Monitoring seasonal changes in environmental variables and chironomid diversity at Shiroro lake, Niger State, Nigeria.

Abstract

Freshwater chironomids are considered to be ideal bioassay organisms since they spend most of their larval stages in surface sediments. This study was carried out with the aim of identifying taxa assemblages and analysing their response to water quality parameters in Shiroro lake. Chironomid larvae samples were collected in three stations along tributary of Shiroro lake using the kick sampling technique over a six months period (August 2013 to January 2014) a total of 11 chironomid species comprising 480 individuals were collected with richness at individual stations ranging rom 3 to 10 taxa. Two chironomid taxa; chironomus (a) spp and Dicrotendipes spp were preponderant and present in all three stations. The most abundant taxon was Chironomus (a) spp with relative abudance of (56%) followed by polypedilum spp (10%) and Ablabesmyia spp (18%). Taxa richness calculated as Margalef index did not show any significance difference (P>0.05) among the sampling stations. Similarly, diversity indices (shannon-Wiener, Simpson dominance indices) did not detect any significance difference between the stations3. Water quality parameters showed that sodium (0.001-0.58mg/g) and potassium (2.9-3.51mg/g) levels in the water were considerably high as a result of anthropogenic activities in the catchment. Other parameters such as dissolved oxygen (2.1-5.6mg/l), Biochemical Oxygen Demand (1.0-9.6mg/l), Conductivity (25-135mg/l) pH (6.4-8.11) and transparency (92-188cm) indicate that the water body is increasingly polluted. Canonical correspondence analysis (CCA) was adopted futher analysis of environmental and biota data indicated that Chironomus sp., polypedilum sp, clinotanypus sp. Ablabemyia sp. and Dicrotendipes sp. Showed a positive relationship with most of the environmental variables. Since chironomid larvae are tolerant to poor water quality conditions, they should be considered as indicators of pollution in Shiroro Lake, Niger State.