ON THE

AMOUNT OF DISSOLVED OXYGEN

CONTAINED IN THE

WATER OF PONDS AND RESERVOIRS

AT

DIFFERENT DEPTHS

IN WINTER, UNDER THE ICE.

BY THOMAS M. DROWN, M.D., CHEMIST OF THE BOARD.

ON THE AMOUNT OF DISSOLVED OXYGEN CONTAINED IN THE WATER OF PONDS AND RESERVOIRS AT DIFFERENT

DEPTHS IN WINTER, UNDER THE ICE.

By THOMAS M. DROWN, M.D., Chemist of the Board.

In the twenty-third annual report of the Board (for the year ending Sept. 30, 1891) there were given the results of determinations of the amount of dissolved oxygen in ponds and reservoirs at different depths during the summer months. There is during the warmer months of the year a stagnant layer of water in all deep ponds, below the level to which the wind acts in disturbing the water near the surface; and also in very shallow ponds there may be a temporarily stagnant layer between the times at which the wind makes a perceptible disturbance of the surface. It was shown, as the result of this summer investigation, that the waters of ponds or reservoirs below the level at which they can receive oxygen by direct contact with air lose their contents of free dissolved oxygen very rapidly if the waters contain much readily decomposable organic matter, or if the bottoms of the ponds are foul with decaying organic matter. When the oxygen is exhausted and no more is obtainable, until the water turns over in the fall as the surface becomes cooler, processes of putrefaction set in, which make the water very offensive. On the other hand, when the waters contain but little organic matter, the free oxygen in the water may not be exhausted during the entire summer. The deep layers of water in a clean reservoir were found to be in good condition as late as August 20, with over fifteen per cent. of its original oxygen contents still remaining.

It seemed desirable to make a parallel series of determinations during the winter, when the supply of air from the surface is shut off by the ice. The winter of 1892-93 proved very favorable for this purpose, as there was a continuous coating of ice on the ponds

and reservoirs in Massachusetts from early in December until the determinations were made, in January, February and March.

Since the activity of the micro-organisms which govern the processes of decay in nature is much less pronounced in cold than in warm weather, we should not expect that the exclusion of air from a body of water in winter would be so speedily felt in the exhaustion of the free oxygen as in summer. Further, the amount of oxygen originally dissolved in water in winter is greater than in summer, owing to the fact that the capacity of water for dissolving gases decreases as the temperature rises. In general, however, the results of the summer investigations are confirmed by those in winter; namely, that the exclusion of air from the water is followed by a diminution of the dissolved oxygen in direct proportion to the decomposable organic matter present, reinforcing the argument for the storing of clean water in clean reservoirs.*

In the following tables of results the amount of oxygen present is expressed as a percentage of the amount required to saturate the water at the temperature when collected.

In all cases the lowest depth given was as near the bottom as samples could be pumped without drawing mud or sand into the tube.

DISSOLVED OXYGEN AT DIFFERENT DEPTHS IN JAMAICA POND, BOSTON.

The odor of the sample nearest the bottom was very disagreeable, of that at forty feet faintly disagreeable, of the others none.

The

* Perhaps as pronounced a case of the evil effects of an ice coating on a polluted stream as has been recorded is that of the Schuylkill River, which is the main water supply of Philadelphia. During the cold winter of 1882-83 Prof. A. R. Leeds found the bad odor of the water to be due to the presence of sulphuretted and carburetted hydrogen, which were formed from the organic matter after the free oxygen in the water had been exhausted.

ice was eight to nine inches thick on the pond, and was the second crop, the first ice formed having been cut by the Jamaica Pond Ice Company.

This pond had been frozen over for five or six weeks, and the ice was eighteen inches thick. The odor of both samples was decidedly disagreeable.

Walden Pond receives a portion of its water from Glen Lewis Pond. The ice was sixteen inches thick.

sample was decidedly disagreeable.

The odor of the bottom

DISSOLVED OXYGEN IN BASIN 2, BOSTON WATER WORKS.