Man-induced regime shifts in small estuaries—II: a comparison of rivers

This is Part II of two papers on man-induced regime shifts in small, narrow, and converging estuaries, with focus on the interaction between effective hydraulic drag, fine sediment import, and tidal amplification, induced by river engineering works, e.g., narrowing and deepening. Paper I describes a simple linear analytical model for the tidal movement in narrow, converging estuaries and a conceptual model on the response of tidal rivers to river engineering works. It is argued that such engineering works may set in motion a snowball effect bringing the river into an alternative steady state. Part II analyses the historic development in tidal range in four rivers, e.g., the Elbe, Ems, Loire, and Scheldt, all in northwest Europe; data are available for many decades, up to a century. We use the analytical model derived in Part I, showing that the effective hydraulic drag in the Ems and Loire has decreased considerably over time, as anticipated in Part I. We did not find evidence that the Upper Sea Scheldt is close to its tipping point towards hyperturbid conditions, but risks have been identified. In the Elbe, tidal reflections against the profound step in bed level around Hamburg seem to have affected the tidal evolution in the last decades. It is emphasized that the conceptual picture sketched in these papers is still hypothetical and needs to be validated, for instance through hind-cast modeling of the evolution of these rivers. This will not be an easy task, as historical data for a proper calibration of the models required are scarce.

     

The solubility of fluorite in hydrothermal solutions,an experimental study

The solubility of fluorite in NaCl solutions increases with increasing temperature at all ionic strengths up to about 100°C. Above this temperature, the solubility passes through a maximum and possibly a minimum with increasing temperature at NaCl concentrations of 1.0M or less, and increases continuously with increasing temperature at NaCl concentrations above 1.0M. At any given temperature, the solubility of fluorite increases with increasing salt concentration in NaCl, KCl and CaCl₂ solutions. The solubility follows Debye-Hückel theory for KCl solutions. In NaCl and CaCl₂ solutions, the solubility of fluorite increases more rapidly than predicted by Debye-Hückel theory: the excess solubility is due to the presence of NaF^c, CaF⁺, and possibly of Na₂F⁺. The solubility of fluorite in NaCl-CaCl₂ and in NaCl-CaCl₂-MgCl₂ solutions is controlled by the common ion effect and by the presence of NaF^c, CaF⁺, and MgF⁺. The solubility of fluorite in NaCl-HCl solutions increases rapidly with increasing initial HCl concentration; the large solubility increase is due to the presence of HF^c. It seems likely that complexes other than those identified in this study rarely play a major role in fluoride transport and fluorite deposition at temperatures below 300°C.     

Xxth International Congress of Photogrammetry and Remote Sensing

The XXth International Congress of Photogrammetry and Remote Sensing was held at the Istanbul Convention and Exhibition Centre (ICEC), Turkey, from 12th to 23rd July 2004. Reports are given on the Congress as a whole, including the General Assembly, some Technical Commission activities and the Congress Exhibition. Papers from the Congress are published in Volume XXXV of the International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences.     

Systematics of the isotopic composition of sulfur in the oceans during the Phanerozoic and its implications for atmospheric oxygen

Past treatments of the variation of δS³⁴ in marine evaporites have either assumed a steady-state ocean or have invoked rather simplified ocean input-output models. This paper derives more completely the relationships between the parameters that influence the time variation of δS³⁴ in ocean water and the relationship between δS³⁴ in ocean water and net gains and losses of atmospheric oxygen due to the operation of the sulfur cycle. The lower and mid-Paleozoic are shown to have been periods of net gain of atmospheric oxygen by the operation of the sulfur cycle; the upper Paleozoic, particularly the Permian, a period of oxygen loss. It is difficult to relate these oxygen gains and losses to variations in the oxygen content of the atmosphere, because the oxygen flux due to the operation of the carbon cycle is approximately twice as large as the flux due to the operation of the sulfur cycle. Data for the organic carbon and sulfide content of sedimentary rocks of the Russian Platform suggest that a decrease in sulfide from the Paleozoic to the Mesozoic and Cenozoic Era was roughly balanced by an increase in the proportion of organic carbon; however, such data are insufficient to define the abundance of atmospheric oxygen during the Phanerozoic. Biologic data and a better understanding of controls on atmospheric P_o2 are more likely to produce convincing evidence regarding variations of atmospheric oxygen in the past.     

