ABSTRACT
ABSTRACT: The impact on water quality related to the kind and quantity of agrochemicals used in the Lake Chilwa catchment area was determined. 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 fertilisers in the catchment area include urea, calcium ammonium nitrate (CAN), 23:21:04 S, D-Compound, diammonium phosphate (DAP), S-mixture and sulphate of ammonia (SA). The total quantity of fertilisers 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 fertiliser 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 raise their values. The accumulation seems however to be high in the southern end of the lake at Swang’oma.
