Geo-ecology of the Lake Urema / Central Mozambique

Diploma thesisBeate Böhme

Prof. B. MerkelDipl. Geol. F. Steinbruch

Prof. R. GloaguenPD H. Heilmeier

Rostock, 23-09-2005

supervised by:

Introduction Study area Methods Results Conclusions 2Questions

Introduction

● important ecological feature in the Gorongosa National Park: ecological diversity, rich wildlife

– after civil war in Mozambique (1976-1992): attempts for rehabilitation and investigation of park area

Introduction Study area Methods Results Conclusions 3Questions

Research questions

concern: extent of lake decreased, siltation

1) Factors regulating the hydrological regime?

2) State of the lake in the dry season 2004?

3) Variations of the lake's extent over the last 20 years?

Reasons?

Introduction Study area Methods Results Conclusions 4Questions

Study area

Introduction Study area Methods Results Conclusions 5Questions

● Southern Africa

● Central Mozambique

● Urema Rift

Gorongosa National Park

Introduction Study area Methods Results Conclusions 6Questions

Cheringoma Plateau (300 m a.s.l.):seaward dipping sequence from Cretaceous to Pleistocene

Rift Floor (< 100 m a.s.l.):unconsolidated pleistocene to recent alluvial deposits

Gorongosa Mountain (max. 1863 m a.s.l.):cretaceous granitic intrusive;steep flanks

Báruè Midlands (300-800 m a.s.l.):Precambrian gneisses and migmatites; undulating to incised landform

Lake Urema

vertical exaggeration 25line of sight N-NE

Geology

40 km

Introduction Study area Methods Results Conclusions 7Questions

● part of Pungoe R. catchment

● inflow from Rift escarpments

● outflow: Urema River

● dry season inflow through

Vunduzi River

● lake extent: 10-200 km²

Gorongosa National Park

Introduction Study area Methods Results Conclusions 8Questions

MethodsRemote Sensing- 11 satellite scenes 1979-2000(Landsat MSS, TM, ETM+, ASTER)- NDVI- supervised classification

Field work- bathymetric survey- water balance- water chemistry- sediment composition - littoral vegetation

Morphological analyses- SRTM DTM 90 m- (ASTER DTM)- satellite images- elevation profiles- stream profiles- morphological parameters

Laboratory analyses- water: major ions, TIC, DOC- sediments: grain size distri-

bution, TOC, mineral compo-sition (XRD)

Introduction Study area Methods Results Conclusions 9Questions

BGW-training sitesResult of supervised classification (Maximum likelihood with null class)Result of supervised classification, sieved, shoreline as polygon

Introduction Study area Methods Results Conclusions 10Questions

Results

Introduction Study area Methods Results Conclusions 11Questions

catchment area:total: 8755 km²

lake:maximum length: 10.1 kmmaximum width: 4.1 kmshore line development: 3.1

land/lake catchment ratio: 461:1

Nhandugue-Mucombeze

Vunduzi

Sungue-Muredeze

Drainage system = blue, catchment area = yellow, Park = red

Morphometric parameters (2nd October 2000)

Introduction Study area Methods Results Conclusions 12Questions

DTM of the Urema Basin

cross section Rift

cross section Muredeze “plug”

[m a.s.l.]

Introduction Study area Methods Results Conclusions 13Questions

● Transpar. = 0.24-0.7 m

● Diss. O2 = 15-115 %

● NO3- < 0.5 mg/l

● NH4+ < 0.1 mg/l

● PO43- < 0.2 mg/l

● SO42- < 20 mg/l

1

2

3

4

6

7

5

Water chemistry

● Twater = 24-28°C

● pH = 5.9-9.1

● EC = 32-171 µS/cm

● Eh = 292-522 mVH

Introduction Study area Methods Results Conclusions 14Questions

● average size: 20.5 km² ± 2.8 km²

● 05/1997: five times of average size due to cyclones

● small inner-annual changes (<1 km²)

08/1979

09/1991

1960

07/1993

05/1994 07/1994

05/1995 09/1995

07/1996 05/1997

10/2000 12/2000

Lake's extent

Introduction Study area Methods Results Conclusions 15Questions

Conclusions

● exorheic lake ● reservoir lake, limited through alluvial fans● permanent freshwater lake

- low mineralization of waters (surface water fed and/or low mineralized groundwater)

- low concentrations of nutrients due to uptake by plants

- small retention time

Factors regulating the hydrological regime? State of the lake in the dry season 2004?

• temporally and spatially constrained pattern of transport and deposition of sediments

• origin of sediments in western Rift escarpments and Rift floor

Introduction Study area Methods Results Conclusions 16Questions

• no trend in variation of lake size between 1979 and 2000

Variations of the lake's extent over the last 20 years? Reasons?

Major threats for maintenance of the lake:� sedimentation and change of the local base level

� change of water supply from the catchment area

Thanks for your attention

and special thanks to:● Franziska Steinbruch (GIS UCM), Prof. Broder Merkel (chair of

hydrogeology TUBAF), Prof. Richard Gloaguen (working group Remote Sensing TUBAF), PD Dr. Hermann Heilmeier (working group biology/ecology TUBAF), Fernando Januario, Roberto Zohlo, Jose Paulino Capece and his team of the Gorongosa National Park

● AG Boden- und Gewässerschutz TUBAF, ARAC Beira, DAAD, INAM Maputo, Ministry of Tourism Mozambique, SUBTECH Diving & Marine Co. Durban, ZGIS Salzburg