Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes

Geochimica et Cosmochimica Acta

Volumn 142, Issue , 2014, Pages 132-148

  Frings, Patrick J ^a   De La Rocha, Christina ^b   Struyf, Eric ^c   van Pelt, Dimitri ^c   Schoelynck, Jonas ^c   Hudson, Mike Murray ^d   Gondwe, Mangaliso J ^d   Wolski, Piotr ^d   Mosimane, Keotsheple ^d   Gray, William ^e   Schaller, Jörg ^f   Conley, Daniel J ^a  

^a LUND UNIVERSITY   (Sweden)

^b INSTITUT UNIVERSITAIRE EUROPÉEN DE LA MER   (France)

^c UNIVERSITY OF ANTWERP   (Belgium)

^d UNIVERSITY OF BOTSWANA   (Botswana)

^e UNIVERSITY COLLEGE LONDON   (United Kingdom)

^f DRESDEN UNIVERSITY OF TECHNOLOGY   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

BASEFLOW; CHEMICAL WEATHERING; CLAY; DISSOLUTION; FLOODPLAIN; POREWATER; SILICA; SILICON; SURFACE WATER; VEGETATION; WETLAND;

BOTSWANA; NGAMILAND; OKAVANGO DELTA;

EID: 84908037173     PISSN: 00167037     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.gca.2014.07.007     Document Type: Article

References (117)

