Methane Formation and Future Extraction in Lake Kivu
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This chapter summarises the current knowledge on the vertical distribution of methane (CH4) and its formation in Lake Kivu. Additionally, we review the objectives and restrictions under consideration for sustainable extraction (safe, environmentally acceptable, and economically effective) of the enormous amount of CH4 from the lake. The harvested CH4 will be used to produce electricity which is desperately needed in both neighbouring countries: the Democratic Republic of the Congo and Rwanda.
From a system-analysis point of view, the following processes need to be included as the minimum for adequately evaluating the vertical and temporal development of the lake CH4 during extraction: (1) in situ CH4 formation occurring in the permanently stratified, anoxic deep-water, (2) CH4 oxidation in the oxic surface water, (3) natural lake-water upwelling caused by subaquatic springs, (4) artificial lake-water up- and downwelling due to extraction- and reinjection-related flows, and (5) upward diffusion caused by double diffusive convection and weak turbulence. Water density is parameterised as a function of temperature, salinity, and the two gases carbon dioxide and CH4. For the sake of clarity of the presentation, we use a simplified 4-box analysis and are neglecting the diffusion process (5). This allows for the essence of the CH4 extraction challenge to be conveyed while avoiding excessive complexities.
The system analysis for different CH4 extraction concepts clearly reveals that the depth of reinjection of the CH4-depleted deep-water is critical for the sustainability of the extraction and an optimal CH4 harvesting plan. Here, the suitability of different reinjection scenarios is compared by evaluating each of them in terms of the objectives “safety” (water column stability), “lake ecological integrity” (nutrient upward fluxes), and “economic viability” (amount of harvestable CH4). Comparison of model simulations, run over 50 years, revealed that (1) using lake surface (dilution) water for adjusting the density of the reinjection water and (2) reinjecting the nutrient-rich deep-water in the top 190 m are both unacceptable in terms of sustainability.
KeywordsNutrient Flux Density Stratification Upward Flux Methane Extraction Acetoclastic Methanogenesis
- Assayag N, Jézéquel D, Ader M, Viollier E, Michard G, Prévot F, Agrinier P (2008) Hydrological budget, carbon sources and biogeochemical processes in Lac Pavin (France): constraints from δ18O of water and δ13C of dissolved inorganic carbon. Appl Geochem 23:2800–2816. doi: 10.1016/j.apgeochem.2008.04.015 CrossRefGoogle Scholar
- Data Environnement (2003) The exploitation of methane in Lake Kivu – pilot station project. Report by Data Environnement France, 69ppGoogle Scholar
- Expert Working Group on Lake Kivu Gas Extraction (2009) Management prescriptions for the development of Lake Kivu gas resources. Report prepared for the Ministry of Infrastructure of the Republic of Rwanda and the Ministry of Hydrocarbons of the Democratic Republic of the Congo, 17 June 2009, 38ppGoogle Scholar
- Jones N (2003) Chock-full of methane, Lake Kivu stores enough energy to power all of Rwanda. New Sci 2384:17Google Scholar
- Sarmento H, Isumbisho M, Stenuite S, Darchambeau F, Leporcq B, Descy J-P (2009) Phytoplankton ecology of Lake Kivu (Eastern Africa): biomass, production and elemental ratios. Int Assoc Theor Appl Limnol 30:709–713Google Scholar
- Schmid M, Tietze K, Halbwachs M, Lorke A, McGinnis D, Wüest A (2004) How hazardous is the gas accumulation in Lake Kivu? Arguments for a risk assessment in light of the Nyiragongo Volcano eruption of 2002. Acta Vulcanol 14/15:115–121Google Scholar
- Tietze K (1978) Geophysikalische Untersuchung des Kivusees und seiner ungewöhnlichen Methangaslagerstätte–Schichtung, Dynamik und Gasgehalt des Seewassers. PhD thesis, Christian-Albrechts-Universität Kiel, 150ppGoogle Scholar
- Tietze K (1992) Cyclic gas bursts: are they a “usual” feature of Lake Nyos and other gas-bearing Lakes? In: Freeth SJ, Onuoha KM, Ofoegbu CO (eds) Natural hazards in West and Central Africa, Earth Evolution Sciences, International Monograph Series on Interdisciplinary Earth Sciences Research and Application. Vieweg, Brunswick and Wiesbaden, pp 97–107Google Scholar
- Tietze K (2007) Basic plan for monitoring, regulating and steering exploitation of the unique methane gas deposit in Lake Kivu: safely, environmentally soundly and with optimal yield. PDT GmbH − Physik-Design-Technik − Sensorik & Consulting, Celle. Report commissioned by the W + S Beteiligungs AG, Dinslaken, prepared for the Ministry of Infrastructure of the Republic of Rwanda, Kigali, 201ppGoogle Scholar
- Wüest A, Jarc L, Schmid M (2009) Modelling the reinjection of deep-water after methane extraction in Lake Kivu, Eawag and BTC for the Governments of Rwanda and the Democratic Republic of the Congo, Kastanienbaum Switzerland, 141pp, www.eawag.ch/forschung/surf/gruppen/kivu/methane_harvesting/kivu_simulation_report_eawag_2009.pdf