The Role Of Cypress Leaves In Promoting Growth Of Coliform Organisms In A Holding Reservoir

Coliforms at levels of up to 4 x 10(4) per 100 ml were detected in the outlet of an open holding service reservoir for domestic water supplied with chlorinated water that contained no more than 3 coliforms per 100 ml and these were identified as mostly Enterobacter cloacae and some Citrobacter freundii. These were also the coliforms isolated most frequently from Melbourne Water catchment reservoirs. Growth of these coliform organisms occur within the holding reservoir. Cypress trees (Cupressus macrocarpa) deposited some 6000 kg of leaves into the reservoir per annum and this had produced a 3 cm sediment layer of decaying leaves. In the laboratory coliforms and other heterotrophs grew in water containing cypress leaves achieving populations of 3 x 10(5) per 100 ml and 4 x 10(8) per ml respectively. Cold water leaf extracts supported the growth of Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Salmonella derby and uncharacterised heterotrophs present in the reservoir sediments. Hot water extracts, however, contained inhibitors of growth of all species tested except for Enterobacter cloacae. Growth of coliform organisms and other heterotrophs was probably supported by nutrients derived from cypress leaves. In order to preserve the quality of water, reservoirs should be protected from receiving cypress leaves.