Wetlands influencing river biogeochemistry: the case study ... · Wetlands influencing river biogeochemistry: the case study of the Zambezi and the Kafue Rivers AFRIVAL Project (AfricanRiver

Wetlands influencing river

biogeochemistry: the case study of the

Zambezi and the Kafue Rivers

AFRIVAL Project (African River Basins)

http://ees.kuleuven.be/project/afrival/

EGU General Assembly 2014, Vienna

Cristian R. Teodoru1, Frank C. Nyoni2, Imasiku Nyambe2, Alberto V. Borges3, and

Steven Bouillon1

1 K.U. Leuven, Belgium; 2 University of Zambia, IWRM Center, Zambia, 3 University of Liege, Belgium

2nd 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-year funding to explore the role of African rivers in carbon cycling

� Fieldwork within AFRIVAL has taking place in:

•Kenya: Tana & Sabaki Rivers

•Niger: Niger River

•Gabon: Ogooué River

•Madagascar: Bestiboka and Rianila Rivers

•DRC Congo & Central African Republic: Congo River Basin

•Zambia & Mozambique: Zambezi River Basin

Tana River Ogooué River

Niger River

Study site: the Zambezi River

The Zambezi River – general characteristics

• 4th largest in Africa and the largest flowing in to the Indian Ocean (from Africa)

• Total length: > 3000 km; Drainage basin: ~ 1.4 x 106 km2 (shared by 8 countries)

• Average annual discharge at Zambezi Delta: 3800-4130 m3 s-1

• 2 large reservoirs: Kariba (5580 km2; 180 km3), and Cahora Bassa (2670 km2; 52 km3)

• 2 major wetlands: Barotse Floodplains (7700 km2), and Chobe Swamps (1500 km2)

Kariba Reservoir

Victoria Falls

Zambezi source

Barotse Floodplains

Chobe Swamps

Barotse Floodplains

Study site: the Kafue River

The Kafue River – general characteristics

• Main tributary of the Zambezi River (entirely within Zambia)

• Total length: > 1500 km; Drainage basin: ~ 156,000 km2

• Average annual discharge at the confluence with Zambezi: 370 m3 s-1

• 2 reservoirs: Itezhi Tehzi (365 km2; 5.5 km3), and Kafue Gorge (13 km2; 0.8 km3)

• Major wetlands: Lukanga Swamps (2100 km2), and Kafue Flats (6500 km2)

Lukanga Swamps 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).

Jul

Aug

Sep Oct

Nov

Dec Jan

Feb

Mar

Apr

May Jun

Jul

Aug

Sep Oct

Nov

Dec Jan

Feb

Mar

Apr

May Jun

Jul0

50

100

150

200

250

Dry SeasonMay-Sep(40 mm)

Mon

thly

Pre

cipi

tatio

n [m

m]

Wet SeasonOct-Apr

(900 mm)

General characteristics: Hydrological cycle

• Driven by seasonality in rainfall patterns resulting in a bimodal distribution with a single

main peak flood (max. Q: Apr/May) and min. flow in Oct/Nov

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

/201

2

11/1

/201

2

12/1

/201

2

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

/201

3

11/1

/201

3

12/1

/201

3

1/1/

2014

0

500

1000

1500

2000

dry season

Kafue (Hook Bridge) Kafue Gorge Dam

Dis

char

ge [m

3 s-1]

Data [mm/dd/yy]

Zambezi River

Kafue River

wet season

0

1000

2000

3000

4000

5000 Zambezi (Victoria Falls) Kariba Dam

Dis

char

ge [m

3 s-1]

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

10/1

/201

011

/1/2

010

12/1

/201

01/

1/20

112/

1/20

113/

1/20

114/

1/20

115/

1/20

116/

1/20

117/

1/20

118/

1/20

119/

1/20

1110

/1/2

011

11/1

/201

112

/1/2

011

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

/201

211

/1/2

012

12/1

/201

21/

1/20

132/

1/20

133/

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134/

1/20

135/

1/20

136/

1/20

137/

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138/

1/20

139/

1/20

1310

/1/2

013

11/1

/201

312

/1/2

013

1/1/

2014

0

1000

2000

3000

4000

5000

6000

7000

8000

2010-2011

Wet Season

Dis

char

ge [m

3 s-1]

