Abstract
Agriculture has both direct and indirect effects on the quality of surface water and groundwater and is among the leading causes of water quality degradation, mainly as a result of the excessive use of agrochemicals. Water samples were collected in a selected catchment area (Bonsma Dam) in KwaZulu-Natal and analysed for physicochemical variables. The concentrations of most of the elements and total dissolved solids, as well as the pH and electrical conductivity values, met the water quality requirements for domestic, agricultural, livestock and aquatic ecosystem uses. However, the inlet streams feeding the dam were found to be eutrophic during the wet season. Analysis of nitrate in the water body of the study area indicated that agricultural applications of manure and fertilisers may be a potential source of nitrate contamination. Most elements were more concentrated in the dam during the wet season. The overall ionic conductivity values were also higher in the wet season, while the pH was lower. The outcome of this work links the concentrations of physicochemical variables to land use, agricultural practice and local geomorphology. Seasonal patterns in the concentration of physicochemical variables occur, as land use, rainfall and farming activities change seasonally, and these concentrations should therefore be determined periodically.
Highlights
South Africa has a robust agricultural industry comprising a well-developed commercial sector and a predominantly subsistence-oriented sector in the rural areas
The macroelements are used in part for determining the water quality as well as determining how the concentrations of constituents in the water change over a certain time or area
The analysis of nitrate in the water body of the study area indicates that agricultural applications of manure and fertilisers may be a potential source of nitrate contamination
Summary
South Africa has a robust agricultural industry comprising a well-developed commercial sector and a predominantly subsistence-oriented sector in the rural areas. As reported by Schilling and Wolter[2], agricultural practices can cause pollution of water bodies and, over time, cumulative effects can lead to the depletion of water quality. Typical sources of water pollution associated with agricultural systems include livestock manure, nitrate and phosphate in fertilisers, metals, pathogens, sediments and pesticides. Many studies have shown that non-point sources of nitrogen from agricultural activities include fertilisers, manure application and leguminous crops. The major point sources include septic tanks and dairy lagoons.[3] Elevated nitrate concentrations in water bodies are associated with dairy and poultry operations, barnyards and feedlots.[4,5] High concentrations of nitrate in drinking water can be detrimental to both humans and other animals – elevated nitrate concentrations in drinking water can cause methaemoglobinemia in infants and stomach cancer in adults.[6]
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