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 analyzing their response to water quality parameters in Shiriro Lake. Chironomid larvae samples were collected in three stations along tributary of Shiroro Lake using the kick sampling technique over a six-month period (August, 2013 to January, 2014). A total of 14 Chironomid species comprising 480 individuals were collected with richness at individual station ranging from 3 to 10 taxa. Two Chironomid taxa; Chironomus (a) spp and Dicrotendipes spp were preponderant and present in all the three stations. The most abundant taxon was Chironomus (a) spp with relative abundance of (56%) followed by Polypedilum spp (10%) and Ablabesmyia spp (8%). Taxa richness calculated as Margalef index did not show any significant difference (p>0.05) among the sampling stations. Similarly, diversity indices (Shannon-Wiener, Simpson dominance indices) did not detect any significant difference between the stations examined. Lower values of diversity and evenness indices were recorded at station 3. Water quality parameters showed that Sodium (0.001-0.58mg/g) and Potassium (2.9-3.51 mg/g) levels in the water were considerably high as a result of anthropogenic activities in the catchment. Other parameters such as Dissolved Oxygen (2.1-5.6 mg/l), Biochemical Oxygen Demand (1.0-9.6mg/l), Conductivity (25-135µS/cm), pH (6.4-8.11) and Transparency (92-188cm) indicate that the water body is increasingly polluted. Canonical Correspondence analysis (CCA) was adopted for the analysis of environment and biota data indicated thatChironomus sp., Polypedilum sp., Clinotanypus sp., Ablabesmyia 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.