Date [mm/dd/yy]

Victoria Falls Kariba DamDry Season

biweekly monitoring: Zambezi and Kafue

Wet 2012

Dry

201

3

2011-2012 2012-2013

Wet 2013

Methods: Measured parameters

• Physico-chemical: pH, O2, t°, conductivity, Total Alkalinity

• Total Suspended Matter (TSM) and sediment characterization

• Concentration and stable isotope (δ13C) composition of POC, DOC, DIC,

• Aquatic metabolism: Bacterial respiration and primary production

• GHG (CO2, CH4, N2O) concentrations and fluxes

• Radiocarbon isotopes dating (Δ14CPOC and Δ14CDOC)

Headspace Technique Membrane Equilibrator

In-situ CO2 measurements

Floating chamber

Results: pH spatio-temporal variability

0 500 1000 1500 2000 2500 30005.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0 C.B. Res. (2012 wet) C.B. Res. (2013 dry)

Kariba Res. (2012 wet) Kariba Res. (2013 wet) kariba Res. (2013 dry)

pH [N

BS

]

Distance from source [km]

Zambezi (2012 wet) Zambezi (2013 wet) Zambezi (2013 dry)

BarotseFloodplains

ChobeSwamps

0 200 400 600 800 1000 1200 1400 16005.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

Kafue GorgeReservoir

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

LukangaSwamps

pH [N

BS

]


Kafue (2012 wet) Kafue (2013 wet) Kafue (2013 dry)

Kafue Flats

Zambezi River Kafue River

pH decreases (more acidic) in-,

and downstream wetlands

Results: DO spatio-temporal variabilityZambezi River Kafue River

Significant DO decrease in-, and

downstream wetlands (below 2 mg L-1)

0 500 1000 1500 2000 2500 30000

20

40

60

80

100

120

140

160

180 Kariba Res. (2012 wet) Kariba Res. (2013 wet) Kariba Res. (2013 dry)

C.B. Res. (2012 wet) C.B. Res. (2013 wet) C.B. Res. (2013 dry)

Dis

solv

ed O

xyen

[%]


ZBZ (2012 wet) ZBZ (2013 wet) ZBZ (2013 dry)

BarotseFloodplains

ChobeSwamps

2 mg L-1

0 200 400 600 800 1000 1200 1400 16000

20

40

60

80

100

120

140

160

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

Dis

solv

ed O

xyge

n [%

]



Kafue Flats

LukangaSwamps

2 mg L-1

Results: CO2 spatio-temporal dynamics

0 500 1000 1500 2000 2500 3000

0

2000

4000

6000

8000

10000

12000

14000 C.B. Res. (2012 wet) C.B. Res. (2013 wet)

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

pCO

2 [ppm

]



BarotseFloodplains

ChobeSwamps

Kariba & CB Damhypolimnetic

water release

Shire>13000 ppm

Degassing Vic. Falls

0 200 400 600 800 1000 1200 1400 1600

0

2000

4000

6000

8000

10000

12000

14000

LukangaSwamps

atm. CO2

pCO

2 [p

pm]


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

Kafue Flats

Kafue GorgeReservoir


Substantial increase in CO2 in-,


Results: CH4 spatio-temporal dynamics

0 500 1000 1500 2000 2500 30001

10

100

1000

10000

100000 C.B. Res. (2012 wet) C.B. Res. (2013 dry)



CH

4 [n

mol

L-1]


BarotseFloodplains

ChobeSwamps

0 200 400 600 800 1000 1200 1400 16001

10

100

1000

10000

100000

CH

4 [n

mol

L-1]


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

LukangaSwamps

Kafue Flats


CH4 increases substantially in-,


Results: TSM & POC spatio-temporal variability

0 200 400 600 800 1000 1200 1400 1600

1

10

100

1000 ITT Res. (2012 wet) ITT Res. (2013 wet) ITT Res. (2013 dry)

TS

M [m

g L-1

]



