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Biogeochemistry

, Volume 114, Issue 1–3, pp 359–380 | Cite as

River-wetland interaction and carbon cycling in a semi-arid riverine system: the Okavango Delta, Botswana

  • Eric Akoko
  • Eliot A. Atekwana
  • Anna M. Cruse
  • Loago Molwalefhe
  • Wellington R. L. Masamba
Article

Abstract

The Okavango River, in semi-arid northwestern Botswana, flows for over 400 km in a pristine wetland developed on a large (>22,000 km2) alluvial fan (Okavango Delta). An annual flood pulse inundates the floodplains of the wetlands and travels across the Delta in 4–6 months. In this study, we assess the effects of long hydraulic residence time, variable hydrologic interaction between river–floodplain–wetland and evapotranspiration on carbon cycling. We measured dissolved inorganic carbon (DIC) concentrations and stable carbon isotopes of DIC (δ13CDIC) from river water when the Delta was not flooded (low water) and during flooding (high water). During low water, the average DIC concentration was 31 % higher and the δ13CDIC 2.1 ‰ more enriched compared to high water. In the lower Delta with seasonally flooded wetlands, the average DIC concentration increased by 70 % during low water and by 331 % during high water compared to the Panhandle with permanently flooded wetlands. The increasing DIC concentration downriver is mostly due to evapoconcentration from transpiration and evaporation with increased transit time. The average δ13CDIC between low and high water decreased by 3.7 ‰ in the permanently flooded reaches compared to an increase of 1.6 ‰ in the seasonally flooded reaches. The lower δ13CDIC during high water in the permanently flooded reaches suggest that DIC influx from the floodplain-wetland affects river’s DIC cycling. In contrast, higher river channel elevations relative to the wetlands along seasonal flooded reaches limit hydrologic interaction and DIC cycling occurs mostly by water column processes and river-atmospheric exchange. We conclude that river-wetlands interaction and evapoconcentration are important factors controlling carbon cycling in the Okavango Delta.

Keywords

Carbon cycle Dissolved inorganic carbon Okavango river Flood pulse River-wetland interaction Evapoconcentration 

Notes

Acknowledgments

Partial funding for this project was provided by the US National Science Foundation (NSF grant # OISE-0927841) under the International Research Experience for Students (IRES) initiative. The University of Botswana provided logistical support for fieldwork. We thank the government of Botswana (Ministry of Education) for providing us with research permits. Field assistance was provided by C. Geyer, N. Paizis, O. Kgaodi and T. Koontse for. We thank the Department of Water Affairs in Mohembo, the owners of Drostky Cabins and Sepopa Swamp Stop for providing access to the river from their property. We also thank the Department of Water Affairs (Botswana) and the Okavango Research Institute Monitoring Unit for discharge data.

