphate added as common ions. The study demonstrates that the full dissolution curve for 5.82 mM loadings of 106-μm particles of gypsum (~1.00 g L −1 ) in de-ionised water barely changed in the presence of either 4.64 or 8.09 mM calcium chloride, or 4.39 mM sodium sulphate. However, this masked a doubling of dissolution rate imposed by comparable increases in ionic strength from sodium chloride. The results are consistent with the ion pair, CaSO 4 0 , being the key species in the rate-determining step of the back-reaction, and perhaps all salt dissolutions, including calcium carbonate. In this case, the rate equation is as follows: \frac\text d c \text d t = \frac S V ·( k 1 - k 2 ¢ ·[\text CaSO 4 0 ]) , where k 1 and k 2 ′ are rate constants. The reported observations are interpreted as effects of ionic strength and common ion concentrations upon the formation equilibrium for the ion pair. This rate equation readily transforms mathematically to one involving the product of [Ca 2+ ] and [SO 4 2− ] in the back-reaction. The parallel of this with the well-known PWP equation used in calcium carbonate dissolution is discussed, with the CaHCO 3 + ion pair of the equation being replaced by that of CaCO 3 0 . Meanwhile, the earlier use of the product, [Ca 2+ ] ½  × [CO 3 2− ] ½ , in the back-reaction term of another dissolution rate equation for calcite is shown to be incorrect. Finally, it is argued that the shrinking object model should be repositioned as a logical derivative of the hydrodynamical approach to dissolution. Content Type Journal Article Category Original Paper Pages 141-164 DOI 10.1007/s10498-010-9112-1 Authors Victor W. Truesdale, School of Life Sciences, Oxford Brookes University, Gipsy Lane, Headington, Oxford, OX3 0BP UK Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 2

Beschreibung:    The sorption behavior and solid-phase associations of phosphorus (P) in fine-grained sediments (〈63 μm) from two upstream tributaries and one downstream main stem site of the Spoon River in west-central Illinois were characterized to better understand phosphorus bioavailability in this agriculturally dominated watershed. The P sorption affinities, as indicated by linear distribution coefficients ( K d ), of all sediments were 330–5,150 L/kg, and negatively correlated with equilibrium phosphorus concentration (EPC o ) values, which ranged between 0.2 and 2.2 μM. pH values measured at the conclusion of the sorption experiments varied only slightly (7.45–8.10) but were nonetheless strongly positively correlated to EPC o values, and negatively correlated to K d values, suggesting the importance of pH to the observed sorption behavior. K d values were generally lower and EPC o values higher at the main stem site than at the upstream tributary sites, suggesting dissolved reactive P (DRP) bioavailability (specifically orthophosphate) increased downstream. The solid phase associations of P were operationally assessed with the streamlined SEDEX (sedimentary extraction) procedure, and most sediment P (≥50%) was released during the step designed to determine iron oxide–associated P. On average, 70–90% of the total sediment P pool was potentially bioavailable, as estimated by the sum of the iron oxide-, authigenic carbonate-, and organic-associated P fractions. Considerable calcium was also extracted from some sediments during the step designed to specifically remove iron oxide–associated P. It is hypothesized that the severe drought conditions that persisted between April and October, 2005 allowed authigenic carbonates (perhaps partly amorphous) to accumulate, and that these carbonates dissolved during the iron oxide extraction step. The extensive benthic algal populations also present may have aided carbonate precipitation, which under more normal hydrologic conditions would be periodically flushed downstream and replaced by fresh sediment. This suggests antecedent hydrologic conditions played a dominant role in the P sorption and solid phase associations identified. Content Type Journal Article Category Original Paper Pages 639-662 DOI 10.1007/s10498-010-9103-2 Authors Michael L. Machesky, Institute of Natural Resource Sustainability, Illinois State Water Survey Division, University of Illinois, 2204 Griffith Drive, Champaign, IL 61820, USA Thomas R. Holm, Institute of Natural Resource Sustainability, Illinois State Water Survey Division, University of Illinois, 2204 Griffith Drive, Champaign, IL 61820, USA James A. Slowikowski, Institute of Natural Resource Sustainability, Illinois State Water Survey Division, University of Illinois, 2204 Griffith Drive, Champaign, IL 61820, USA Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 16 Journal Issue Volume 16, Number 4

