The Makgadikgadi Basin, a Dynamic Hydrological Input and Aeolian Output System

The Makgadikgadi basin, a dynamic hydrological input and aeolian output system.

Frank D. Eckardt a,* , Robert G. Bryant b, Warren W. Wood c, Kevin White d, Baruch Spiro e, Graham McCulloch f a Environmental and Geographical Sciences, U niversity of Cape T own, P Bag X3, Rondebosch, 7701, South Africa b Department of Geography, Uni versity of Sheffiel d, Dept. of Geography, Wi nter Street, Sheffiel d, S10 2TN, U K c Department of Geol ogical Sciences, Michigan State Uni versity, East Lansi ng, Michigan 48824, USA d Department of Geography, The Uni versity of R eading, Whiteknights, R eading, UK e Department of Miner alogy, The Natural Histor y Museum, Cromwell Road, London SW7 5BD, UK f Department of Z ool ogy, Uni versity of Dublin, Trinity College, Dublin 2, Irel and * Correspondi ng author: [email protected]

This study focuses on modern day processes surrounding the Makgadikgadi pan basin system in NE Botswana. We present results on the chemistry and dynamics of fluvial surface water inputs, examine the nature and chemistry of various surface and subsurface evaporation products, provide data on the nature and chemistry of aeolian outputs and demonstrate the impact of aerosol deposition in the downwind sector of the pans. During the wet season surface water enters the saline pans and precipitates mostly calcite and halite, as well as dolomite and traces of other salts associated with the desiccation of the lake. The hypersaline subsurface brine (up to TDS 190,000 mg/l) is homogenous with minor variations due to pumping by BotAsh mine (Botswana Ash (Pty) Ltd), which extracts 2400 m 3 of brine/h from a depth of 38m. Average Pan surface sediments yielded 15 % Na and 22 % Cl which has been identified in the downwind dust and could be traced as far as Johannesburg during a single dust episode in 2003 . Data for the 1980–2000 period suggest that dust loadings are intermittently influenced by the extent and frequency of lake inundation, fluvial sediment influx, and surface wind speed variability. In addition, a significant proportion of the observed variability in the dust and hydrological cycle of this source could be attributed to El Nino-Southern Oscillation (ENSO) and Indian Ocean sea surface temperature anomalies. Detailed soil chemistry data suggests that the pans produce over three million metric tons of chloride, sodium, and bicarbonate each year. In addition it was noted that significant masses of naturally-occurring radioactive 226-radium and 238-uranium are present in the aerosol load.

Keywords: Makgadikgadi, hydrology, brine, evaporites, aerosols The Makgadikgadi Basin

A Dynamic Hydrological input and Aeolian Output System

Presented By Frank Eckardt EGS Department University of Cape Town Rondebosch South Africa

945 m Gamsberg Southern African Topography 2000 Kalahari Basin Escarpment

1500 Elevation (m) Windhoek Ghanzi

1000

500 Kuiseb Limpopo

0 Rainfall (mm) Southern African Rainfall 800 Tropical 600

400

200 Semi-arid Hyper-arid 0 i s zi s n e g ek le i n p we w ur itv o ron W bab ako o sb Karibib o Gha R Ser ne Maputo Windho G Gab Francisto han Swakopmund Jo A Dynamic System Florida Air Boat

