The Effect of Algae on Bicarbonates in Shallow Reservoirs

The microscopical examinations of public water supplies have become universal, and in many places constitute routine laboratory tests, but these determinations are made principally for the purpose of the treatment of the supplies for the removal of algae and similar micro-organisms causing tastes and odors in the water. Water works superintendents and chemists in charge of such works have given but little study to the biochemical reactions of such plant life when present in reservoirs, and with the exception of various limological investigations that have been made, little data of this character are available. It is a well known fact, however, that these organisms do have a great effect upon the physical, chemical and biological quality of stored water. In a recent investigation undertaken to determine the effect of dissolved gases in stored water upon ozonization of the supply of the Baltimore County Water and Electric Company, it was clearly demonstrated that certain forms of algae can within a comparatively short time entirely remove the free carbon dioxide from the water, . as well as use up a considerable amount of the half bound carbon dioxide, thereby reducing the bicarbonate of calcium and magnesium to normal carbonates of these salts; at the same time causing the dissolved oxygen content of the supply to rise to a point of excessive supersaturation. Such conditions have been noted by many investigators, but these phenomena are not usually to be found in shallow reservoirs where the storage period of the water is relatively short and where the supply of free CO2 in the raw water is considerable, due to high organic contents. The two reservoirs used for storage purposes on the Herring Run system of this company are operated continuously, and have a combined storage capacity sufficient for twenty-one days' supply.