Investigating Temperature and Nutrients as Drivers of Primary Productivity in Aquatic Environment

Abstract

An investigation into the relationship between temperature and the nutrients (3 NO − , 3 4 PO − , 2 4 SO −) in pelagial primary productivity of the middle reaches of Otamiri River in Owerri, Southeastern Nigeria was carried out between October and November, 2018 at ten sampling points (OTP 1-OTP 10). The estimation of productivity was made with the light and dark bottle technique. Maximum yields in Gross Primary Productivity (GPP) (0.8738 mgCL −1 d −1), Net Primary Productivity (NPP) (0.8513 mgCL −1 d −1), as well as Community Respiration (CR) (0.1613 mgCL −1 d −1) were recorded at OTP 3, OTP 3 and OTP 8 respectively that had more vegetation covers than in segments without cover. GPP is correlated with 3 4 PO − ions (r = 0.400), 2 4 SO − ions (r = 0.418), and water temperature (r = 0.379) (p < 0.05), while CR is correlated with 2 4 SO − ions (r = 0.500) (p < 0.01). The variability of GPP increased mildly with increasing temperature and the nutrients; with predicted regression model productivities of 0.1388, 0.5621, and 0.6066 mgCL −1 d −1 , corresponding with mean values of 28.41˚C, 0.33 mg/L, 1.04 mg/L and 10.25 mg/L recorded for temperature, 3 NO − , 3 4 PO − , and 2 4 SO − ions concentrations. Mean GPP was estimated to result in a comparatively low annual productivity of 188.75 mgCL −1 yr −1. Conservation and restoration of riparian vegetation covers in watershed corridors of the river for optimal driver roles were recommended.