Beschreibung:    Recent work has emphasized that the empirical rate equation for batch dissolution of a solid consists of a forward term involving the surface area minus a back reaction term involving surface area and concentration of dissolved solid. Integrated forms exist for use at extremes of high under-saturation and of very heavy solid loadings which lead to saturation. A middle condition allows for significant decrease in solid supply and simultaneous arrival at saturation. This study tests the three approaches simultaneously to the batch dissolution of gypsum, thereby demonstrating a consistent applicability of the afore-mentioned rate equation. Previously, some mineral dissolutions have displayed so-called nonlinear kinetics and hence have not appeared to conform to this rate equation. This paper provides a template for future investigation of those situations; dissolution experiments are not easy to perform, and instances of the so-called nonlinear kinetics may represent experimental artefact. The relationship between this empirical approach and that of Transition State Theory used in mineral dissolution is discussed, and a new, linear proof for the applicability of the ‘middle ground’ equations is demonstrated. Stirring experiments highlight the difference between the conditions in fluidized bed and laminar flow reactors. Gypsum dissolution is found to be transport limited at all but very vigorous laboratory stirring conditions, although the relationship between the rate of shrinkage of gypsum particles and stirring seems to be relatively simple. A stirring factor is applied to the rate equation overall to allow for differences in reactor design, and it is suggested that this should also be applicable to laminar flow reactors. The link between batch and chemo-stat dissolutions is stressed, together with a need to contour dissolution data on a new graph of particle size versus stirring rate. Content Type Journal Article Category Original Paper Pages 21-50 DOI 10.1007/s10498-010-9105-0 Authors Victor W. Truesdale, School of Life Sciences, Oxford Brookes University, Gipsy Lane, Headington, Oxford, OX3 0BP UK Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 1

Beschreibung:    The interacting effect of pH, phosphate and time on the release of arsenic (As) from As-rich river bed sediments was studied. Arsenic release edges and kinetic release experiments (pH range 3–10), in the absence and presence of phosphate, coupled with sequential extraction procedures, SEM/EDX analyses and geochemical calculations, were carried out to evaluate As remobilisation and to elucidate the mechanisms involved. The results showed that As release underwent pronounced kinetic effects, which were strongly influenced by pH and phosphate. Remobilisation of As after 24 h was low (between ~1 and 5%) and varied slightly with pH, whereas alkaline conditions generally promoted As remobilisation after 168 h, with up to 12–21% of total As released. The results showed that depending on the pH and sediment considered, the release of As increased dramatically after ~48–72 h, suggesting that different processes are involved at different reaction periods. The addition of phosphate (1 mM) increased both the amount of As released (between 2 and 8 times) and the rate of As release from the sediments within the entire pH range (3–10) and period (168 h) studied. Moreover, in some cases, it also affected the shape of the As release edges and kinetic profiles. The similarities in the release profiles and the positive correlations between As and some sediment components, especially Fe and Al hydroxides, and organic matter—which appears to play a key role at high pH—suggest that As release from the studied sediments may be associated with solid phase dissolution processes under both acid and alkaline pH, whereas desorption plays a key role in the short term and at natural pH conditions, especially in the presence of phosphate, which acts as an As-displacing ligand. Evaluation of As mobility based on short-time leaching experiments may seriously underestimate the mobilisation of As from sediments. Content Type Journal Article Category Original Paper Pages 281-306 DOI 10.1007/s10498-011-9135-2 Authors David A. Rubinos, Departamento de Edafoloxía e Química Agrícola, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Sur, 15782 Santiago de Compostela, Spain Luz Iglesias, Departamento de Edafoloxía e Química Agrícola, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Sur, 15782 Santiago de Compostela, Spain Francisco Díaz-Fierros, Departamento de Edafoloxía e Química Agrícola, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Sur, 15782 Santiago de Compostela, Spain María Teresa Barral, Departamento de Edafoloxía e Química Agrícola, Facultade de Farmacia, Universidade de Santiago de Compostela, Campus Sur, 15782 Santiago de Compostela, Spain Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 3

