Effect of fertilization regime on nutrient and plankton development in impounded run-off from a dystrophic reservoir

Abstract

Plankton assemblage and productivity status of an artificial reservoir were studied. The overflow of the reservoir was impounded in earthen ponds of the Department of Fisheries and Aquatic Resources Management, Michael Okpara University of Agriculture, Umudike, Nigeria. Groups of three such ponds measuring 9 x4x1.5m each were fertilized with chicken droppings (to obtain higher quantities of phosphorus) (treatment 1) and organic matter (to obtain higher levels of organic matter) (treatment 2). Composite water and sediment samples were collected weekly from transects of the reservoir, and ponds, for 8 weeks. Triplicate samples were investigated for plankton species density in the water column; total phosphorus, total nitrogen, organic matter; and bacterial cell counts in the sediment. Data were analyzed using the ANOVA and means separated using Fisher’s LSD_(0.05). Water column N and P were significantly higher in treatments 2 and 1 respectively (p<0.05). Sediment N followed the same trend. Sediment P was significantly higher in the reservoir p<0.05). Plankton densities were significantly higher in treatments 1 and 2 respectively (p<0.05). Protists excluded, zooplankton in treatment 2 was predominated 55% by cyclopoid copepods. Rotifers were the least encountered zooplankton in the three environments. The aquaculture significance of the findings is discussed.

Key words: Dystrophic, impoundment, water column, bacteria, zooplankton, phytoplankton, fertilization.