Benthic macroinvertebrates as indicators of environmental quality of an urban stream, Zaria, Northern Nigeria

Abstract

For a period of 2 years (from July, 1997 to June, 1999), 87 benthic macroinvertebrate taxa, composed of 12,078 individuals were collected from four stations of Bindare stream and one station on River Galma. Samples were collected monthly, using a Van Veen grap. Physicochemical variables were also determined using standard methods. The catchment areas of Bindare upstream (stations 1 and 2) are farmlands, with few isolated human settlements suggesting a less polluted water environment. The BOD which ranged between 1.88 ± 1.67 mg/l to 8.0 ± 4.76 mg/l increased downstream of the point of discharge. This allowed the survival of sensitive species such as Ephemeroptera, Hemiptera, Plecoptera, Odonata and Neuroptera at upstream. The great preponderance of the class Diptera and Oligochaeta at stations 3 and 4 are attributed to various domestic and agricultural effluents discharged into the stream at these points. The organic pollution of Bindare stream resulted in a decrease in benthic macroinvertebrate species richness and an increase in species density. Compared to background values, these changes in both species richness and density contributed to a reduction in the calculated Magarlef water quality index, hence a deteriorated water quality.


Key words: stream, effluents, water quality, macro benthos, indicator species.


Journal of Aquatic Sciences Vol.18(2) 2003: 85-92