Fertilization of Earth Ponds. III: Effects on Benthic Macro Invertebrates and Ecological Inter-Relationship with Aquatic Macrophytes

Organic fertilizers in form of cow and chicken manure were applied in oligotrophic or unproductive pond water over a period of one year to stimulate the production of benthic macro invertebrates for the benefit of trout culture, while maintaining adequate water quality. Development of aquatic macrophytes during both inorganic and organic fertilization in all the ponds was also evaluated with respect to the mutually beneficial relationship or `trade off' between the macrophytes and benthos. For the organic fertilization, replicate ponds were treated with low and high chicken manure (LC, HC), combination of high chicken and cow manure (HCC) and untreated controls (CTRL). The results showed that the application of HC and combination of HCC gave the highest numbers and biomass of benthos. The dominant groups encountered were in the order: Oligochaeta > Chironomidae > Asellidae > Sialidae > Hirudinea > Mollusca. Total abundance, biomass and dry weight production estimates of the benthos during the culture period were in the range, 3.5 - 134.0 x 103 ind. m-2; 26.0 - 113. gm-2 and 14.7 - 70.0g dry wt m-2 respectively. Throughout the inorganic and organic fertilization trials, pond 2, which was at various times treated with high phosphorus (HP) fertilizer and HCC had the most abundant macrophytes, with Elodea canadensis, Lemna mino, Glyceria fluitans and Alisma plantago-aquatica dominating, especially in the warm summer periods of July - August. The development of aquatic macrophytes in some ponds favoured production of some benthos, presumably due to greater foliage surface area that influenced plankton development, which are good sources of diet for the benthos. The results are discussed with respect to the mutually beneficial relationship or `trade-off' between the macrophytes and benthos, nutrient circulation and pond ecosystem stability. Journal of Aquatic Sciences Volume 14, April 1999, pp. 19-28 KEY WORDS: Fertilization, earth pond, macro invertebrates, macrophytes and ecological inter-relationship