Page 19 - Spring Graduation Booklet (SESSION-1)(19Oct2022)

SCHOOL OF SCIENCE
FACULTY OF AGRICULTURE, ENGINEERING
& NATURAL RESOURCES
DOCTOR OF PHILOSOPHY IN SCIENCE (GEOLOGY)

CANDIDATE: UUGULU Katrina Shoopala

CANDIDATE’S DISSERTATION

ESTIMATION OF GROUNDWATER RECHARGE ALONG A
PRECIPITATION GRADIENT FOR SAVANNAH AQUIFERS IN
NAMIBIA WITH SPECIAL EMPHASIS ON THE IMPACT OF
VEGETATION
The doctoral study was undertaken and completed under the supervision of Dr. Heike
Wanke of the University of the West of England, UWE Bristol as Main-Supervisor and Dr.
Paul Koeniger from the Federal Institute for Geosciences and Natural Resources (BGR)
as Co-Supervisor.

The candidate investigated groundwater recharge along a precipitation gradient in
Namibia. The study firstly identified groundwater recharge processes and quantified
such along a precipitation gradient in Namibian savannah aquifers. Secondly, it focused
on the influence of savannah vegetation on groundwater recharge by determining the
active root depth and source water for Senegalia mellifera (S. mellifera) and Boscia
albitrunca (B. albitrunca). The study was carried out at three sites: Tsumeb; Waterberg
and Kuzikus/Ebenhaezer. The study has contributed to knowledge by determining local
meteoric water lines along a precipitation gradient which has never been done before
in Namibia. This is an initial step for future isotope hydrology studies in the three study
areas. The study revealed that savannah aquifers are recharged at low rates, mostly
below 10% of the annual precipitation. The estimated groundwater recharge rates can
help to predict water availability under scenarios of climate change. Furthermore, the
study emphasised on the impact of woody vegetation on groundwater recharge by
using a deuterium tracer. A possible active root depth for S. mellifera was estimated
to be between 2.5 m and 3 m while that of B. albitrunca could not be determined
as the deuterium tracer was not taken up. The determined active root depth for S.
mellifera can be integrated in groundwater recharge models when estimating the net
groundwater recharge. Moreover, B. albitrunca xylem isotope composition is similar to
that of groundwater which indicates that it is using groundwater. S. mellifera xylem
isotope composition is in-between that of soil water and groundwater and indicates
that it is using both water sources, thus S. mellifera has an influence on groundwater
recharge by using up water available for recharge. The influence of vegetation on
groundwater recharge in drylands is still not well enough understood; hence more
studies of this nature are recommended to develop a true picture.

19