1. Basile-Doelsch I., Meunier J.D., Parron C. Another continental pool in the terrestrial silicon cycle. Nature 2005, 433:399-402.
2. Bauer P., Supper R., Zimmermann S., Kinzelbach W. Geoelectrical imaging of groundwater salinization in the Okavango Delta, Botswana. J. Appl. Geophys. 2006, 60:126-141.
3. Bauer P., Thabeng G., Stauffer F., Kinzelbach W. Estimation of the evapotranspiration rate from diurnal groundwater level fluctuations in the Okavango Delta, Botswana. J. Hydrol. 2004, 288:344-355.
4. 2 levels on continental silicate weathering. Geochem. Geophys. Geosyst. 2010, 11:18.
5. Bernal B., Mitsch W.J. Carbon sequestration in freshwater wetlands in Costa Rica and Botswana. Biogeochemistry 2013, 115:77-93.
6. Berner R.A., Lasaga A.C., Garrels R.M. The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100millionyears. Am. J. Sci. 1983, 283:641-683.
7. Bigeleisen J. Chemistry of Isotopes: Isotope chemistry has opened new areas of chemical physics, geochemistry, and molecular biology. Science 1965, 147:463-471.
8. Bouchez J., Gaillardet J., Lupker M., Louvat P., France-Lanord C., Maurice L., Armijos E., Moquet J.-S. Floodplains of large rivers: weathering reactors or simple silos?. Chem. Geol. 2012, 332-333:166-184.
9. Brewer T.S., Leng M.J., Mackay A.W., Lamb A.L., Tyler J.J., Marsh N.G. Unravelling contamination signals in biogenic silica oxygen isotope composition: the role of major and trace element geochemistry. J. Quaternary Sci. 2008, 23:321-330.
10. Bricker O.P., Jones B.F., Bowser C.J. Mass-balance approach to interpreting weathering reactions in watershed systems. Surface and Ground Water, Weathering, and Soils 2005, 119-132. Elsevier, London. J.I. Drever (Ed.).
11. Bristow T.F., Milliken R.E. Terrestrial perspective on authigenic clay mineral production in ancient Martian lakes. Clays Clay Miner. 2011, 59:339-358.
12. Cardinal D., Alleman L.Y., de Jong J., Ziegler K., Andre L. Isotopic composition of silicon measured by multicollector plasma source mass spectrometry in dry plasma mode. J. Anal. At. Spectrom. 2003, 18:213-218.
13. Cardinal D., Gaillardet J., Hughes H.J., Opfergelt S., Andre L. Contrasting silicon isotope signatures in rivers from the Congo Basin and the specific behaviour of organic-rich waters. Geophys. Res. Lett. 2010, 37.
14. Cawley K., Wolski P., Mladenov N., Jaffé R. Dissolved organic matter biogeochemistry along a transect of the Okavango Delta, Botswana. Wetlands 2012, 32:475-486.
15. Cockerton H.E., Street-Perrott F.A., Leng M.J., Barker P.A., Horstwood M.S.A., Pashley V. Stable-isotope (H, O, and Si) evidence for seasonal variations in hydrology and Si cycling from modern waters in the Nile Basin: implications for interpreting the Quaternary record. Quatern. Sci. Rev. 2013, 66:4-21.
16. Cornelis J.T., Delvaux B., Cardinal D., Andre L., Ranger J., Opfergelt S. Tracing mechanisms controlling the release of dissolved silicon in forest soil solutions using Si isotopes and Ge/Si ratios. Geochim. Cosmochim. Acta 2010, 74:3913-3924.
17. Cornelis J.T., Delvaux B., Georg R.B., Lucas Y., Ranger J., Opfergelt S. Tracing the origin of dissolved silicon transferred from various soil-plant systems towards rivers: a review. Biogeosciences 2011, 8:89-112.
18. De La Rocha C.L., Brzezinski M.A., DeNiro M.J. Purification, recovery, and laser-driven fluorination of silicon from dissolved and particulate silica for the measurement of natural stable isotope abundances. Anal. Chem. 1996, 68:3746-3750.
19. De La Rocha C.L., Brzezinski M.A., DeNiro M.J. A first look at the distribution of the stable isotopes of silicon in natural waters. Geochim. Cosmochim. Acta 2000, 64:2467-2477.
