Determination Of the Physico-Chemical and Primary Productivity Levels of The Owabi Lake, Ghana

Abstract

The primary productivity of water bodies is important in considering the health and resilience of aquatic ecosystems. Primary productivity depends on free oxygen and the chlorophyll a contents of a water body. The study determined the primary productivity and chlorophyll ‘a’ level of the Owabi lake to serve as a primary data upon which further studies could rely on. Twenty six sites along the margins of the lake were mapped with GPS and 5.0 meter x 5.0 meter quadrats laid. Within each of the demarcated site, some physico-chemical parameters were measured by standard procedure on the field and in the laboratory, and 100ml of the water sample was sent to the laboratory for chlorophyll ‘a’ determination. The dissolved oxygen concentrations in the bottles were measured with an OAKTON DO multimeter and the physico-chemicals, with a multi-purpose field meter. Within each quadrat, three dissolved oxygen measurement bottles, representing oxygen levels during day period, dark period and a control, were laid 5.0 cm depth into the water body overnight. The physico-chemical parameters recorded mean values that were lower than the WHO limits with p=0.553 indicating non-significant differences within the studied sites. The nutrients values were low but increased in concentrations at the lower portion of the lake. The chlorophyll ‘a’ indicated highest value (53.71±2.06 μg/L) at the lower part of the lake, while the lowest (34.09±0.99 μg/L) was recorded at the upper portion indicating eutrophic status. The Net Primary Productivity (NPP) was higher at the middle portion with 5.20±0.05mg/L, while the oxygen production in the dark (respiration) indicated 4.33±0.32mg/L at the lower part. The highest Gross Primary Productivity (GPP) value of 18.74±0.16mg/L/hr was found at the lower part of the lake with free oxygen registering 0.67±0.07mg/L in the middle portion. Though, the physico-chemical values were within the WHO acceptable ranges, the lower and inadequate levels of the NPP and free oxygen with a hyper-eutrophy in chlorophyll a concentration render the lake unhealthy and unsustainable for the life of aquatic organisms.