Beschreibung:    The effect of Mg-, Ca-, and Sr–Uranyl-Carbonato complexes with respect to sorption on quartz was studied by means of batch experiments with U(VI) concentration of 0.126 × 10 −6  M in the presence and absence of Mg, Ca, and Sr (each 1 mM) at pH from 6.5 to 9. In the absence of alkaline earth elements, 90% of the U(VI) sorbed on the quartz surface at all pH. In the presence of Mg, Ca, and Sr, the sorption of U(VI) on quartz decreased to 50, 10, and 30%, respectively. Sorption kinetics of U(VI) on quartz is faster in the absence of alkaline earth elements and reached equilibrium after 12 h, whereas in the presence of Mg, Ca and Sr, the kinetics of U(VI) sorption on quartz is pH dependent and attained equilibrium after 24 h. Aqueous speciation calculations for alkaline earth uranyl carbonates were carried out by using PHREEQC with the Nuclear Energy Agency thermodynamic database (NEA_2007) by adding constants for MUO 2 (CO 3 ) 3 2− and M 2 UO 2 (CO 3 ) 3 0 (M = Ca, Mg, Sr). This study reveals that alkaline earth elements can have a significant effect on the aqueous speciation of U(VI) under neutral to alkaline pH conditions and subsequently sorption behavior and mobility of U(VI) in aqueous environments. Content Type Journal Article Category Original Paper Pages 209-219 DOI 10.1007/s10498-011-9120-9 Authors Sreejesh Nair, Department of Hydrogeology, Technische Universität Bergakademie Freiberg, Gustav-Zeuner Str.12, 09599 Freiberg, Germany Broder J. Merkel, Department of Hydrogeology, Technische Universität Bergakademie Freiberg, Gustav-Zeuner Str.12, 09599 Freiberg, Germany Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 3

Beschreibung:    High resolution chemical data collected during summer 2003 indicate that the lower water mass (LWM) of the thermally stratified Lake Kinneret (LK) can be subdivided into three layers: a benthic boundary layer (BBL), overlain by the hypolimnion (HYP), and on top, the lower part of the metalimnion (ME-L). After onset of thermal stratification, the BBL is the first layer that turns anoxic, followed shortly afterward by the ME-L, while the HYP remains oxic and has relatively higher pH until later in summer. Thus, during the early summer, the HYP forms an oxygen-containing layer in-between two DO-deficient layers. Somewhat later, the HYP is characterized by still having significant levels of nitrate NO 3 , while in both adjacent layers nitrate is already removed through denitrification. The mechanisms controlling the gradual decline of dissolved oxygen (DO) in the HYP during the summer were studied. The seasonal mean lake-wide vertical eddy diffusion coefficient in this layer, evaluated from heat flux measurements, is approximately 4 × 10 −6  m 2  s −1 . The vertical oxygen flux due to diffusion from within the HYP toward its oxygen-deficient upper and lower boundaries accounts for most of the slow summer decline in DO in this layer. A smaller portion of this decline can be attributed to in-layer respiratory processes. The low turbidity, relatively high pH, and slow accumulation rate of NH 4 in the HYP support the notion that the slower mineralization processes occurring in this layer result from relatively low ambient concentrations of biodegradable organic matter, most probably due to the short residence time of the particles settling through this layer. Content Type Journal Article Category Original Paper Pages 195-207 DOI 10.1007/s10498-011-9119-2 Authors Ami Nishri, Kinneret Limnological Laboratory, IOLR, Haifa, Israel Alon Rimmer, Kinneret Limnological Laboratory, IOLR, Haifa, Israel Udi Wagner, Kinneret Limnological Laboratory, IOLR, Haifa, Israel Zvi Rosentraub, Physics Department, IOLR, Haifa, Israel Peter Yeates, Centre for Water Research, University of Western Australia, Perth, WA, Australia Journal Aquatic Geochemistry Online ISSN 1573-1421 Print ISSN 1380-6165 Journal Volume Volume 17 Journal Issue Volume 17, Number 3