Phosphorus contamination of water resources and factors governing phosphorus transformation by microorganisms
Phosphorus is an essential element in the fertility and productivity of natural waters and results in the production of algal blooms. Contamination of surface waters may be derived from a variety of sources such as agriculture, urban and industrial wastes, forestry and uncultivated land. The form of the phosphorus from such sources varies from insoluble, particulate inorganic phosphorus compounds to organic and inorganic soluble phosphorus compounds. The phytoplankton require biologically available soluble orthophosphate and bacteria have been considered to play an essential role in the provision of phosphorus to phytoplanktonic communities. It was considered necessary to assess the significance of the various sources of phosphorus with respect to the type of phosphorus compounds and the quantity supplied to a water resource and in addition examine the role and identity of bacteria in the conversion of insoluble phosphate to soluble biologically-available orthophosphate. Loch of Skene in Aberdeenshire, which has a history of eutrophication, was selected as a suitable site for the survey of phosphorus inputs to a lake and to examine the effect of the lake on the quality of the outgoing water. Agricultural sources of phosphorus contamination were found to provide mainly soluble orthophosphate but it was considered that it was not significant because the supply was limited to Spring and early Summer, that its residence time was short and the quantity supplied was less than that leaving the lake as algal particles. Particulate phosphorus was found to constitute the major input of phosphorus and most of this was carried by a stream showing no obvious signs of agricultural contamination and which flowed through land bounded mainly by forest and marginal land. It was concluded that the lake was a major factor in eutrophication because it provided a sufficiently long residence time for the growth of algae using the phosphorus which had accumulated in the sediments as a result of the reduction in flow rate and subsequently made soluble as a result of biological activity in the sediment. The major types of bacteria capable of solubilising phosphorus and found in the sediments of the inlet streams were Pseudomonas fluorescens group, Pseudomonas putida, Yersinia enterocolitica, Enterobacter cloacae and Enterobacter agglomerans. These organisms were differentiated using a range of conventional bacteriological tests, a miniaturised biotyping system designed for the identification of gram-negative bacteria, and electrofocussing of cell free proteins. The latter was shown to be useful as a rapid method for screening ecological isolates and aiding the differentiation of organisms when biotyping methods were in disagreement or failed to identify an organism. Representatives of the isolates were found to solubilise inorganic phosphate in the range 4°C-25°C and produce highly acidic conditions in liquid culture (pH 3.2-3.5). Examination of the phosphatase activity of the isolates produced no evidence to support the use of an enzymic mechanism for phospholysis. Selected isolates were shown by gas chromatography to produce acids in liquid culture in agreement with the results of other workers, and an organic acid mechanism has been postulated as the main process by which phospholysis occurs but further work is required to prove the role of the mechanism.