References

  1. Atekwana EA, Krishnamurthy RV (1998) Seasonal variations of dissolved inorganic carbon and δ13C of surface waters: application of a modified gas evolution technique. J Hydrol 205:265–278CrossRefGoogle Scholar
  2. Aucour AM, Sheppard SMF, Guyomar O, Wattelet J (1999) Use of 13C to trace origin and cycling of inorganic carbon in the Rhône river system. Chem Geol 159(1–4):87–105CrossRefGoogle Scholar
  3. Baron J, McKnight D, Denning AS (1991) Sources of dissolved and particulate organic material in Loch Vale watershed, Rocky Mountain National Park, Colorado. USA. Biogeochemistry 15(2):89–110Google Scholar
  4. Bauer-Gottwein P, Langer T, Prommer H, Wolski P, Kinzelbach W (2007) Okavango Delta islands: interactions between density-driven flow and geochemical reactions under evapo-concentration. J Hydrol 335:389–405CrossRefGoogle Scholar
  5. Benson NM (2000) Geology and mineralization in the Meso- to Neoproterozoic Ghanzi-Chobe belt of northwest Botswana. J Afr Earth Sc 30(3):467–474CrossRefGoogle Scholar
  6. Boutton PW, Wong WW, Hachey DL, Lee LS, Cabrera MP, Klein PD (1983) Comparison of quartz and Pyrex tubes for combustion of organic samples for stable carbon isotope analysis. Anal Chem 55:1832–1833CrossRefGoogle Scholar
  7. Boyer EW, Hornberger GM, Bencala KE, McKnight DM (1997) Response characteristics of DOC flushing in an alpine catchment. Hydrol Process 11:1635–1647CrossRefGoogle Scholar
  8. Brunet F, Gaiero D, Probst JL, Depetris PJ, Gauthier Lafaye F, Stille P (2005) δ13C tracing of dissolved inorganic carbon sources in Patagonian rivers (Argentina). Hydrol Process 19(17):3321–3344CrossRefGoogle Scholar
  9. Brunet F, Dubois K, Veizer J, Nkoue Ndondo GR, Ndam Ngoupayou JR, Boeglin JL, Probst JL (2009) Terrestrial and fluvial carbon fluxes in a tropical watershed: Nyong basin Cameroon. Chemical Geology 265(3–4):563–572CrossRefGoogle Scholar
  10. Cartwright I (2010) The origins and behaviour of carbon in a major semi-arid river, the Murray River, Australia, as constrained by carbon isotopes and hydrochemistry. Appl Geochem 25(11):1734–1745CrossRefGoogle Scholar
  11. Cawley KM, Wolski P, Mladenov N, Rudolf Jaffé R (2012) Dissolved organic matter biogeochemistry along a transect of the Okavango Delta, Botswana. Wetlands. doi: 10.1007/s13157-012-0281-0 Google Scholar
  12. Cole JJ, Prairie YT, Caraco NF, McDowell WH, Tranvik LJ, Striegl RG, Duarte CM, Kortelainen P, Downing JA, Middelburg JJ, Melack J (2007) Plumbing the global carbon cycle: integrating inland waters into the terrestrial carbon budget. Ecosystems 10:171–184CrossRefGoogle Scholar
  13. Company Hach (1992) Water analysis handbook. Hach Company, LovelandGoogle Scholar
  14. Cronberg G, Gieske A, Martins E, Prince Nengu J, Stenstrom I-M (1996) Major ion chemistry, plankton, and bacterial assemblages of the Jao/Boro River, Okavango Delta, Botswana: the swamps and flood plains. Arch Fur Hydrobiol 107(Suppl):335–407Google Scholar
  15. Dalzell BJ, Filley TR, Harbor JM (2007) The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a mid-western agricultural watershed. Geochim Cosmochim Acta 71(6):1448–1462CrossRefGoogle Scholar
  16. Dincer T, Hutton LG, Kupee BBJ (1979) Study, using stable isotopes, of flow distribution, surface-groundwater relations and evapotranspiration in the Okavango Swamp, Botswana. Isotope Hydrology 1978, vol. 1. International Atomic Energy Agency, Vienna, pp 3–25Google Scholar
  17. Doctor DH, Kendall C, Sebestyen SD, Shanley JB, Ohte N, Boyer EW (2008) Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream. Hydrol Process 22:2410–2423CrossRefGoogle Scholar
  18. Ellery K, Ellery WN, Verhagen BTh (1992) The distribution of C3 plant and C4 plants in a successional sequence in the Okavango Delta. S Afr J Bot 58:400–402Google Scholar
  19. Ellery W, McCarthy T, Smith N (2003) Vegetation, hydrology, and sedimentation patterns on the major distributary system of the Okavango fan, Botswana. Wetlands 23:357–375CrossRefGoogle Scholar
  20. Finlay JC (2003) Controls of stream water dissolved inorganic carbon dynamics in a forested watershed. Biogeochemistry 62(3):231–252CrossRefGoogle Scholar
  21. Gehre M, Geilmann H, Richter J, Werner RA, Brand WA (2004) Continuous flow 2H/1H and 18O/16O analysis of water samples with dual inlet precision. Rapid Commun Mass Spectrom 18:2650–2660CrossRefGoogle Scholar
  22. Gieske A (1997) Modeling outflow from the Jao/Boro River system in the Okavango Delta, Botswana. J Hydrol 193:214–239CrossRefGoogle Scholar