20. De La Rocha C.L., Bescont P., Croguennoc A., Ponzevera E. The silicon isotopic composition of surface waters in the Atlantic and Indian sectors of the Southern Ocean. Geochim. Cosmochim. Acta 2011, 75:5283-5295.
21. De La Rocha C.L., Brzezinski M.A., DeNiro M.J., Shemesh A. Silicon-isotope composition of diatoms as an indicator of past oceanic change. Nature 1998, 395:680-683.
22. Delstanche S., Opfergelt S., Cardinal D., Elsass F., André L., Delvaux B. Silicon isotopic fractionation during adsorption of aqueous monosilicic acid onto iron oxide. Geochim. Cosmochim. Acta 2009, 73:923-934.
23. 30Si signatures in a temperate watershed under high anthropogenic pressure (Scheldt - Belgium). J. Mar. Syst. 2013, 128:40-51.
24. Delvigne C., Opfergelt S., Cardinal D., Delvaux B., Andre L. Distinct silicon and germanium pathways in the soil-plant system: evidence from banana and horsetail. J. Geophys. Res. Biogeosci. 2009, 114:11.
25. Demarest M.S., Brzezinski M.A., Beucher C.P. Fractionation of silicon isotopes during biogenic silica dissolution. Geochim. Cosmochim. Acta 2009, 73:5572-5583.
26. DeMaster D.J. Measuring biogenic silica in marine-sediments and suspended matter. Marine Particles: Analysis and Characterization 1991, 363-367. Amer Geophysical Union, Washington. D.C. Hurd, D.W. Spencer (Eds.).
27. Ding T., Jiang M.S., Wan D., Li Y., Li J., Song H., Liu Z., Yao X. Silicon Isotope Geochemistry 1996, Geological Publishing House, Beijing, China.
28. Ding T.P., Tian S.H., Sun L., Wu L.H., Zhou J.X., Chen Z.Y. Silicon isotope fractionation between rice plants and nutrient solution and its significance to the study of the silicon cycle. Geochim. Cosmochim. Acta 2008, 72:5600-5615.
29. Douthitt C.B. The geochemistry of the stable isotopes of silicon. Geochim. Cosmochim. Acta 1982, 46:1449-1458.
30. Engström E., Rodushkin I., Baxter D.C., Öhlander B. Chromatographic purification for the determination of dissolved silicon isotopic compositions in natural waters by high-resolution multicollector inductively coupled plasma mass spectrometry. Anal. Chem. 2005, 78:250-257.
31. Engstrom E., Rodushkin I., Ingri J., Baxter D.C., Ecke F., Osterlund H., Ohlander B. Temporal isotopic variations of dissolved silicon in a pristine boreal river. Chem. Geol. 2010, 271:142-152.
32. Epstein E. Silicon. Ann. Rev. Plant Physiol. Plant Mol. Biol. 1999, 50:641-664.
33. Fontorbe G., De La Rocha C.L., Chapman H.J., Bickle M.J. The silicon isotopic composition of the ganges and its tributaries. Earth Planet. Sci. Lett. 2013, 381:21-30.
34. Furquim S., Graham R., Barbiéro L., Queiroz Neto J., Vidal-Torrado P. Soil mineral genesis and distribution in a saline lake landscape of the Pantanal Wetland, Brazil. Geoderma 2010, 154:518-528.
35. Furquim S.A.C., Barbiero L., Graham R.C., Neto J., Ferreira R.P.D., Furian S. Neoformation of micas in soils surrounding an alkaline-saline lake of Pantanal wetland, Brazil. Geoderma 2010, 158:331-342.
36. 2 consumption rates deduced from the chemistry of large rivers. Chem. Geol. 1999, 159:3-30.
37. Galy A., France-Lanord C. Weathering processes in the Ganges-Brahmaputra basin and the riverine alkalinity budget. Chem. Geol. 1999, 159:31-60.
38. Garrels R.M. and Mackenzie F.T. (1967) Origin of the Chemical Compositions of Some Springs and Lakes. In Equilibrium Concepts in Natural Water Systems. American Chemical Society, pp. 222-242.
39. Garstang M., Ellery W.N., McCarthy T.S., Scholes M.C., Scholes R.J., Swap R.J., Tyson P.D. The contribution of aerosol- and water-borne nutrients to the functioning of the Okavango Delta. S. Afr. J. Sci. 1998, 94:223.
