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Temporal variability and spatial distribution of suspended matter and organic carbon pool in the Zambezi River system

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(1)

Teodoru, C.R.

1

,

Borges, A.V.

2

, Nyoni, F.

3

, Nyambe, I.

(3)

, Darchambeau F.

2

& Bouillon, S.

1

1

K.U. Leuven, Department of Earth and Environmental Sciences, Leuven, Belgium

2

University of Liège, Chemical Oceanography Unit, Liège, Belgium

3

University of Zambia, IWRM Centre, Lusaka, Zambia

Temporal variability and spatial distribution of

suspended matter and organic C pool

in the Zambezi River system

AFRIVAL Project (African River Basins) http://ees.kuleuven.be/project/afrival/

(2)

The Zambezi River Basin – general characteristics

4

th

largest in Africa and the largest flowing in to the Indian Ocean (from Africa)

Total length: > 3000 km; Drainage basin: ~ 1.4 x 10

6

km

2

(shared by 8 countries)

Main tributaries: Kabompo (

270 m

3

/s

), Luangina (

65 m

3

/s

), Kwando (

53 m

3

/s

),

Gwayi (

85 m

3

/s

), Kafue (

370 m

3

/s

), Luangwa (

520 m

3

/s

), Shire (

115 m

3

/s

)

2 main reservoirs: Kariba (

5600 km

2

; 180 km

3

), and Cahora Bassa (

2600 km

2

; 50

km

3

)

Kariba Res.

Cahora Bassa Res.

Victoria Falls Zambezi Delta

Zambezi source Barotse Floodplains Foto: Patrick Wagner LUKANGA

(3)

The Zambezi River Basin – climate and 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

2. Dry season (May – Sep/Oct), corresponding to winter, with 5% of annual rainfall

Temperature across basin varies with elevation and, and less with latitude

Mean monthly t°: 13°C for higher elevation in S to 23°C in E (July); and 23°C

-31°C (Oct)

J u l A u g S e p O c t N o v D e c J a n F e b M a r A p r M a y J u n J u l A u g S e p O c t N o v D e c J a n F e b M a r A p r M a y J u n J u l 0 50 100 150 200 250 Dry Season May-Sep (40 mm) M o n th ly P re c ip it a ti o n [ m m ] Wet Season Oct-Apr (900 mm)

(4)

The Zambezi River Basin – hydrological cycle

Driven by seasonality in rainfall patterns, hydrological cycle of the basin has a

bimodal distribution with a single main peak flood (max. Q: Apr/May) and min.

flow in Oct/Nov

Due to regional rainfall distribution, northern tributaries contribute much more

water than southern ones

Average annual discharge at Zambezi Delta: 3500-4000 m

3

s

-1

1 0 /1 /2 0 1 0 1 1 /1 /2 0 1 0 1 2 /1 /2 0 1 0 1 /1 /2 0 1 1 2 /1 /2 0 1 1 3 /1 /2 0 1 1 4 /1 /2 0 1 1 5 /1 /2 0 1 1 6 /1 /2 0 1 1 7 /1 /2 0 1 1 8 /1 /2 0 1 1 9 /1 /2 0 1 1 1 0 /1 /2 0 1 1 1 1 /1 /2 0 1 1 1 2 /1 /2 0 1 1 1 /1 /2 0 1 2 2 /1 /2 0 1 2 3 /1 /2 0 1 2 4 /1 /2 0 1 2 5 /1 /2 0 1 2 6 /1 /2 0 1 2 7 /1 /2 0 1 2 8 /1 /2 0 1 2 9 /1 /2 0 1 2 1 0 /1 /2 0 1 2 1 1 /1 /2 0 1 2 1 2 /1 /2 0 1 2 1 /1 /2 0 1 3 2 /1 /2 0 1 3 3 /1 /2 0 1 3 4 /1 /2 0 1 3 5 /1 /2 0 1 3 6 /1 /2 0 1 3 7 /1 /2 0 1 3 8 /1 /2 0 1 3 9 /1 /2 0 1 3 1 0 /1 /2 0 1 3 1 1 /1 /2 0 1 3 1 2 /1 /2 0 1 3 1 /1 /2 0 1 4

0

1000

2000

3000

4000

5000

6000

7000

8000

2010-2011 Wet Season

D

is

c

h

a

rg

e

[

m

3

s

-1

]

Date [mm/dd/yy]

Victoria Falls Kariba Dam Dry Season 2011-2012 2012-2013

(5)

Sampling Strategy

3 campaigns: Wet (Feb-Apr) 2012, Wet (Jan-Apr) 2013, Dry (Oct-Dec) 2013

56 sites: 26 along Zambezi (Kariba & CB Res.), and 30 on tributaries (ITT Res.)