Calculated greenschist facies mineral equilibria in the system CaO−FeO−MgO−Al2O3−SiO2−CO2−H2O

The kinetic problems associated with the experimental determination of reactions among complex solidsolution phases at low temperatures have hindered our understanding of the phase relations in greenschist facies rocks. In the absence of reliable experimental data, we have used the new, expanded internally-consistent thermodynamic dataset of Holland and Powell (1990), to present calculated phase equilibria for the system CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–CO₂ (CaFMASCH) with quartz in eccess, in the range 400°–500°C at low to intermediate pressures, involving the minerals amphibole, chlorite, anorthite, clinozoisite, dolomite, chloritoid, garnet, margarite, andalusite, and calcite. By solving independent sets of non-linear equations formed from equilibrium relationships, we calculate not only the loci of reactions in pressuretemperature-x(CO₂) space, but also the compositions of coexisting minerals in terms of the substitutions, FeMg_-1 and (Fe,Mg)SiAl_-1Al_-1. Invariant, univariant and divariant equilibria are calculated and discussed in relation to naturally-occurring greenschist facies metabasic and siliceous dolomitic mineral assemblages. We thus avoid the use of activity-corrected curves so commonly presented in the literature as a substitute for genuine univariant phase diagram boundaries.     

Quantifying inorganic sources of geochemical energy in hydrothermal ecosystems, Yellowstone National Park, USA

Combining analytical data from hot spring samples with thermodynamic calculations permits a quantitative assessment of the availability and ranking of various potential sources of inorganic chemical energy that may support microbial life in hydrothermal ecosystems. Yellowstone hot springs of diverse geochemical composition, ranging in pH from <2 to >9 were chosen for this study, and dozens of samples were collected during three field seasons. Field measurements of dissolved oxygen, nitrate, nitrite, total ammonia, total sulfide, alkalinity, and ferrous iron were combined with laboratory analyses of sulfate and other major ions from water samples, and carbon dioxide, hydrogen, methane, and carbon monoxide in gas samples to evaluate activity products for ∼300 coupled oxidation-reduction reactions. Comparison of activity products and independently calculated equilibrium constants leads to values of the chemical affinity for each of the reactions, which quantifies how far each reaction is from equilibrium. Affinities, in turn, show systematic behavior that is independent of temperature but can be correlated with pH of the hot springs as a proxy for the full spectrum of geochemical variability. Many affinities are slightly to somewhat dependent on pH, while others are dramatically influenced by changes in chemical composition. All reactions involving dissolved oxygen as the electron acceptor are potential energy sources in all hot spring samples collected, but the ranking of dominant electron donors changes from ferrous iron, and sulfur at high pH to carbon monoxide, hydrogen, and magnetite as pH decreases. There is a general trend of decreasing energy yields depending on electron acceptors that follows the sequence: O₂(aq) > NO₃⁻ ≈ NO₂⁻ ≈ S > pyrite ≈ SO₄⁻² ≈ CO(g) ≈ CO₂(g) at high pH, and O₂(aq) ≈ magnetite > hematite ≈ goethite > NO₃⁻ ≈ NO₂⁻ ≈ S ≈ pyrite ≈ SO₄⁻² at low pH. Many reactions that are favorable sources of chemical energy at one set of geochemical conditions fail to provide energy at other conditions, and vice versa. This results in energy profiles supplied by geochemical processes that provide fundamentally different foundations for chemotrophic microbial communities as composition changes.     

The mineralogy and the isotopic composition of sulfur in hydrothermal sulfide/sulfate deposits on the East Pacific Rise, 21°N latitude

The mineralogy of five groups of hydrothermal chimneys from the East Pacific Rise has been examined. Three of the chimneys, where the exit temperature of the hydrothermal fluids was close to 350°C, are rich in copper sulfides. Exit temperatures from the other two chimneys were less than 300°C; in these, the chimney walls are rich in zinc sulfide. The major sulfides in the chimneys as a whole were found to be wurtzite, chalcopyrite, pyrite, and cubanite. Anhydrite is always the dominant sulfate, and is present in all the deposits. Silicates are also present but in relatively minor amounts. There are considerable differences in the mineralogy of sulfides, sulfates, and silicates between the active and inactive vent deposits.The isotopic composition of sulfur in anhydrites from active vents is close to that of seawater; the δ³⁴S values of the sulfides range from +1.3 to +4.1‰. The isotopic composition of sulfur in the anhydrites is consistent with a derivation predominantly from seawater sulfate. The sulfur in the sulfides must have a complex origin including contributions from both sulfur in basalts and sulfide produced by reduction of sulfate in seawater. Mixing of H₂S-dominated hydrothermal fluids with cold seawater near the seafloor resulted in the precipitation of non-equilibrium assemblages of sulfides and sulfates.     

A model for the propagation of nonlinear surface waves over viscous muds

The effect of a thin viscous fluid–mud layer on nearshore nonlinear wave–wave interactions is studied using a parabolic frequency-domain nonlinear wave model, modified to incorporate a bottom dissipation mechanism based on a viscous boundary layer approach. The boundary-layer formulation allows for explicit calculation of the mud-induced wave damping rate. The model performed well in tests based on laboratory data. Numerical tests show that damping of high frequency waves occurs, mediated by “difference” nonlinear interactions. Simulations of 2-dimensional wave propagation over a mud “patch” of finite extent show that the wave dissipation causes significant downwave diffraction effects.