AFRIVAL Project (African River Basins) http://ees.kuleuven.be/project/afrival/ EGU General Assembly 2014, Vienna Wetlands influencing river biogeochemistry: the case study of the Zambezi and the Kafue Rivers Cristian R. Teodoru 1, Frank C. Nyoni 2,ImasikuNyambe 2, Alberto V. Borges 3, and Steven Bouillon 1 1 K.U. Leuven, Belgium; 2 University of Zambia, IWRM Center, Zambia, 3 University of Liege, Belgium 2 nd International Conference Water Resources and Wetlands Tulcea, 11-13 Sept, 2014
Introduction: AFRIVAL project (2009-2014) AFRIVAL African river basin: catchment scale carbon fluxes and transformation (http://ees.kuleuven.be/project/afrival/) joint European Research Council Starting Grant project hosted at the Department of Earth & Environmental Sciences (K.U. Leuven, Belgium) and the Chemical Oceanography Unit(Université de Liège, Belgium) 5-yearfundingtoexploretheroleofAfricanriversincarboncycling Fieldwork within AFRIVAL has taking place in: Kenya: Tana& Sabaki Rivers Niger: Niger River Gabon: Ogooué River Madagascar: Bestiboka and Rianila Rivers Tana River DRC Congo & Central African Republic: Congo River Basin Zambia& Mozambique: Zambezi River Basin Ogooué River Niger River
Study site: the Zambezi River The Zambezi River general characteristics 4 th largestinafricaandthelargestflowingintotheindianocean(fromafrica) Totallength:>3000km;Drainagebasin:~1.4x10 6 km 2 (sharedby8countries) AverageannualdischargeatZambeziDelta:3800-4130m 3 s -1 2largereservoirs:Kariba(5580km 2 ;180km 3 ),andcahorabassa(2670km 2 ;52km 3 ) 2majorwetlands:BarotseFloodplains(7700km 2 ),andchobe(1500km 2 ) Barotse Floodplains Zambezi source Victoria Falls Barotse Floodplains Chobe Kariba Reservoir
Study site: the Kafue River The Kafue River general characteristics Main tributary of the Zambezi River(entirely within Zambia) Totallength:>1500km;Drainagebasin:~156,000km 2 AverageannualdischargeattheconfluencewithZambezi:370m 3 s -1 2reservoirs:ItezhiTehzi(365km 2 ;5.5km 3 ),andkafuegorge(13km 2 ;0.8km 3 ) Majorwetlands:Lukanga(2100km 2 ),andkafueflats(6500km 2 ) Lukanga Kafue Flats
General characteristics: Climate & Rainfall Climate is classified as humid subtropical or tropical wet and dry Annual rainfall varies with latitude: 1400 mm in N to 400-500 mm in S (mean average rainfall for entire basin: 940 mm) Two seasons: 1. Wet season(oct/nov Apr) corresponding to summer, with 95% of annual rainfall(900 mm) 2. Dry season (May Sep/Oct), corresponding to winter, with 5% of annual rainfall(40 mm). Monthly Precipitation [mm] 250 200 150 100 50 Wet Season Oct-Apr (900 mm) Dry Season May-Sep (40 mm) 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
General characteristics: Hydrological cycle Driven by seasonality in rainfall patterns resulting in a bimodal distribution with a single main peakflood(max. Q: Apr/May) and min. flow in Oct/Nov 5000 4000 3000 2000 1000 wet season dry season Zambezi River Zambezi (Victoria Falls) Kariba Dam 0 2000 1500 1000 500 Kafue River Kafue (Hook Bridge) Kafue Gorge Dam 0 1/1/2012 2/1/2012 3/1/2012 4/1/2012 5/1/2012 6/1/2012 7/1/2012 8/1/2012 9/1/2012 10/1/2012 11/1/2012 12/1/2012 1/1/2013 2/1/2013 3/1/2013 4/1/2013 5/1/2013 6/1/2013 7/1/2013 8/1/2013 9/1/2013 10/1/2013 11/1/2013 12/1/2013 1/1/2014 Discharge [m 3 s -1 ] Discharge [m 3 s -1 ] Data [mm/dd/yy]