2 monitoring stations

(Feb 2012 – Dec 2013)

:

ZBZ.11

~ 5 km upstream the confluence with Kafue

KAF.10

~ 6 km upstream the confluence with Zambezi

1 0 /1 /2 0 1 0 1 1 /1 /2 0 1 0 1 2 /1 /2 0 1 0 1 /1 /2 0 1 1 2 /1 /2 0 1 1 3 /1 /2 0 1 1 4 /1 /2 0 1 1 5 /1 /2 0 1 1 6 /1 /2 0 1 1 7 /1 /2 0 1 1 8 /1 /2 0 1 1 9 /1 /2 0 1 1 1 0 /1 /2 0 1 1 1 1 /1 /2 0 1 1 1 2 /1 /2 0 1 1 1 /1 /2 0 1 2 2 /1 /2 0 1 2 3 /1 /2 0 1 2 4 /1 /2 0 1 2 5 /1 /2 0 1 2 6 /1 /2 0 1 2 7 /1 /2 0 1 2 8 /1 /2 0 1 2 9 /1 /2 0 1 2 1 0 /1 /2 0 1 2 1 1 /1 /2 0 1 2 1 2 /1 /2 0 1 2 1 /1 /2 0 1 3 2 /1 /2 0 1 3 3 /1 /2 0 1 3 4 /1 /2 0 1 3 5 /1 /2 0 1 3 6 /1 /2 0 1 3 7 /1 /2 0 1 3 8 /1 /2 0 1 3 9 /1 /2 0 1 3 1 0 /1 /2 0 1 3 1 1 /1 /2 0 1 3 1 2 /1 /2 0 1 3 1 /1 /2 0 1 4 0 1000 2000 3000 4000 5000 6000 7000 8000 2010-2011 Wet Season D is c h a rg e [ m 3 s -1] Date [mm/dd/yy] Victoria Falls Kariba Dam Dry Season

biweekly monitoring: Zambezi and Kafue

Wet 2012 D ry 2 0 1 3 2011-2012 2012-2013 Wet 2013

(6)

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 and δ

15

N) composition

of

POC, PN, DOC, DIC

Aquatic metabolism: community respiration, primary production

GHG (CO

2

, CH

4

, N

2

O) concentrations and fluxes

Headspace Technique

Membrane Equilibrator

Floating chamber

(7)

TSM – spatio-temporal dynamics

0 200 400 600 800 1000 1200 1400 1600 1 10 100 1000 Lukanga Swamps

ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry)

T S M K a fu e R iv e r [m g L -1 ]

Distance from source [km]

Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) Kafue Flats 0 500 1000 1500 2000 2500 3000 1 10 100 1000 Barotse Floodplains C.B. Res. (2012 wet) C.B. Res. (2013 wet) Kariba Res. (2012 wet)

Kariba Res. (2013 wet) Kariba Res. (2013 dry) ZBZ (2012 wet) ZBZ (2013 wet) ZBZ (2013 dry) T S M Z a m b e z i R iv e r [m g L -1 ]

Distance from source [km]

Shire River (6-11 mg L-1)

Zambezi River

Kafue River

Wet 2012 Wet 2013 Dry 2013 D Wet 2012 Wet 2013 Dry 2013

1 10 100 1000

Zambezi

Kafue

p>0.093 p>0.293 T S M [ m g L -1 ] p>0.109 p>0.912 NO interannual variability NO distinct seasonality

(8)

TSM – spatio-temporal dynamics

0 200 400 600 800 1000 1200 1400 1600 1 10 100 1000 Lukanga Swamps

ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry)

T S M K a fu e R iv e r [m g L -1 ]

Distance from source [km]

Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) Kafue Flats 0 500 1000 1500 2000 2500 3000 1 10 100 1000 Barotse Floodplains C.B. Res. (2012 wet) C.B. Res. (2013 wet) Kariba Res. (2012 wet)

Kariba Res. (2013 wet) Kariba Res. (2013 dry) ZBZ (2012 wet) ZBZ (2013 wet) ZBZ (2013 dry) T S M Z a m b e z i R iv e r [m g L -1 ]

Distance from source [km]

Shire River (6-11 mg L-1)

Zambezi River

Kafue River

Zam bezi Karib a R es. C.B. Res . Kabo mpo Kafue ITT Res . Lung a Luan gwa Luns emfw a Maz oe Shire 1 10 100 1000 T S M r a n g e [ m g L -1 ]

