Temporal changes in limno-morphometric characteristics in a floodplain lake within Cross River ecosystem during low water period

Abstract

Iyieke Lake is one of the floodplain lakes within the middle reaches of the Cross River, it is a major foraging and breeding site of several fish species. It is not directly connected to any river, so the water level depends on seasonal inundation by the Cross River. With gradual changes in precipitation and consequent alteration in flooding pattern, and increased agricultural activities around the lake, there are indications of steady annual decline in water level and quality, and lake area. In order to understand the effect of these changes on the aquatic biota, the morphology and some limnological parameters of the lake were studied during low water period (March-May) in 2005, 2011 and 2019 at interval of 6.5 years. Water samples were collected from the lake and the limno-morphological parameters measured at the littoral and limnetic zones of the lake following standard procedures. The results showed that monthly rainfall was significantly (p<0.05) lower in 2019 compared to 2005 and 2011, while minimum and maximum temperature trended conversely (p<0.05). The mean total dissolved solids (TDS) increased from 13.00mg/l in 2005 to 39.33mg/l in 2019 and conductivity trended the same. Mean nitrate (0.92mg/l) and phosphate (1.78mg/l) were higher in 2019 compared to 2005 and 2011. Contrarily, transparency decreased from 0.45m in 2005 to 0.19m in 2019. Similarly, mean dissolved oxygen (3.80mg/l), maximum length (443.20m) and width (314.50m) declined significantly toward 2019 (p<0.05). Lake length, transparency, conductivity and TDS that were seemingly good predictors of water deterioration could be useful in modelling, which is vital in conserving the biodiversity of the Cross River floodplain ecosystem.