PHYSICOCHEMICAL CHARACTERISTICS OF SURFACE AND
GROUNDWATER IN THE LAKE CHILWA BASIN, MALAWI1
J.D. Kalenga Saka
Chemistry Department, Chancellor College, P.O. Box 280, Zomba, Malawi
Abstract
The effect of to the kind and quantity of agrochemicals used on water quality in the Lake
Chilwa catchment area was determined during the 1999/2000 season. The major sources
of water pollution in the Lake Chilwa Basin are agricultural and horticultural materials
and residuals, use and disposal of metal commodities including electronic appliances,
fossil fuel combustion, industrial and household waste disposal and military training at
Zomba Barracks. The most widely used fertilizers in the catchment area include urea,
calcium ammonium nitrate (CAN), 23:21:0_4 S, D-Compound, diammonium phosphate
(DAP), S-mixture and sulphate of ammonia (SA). The total quantity of fertilizers for the
seasons 1994/95–1998/98 was 46,000 metric tonnes. The estate sector in the Lake Chilwa
Basin contributes significantly to the total tonnage of fertilizer with the D-Compound
being the major source of plant nutrients. Water quality data and results on soil sediments
from the catchment reveal that the lake and the groundwaters are sinks of the residues of
the industrial and agricultural activities. The lake is fairly alkaline due to high levels of
carbonates and bicarbonates. Soil sediments gave higher levels of phosphates, nitrates
and metals than fresh water from rivers, land reservoirs and the lake itself. These are
released into both the ground- and lake waters and thereby raising their values. The
accumulation seems however to be high in the southern end of the lake at Swang’oma.
Keywords: Lake Chilwa Basin, groundwater, surface water, quality, Malawi.
1
Abstract of a paper to be presented at the WARFSA/WATERNET Workshop, Lilongwe Malawi,
November, 2006