  23. Graneli W, Lindell M, Tranvik L (1996) Photo-oxidative production of dissolved inorganic carbon in lakes of different humic content. Limnol Oceanogr 41:698–706CrossRefGoogle Scholar
  24. Gumbricht T, McCarthy J, McCarthy TS (2004) Channels, wetlands and islands in the Okavango Delta, Botswana, and their relation to hydrological and sedimentological processes. Earth Surf Proc Land 29:15–29CrossRefGoogle Scholar
  25. Hem JD (1985) Study and interpretation of the chemical characteristics of natural water. US Geological Survey Water-Supply Paper 2254. Washington, DCGoogle Scholar
  26. Hornberger GM, Bencala KE, McKnight DM (1994) Hydrological controls on dissolved organic carbon during snow melt in the Snake River near Montezuma, Colorado. Biogeochemistry 25(3):147–165CrossRefGoogle Scholar
  27. Huntsman-Mapila P, Mapila T, Letshwenyo M, Wolski P, Hemond C (2006) Characterization of arsenic occurrence in the water and sediments of the Okavango Delta, NW Botswana. Applied Geochemistry 21(8):1376–1391CrossRefGoogle Scholar
  28. Huntsman-Mapila P, Nsengimana H, Torto N, Diskin S (2011) Arsenic distribution and geochemistry in island groundwater of the Okavango Delta in Botswana. Sustain Groundw Resour 55–67:67. doi: 10.1007/978-90-481-3426-7_4 Google Scholar
  29. Kanduč T, Szramek K, Ogrinc N, Walter L (2007) Origin and cycling of riverine inorganic carbon in the Sava River watershed (Slovenia) inferred from major solutes and stable carbon isotopes. Biogeochemistry 86(2):137–154CrossRefGoogle Scholar
  30. Karberg NJ, Pregitzer KS, King JS, Friend AL, Wood JR (2005) Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone. Oecologia 142(2):296–306CrossRefGoogle Scholar
  31. Kinabo BD, Atekwana EA, Hogan JP, Modisi MP, Wheaton DD, Kampunzu AB (2007) Early structural development of the Okavango rift zone, NW Botswana. Afr Earth Sci 48:125–136CrossRefGoogle Scholar
  32. Kinabo BD, Hogan JP, Atekwana EA, Abdelsalam MG, Modisi MP (2008) Fault growth and propagation during incipient continental rifting: insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana. Tectonics 27:3013CrossRefGoogle Scholar
  33. Mackay A, Davidson T, Wolski P, Mazebedi R, Masamba W, Huntsman-Mapila P, Todd M (2011) Spatial and seasonal variability in surface water chemistry in the Okavango Delta, Botswana: a multivariate approach. Wetlands 31:815–829CrossRefGoogle Scholar
  34. Masamba WRL, Mazvimavi D (2008) Impact on water quality of land uses along Thamalakane-Boteti River: an outlet of the Okavango Delta. Phys Chem Earth Parts A/B/C 33(8–13):687–694CrossRefGoogle Scholar
  35. McCarthy TS, Ellery WN (1994) The effect of vegetation on soil and ground water chemistry and hydrology of islands in the seasonal swamps of the Okavango Fan, Botswana. J Hydrol 154:169–193CrossRefGoogle Scholar
  36. McCarthy TS, Ellery WN (1995) Sedimentation on the distal reaches of the Okavango Fan, Botswana, and its bearing on calcrete and silcrete (ganister) formation. J Sediment Res 65:77–90CrossRefGoogle Scholar
  37. McCarthy TS, Metcalfe J (1990) Chemical sedimentation in the semi-arid environment of the Okavango Delta, Botswana. Chem Geol 89(1–2):157–178CrossRefGoogle Scholar
  38. McCarthy TS, Ellery WN, Stanistreet IG (1992) Avulsion mechanisms on the Okavango fan, Botswana: the control of a fluvial system by vegetation. Sedimentology 39:779–795CrossRefGoogle Scholar
  39. McCarthy TS, Ellery WN, Ellery K (1993) Vegetation-induced, subsurface precipitation of carbonate as an aggradational process in the permanent swamps of the Okavango (delta) fan, Botswana. Chem Geol 107:111–131CrossRefGoogle Scholar
  40. McCarthy TS, Ellery WN, Bloem A (1998) Some observations on the geomorphological impact of hippopotamus (Hippopotamus amphibius L.) in the Okavango Delta, Botswana. Afr J Ecol 36:44–56CrossRefGoogle Scholar
  41. McCarthy TS, Cooper GRJ, Tyson PD, Ellery WN (2000) Seasonal flooding in the Okavango Delta, Botswana-recent history and future prospects. S Afr J Sci 96:25–33Google Scholar
  42. McCarthy JM, Gumbricht T, McCarthy T, Frost P, Wessels K, Seidel F (2003) Flooding patterns of the Okavango wetland in Botswana between 1972 and 2000. Ambio 32(7):453–457Google Scholar
  43. Meybeck M (1982) Carbon, nitrogen and phosphorus transport by World Rivers. Am J Sci 282:401–450CrossRefGoogle Scholar
  44. Milzow C, Kgotlhang L, Bauer-Gottwein P, Meier P, Kinzelbach W (2009) Regional review: the hydrology of the Okavango Delta, Botswana-processes, data and modeling. Hydrogeol J 17:1297–1328CrossRefGoogle Scholar