June 2005 April 2000

April 2008

August 2003

Regatta on Sua Pan Bigg G - Department of Geography, University of Sheffield, Sheffield, UK Bryant RG - Department of Geography, University of Sheffield, Sheffield, UK Coetzee S - University of Botswana, Gaborone Botswana Eng K - U. S. Geological Survey, Reston, Virginia , USA Helmlinger M – NASA JPL, Pasadena, California USA Irvine K - Department of Zoology, University of Dublin, Trinity College, Dublin, Ireland Kraemer T U. S. Geological Survey, Reston, Virginia, USA Nkala G - Botash Pty. Ltd, Sua Town, Botswana Mahowald N - National Centre for Atmospheric Research, Boulder, Colorado, USA McCulloch G - Department of Zoology, University of Dublin, Dublin , Ireland Resane T - University of the Witwatersrand, Johannesburg, South Africa Ross S - Department of Geography, University of Sheffield, Sheffield, UK Spiro B Department of Mineralogy, The Natural History Museum, London Vickery K - Environmental and Geographical Science, Uni of Cape Town, South Africa Washington R – School of Geography, Oxford, UK White K - Department of Geography, The University of Reading, Reading, UK Wood WW - Department of Geological Sciences, Michigan State University,USA Wood WW, Eckardt FD, Kraemer TF, Eng K.(in press) Quantitative eolian transport of evaporate salts from the Makgadikgadi Depression (Ntwetwe and Sua Pans) in northeastern Botswana. Implications for regional ground-water quality. In Sabka Ecosystems Volume 3, Africa, Barth H-J, Böer B (eds) Kluwer: Dordrecht.

Eckardt FD, R.G. Bryant, G. McCulloch, B. Spiro, W. W. Wood (2008) The hydrogeochemistry of a semi-arid pan basin case study: Makgadikgadi, Botswana Applied Geochemistry, Volume 23, Issue 6, Pages 1563-1580

Bryant R.G. Bigg G., Mahowald N, Eckardt FD, and Ross S. (2007). Climate controls on dust emissions from S African sources. Journal of Geophysical Research - Atmospheres. Volume 23, Issue 6, June 2008, Pages 1563-1580

McCulloch, G., Irvine, K., Eckardt, FD. and Bryant, R. (2007).Hydrochemical fluctuations and crustacean community composition in an ephemeral saline lake (Sua Pan, Makgadikgadi Botswana). Hydrobiologia, vol. 596, no. 1, pp. 31-46

White K, Eckardt FD (2006) Geochemical mapping of the Makgadikgadi basin, Botswana using moderate and high resolution remote sensing instruments, Earth Surface Processes and Landforms, 31: 665-681 SAFARI 2000 Aerosols in Southern Africa Drought

2000 Lake

Bryant R.G. et al Input Flamingo Tracking Brine Shrimp & Water

Feed

Breed

Data via McCulloch Surface Water Samples Input Inflow water 87 mg/l to 1,711 mg/l • River Inputs and Dec Lake samples 258 mg/l to 17,788 mg/l • Lake Brine Evolution April Lake samples 709 mg/l to 31,172 mg/l Eckardt FD et al.

North Lake (NL)

Middle Lake (ML)

Flood Water (FW)

South Lake (SL) From Input to Storage

• The soils in the catchment add much of the Ca, HCO3, Mg and K • Inflow into Sua generally Ca–HCO3 • Transformation from calcium and bicarbonate rich water to sodium and chloride domination • Mixing of surface waters and recycling of surface salts • Production wells and lake waters are tightly grouped in the Na and Cl sectors • Na and Cl are most likely provided by marine atmospheric aerosols

Cations Anions

• Subsurface Brine Wellfield • Production and Monitoring Wells 38m depth

Wellfield (WF) From Input to Storage Ion log concentration (mmol/L) plotted against Cl Average Flood Water (FW) North Lake (NL) Middle Lake (ML) South Lake (SL) Na and K and remain in solution Wellfield (WF)

Eckardt FD et al. From Input to Storage

Ca and Mg are lost from solution as evaporation products (calcite and dolomite formation)

Eckardt FD et al. From Input to Storage

SO2 remains in solution

Eckardt FD et al. The Earth Observatory Storage & Brine Product • 98 wells operational since 1991 • brine 90,000-190,000 mg/l • rate of 2400m 3/h • deposit 1 billion m 3 • semi-confined clay aquifer

