ABSTRACT

The release of nutrients from plant- derived organic matter used as fertilizer was monitored. The experimental units were 12m2concrete ponds. Water supply was from an oligotrophic slow - flowing perennial stream. The organic matter were applied in two batches. In the first 13kg dry grasses was applied. This was followed 2 weeks later with 12kg dried grasses and 2kg chicken dropping. This treatment was replicated. Water sediment samples were collected on a weekly basis. The water samples were analyzed for total, nitrogen, total phosphorus, potassium, magnesium, sodium and calcium. The sediment samples were analyzed for the same elements as for water, in addition to organic carbon. The organic fertilizer added had no negative impact on water pH, temperature and oxygen levels. Sediment nitrogen correlated with sediment phosphorus (r = 0.98, p = 0.001). The mean levels of the elements were always higher in sediments than in water except for potassium. The elements nitrogen, phosphorus, protein, organic carbon, varied with fertilization, experiencing increases shortly after fertilization in contrast with the rest which remained conservative. The fertilization seems to have no effect on the pattern of variation of the conservative elements in the water column and the sediment considered separately. In the sediment, the levels of some of the various non — conservative elements remained fairly stable, while organic carbon experienced a continual increase. In the water column there was more variability in the levels of the various element. The successful boosting of zooplankton production by fertilization with organic matter as done in this study seems to be the combination that is required to successfully improve the productivity of the oligotrophic water system as reported in a sister study. The chain of events in nutrient dynamics between fertilization with organic matter and zooplankton production is discussed.