40. Georg R.B., Reynolds B.C., Frank M., Halliday A.N. Mechanisms controlling the silicon isotopic compositions of river waters. Earth Planet. Sci. Lett. 2006, 249:290-306.
41. Gieske A. Modelling outflow from the Jao/Boro River system in the Okavango Delta, Botswana. J. Hydrol. 1997, 193:214-239.
42. Gumbricht T., McCarthy T.S., Bauer P. The micro-topography of the wetlands of the Okavango Delta, Botswana. Earth Surf. Proc. Land. 2005, 30:27-39.
43. Gumbricht T., Wolski P., Frost P., McCarthy T.S. Forecasting the spatial extent of the annual flood in the Okavango delta, Botswana. J. Hydrol. 2004, 290:178-191.
44. House W.A., Denison F.H., Warwick M.S., Zhmud B.V. Dissolution of silica and the development of concentration profiles in freshwater sediments. Appl. Geochem. 2000, 15:425-438.
45. Hughes H.J., Sondag F., Cocquyt C., Laraque A., Pandi A., Andre L., Cardinal D. Effect of seasonal biogenic silica variations on dissolved silicon fluxes and isotopic signatures in the Congo River. Limnol. Oceanogr. 2011, 56:551-561.
46. Hughes H.J., Sondag F., Santos R.V., André L., Cardinal D. The riverine silicon isotope composition of the Amazon Basin. Geochim. Cosmochim. Acta 2013, 121:637-651.
47. Humphries M., Kindness A., Ellery W., Hughes J. Water chemistry and effect of evapotranspiration on chemical sedimentation on the Mkuze River floodplain, South Africa. J. Arid Environ. 2011, 75:555-565.
48. Humphries M.S., Kindness A., Ellery W.N., Hughes J.C. Sediment geochemistry, mineral precipitation and clay neoformation on the Mkuze River floodplain, South Africa. Geoderma 2010, 157:15-26.
49. Humphries M.S., McCarthy T.S., Cooper G.R.J., Stewart R.A., Stewart R.D. The role of airborne dust in the growth of tree islands in the Okavango Delta, Botswana. Geomorphology 2014, 206:307-317.
50. Johnsson M.J., Meade R.H. Chemical weathering of fluvial sediments during alluvial storage: the Macuapanim Island point bar, Solimões River, Brazil. J. Sediment. Res. 1990, 60.
51. Jones M. J. (2010) The groundwater hydrology of the Okavango. FAO internal reports, Okavango River Basin Water Commission (OKACOM), Maun, Botswana.
52. Kihwele E., Mnaya B., Meng'ataki G., Birkett C., Wolanski E. The role of vegetation in the water budget of the Usangu wetlands, Tanzania. Wetlands Ecol. Manage. 2012, 20:389-398.
53. Klančnik K., Vogel-Mikuš K., Gaberščik A. Silicified structures affect leaf optical properties in grasses and sedge. J. Photochem. Photobiol. B 2013, 130:1-10.
54. Krah M., McCarthy T.S., Huntsman-Mapila P., Wolski P., Annegarn H., Sethebe K. Nutrient budget in the seasonal wetland of the Okavango Delta, Botswana. Wetlands Ecol. Manage. 2006, 14:253-267.
55. Kurtz A.C., Derry L.A., Chadwick O.A. Germanium-silicon fractionation in the weathering environment. Geochim. Cosmochim. Acta 2002, 66:1525-1537.
56. Lancaster N. Grain-size characteristics of linear dunes in the southwestern Kalahari. J. Sediment. Res. 1986, 56:395-400.
57. Lewis B.L., Andreae M.O., Froelich P.N., Mortlock R.A. A review of the biogeochemistry of germanium in natural waters. Sci. Total Environ. 1988, 73:107-120.
58. Livingstone I., Bullard J.E., Wiggs G.F.S., Thomas D.S.T. Grain-size variation on dunes in the Southwest Kalahari, Southern Africa. J. Sediment. Res. 1999, 69:546-552.
59. Lupker M., France-Lanord C., Galy V., Lavé J., Gaillardet J., Gajurel A.P., Guilmette C., Rahman M., Singh S.K., Sinha R. Predominant floodplain over mountain weathering of Himalayan sediments (Ganga basin). Geochim. Cosmochim. Acta 2012, 84:410-432.