Wet 2012 Wet 2013 Dry 2013 D Wet 2012 Wet 2013 Dry 2013

1 10 100 1000

Zambezi

Kafue

p>0.093 p>0.293 T S M [ m g L -1 ] p>0.109 p>0.912 NO interannual variability NO distinct seasonality

(9)

POC, PN, δ

13

C

POC

, C:N ratio

1 10 100 1000 0.1 1 10 100 % P N [ % ] TSM [mg L-1] 1 10 100 1000 0.1 1 10 100 ITT Res. Lunga Luangwa Lunsemfwa Mazoe Shire Zambezi Kariba Res. C.B. Res. Kabompo Kafue % P O C [ % ] -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 0.1 1 10 100 Lunga Luangwa Lunsemfwa Mazoe Shire Zambezi Kariba Res. C.B. Res Kabompo Kafue ITT Res. P e rc e n t P O C [ % ] δ13C POC [‰] -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 2 4 6 8 10 12 14 16 18 20 22 Kafue ITT Res. Lunga Luangwa Lunsemfwa Mazoe Shire Zambezi Kariba res. C.B. Res. Kabompo M o la r C :N r a tio δ13C POC [‰]

POC - predominantly terrestrial (C3) origin:

Luangwa

– more towards C4 soil C;

Reservoirs – fraction from phytoplankton

(10)

DOC– spatio-temporal dynamics

Zambezi River

Kafue River

0 500 1000 1500 2000 2500 3000 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Shire River C.B. Res. (2012 wet) C.B. Res. (2013 wet) Kariba Res. (2012 wet)

Kariba Res. (2013 wet) Kariba res. (2013 dry) ZBZ (2012 wet) ZBZ (2013 wet) ZBZ (2013 dry) D O C Z a m b e z i R iv e r [m g L -1 ]

Distance from source [km]

Barotse Floodplains 0 200 400 600 800 1000 1200 1400 1600 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Kafue Flats Lukanga Swamps

ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry)

D O C K a fu e R iv e r [m g L -1 ]

Distance from source [km]

Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry) Zam bezi Karib a R es. C.B . Res . Kabo mpo Kafue I.T.T . Res . Lung a Luan gwa Luns emfw a Maz oe Shire 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 R a n g e D O C [ m g L -1 ]

Wet 2012 Wet 2013 Dry 2013 G1 Wet 2012 Wet 2013 Dry 2013

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 D O C [ m g L -1 ]

Zambezi

Kafue

p>0.002 p>0.018 p>0.258 p>0.019 Distinct seasonality

(11)

DOC isotopic signature (δ

13

C

DOC

), and Age (∆

14

C

POC

, ∆

14

C

DOC

)

-32 -30 -28 -26 -24 -22 -20 -18 -32 -30 -28 -26 -24 -22 -20 -18 Lunga Luangwa Lunsemfwa Mazoe Shire Zambezi Kariba Res. C.B. Res. Kabompo Kafue I.T.T. Res. δ 1 3 C D O C [ ‰ ] δ13C POC [‰] 1:1 0 1000 2000 3000 -20 -10 0 10 20 30 40 50 60 70 80

Distance from source [km]

∆ 1 4 C P O C [ ‰ ] 20 30 40 50 60 70 80 90 100 110 120 Zambezi (∆14C DOC) Reservoirs (∆14CDOC) Tributaries (∆14CDOC) Zambezi (∆14C POC) Reservoirs (∆14CPOC) Tributaries (∆14CPOC) ∆ 1 4 C D O C [ ‰ ] 0 500 1000 1500 2000 2500 3000 -28 -26 -24 -22 -20 -18 1.0 2.0 3.0 4.0 5.0 6.0 -28 -26 -24 -22 -20 -18

Distance from source [km]

δ 1 3 C D O C [ ‰ ] Zambezi Reservoirs δ 1 3 C D O C [ ‰ ] DOC [mg L-1] r2 = 0.5

DOC – mostly C3 origin with minimal

in-stream autochthonous production

δ

13

C

DOC

: δ

13

POC

– decupling

between DOC and POC sources

14

C – modern nature of riverine

(12)

Carbon Mass

Balance

Area Q TSM POC DOC DIC CO2 CH4 C Yield GHG C Deposition C Export

[km2] [m3s-1] [kt C yr-1]

Zambezi at Delta 11445 3779

9558

306

263

3672

2681 46.1 7163 2727 196 4240

Kafue at M.S. 658 314

196

8

45

205

459 4.6 738

464

16

258

Zambezi at M.S. 6403 1237

282

34

99

398

385 20.2 1042

391

120

531

Zambezi + Kafue =>

Zambezi & Kafue =>

at monitoring stations (M.S.)

(13)

Thank you for your attention!

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