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TECHNICAL REPORTS

Landscape and Watershed Processes

The Impact of Agricultural Runoff on the Quality of Two Streams in Vegetable Farm Areas in Ghana

^a CSIR Water Research Inst., P.O.Box AH 38, Achimota, Ghana
^b West Africa Office, International Water Management Inst., Accra, Ghana
^c Univ. of Ghana, Chemistry Dep., Legon, Ghana
^d UNESCO-IHE Inst. for Water Education, Westvest 7, 2611 AX Delft, The Netherlands
^e UNESCO Jakarta Office, Regional Bureau for Science for Asia and Pacific, JI. Galuh II, Kebayoran Baru, Jakarta 12110, Indonesia

^* Corresponding author (ntow{at}excite.com; w_ntow{at}yahoo.co.uk).

Received for publication March 19, 2007. A study of two small streams at Akumadan and Tono, Ghana, was undertaken during the rain and dry season periods between February 2005 and January 2006 to investigate the impact of vegetable field runoff on their quality. In each stream we compared the concentration of current-use pesticides in one site immediately upstream of a vegetable field with a second site immediately downstream. Only trace concentrations of endosulfan and chlorpyrifos were detected at both sites in both streams in the dry season. In the wet season, rain-induced runoff transported pesticides into downstream stretches of the streams. Average peak levels in the streams themselves were 0.07 µg L^–1 endosulfan, 0.02 µg L^–1 chlorpyrifos (the Akumadan stream); 0.04 µg L^–1 endosulfan, 0.02 µg L^–1 chlorpyrifos (the Tono stream). Respective average pesticide levels associated with streambed sediment were 1.34 and 0.32 µg kg^–1 (the Akumadan stream), and 0.92 and 0.84 µg kg^–1 (the Tono stream). Further investigations are needed to establish the potential endosulfan and chlorpyrifos effects on aquatic invertebrate and fish in these streams. Meanwhile measures should be undertaken to reduce the input of these chemicals via runoff.