Evaporation Products

Sodium Carbonate Na2CO 3 Sodium Sulphate Na2SO 4 Sodium Chloride NaCl

Eckardt FD et al. Storage δ34 S average 34.35 (Sulphur Isotopes) Makgadikadi

Namibia

• It appears that the major control on the variability of d34S is its source. • Schroder et al. (2004) studied the d34S of sulfates in Oman across the Neoproterozoic Cambrian boundary • Global marine value for that period is in the range 35–40‰. • Further high values of d34S are reported from sulfates of Cambrian age elsewhere • Claypool et al., (1980), Irkutsk Basin, 26.7–34.2‰, Amadeus Basin, 26.8–32.0‰, • Peryt et al. (2005), East Siberian Basin, 22.6–34.5‰. Eckardt FD et al. Storage 87 Sr/ 86 Sr (Strontium Isotopes) Nata River North Lake Subsurface Brine

0.730000

0.728000

0.726000

0.724000 Min Max 0.722000

0.720000

0.718000

0.716000

d rth le oo tse Lake Nat a e dd Fl os No Mi South mowane M e S Subsurface

•Sr isotope for surface water from the Nata River and Lake are decoupled from the underlying brine •The variability indicator of the heterogeneity of the sources at Sua Pan •Subsurface water has a limited response to changes in surface processes.

Eckardt FD et al.

Output Southern Africa Burning Biomass 6000 km 2 Peak Aerosol Emission in September JAS TOMS Mean 1980-1999

Worlds Dustiest Place (Top11) TOMS AI Rainfall mm Bodele D epressi on of south central Sahara >30 17

West Sahar a in Mali and Mauritania >24 5–100

Arabia (souther n Oman/Saudi border) >21 <100

Eastern Sahara (Li bya) >15 22 Southwest Asi a (Makran coast) >12 98

Taklamakan/Tarim Basin >11 <25

Etosha Pan (Namibia) >11 435–530

Lake Eyre Basi n (Australia) >11 150–200

9 Makg adikg adi Basin (Botswan a) >8 460

Salar de U yuni (Bolivia) >7 178

Great Basi n (United States) >5 400

9 Etosha Makadikadi 8

3 Mea Monthly n TOMSA AI

0 jan feb mar apr m ay jun jul aug s ep oct nov dec Via Richard Washington Output • Historic stockpile – Loess soils (China), Bodele (Transport Ltd.) Global Dust • Pan – Seasonal replenishment (Amadeus, Etosha) (Supply Ltd.)

Point Sources • Desertification (Dust Bowl 1934/Sahel 60-70‘s) • Palaeolake margin – recent exposure (Aral Sea, Owens L.) Output Meteosat Daily Dust 2005-2008 MSG Brightness Temperature Temperature Brightness Product “Pink Dust Method” MODIS True Colour

Kathryn Vickery - EGS MSc Dust Samples Dust Quartz Output

Si is the prevailing element

Sticky SEM Stub

Halite

NaCl is a pan/evaporative indicator

Clay Calcium

Also found Al, Fe, Ca as well as K and Mg

Eckardt FD et al. Output Dust Samples Na • Upwind (East) Cl • Downwind (West)

Pan surface samples yielded 15 % (Na) and 22 % (Cl) Dust Samples Output

25.0 Downwind concentrations range from 12 – 7 % (Na) and 14 to 9 % (Cl) 20.0 Gaborone dust is at 13 % Na and 19 % Cl. Traces of NaCl in Joburg and Okavango Delta

15.0 Na Cl 10.0

5.0 % concentration

0.0 o d d ce nd g n me i one n u or oster pwi urfa pl b K ava U S h a k G O an arc Downw annesburg Eckardt FD et al. P Pan h Pan Sidewin M Jo Output Long Range Transport Output

Too much water produces no dust

Bryant R.G. et al Cyclone Eline February 2000

The Earth Observatory • Variations in rainfall entering the Nata catchment are consistent with SST controls. • Close relationships between extreme regional rainfall events, flow in the Nata River catchment, and subsequent flooding events on the surface of Sua Pan. • Importance of rare landfall of tropical storms and depression • Relationship between ENSO and dust

