Assessment Method for Leaf Litters Allelopathic Effect on Cyanobacteria

A new bioassay technique combining leaf disk and softagar over-layer methods was developed to investigate the allelopathic effect of deciduous leaf litters on the growth of cyanobacteria ( Microcystis aeruginosa Kütz.). Bioactive substances exuded from leaf disks caused inhibitory plaques on the agar plate containing cyanobacteria , and the rate of diffusion depended on the specific leaf disk area. Most of the leaf litters collected around reservoirs in Japan showed inhibitory activity to M. aeruginosa , with Rhus trichocarpa Miq., Quercus variabilis Blume and Mallotus japonicus (Thunb.) Muell. Arg. being the strongest among the 22 tested species.(PDF has 4 pages.)

Relationships between secchi disk visibility, water temperature and dissolved oxygen in freshwater fishpond

A study was conducted to determine the relationships between secchi disk variability, water temperature and dissolved oxygen in fish ponds. Multiple regression correlation analysis was done to evaluate the relationships between the variables. Results indicated that the ranges of secchi disk visibility, water temperature and dissolved oxygen in the study ponds were just within the ranges of the variables for tilapia culture. Multiple regression correlation showed no (or insignificant) relationships with dissolved oxygen and water temperature, dissolved oxygen with secchi disk visibility and water temperature with secchi disk visibility.