416
T. J. Ballatore et al.
20.6.1 An Illustrative Case: Lake Victoria
The case of Lake Victoria (Fig. 20.2) provides a concrete example of the ability of
remote sensing techniques to contribute to improved lake management and should
serve as an inspiration to African scientists and policy makers.
The lake’s importance as well as its large areal extent (which makes direct sampling particularly difficult) mean that Lake Victoria has seen more applications of
remote sensing than most African lakes. As discussed above, these applications cover
a wide spatial range from enclosed areas of the lake to the drainage basin scale; they
also illustrate the wide variety of sensors and techniques that can be brought to bear
on policy-relevant questions.
One of issues attracting much concern over the years has been the infestation by
water hyacinth in shoreline areas along the Ugandan and Kenyan coasts (Williams
et al. 2005). Cavalli et al. (2009a, b) and Fusilli et al. (2011) were able to use
a range of sensors (MODIS, MERIS, ASTER and CHRIS) to map aquatic weed
infestations in Winam Gulf. The ability of remote sensing to elucidate the evolution
of weed cover, including the abnormal proliferation from October 2006 to January
2008 which was attributed to an unusually heavy rainy season and the consequent
large inflows of nutrients and sediment from surrounding land, has proven important
for policy makers.
Related to the localized water hyacinth infestation is the lake-wide eutrophication
which has been driven by nutrient loadings which began increasing as far back
as the 1930s (Verschuren et al. 2002, Hecky et al. 2010). Loiselle et al. (2006)
used SeaWiFS-derived chlorophyll-a measurements to show the influence of littoral
population on the inshore areas of the lake (see Fig. 20.2). Sørensen et al. (2008)
showed the utility of MERIS for lake-wide chlorophyll-a measurements. Cózar et al.
(2012) used SeaWIFS for chlorophyll-a and AVHRR for surface temperature to show
how interannual changes in physical conditions can greatly affect phytoplankton
dynamics across the lake. The important implication is that policy makers need to
look beyond just phytoplankton biomass as an indicator of eutrophication and expand
their consideration of climatic effects.
Finally, the water balance of Lake Victoria has been a contentious policy issue
which altimetric and gravimetric data have been able to impartially elucidate. In
particular, Swenson and Wahr (2009) used changes in catchment water storage, as
measured by GRACE, along with altimetric lake level data to show that increased lake
discharge (and not drought alone) contributed to the decline in lake level observed
in the early 2000s.
Overall, these examples demonstrate how remote sensing can be applied to policyrelevant questions in an important African lake. They should serve as motivation,
along with all the other cases discussed in this review, for those hoping to make
similar contributions at other lakes.
T. J. Ballatore et al.
20.6.1 An Illustrative Case: Lake Victoria
The case of Lake Victoria (Fig. 20.2) provides a concrete example of the ability of
remote sensing techniques to contribute to improved lake management and should
serve as an inspiration to African scientists and policy makers.
The lake’s importance as well as its large areal extent (which makes direct sampling particularly difficult) mean that Lake Victoria has seen more applications of
remote sensing than most African lakes. As discussed above, these applications cover
a wide spatial range from enclosed areas of the lake to the drainage basin scale; they
also illustrate the wide variety of sensors and techniques that can be brought to bear
on policy-relevant questions.
One of issues attracting much concern over the years has been the infestation by
water hyacinth in shoreline areas along the Ugandan and Kenyan coasts (Williams
et al. 2005). Cavalli et al. (2009a, b) and Fusilli et al. (2011) were able to use
a range of sensors (MODIS, MERIS, ASTER and CHRIS) to map aquatic weed
infestations in Winam Gulf. The ability of remote sensing to elucidate the evolution
of weed cover, including the abnormal proliferation from October 2006 to January
2008 which was attributed to an unusually heavy rainy season and the consequent
large inflows of nutrients and sediment from surrounding land, has proven important
for policy makers.
Related to the localized water hyacinth infestation is the lake-wide eutrophication
which has been driven by nutrient loadings which began increasing as far back
as the 1930s (Verschuren et al. 2002, Hecky et al. 2010). Loiselle et al. (2006)
used SeaWiFS-derived chlorophyll-a measurements to show the influence of littoral
population on the inshore areas of the lake (see Fig. 20.2). Sørensen et al. (2008)
showed the utility of MERIS for lake-wide chlorophyll-a measurements. Cózar et al.
(2012) used SeaWIFS for chlorophyll-a and AVHRR for surface temperature to show
how interannual changes in physical conditions can greatly affect phytoplankton
dynamics across the lake. The important implication is that policy makers need to
look beyond just phytoplankton biomass as an indicator of eutrophication and expand
their consideration of climatic effects.
Finally, the water balance of Lake Victoria has been a contentious policy issue
which altimetric and gravimetric data have been able to impartially elucidate. In
particular, Swenson and Wahr (2009) used changes in catchment water storage, as
measured by GRACE, along with altimetric lake level data to show that increased lake
discharge (and not drought alone) contributed to the decline in lake level observed
in the early 2000s.
Overall, these examples demonstrate how remote sensing can be applied to policyrelevant questions in an important African lake. They should serve as motivation,
along with all the other cases discussed in this review, for those hoping to make
similar contributions at other lakes.