Bryant R.G. et al Double Lake Deposition Texas High Plains

Wood, W. W., and W. E. Sanford (1995) Eolian Transport, Saline Lake Basins, and Groundwater Solutes, Water Resour. Res. , 31(12), 3121–3129. Deposition Soil Samples • Soil Contribution to Floodwaters

Terra MODIS Mixture Map • Pan Aerosol Deposition (Trace)

•Surface Carbonate Concentration

0% 100%

White K, Eckardt FD (2006) Geochemical Wood WW, Eckardt FD, Kraemer TF, Eng K.(in press) Quantitative eolian mapping of the Makgadikgadi basin, Botswana transport of evaporate salts from the Makgadikgadi Depression (Ntwetwe and using moderate and high resolution remote Sua Pans) in northeastern Botswana. Implications for regional ground-water sensing instruments, Earth Surface Processes quality. In Sabka Ecosystems Volume 3, Africa , Barth H-J, Böer B (eds) and Landforms, 31: 665-681 Kluwer: Dordrecht. Deposition Logarithmic concentration of soil leaches as a Wood WW et al function of logarithm of distance from the source

Metric Tons Per Annum Solute footprint Sodium 309,905 2 140 km wide and 125 km long (17,500 km )in size Bicarbonate 2,737,266 Chloride 176,615 Deposition

Naturally occurring 226-radium 0.0154 238-uranium 52,159 (Metric Tons Per Annum)

Wood WW et al The Makgadikgadi Is Not A Complicated System

• Inflow into Sua generally Ca–HCO 3 (Soils)

• Mixing of surface runoff and pan surface salts (NaCl)

• ENSO and cyclones influence lake hydrology

•Surface evaporation produces calcite, dolomite and halite

• Subsurface brine is similar but has bedrock contributions

• Dust depends on surface water recharge but limited by lake cover

• Dust rich in clays, salt and calcium carbonate

• Chemical footprint 17,500 km 2

• Regional Dust Dispersal Possible Pans – Soils, Duricrust, Groundwater

Chivas, A.R., Andrew, A.S., Lyons, W.B., Bird, M.I., Donnelly, T.H., 1991. Isotopic constraints on the origin of salts in Australian plays, 1. Sulphur. Palaeogeogr., Palaeoclimatol., Palaeoecol. 84, 309–332

Drake NA, Eckardt FD, White KH (2004) Sources of sulphur in gypsiferous sediments and crusts and pathways of gypsum redistribution in southern Tunisia. Earth Surface Processes and Landforms 29, 1459-1471.

Risacher, F., Alonso, H., Salazar, C., 2003. The origin of brines and salts in Chilean salars: a hydrochemical review. Earth Sci. Rev. 45, 249–293. 4mm/yr or 4 L/m2yr of Recharge

Solute a b R2 RMSE Area Under Background Average Conc. Bulk Amount Curve Conc. Over 125km Deposited Metric Tons/yr Sodium 341.8 -1.1305 0.816 0.285 790.902 1.9 4.427 310,000 Bicarbonate 1064.8 -0.6687 0.571 0.309 10825.476 47.5 39.104 2,740,000 Chloride 39.956 -0.2042 0.582 0.089 2190.206 15 2.522 177,000 226-Radium 2.3491 -0.3895 0.434 1.757 98.452 0.3 0.488 0.0154 238-Uranium 2.4142 -0.3939 0.347 1.848 104.230 0.275 0.559 52,000

y = a xb Regression: recharge flux of 4 mm/yr y is the concentration x is the distance from source (km) a is the intercept b is the slope

• Establishing a linear regression between the sample concentrations and the distance from the source •The distance where the sampled concentrations reached a background value was identified as the upper limit •The area beneath the curves was determined by integration from the closest site at 4 km to approximately 125 km downwind. . •Average concentrations was obtained by dividing the area underneath the curve by the effective distance of transport 125 k •The background concentrations were then subtracted from these average concentrations before any bulk estimates were calculated.

Wood WW et al The Makgadikgadi basin, a dynamic hydrological input and aeolian output system.

Keywords: Makgadikgadi, hydrology, brine, evaporites, aerosols