Methods: Sampling strategy 3 sampling campaigns: Wet(Feb-Apr) 2012, Wet(Jan-Apr) 2013, Dry(Oct-Dec) 2013 56 sampling sites: 26 along Zambezi (Kariba & CB Res.), 13 along the Kafue (ITT Res.), and 17 on different tributaries 8000 7000 Wet Season Dry Season Victoria Falls Kariba Dam 6000 biweekly monitoring: Zambezi and Kafue 5000 Wet 2012 Wet 2013 4000 3000 2000 1000 0 2010-2011 Discharge [m 3 s -1 ] 10/1/2010 11/1/2010 12/1/2010 1/1/2011 2/1/2011 3/1/2011 4/1/2011 5/1/2011 6/1/2011 7/1/2011 8/1/2011 9/1/2011 10/1/2011 11/1/2011 12/1/2011 1/1/2012 2/1/2012 3/1/2012 4/1/2012 5/1/2012 6/1/2012 7/1/2012 8/1/2012 9/1/2012 10/1/2012 11/1/2012 12/1/2012 1/1/2013 2/1/2013 3/1/2013 4/1/2013 5/1/2013 6/1/2013 7/1/2013 8/1/2013 9/1/2013 10/1/2013 11/1/2013 12/1/2013 1/1/2014 Dry 2013 2011-2012 2012-2013 Date [mm/dd/yy]
Methods: Measured parameters Physico-chemical: ph, O 2, t, conductivity, Total Alkalinity Total Suspended Matter (TSM) and sediment characterization Concentration and stable isotope (δ 13 C) composition of POC, DOC, DIC, Aquatic metabolism: Bacterial respiration and primary production GHG (CO 2, CH 4, N 2 O) concentrations and fluxes Radiocarbon isotopes dating (Δ 14 C POC and Δ 14 C DOC ) In-situ CO 2 measurements Headspace Technique Membrane Equilibrator Floating chamber
Results: ph spatio-temporal variability ph [NBS] 10.0 Zambezi (2012 wet) Kariba Res. (2012 wet) C.B. Res. (2012 wet) Zambezi (2013 wet) Kariba Res. (2013 wet) C.B. Res. (2013 dry) Zambezi (2013 dry) kariba Res. (2013 dry) 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 Barotse Floodplains Zambezi River Chobe 0 500 1000 1500 2000 2500 3000 ph [NBS] 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) Kafue River ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry) Lukanga Kafue Gorge Reservoir Kafue Flats 5.0 0 200 400 600 800 1000 1200 1400 1600 ph decreases(more acidic) in-, and downstream wetlands
Results: DO spatio-temporal variability Zambezi River Kafue River Dissolved Oxyen [%] 180 ZBZ (2012 wet) Kariba Res. (2012 wet) ZBZ (2013 wet) Kariba Res. (2013 wet) ZBZ (2013 dry) Kariba Res. (2013 dry) 160 140 120 100 80 60 40 20 Barotse Floodplains Chobe 2 mg L -1 C.B. Res. (2012 wet) C.B. Res. (2013 wet) C.B. Res. (2013 dry) Dissolved Oxygen [%] 180 Kafue (2012 wet) ITT Res. (2012 wet) Kafue (2013 wet) ITT Res. (2013 wet) Kafue (2013 dry) ITT Res. (2013 dry) 160 140 120 100 80 60 40 20 2 mg L -1 Lukanga Kafue Flats 0 0 500 1000 1500 2000 2500 3000 0 0 200 400 600 800 1000 1200 1400 1600 SignificantDO decreasein-, and downstream wetlands (below2 mg L -1 )
Results: CO 2 spatio-temporal dynamics Zambezi River Kafue River 14000 Zambezi (2012 wet) Kariba Res. (2012 wet) C.B. Res. (2012 wet) Zambezi (2013 wet) Kariba Res. (2013 wet) C.B. Res. (2013 wet) Zambezi (2013 dry) Kariba Res. (2013 dry) 12000 10000 Chobe Shire >13000 ppm 14000 12000 10000 Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry) Kafue Flats Kafue Gorge Reservoir pco 2 [ppm] 8000 6000 4000 Barotse Floodplains Kariba & CB Dam hypolimnetic water release pco 2 [ppm] 8000 6000 4000 Lukanga 2000 2000 0 Degassing Vic. Falls 0 500 1000 1500 2000 2500 3000 0 atm. CO 2 0 200 400 600 800 1000 1200 1400 1600 Substantialincreasein CO 2 in-, and downstream wetlands