60. Ma J.F., Yamaji N. Functions and transport of silicon in plants. Cell. Mol. Life Sci. 2008, 65:3049-3057.
61. Mackay A.W., Davidson T., Wolski P., Mazebedi R., Masamba W.R.L., Huntsman-Mapila P., Todd M. Spatial and seasonal variability in surface water chemistry in the Okavango Delta, Botswana: a multivariate approach. Wetlands 2011, 31:815-829.
62. Maher K., Steefel C.I., White A.F., Stonestrom D.A. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California. Geochim. Cosmochim. Acta 2009, 73:2804-2831.
63. Mackenzie F.T., Garrels R.M. Chemical mass balance between rivers and oceans. Am. J. Sci. 1966, 264:507-525.
64. McCarthy T., Stanistreet I., Cairncross B. The sedimentary dynamics of active fluvial channels on the Okavango fan, Botswana. Sedimentology 1991, 38:471-487.
65. McCarthy T.S., Barry M., Bloem A., Ellery W.N., Heister H., Merry C.L., Röther H., Sternberg H. The gradient of the Okavango fan, Botswana, and its sedimentological and tectonic implications. J. Afr. Earth Sci. 1997, 24:65-78.
66. McCarthy T.S., Ellery W.N. The Okavango Delta. Trans. R. Soc. S. Afr. 1998, 53:157-182.
67. McCarthy T.S., Humphries M.S., Mahomed I., Le Roux P., Verhagen B.T. Island forming processes in the Okavango Delta, Botswana. Geomorphology 2012, 179:249-257.
68. McCarthy T.S., McIver J.R., Cairncross B., Ellery W.N., Ellery K. The inorganic chemistry of peat from the Maunachira channel-swamp system, Okavango Delta, Botswana. Geochim. Cosmochim. Acta 1989, 53:1077-1089.
69. McCarthy T.S., Stanistreet I.G., Cairncross B. The sedimentary dynamics of active fluvial channels on the Okavango fan, Botswana. Sedimentology 1991, 38:471-487.
70. MacDonald R., McLaughlin F. The effect of storage by freezing on dissolved inorganic phosphate, nitrate and reactive silicate for samples from coastal and estuarine waters. Water Res. 1982, 16:95-104.
71. Mariotti A., Germon J.C., Hubert P., Kaiser P., Letolle R., Tardieux A., Tardieux P. Experimental determination of nitrogen kinetic isotope fractionation: some principles; illustration for the denitrification and nitrification processes. Plant Soil 1981, 62:413-430.
72. McKeague J.A., Cline M.G. Silica in soil solutions: II. The adsorption of monosilicic acid by soil and by other substances. Can. J. Soil Sci. 1963, 43:83-96.
73. Michalopoulos P., Aller R.C. Rapid clay mineral formation in Amazon Delta sediments - reverse weathering and oceanic elemental cycles. Science 1995, 270:614-617.
74. Milzow C., Kgotlhang L., Bauer-Gottwein P., Meier P., Kinzelbach W. Regional review: the hydrology of the Okavango Delta, Botswana-processes, data and modelling. Hydrogeol. J. 2009, 17:1297-1328.
75. Milzow C., Kgotlhang L., Kinzelbach W., Meier P., Bauer-Gottwein P. The role of remote sensing in hydrological modelling of the Okavango Delta, Botswana. J. Environ. Manage. 2009, 90:2252-2260.
76. Mladenov N., McKnight D.M., Macko S.A., Norris M., Cory R.M., Ramberg L. Chemical characterization of DOM in channels of a seasonal wetland. Aquat. Sci. 2007, 69:456-471.
77. Mladenov N., McKnight D.M., Wolski P., Ramberg L. Effects of annual flooding on dissolved organic carbon dynamics within a pristine wetland, the Okavango Delta, Botswana. Wetlands 2005, 25:622-638.
78. 2 consumption with Ca isotopes: Southern Alps, New Zealand. Chem. Geol. 2013, 341:110-127.
79. Oelze M., von Blanckenburg F., Hoellen D., Dietzel M., Bouchez J. Si stable isotope fractionation during adsorption and the competition between kinetic and equilibrium isotope fractionation: Implications for weathering systems. Chem. Geol. 2014, 380:161-171.
