http://netedu.xauat.edu.cn/jpkc/netedu/jpkc2009/szylyybh/content/wlzy/1/Review%20of%20Arsenic%20in%20natural%20water%20-%20Smedly.pdf

A review of the source, behaviour and distribution of arsenic in natural waters

Interactions between organisms are a major determinant of the distribution and abundance of species. Ecology textbooks (e.g., Ricklefs 1984, Krebs 1985, Begon et al. 1990) summarise these important interactions as intra- and interspecific competition for abiotic and biotic resources, predation, parasitism and mutualism. Conspicuously lacking from the list of key processes in most text books is the role that many organisms play in the creation, modification and maintenance of habitats. These activities do not involve direct trophic interactions between species, but they are nevertheless important and common. The ecological literature is rich in examples of habitat modification by organisms, some of which have been extensively studied (e.g. Thayer 1979, Naiman et al. 1988).

Organisms as ecosystem engineers

This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.

Organic geochemistry of natural waters

Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.

Organic acids in the rhizosphere: a critical review

Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.

Tectonic forcing of late Cenozoic climate

1 The Hydrologic Cycle 2 Chemical Background 3 Organic Compounds in Natural Waters 4 The Carbonate System and pH Control 5 Clay Minerals and Ion Exchange 6 Stability Relationships and Silicate Equilibria 7 Kinetics 8 Weathering and Water Chemistry, I: Principles 9 Weathering and Water Chemistry, II: Examples 10 Acid Deposition and Surface Water Chemistry 11 Evaporation and Saline Waters 12 The Oceans 13 Redox Equilibria 14 Redox Conditions in Natural Waters 15 Trace Elements 16 Mathematical and Numerical Models 17 Isotopes Appendices

The geochemistry of natural waters

1. The Hydrologic Cycle. 2. Chemical Background. 3. The Carbonate System and pH Control 4. Clay Minerals and Cation Exchange. 5. Adsorption. 6. Organic Compounds in Natural Waters. 7. Redox Equilibria. 8. Redox Conditions in Natural Waters. 9. Heavy Metals and Metalloids. 10. Stability Relationships and Silicate Equilibria. 11. Kinetics. 12. Weathering and Water Chemistry. 13. Acid Water. 14. Isotopes. 15. Evaporation and Saline Waters. 16. Transport and Reaction Modeling References. Glossary of Geologic Terms. Appendix I: Piper and Stiff Diagrams. Appendix II: Standard-State Thermodynamic Data for Some Common Species. Appendix III: Equilibrium Constants at 25 C and Enthalpies of Reaction for Selected Reactions. Answers to Problems. Author Index. Subject Index.

The Geochemistry of Natural Waters: Surface and Groundwater Environments

The effect of land plants on weathering rates of silicate minerals

The role of organic acids in mineral weathering

Do glaciers enhance or inhibit chemical weathering rates relative to other environments? The importance of glaciers in the global carbon cycle and climate change hinges on the answer. We show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge. Silica denudation rates are distinctly lower in glacier-covered catchments than in their nonglacial counterparts. Because sediment yields are high from glaciers, this suggests that water flux, rather than physical erosion, exerts the primary control on chemical erosion by glaciers. Potassium and calcium concentrations are high relative to other cations in glacial water, probably due to dissolution of soluble trace phases, such as carbonates, exposed by comminution, and cation leaching from biotite. Preferential weathering of biotite may result in higher 87 Sr/ 86 Sr in glacial runoff than expected from whole-rock compositions. Thus, although glaciers do not influence total chemical denudation rates at a given runoff, they may yield compositionally distinctive chemical fluxes to the oceans. Disruption of mineral lattices by grinding increases dissolution rates; this and high surface area should make glacial sediments exceptionally weatherable. Weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles.

James I. Drever

Papers

The geochemistry of natural waters

The Geochemistry of Natural Waters: Surface and Groundwater Environments

The effect of land plants on weathering rates of silicate minerals

The role of organic acids in mineral weathering

Chemical weathering in glacial environments