Kafue Flats

LukangaSwamps

0 500 1000 1500 2000 2500 3000

1

10

100

1000 C.B. Res. (2012 wet) C.B. Res. (2013 wet)



TS

M [m

g L-1

]


BarotseFloodplains

ChobeSwamps


UPSTREAM DOWNSTREAM6

8

10

12

14

16

18

20

22

24

26

% P

OC

of T

SM

[%]

Barotse Floodplains Chobe Swamps Lukanga Swamps Kafue Flats

2% increase

5% increase

11% increase

- No clear TSM trend

- Notable increase in the relative

contribution of POC to the TSM in-,


Results: DOC spatio-temporal variability

0 500 1000 1500 2000 2500 30000.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0 C.B. Res. (2012 wet) C.B. Res. (2013 wet)

Kariba Res. (2012 wet) Kariba Res. (2013 wet) Kariba res. (2013 dry)


DO

C [m

g L-1

]


BarotseFloodplains

ChobeSwamps


DOC increases in-, and

downstream wetlands

0 200 400 600 800 1000 1200 1400 16000.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

LukangaSwamps

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

DO

C [m

g L-1

]



Kafue Flats

River / Reservoir Area CO2 flux CH4 flux CO2 load CH4 load Emission Deposition

[km2] [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 16Kafue Gorge Reservoir 13 956 17.4 5 0.1 5 1**

Kafue River with reservoirs 664 1903* 18.9* 461 4.6 466 17

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

Results: Carbon Budget

Total C Yield: 7165 kt C yr-1

Total C Yield: 23,485 kt C yr-1

Emissions increase 7 fold

(16,300 kt C yr-1)

Concluding remarks

� Wetlands/floodplains have large influence on river biogeochemisty:

� Decreasing the pH and Dissolved Oxygen concentrations

� Increasing the Temperature and Evaporation

� Increasing CO2 and CH4, DOC and POC concentrations

� 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 of wetlands in both regional and global C budgets, which so far has

been largely overlooked.

Thank you for your attention!

“Pirates of the Zambezi”

The global carbon cycle

Global C budget studies are mostly limited to the three major carbon reservoirs

with little or no focus on inland waters

Major carbon

reservoirs

• Atmosphere

• Biosphere

• Ocean

Introduction: Inland waters in global C cycle

Historical perception

Land 0.9 Pg C y-1 Ocean 0.9 Pg C y-1Inland waters

River are passive “pipes” transporting to oceans terrestrial carbon

(Cole et al., 2007. Plumbing the global

carbon cycle: integrating inland waters into

the terrestrial carbon budget. Ecosystems 10,

172–185)


Research on inland waters suggest that:

� beside Transport

� Emitting

�Storing

Canadell & Raupach, 2008

Global NEP ~3.0 Pg C yr-1

Terrestrial

Freshwater systems function as biogeochemical “hot spots”

(Aufdenkampe et al., 2011. Rivers key to coupling biogeochemical cycles between land, oceans and

atmosphere. Front. Ecol. Environ. 9, 53–60) based on Batin el al., 2009

3.3 (70%)

4.8

0.6 0.6 2.1


More recent research

(NEP = GPP + total ER)

Overlooked importance of wetlands

“Three-quarters of the world’s flooded land consists of temporary wetlands,

but the contribution of these productive ecosystems to the inland water

carbon budget has been largely overlooked”.

“Flooded forests and floating macrophytes provide,

through litterfall and submerged root respiration, a

total of 305±120 Tg C yr-1 of atmospheric carbon to

the waters”….“not significantly different from the CO2

outgassing flux of 210±60 Tg C yr-1. Central

Amazonian waters thus receive at least as much

carbon from semi-aquatic plants as they emit to the

atmosphere”

Documents

Wetlands influencing river biogeochemistry: the case study ... · Wetlands influencing river biogeochemistry: the case study of the Zambezi and the Kafue Rivers AFRIVAL Project (AfricanRiver