80. Oliva P., Viers J., Dupré B., Fortuné J.P., Martin F., Braun J.J., Nahon D., Robain H. The effect of organic matter on chemical weathering: study of a small tropical watershed: nsimi-zoétélé site, Cameroon. Geochim. Cosmochim. Acta 1999, 63:4013-4035.
81. Opfergelt S., de Bournonville G., Cardinal D., André L., Delstanche S., Delvaux B. Impact of soil weathering degree on silicon isotopic fractionation during adsorption onto iron oxides in basaltic ash soils, Cameroon. Geochim. Cosmochim. Acta 2009, 73:7226-7240.
82. 30Si and Ge/Si with weathering and biogenic input in tropical basaltic ash soils under monoculture. Geochim. Cosmochim. Acta 2010, 74:225-240.
83. Opfergelt S., Cardinal D., Henriet C., Draye X., André L., Delvaux B. Silicon isotopic fractionation by banana (Musa spp.) grown in a continuous nutrient flow device. Plant Soil 2006, 285:333-345.
84. Opfergelt S., Delmelle P. Silicon isotopes and continental weathering processes: assessing controls on Si transfer to the ocean. C. R. Geosci. 2012, 344:723-738.
85. Opfergelt S., Georg R.B., Delvaux B., Cabidoche Y.M., Burton K.W., Halliday A.N. Silicon isotopes and the tracing of desilication in volcanic soil weathering sequences, Guadeloupe. Chem. Geol. 2012, 326-327:113-122.
86. Pearce C.R., Saldi G.D., Schott J., Oelkers E.H. Isotopic fractionation during congruent dissolution, precipitation and at equilibrium: evidence from Mg isotopes. Geochim. Cosmochim. Acta 2012, 92:170-183.
87. Pogge von Strandmann P.A.E., Opfergelt S., Lai Y.-J., Sigfússon B., Gislason S.R., Burton K.W. Lithium, magnesium and silicon isotope behaviour accompanying weathering in a basaltic soil and pore water profile in Iceland. Earth Planet. Sci. Lett. 2012, 339-340:11-23.
88. Pokrovsky O.S., Reynolds B.C., Prokushkin A.S., Schott J., Viers J. Silicon isotope variations in Central Siberian rivers during basalt weathering in permafrost-dominated larch forests. Chem. Geol. 2013, 355:103-116.
89. Ramberg L., Wolski P. Growing islands and sinking solutes: processes maintaining the endorheic Okavango Delta as a freshwater system. Plant Ecol. 2008, 196:215-231.
90. Ramberg L., Wolski P., Krah M. Water balance and infiltration in a seasonal floodplain in the Okavango Delta, Botswana. Wetlands 2006, 26:677-690.
91. Righi D., Meunier A. Origin of clays by rock weathering and soil formation. Origin and Mineralogy of Clays 1995, 43-161. Springer, Berlin Heidelberg. B. Velde (Ed.).
92. Sagan C., Mullen G. Earth and mars: evolution of atmospheres and surface temperatures. Science 1972, 177:52-56.
93. Savage P.S., Georg R.B., Williams H.M., Halliday A.N. The silicon isotope composition of the upper continental crust. Geochim. Cosmochim. Acta 2013, 109:384-399.
94. Sawula G., Martins E. Major ion chemistry of the lower Boro River, Okavango Delta, Botswana. Freshw. Biol. 1991, 26:481-493.
95. Schaller J., Struyf E. Silicon controls microbial decay and nutrient release of grass litter during aquatic decomposition. Hydrobiologia 2013, 709:201-212.
96. Schoelynck J., Bal K., Backx H., Okruszko T., Meire P., Struyf S. Silica uptake in aquatic and wetland macrophytes: a strategic choice between silica, lignin and cellulose?. New Phytol. 2010, 186:385-391.
97. Shemesh A., Mortlock R.A., Smith R.J., Froelich P.N. Determination of Ge/Si in marine siliceous microfossils: separation, cleaning and dissolution of diatoms and radiolaria. Mar. Chem. 1988, 25:305-323.
98. Scribner A.M., Kurtz A.C., Chadwick O.A. Germanium sequestration by soil: targeting the roles of secondary clays and Fe-oxyhydroxides. Earth Planet. Sci. Lett. 2006, 243:760-770.
