In situ yields in primary productivity of sand mine ponds of the Otamiri River in a southeastern city of Nigeria

Abstract

In situ yields inprimary productivity of sand mine ponds of the Otamiri River in Owerri,southeastern Nigeria was investigated during the wet and dry seasons of2012/2013. Eighteen sampling points designated as WC 1-WC 18 and located within9 artificial ponds where active sand mining was ongoing and 9 ponds where ithad ceased were studied. In situ measurements were made for surface watertemperature, dissolved oxygen (DO), pH, conductivity, salinity and totaldissolved solids (TDS) using standard methods. Measurements were also made ofother physicochemical variables. The single factor ANOVA, means plots,Principal Components Analysis (PCA), Pearson correlation (r) and student’st-test were used to analyse data. Gross and net primary productivity (GPP &NPP) as well as community respiration (CR) varied as follows: 0.1800-0.6550(0.3121 ± 0.0377), 0.1013-0.6000 (0.2761 ± 0.0382) and 0.0100-0.0810 (0.03363 ±0.0055) mgCL-1d-1 respectively. There was significant spatial heterogeneity inmean variance of primary productivity [F(169.80)>Fcrit(3.93)] at P<0.05,with the actively sand mined pond showing higher productivity, accompanied withhigher nutrients (PO42-, NO3-, SO42-) concentrations and slightly higherturbidities than the non-mined pond. Productivities also differed markedly(Sig. t=0.000) between the seasons, with higher dry than wet season yields. Thefirst four PCs formed the extraction solution in the original 16physicochemical parameters measured with a cumulative 95% variabilitycontribution. The components had high loadings for the nutrients and turbidityfactors. GPP correlated with PO42- (r=0.976), NO3- (r=0.955) and turbidity(r=-0.946) at P<0.01. Active sand mining appeared to enhance primaryproductivity in the mine pond through re-suspension and elevation of growthnutrients in water column, even as this was associated with slightly increasingturbidities.