8 Dr Hayford COMPUTING THE NET PRIMARY PRODUCTIVITY

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8 Dr Hayford COMPUTING THE NET PRIMARY PRODUCTIVITY Powered By Docstoc
					Computing the net primary productivity
 for a savanna-dominated ecosystem
 using stable isotopes : A case study of
         the Volta River Basin.


               Dr Ebenezer Kofi Hayford
      Department of Geology, University of Ghana,
                        Legon
        Associate Research Fellow - Volta Basin
                   Research Project
    Talk outline
    Terrestrial nature of the watershed.
   Experimental work :      DH2O ‘ 18OH2O ,
     13CDIC and dissolved 87Sr/86Sr.
   Chemical characteristics of water in the
    Volta River System.
   Results
   Conclusion.
   Recommendation
    Objectives of the Study.
   To provide data on the Chemical dynamics of
    the Volta River System.

   To quantify the water budget and the net
    primary productivity of the Volta River System.

   To extrapolate computed data to assist in the
      solution of some related problems in Ghana.
Bird’s view of the Volta Lake.
Southern part of the Volta Lake:
 Contact point to the Turbines.
An outcrop on the Western side of the Volta
     Lake showing multiple foliations.
Political nature of the basin.

                    Approx. 406,000km2
                    Burkina Faso (42%)
                    Ghana (40.2%)
                    Togo (5.2%)
                    Mali (4.8%)
                    Ivory Coast (4.0%)
                    Benin (3.8%)
GLC2000 from SPOT-4 Satellite
           (NASA).
                     SUB-BASINS
                  B. V.   156900km2
                  W. V.   111800km2
                  Oti      78800km2
                  Lower V. 58200km2
                  Lake V.   8500km2
           GEOGENE FACTORS
               The catchments area in
    BURKINA FASO:
the North, is dominated by the Precambrian
formation of the West African craton (the
Baoule-Mossi block) dating from 2.6Ga-
1.6Ga (Sattran et al.,2002).
     Ghana :
1) The Voltaian sediments
2) The Dahomeyan system
3) The Togo series.
             Rock Mineralogy

   Muscovite -     KAl3Si3O10(OH,F)2
   Biotite     – K(Mg,Fe)3AlSi3O10(OH,F)2
   Hornblende –    NaCa2(Mg,Fe)4AlSi6Al2O22(OH,F)2
   Feldspar Group- NaAlSi3O8-KAlSi3O8-CaAl2Si2O8
   Quartz      -   SiO2
   Calcium Carbonate – CaCO3
    Tremolite – Ca2Mg5Si8O22(OH)2
          SAMPLING
   5 Sample Stations
   Samples from GNIP (in Kano, Bamako,
    Borogo and Niamey)
   Rainfall Samples
   Samples from Lake Volta: Surface (1m),
    Bottom (18m)
         Analytical procedure.

   Analysis :Samples for major cation and
    Strontium analysis were acidified with
    conc. HNO3 and analyzed using Thermo
    Jarrell Ash Atom-scan 25 Argon ICP.

   The 13C/12C : Samples for isotopes of
    carbon were poisoned with HgCl2.
     and conc. H3PO4 was added to the
     compositions under vacuum to liberate.
        CO2 .
    ISOTOPES: Dissolved  DH2O , 18ODO,
      13CDIC and 87Sr/86Sr were determined as
     follows :
   METHOD: Samples were converted to
    hydrogen and oxygen with hot zinc. The
    18O/16O ratio was determined by

    equilibrating a small amount of CO2 with
    3mL of sample and analyzing the resulting
    solution on a triple collector VG SIRA 12
    mass spectrometer.
    DH2O , 18ODO,  13CDIC are reported
          relative to SMOW.
     CALCULATIONS

Calculations for fluxes in the isotope
   systematic for the Volta River is
  based on equations put forward by
         Confiantini (1986).
                          RESULTS :
             Net Ecosystem Productivity

Sub-Basin     Trans. NPP      ET    Precipi. Int   Discharge
            (km3) g Cm2yr-1   km3    km3     km3    km3

Black Volta 75      437       133   140     34      7
White Volta 58      461        94   101     24      7
Oti River   34      389        73    84     19     11
Lower Volta 23      400        41    47     10      6
        Vegetation Characteristics:
        from SPOT-4 (NASA-Satellite)
Sub-Basin     Trees Shrubs   Grass   Crops   C4        WUE
              %      %       %       %       %    (molH2Oper mol
  CO)



Black Volta   18.0   16.7    44.0    21.3    39        730
White Volta   18.8   17.6    40.0    23.6    35        750
Oti River     22.3   21.4    42.5    13.7    37        740
Lower Volta   25.9   23.6    40.4    14.4    35        750
                                   Sr and 87Sr/86Sr

                        14

                        12
Concentration in um/l




                        10

                         8
                                                                                                              Sr
                         6                                                               Lake Volata          87Sr/86Sr

                         4
                                               Northern
                         2
                              Burkin
                         0
                         30


                              90


                                         0


                                               0


                                                     0


                                                            0


                                                                  0


                                                                        0


                                                                              0


                                                                                     0




                                                                                                    0


                                                                                                          0
                                                                                              a
                                       15


                                             21


                                                   27


                                                          33


                                                                39


                                                                      45


                                                                            51


                                                                                   57




                                                                                                  69


                                                                                                        75
                                                                                           ek
                                                                                         D
                                                          Distance in kilometres
                          Geogene and Anthropogenic influences
                          2500


                          2000
Concentration in umol/l




                                                                                                     HCO- 3
                          1500                                                                       C l l-
                                                                                                     Ca 2+
                                                                                                     Mg 2+
                          1000                                                                       Na+
                                                                                                     K+
                          500


                            0
                                 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

                                                         Sample number
            CONCLUSION
Empirical Data on Evapotranspiration in
            the Volta Basin.
      RECOMMENDATION
   Projected attempts to reduce
    Evaporation on Lake Volta.

   Development of a concept of
    rainwater harvesting.

   Regular controls of radiogenic
    elements in the Lake and Rivers.
      ACKNOWLEDGEMENTS :

    This Project was financed by
    1) The National Science Research Council, Canada.
    2) Canadian Institute for Advanced Research.

    Research Team :
•   Prof. J. Veizer : Environmental Geoscience Center,
                      University of Ottawa, Canada; and
                      Member of NASA Research Council.

•   Dr. Heiko Freitag : Isotope Laboratory, Dept. of
                        Chemistry University of Bochum,
                        Germany.

•    Dr. E.K.Hayford : Dept. of Geology, University of
                      Ghana, Legon.
THANK
YOU

				
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posted:5/25/2012
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