99. Scott D.T., Keim R.F., Edwards B.L., Jones C.N., Kroes D.E. Floodplain biogeochemical processing of floodwaters in the Atchafalaya River Basin during the Mississippi River flood of 2011. J. Geophys. Res. Biogeosci. 2014, 119. 2013JG002477.
100. Seeberg-Elverfeldt J., Schluter M., Feseker T., Kolling M. Rhizon sampling of porewaters near the sediment-water interface of aquatic systems. Limnol. Oceanogr. Meth. 2005, 3:361-371.
101. Souza-Júnior V.S.d., Vidal-Torrado P., Garcia-González M.T., Macías F., Otero X.L. Smectite in mangrove soils of the State of São Paulo, Brazil. Sci. Agric. 2010, 67:47-52.
102. Steinhoefel G., Breuer J., von Blanckenburg F., Horn I., Kaczorek D., Sommer M. Micrometer silicon isotope diagnostics of soils by UV femtosecond laser ablation. Chem. Geol. 2011, 286:280-289.
103. Strickland J.D.H., Parsons T.R. Determination of reactive silicate. A Practical Handbook of Seawater Analysis 1968, Fisheries Research Board of Canada, pp. 65-70.
104. Struyf E., Van Damme S., Gribsholt B., Bal K., Beauchard O., Middelburg J.J., Meire P. Phragmites australis and silica cycling in tidal wetlands. Aquat. Bot. 2007, 87:134-140.
105. Struyf E., Mosimane K., Van Pelt D., Murray-Hudson M., Meire P., Frings P., Wolski P., Schaller J., Gondwe M., Schoelynck J. and Conley D. J. (submitted) The role of vegetation in the Okavango Delta silica sink. Submitted to Wetlands.
106. Sun X., Olofsson M., Andersson P.S., Fry B., Legrand C., Humborg C., Mörth C.-M. Effects of growth and dissolution on the fractionation of silicon isotopes by estuarine diatoms. Geochim. Cosmochim. Acta 2014, 130:156-166.
107. Valett H., Baker M., Morrice J., Crawford C., Molles M., Dahm C., Moyer D., Thibault J., Ellis L.M. Biogeochemical and metabolic responses to the flood pulse in a semiarid floodplain. Ecology 2005, 86:220-234.
108. Viers J., Dupré B., Polvé M., Schott J., Dandurand J.-L., Braun J.-J. Chemical weathering in the drainage basin of a tropical watershed (Nsimi-Zoetele site, Cameroon): comparison between organic-poor and organic-rich waters. Chem. Geol. 1997, 140:181-206.
109. Walker J.C.G., Hays P.B., Kasting J.F. A negative feedback mechanism for the long-term stabilization of Earths surface-temperature. J. Geophys. Res. Oceans Atmos. 1981, 86:9776-9782.
110. Wetzel F., de Souza G.F., Reynolds B.C. What controls silicon isotope fractionation during dissolution of diatom opal?. Geochim. Cosmochim. Acta 2014, 131:128-137.
111. White A.F., Schulz M.S., Stonestrom D.A., Vivit D.V., Fitzpatrick J., Bullen T.D., Maher K., Blum A.E. Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: solute profiles, gradients and the comparisons of contemporary and long-term weathering rates. Geochim. Cosmochim. Acta 2009, 73:2769-2803.
112. Wolski P., Murray-Hudson M. Flooding dynamics in a large low-gradient alluvial fan, the Okavango Delta, Botswana, from analysis and interpretation of a 30-year hydrometric record. Hydrol. Earth Syst. Sci. 2006, 10:127-137.
113. Wolski P., Savenije H.H.G. Dynamics of floodplain-island groundwater flow in the Okavango Delta, Botswana. J. Hydrol. 2006, 320:283-301.
114. Yang L., Steefel C.I. Kaolinite dissolution and precipitation kinetics at 22°C and pH 4. Geochim. Cosmochim. Acta 2008, 72:99-116.
115. 30Si ratios during progressive basalt weathering, Hawaiian Islands. Geochim. Cosmochim. Acta 2005, 69:4597-4610.
116. 30Si systematics in a granitic saprolite, Puerto Rico. Geology 2005, 33:817-820.
117. Zimmermann S., Bauer P., Held R., Kinzelbach W., Walther J.H. Salt transport on islands in the Okavango Delta: numerical investigations. Adv. Water Resour. 2006, 29:11-29.