Results: CH 4 spatio-temporal dynamics Zambezi River Kafue River 100000 10000 CH 4 [nmol L -1 ] 1000 100 Zambezi (2012 wet) Zambezi (2013 wet) Zambezi (2013 dry) Barotse Floodplains Kariba Res. (2012 wet) Kariba Res. (2013 wet) Kariba Res. (2013 dry) Chobe C.B. Res. (2012 wet) C.B. Res. (2013 dry) 100000 10000 CH 4 [nmol L -1 ] 1000 100 Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry) Kafue Flats 10 10 Lukanga 1 0 500 1000 1500 2000 2500 3000 1 0 200 400 600 800 1000 1200 1400 1600 CH 4 increases substantiallyin-, and downstream wetlands
Results: TSM & POC spatio-temporal variability Zambezi River Kafue River 1000 ZBZ (2012 wet) ZBZ (2013 wet) ZBZ (2013 dry) Kariba Res. (2012 wet) Kariba Res. (2013 wet) Kariba Res. (2013 dry) C.B. Res. (2012 wet) C.B. Res. (2013 wet) 1000 Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry) Chobe Kafue Flats TSM [mg L -1 ] 100 10 Barotse Floodplains TSM [mg L -1 ] 100 10 Lukanga 1 1 0 500 1000 1500 2000 2500 3000 0 200 400 600 800 1000 1200 1400 1600 26 24 22 Barotse Floodplains Chobe Lukanga Kafue Flats % POC of TSM [%] 20 18 16 14 12 10 8 5% increase 2% increase 11% increase -No clear TSM trend -Notable increasein the relative contribution ofpoc to the TSMin-, and downstream wetlands 6 UPSTREAM DOWNSTREAM
Results: DOC spatio-temporal variability Zambezi River Kafue River 8.0 ZBZ (2012 wet) Kariba Res. (2012 wet) C.B. Res. (2012 wet) ZBZ (2013 wet) Kariba Res. (2013 wet) C.B. Res. (2013 wet) ZBZ (2013 dry) Kariba res. (2013 dry) 7.0 6.0 Barotse Floodplains Chobe 8.0 7.0 6.0 Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) Lukanga ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry) Kafue Flats DOC [mg L -1 ] 5.0 4.0 3.0 DOC [mg L -1 ] 5.0 4.0 3.0 2.0 2.0 1.0 1.0 0.0 0 500 1000 1500 2000 2500 3000 0.0 0 200 400 600 800 1000 1200 1400 1600 DOC increasesin-, and downstream wetlands
Results: Carbon Budget Total C Yield: 7165 ktc yr -1 River / Reservoir Area CO 2 flux CH 4 flux CO 2 load CH 4 load Emission Deposition [km 2 ] [mg C m -2 d -1 ] [kt C yr -1 ] Kafue River without reservoirs 287 2962 20.0 310 2.1 312 - Itezhi Tezhi Reservoir 364 1102 18.1 146 2.4 149 16 Kafue Gorge Reservoir 13 956 17.4 5 0.1 5 1** Kafue River with reservoirs 664 1903* 18.9* 461 4.6 466 17 Total C Yield: 23,485 ktc yr -1 Emissions increase 7 fold (16,300 ktc yr -1 ) Zambezi River without reservoirs 1879 4291 45.0 2943 30.8 2974 - Kariba Reservoir 5364-191 4.8-374 9.3-364 120 Cahora Bassa Reservoir 2670-356 1.4-347 1.4-346 60** Zambezi River with reservoirs 9913 614* 11.5* 2222 41.5 2264 180 Zambezi & Kafue Rivers with reservoirs 10576 695* 12.0* 2683 46.1 2729 196
Concluding remarks Wetlands/floodplains have large influence on river biogeochemisty: Decreasing the ph and Dissolved Oxygen concentrations Increasing the Temperature and Evaporation IncreasingCO 2 andch 4,DOCandPOCconcentrations Highly productive ecosystems, wetlands are essential elements of carbon cycle, capable of shifting significantly the balance between Emissions, Storage and Transport components of carbon budgets. Further research (more quantitative data) are needed to better constrain the role ofwetlandsinboth regionaland globalcbudgets,which sofarhas been largely overlooked.
Thank you for your attention! Pirates of the Zambezi
Introduction: Inland waters in global C cycle The global carbon cycle Major carbon reservoirs Atmosphere Biosphere Ocean Global C budget studies are mostly limited to the three major carbon reservoirs with little or no focus on inland waters
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