  45. Mladenov N, McKnight D, Wolski P, Ramberg L (2005) Effects of annual flooding on dissolved organic carbon dynamics within a pristine wetland, the Okavango Delta, Botswana. Wetlands 25:622–638CrossRefGoogle Scholar
  46. Mladenov N, McKnight DM, Macko SA, Ramberg L, Cory RM, Norris M (2007a) Chemical characterization of DOM in channels of a seasonal wetland. Aquat Sci 69:456–471CrossRefGoogle Scholar
  47. Mladenov N, McKnight DM, Wolski P, Murray-Hudson M (2007b) Simulation of DOM fluxes in a seasonal floodplain of the Okavango Delta, Botswana. Ecol Model 205:181–195CrossRefGoogle Scholar
  48. Mmualefe LC, Torto N (2011) Water quality in the Okavango Delta. Water SA 37(3):411–418CrossRefGoogle Scholar
  49. Modisi MP, Atekwana EA, Kampunzu AB, Ngwisanyi TH (2000) Rift kinematics during the incipient stages of continental extension: evidence from the nascent Okavango rift basin, northwest Botswana. Geology 28:939–942CrossRefGoogle Scholar
  50. Mook WG, Bommerson JC, Staverman WH (1974) Carbon isotope fractionation between dissolved bicarbonate and gaseous carbon dioxide. Earth Planet Sci Lett 22:169–176CrossRefGoogle Scholar
  51. Mosley-Bufford K, Atekwana EA, Abdelsalamc MG, Shemang E, Atekwana EA, Mickuse K, Moikwathai Moidaki M, Modisi MotsoptseP, Molwalefhe L (2012) Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana: evidence from magnetotelluric and electrical resistivity tomography imaging. J Afr Earth Sc 65:61–71CrossRefGoogle Scholar
  52. Murphy KJ, Dickinson G, Thomaz SM, Bini LM, Dick K, Greaves K, Kennedy MP, Livingstone S, McFerran H, Milne JM, Oldroyd J, Wingfield RA (2003) Aquatic plant communities and predictors of diversity in a sub-tropical river floodplain: the upper Rio Paraná, Brazil. Aquat Bot 77(4):257–276CrossRefGoogle Scholar
  53. Nash DJ, Endfield GH (2002) A 19th century climate chronology for the Kalahari region of central southern Africa derived from missionary correspondence. Int J Climatol 22:821–841CrossRefGoogle Scholar
  54. Quay PD, Wilbur DO, Richey JE, Hedges JI, Devol AH (1992) Carbon cycling in the Amazon River: implications from the 13C compositions of particles and solutes. Limnol Oceanogr 37(4):857–871CrossRefGoogle Scholar
  55. Raymond PA, Bauer JE, Caraco NF, Cole JJ, Longworth B, Petsch ST (2004) Controls on the variability of organic matter and dissolved inorganic carbon ages in northeast US rivers. Mar Chem 92(1–4):353–366CrossRefGoogle Scholar
  56. Richey JE, Melack JM, Aufdenkampe AK, Ballester VM, Hess LL (2002) Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO2. Nature 416:617–620CrossRefGoogle Scholar
  57. Ringrose S, Harris C, Huntsman-Mapila P, Vink BW, Diskins S, Vanderpost C, Matheson W (2009) Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition. Sediment Geol 219:262–279CrossRefGoogle Scholar
  58. Sawula G, Martins E (1991) Major ion chemistry of the lower Boro River, Okavango Delta, Botswana. Freshw Biol 26:481–493CrossRefGoogle Scholar
  59. Telmer K, Veizer J (1999) Carbon fluxes, pCO2 and substrate weathering in a large northern river basin, Canada: carbon isotope perspectives. Chem Geol 159:61–86CrossRefGoogle Scholar
  60. Walker CD, Richardson SB (1991) The use of stable isotopes of water in characterizing the source of water in vegetation. Chem Geol 94:145–158CrossRefGoogle Scholar
  61. Wilson BH, Dincer T (1976) An introduction to the hydrology and hydrography of the Okavango Delta. In: Symposium on the Okavango Delta, Botswana Society, Gaborone, 33–48Google Scholar
  62. Wolski P, Savenije HHG, Murray-Hudson M, Gumbricht T (2006) Modelling of the flooding in the Okavango Delta, Botswana, using a hybrid reservoir-GIS model. J Hydrol 331:58–72CrossRefGoogle Scholar
  63. Zeng FW, Masiello C (2010) Sources of CO2 evasion from two subtropical rivers in North America. Biogeochemistry 100(1):211–225CrossRefGoogle Scholar
  64. Zeng FW, Masiello C, Hockaday W (2011) Controls on the origin and cycling of riverine dissolved inorganic carbon in the Brazos River, Texas. Biogeochemistry 104(1):275–291CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Eric Akoko
    • 1
  • Eliot A. Atekwana
    • 1
  • Anna M. Cruse
    • 1
  • Loago Molwalefhe
    • 2
  • Wellington R. L. Masamba
    • 3
  1. 1.Boone Pickens School of Geology, 105 Noble Research CenterOklahoma State UniversityStillwaterUSA
  2. 2.Department of GeologyUniversity of BotswanaGaboroneBotswana
  3. 3.Okavango Research InstituteUniversity of BotswanaMaunBotswana

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