An investigation of the amount and environmental impact of chemical fertilizers and pesticides running off from commercial and traditional farmlands in the upper Kaleya catchment , Mazabuka, Zambia

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Zgambo, Astrida Chipili
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Real and potential environmental quality problems have accompanied the changes in agricultural productivity in recent decades. The development of agriculture has given rise to negative environmental impacts as large quantities of fertilizers and pesticides are used in modern agriculture to increase crop production. Historically, Zambia's efforts to maintain and enhance the quality of the environment have been directed more toward problems caused by urban centers and industrial operations than by agriculture. Upper Kaleya Catchment is an important agricultural area where farmers use fertilizers and pesticides. This, compounded by the occurrence of torrential rainfall that causes a lot of runoff on land that is almost devoid of vegetation and no riparian zone, has contributed to pollution of the Kaleya River.This study investigated the amount and impact of fertilizer loading into Upper Kaleya River of Mazabuka District in Southern Province of Zambia. It provides an opportunity to evaluate water quality associated with nutrient and pesticide use, due to prominence of intensive agriculture in the area. Storm water runoff of fertilizers and pesticides applied on farmlands have appeared to be the predominant source of non-point source nutrients and contaminants affecting surface water quality in Upper Kaleya River, a factor very much dependent on land use in the catchment.The study involved collection of soil and water samples (river water and surface runoff)between November 1999 and March 2000 from eight sampling stations. A total of 132 samples were collected, comprising 80 soil samples, 20 river water samples, and 32 runoff samples. Parameters analysed for were pH, conductivity, nitrate (NOs-N) and nitrite (NCVN) for nitrogen and phosphorus. Ancillary data used were rainfall from Kafue Polder and discharge data from Kaleya Sediment Project, University of Zambia. A questionnaire using systematic sampling was employed capturing a sample size of 30 farmers (20 traditional farmers and 10 commercial farmers). Interviews with farmers and various authorities were also conducted. The results have been presented graphically and in tables. Correlation analysis was used to determine the relationship between rainfall and discharge. Student t-tests were carried out to test significance of differences in nutrients concentration between commercial and traditional farms. The Chi-square statistic (N2) was employed to compare educational background between commercial and traditional farmers as well as fanners' awareness of polluting effects of nutrients and pesticides.Frequency of use of pesticides and fertilizers was also analysed. Analysis of data revealed that nutrients and contaminants from farmlands have washed into Upper Kaleya River and more of it was from commercial than traditional farmers. In soil NC>2 - N was found from trace to 28.25 mg/kg on commercial farms and from trace to 24.25 mg/kg on traditional farms. In water concentrations of NOa - N at commercial farms ranged from 7.1 to 17.84 mg/1 while at traditional farms it was from 8.4 to 13.86 mg/1. Pollution of the Kaleya River from agriculture was evidently taking place. The pH (5.9-8.0) in river water was not in conformity with WHO standards (6.5-8.5) for drinking water. Conductivity in river water (26.0 - 877.0 (JS/cm) exceeded WHO standards for drinking water (0.7|jS/cm) and was severe for irrigation whose limit according to WHO standards is 3.0 |jS/cm. Phosphorus concentration was higher (0.20-3.40 mg/1) than the WHO recommended limit (0.3 mg/1) but was within boundary values for fixed trophic classification system whose eutrophic limit is between 35-100 mg/1, hence rendering the Upper Kaleya River the status of not being eutrophic. This suggested that the river had no sufficient phosphorus to support the growth of aquatic weeds.It can be concluded that Upper Kaleya River is polluted from applications of fertilizers and pesticides as used by commercial and traditional farmers. However, at the time of the study nutrient concentrations seemed not to be high. But according to WHO standards the mere presence of NO2 -N in water renders it polluted. Nitrite preferable limit is for it to be absent in drinking water, but it was present in Upper Kaleya River. Furthermore over 90% of the farmers (subsistence farmers in particular) were not aware of the polluting effects of these chemicals in the river. The excess amount of chemicals used and the fact that rainfall is often in the form of torrential thunderstorm, which enhances erosion, may in future lead to the river becoming heavily polluted. More and long-term studies are required to evaluate environmental effects of fertilizer /pesticide use in order to provide assessments of pollution and for developing cost effective pollution control and monitoring programmes.
Environmental policy -- Mazabuka , Agriculture -- Environmental aspects -- Mazabuka , Chemicals , Pesticides