Abstract:
A study was conducted in Ihale Village, Magu District, Tanzania aimed to assess the
effectiveness of selected vegetation cover types as Vegetative Buffer Strip Filters
and their corresponding vegetation strip widths in filtering sediment delivery that are
likely to enter the surface waters of the Lake Victoria from agricultural lands.
Sediment laden runoff plots measuring 2 m by 20, 15, 12.5 and 10 m were
established to determine the effectiveness of the selected filters and strip filter
widths set at 10, 5 and 2.5 m against a standard width of 10 m which was planted
with maize (Zea mays). The filters evaluated include elephant grass (Pennisetum
sp) and Lemon grass (Cymbopogon citratus). Variables measured include: daily
sediment for the rainy days, daily rainfall, infiltration rates, plant vigour of the filters
(plant height) and percent vegetation cover. Data was analysed statistically using
Excel, SAS and SPSS statistical packages. The results demonstrate that mass of
sediment delivery through the tested filters decreases exponentially with increasing
filter widths for all tested vegetation types with correlation coefficient (R 2 ) ranging
from = 0.6 to 0.8. The trapping efficiency of the tested filters increases
logarithmically with increasing filter widths. Sediment trapping efficiency increased
from 54% at 2.5 m to 78% at 10 m vegetative filter widths for all tested vegetation
types. A significant correlation exists between sediment delivery through elephant
grass and lemon grass with filter strip width, percent vegetation cover and plant
growth characteristics. About 30 to 40% of the observed variation in the prediction
of sediment delivery through selected vegetation types could be explained by the
percent vegetation cover alone. The study demonstrates that the tested Vegetative
Buffer Strip Filters have the potential to purify water from sediment that has been
transported into the riparian zone from the agricultural lands. Further research is
recommended.
