Original Communications.

OYSTERS AND SEWAGE IN NARRAGANSETT BAY.

By C. A. FULLER, Ph.D.
Providence.

In 1900 the State of Rhode Island leased three thousand acres of land for oyster culture in the Providence River and Narragansett Bay. The accompanying map shows the locations of these oyster grounds as given in the plan published with the report of the Rhode Island Commissioners of Shell Fisheries for 1900. The areas occupied by the beds are outlined in dotted lines. It will be seen that the most extensive oyster grounds are in the Providence River, between Warwick Neck and Bullock Neck. There is, however, one small cultivated bed farther up the river nearer the city. This bed is the first one we come upon passing down stream from Providence. It is planted on the eastern side of the river just off Sabins Point, its southern limit reaching to Sabins Point Light. The stakes marking the northern boundary of these layings are about two miles below the outlet of the Providence sewer. About a mile below the Sabins Point bed we find the northern limits of the extensive layings which extend from Bullock Neck nearly to Rumstick Neck. These beds follow the eastern shore of the river without a break for nearly three miles. The third oyster bed lies directly across the river, off the northern shore of Conimicut Point about five miles below the city sewer outlet. Above Conimicut the river is scarcely one mile wide, but below this point it broadens abruptly to twice that distance. In this larger water are the most extensive oyster layings in the Providence River. They form a continuous area of over a thousand acres, extending from a short distance below Conimicut Point Light, on the western side of the ship channel to the lower end of Warwick Neck. A strong tide sweeps the western shore of the river causing a constant circulation of water over these beds. Turning again to the eastern shore of the river, we find there are extensive beds in the Warren River. These beds occupy ground off the south shore of Rumstick Neck and reach up the Warren river almost to the town of Warren. The northern areas of these layings extend from bank to bank, occupying the channel as well as the shallower water of the river.

The largest beds in Narragansett Bay are located in the Western Passage south of Pine Hill Point, Prudence Island. These beds are twelve miles from the outlet of the Providence city sewer and out of the direct course of the river currents. Still farther down the Western Passage in Wickford Harbor is another smaller bed which is not shown on the map.

The remaining grounds leased in 1900 are located in or near Mt. Hope Bay. Entering this body of water from the Eastern Passage of Narragansett Bay, the first oyster bed noticed is planted on the shoals south of Hog Island. The second bed in this section of the Bay occupies an area close under the shore of the Island of Rhode Island at Bristol Ferry, thus in the narrow entrance to Mt. Hope Bay. Another larger bed is located off the northern shore of Common Fence Point still farther into the bay. Crossing now to Warren Neck, the north-western boundary of the bay, we find other extensive oyster grounds near the mouth of the Kickemuit River. Around the neck into Kickemuit River, are the only remaining beds leased by the State in 1900.

Having located the oyster bed in the river and bay, the next important points to consider are the sources from which pollution may enter the river and be distributed from place to place by tides and river currents. The principal source of pollution of the river is the sewer which collects the larger part of the drainage of the city of Providence and immediate vicinity, and discharges it through a single main into the ship channel of the river, just off Fields Point. Though the outlet of this main is covered by twenty-five feet of water at mean low tide, it can be readily located on a quiet day by the smoky greasy stream of sewage that rises rapidly to the surface of the water at that point. This grease and a gray scum are carried off by tide currents and can be seen floating on the water several miles below the sewer outfall. In 1900 an average amount of nearly 14,000,000 gallons of sewage daily was pumped into the river through the Fields Point sewer. At this time the sewage was discharged in a crude state into the river. That is, it was simply sent through a screen, composed of a rack of parallel iron rods about an inch apart, and passed on to the outlet. This apparatus removed some of the more bulky material, but as the stream of sewage was passed through the screen with considerable force, much solid matter was carried on into the river. The collections of refuse on the beaches in the neighborhood of Fields Point bear witness to the veracity of this statement. Around the point nearer the city is the outlet of another large drain which is used as an overflow or in case of an accident to the main sewer. This culvert is built into the river bank and is entirely out of water at low tide. The outlets of these two large drains are located on the accompanying map; the main sewer, in the narrowest section of the river, east of the point; the overflow around the point on the north-eastern exposure. Two other small overflow, or storm sewers, discharge into the Seekonk River, one near Red Bridge, one just above Washington Bridge.

These four drains contribute the great bulk of the sewage poured into the Providence River. But there are a number of small sewers, mostly the drains from shore resorts and summer cottages located near the river banks that are a secondary source of pollution. For the most part these drains are in use only during the summer months at a time when fewest oysters are dredged for market. The amount of sewage discharged by them at any rate is so small in comparison with that thrown into the river through the city sewers, that they can not be considered of great moment in the general sewage pollution of the river.

From seven to eight miles below the outlet of the main city sewer, the Providence River is joined by the Warren River which receives the waste of the town of Warren. The principal sources of contamination of this stream are the mills located on the banks of this river two miles above its union with the Providence River. All visible evidence of contamination disappears from the water, however, before it enters the larger body of water.

The third factor in the general pollution of Rhode Island waters is the sewage of the city of Fall River. The waste of this city is discharged into the Taunton River near the head of Mt. Hope Bay. The outfall of this sewer is of course at a considerable distance from the Providence River, and the formation of the land about the entrance of Mt. Hope Bay, make it very improbable that the waters of this bay should become a source of pollution to the river. The oyster beds within Mt. Hope Bay are, on the other hand, more or less exposed to contamination from the Fall River sewers.

These three, then, the Providence sewage, the Warren mill waste and the Fall River sewage are the principal sources from which pollution can be spread to the oyster beds of Rhode Island waters. The sewage of Newport never reaches the oyster beds, the nearest of which are at least twelve miles above Newport Harbor.

In view of the existing conditions in Rhode Island waters and of the fact that the Providence River has long been famous for its oysters, some experiments were undertaken not long ago, to determine by bacteriological examination to what extent the waters of our State were contaminated by sewage; and also to determine, if possible, the presence of sewage in oysters grown in these waters. Bacillus coli communis was taken as an index of sewage pollution, and samples of water and oysters containing this organism were regarded as contaminated by sewage.

The usual methods for the isolation of B. coli from water were used in this work. Fermentation tubes containing dextrose broth were inoculated directly with the material to be examined. In some cases carbol broth was inoculated directly from the samples. If the fermentation tubes did not show the formation of gas within twenty-four hours time at thirty-seven degrees C., the test was considered negative. If, on the other hand, any considerable

quantity of gas developed within this time, litmus lactose agar plates were made and the red colonies fished out and studied in pure culture.

Water samples were collected in twenty-five cubic centimetre tubes by means of an apparatus designed for use in deep wells. After collection the samples were taken directly to the laboratory and transferred to the media already described. The localities at which samples were taken are indicated on the map by the large black dots. Some of these localities were visited several times and collections made under different conditions of tide and weather. Usually two samples were taken at each place visited; one, a foot below the surface, and a second a foot off the bottom of the river. When samples were taken in the shallow water near the shore, sterile bottles were plunged below the surface and allowed to fill with water.

The first series of samples examined in this work were taken in the immediate neighborhood of Fields Point. Then following down the river, other collections were made at different points below until the zone of sewage pollution was passed. As has been already stated, the water about Fields Point contains visible evidence of pollution. Eleven stations, all within half a mile of the main Providence sewer outlet were visited. Samples of water taken at these localities in January and April of 1901, all gave positive reactions for the colon bacillus. In addition several other forms frequently found in sewage or sewage polluted streams were observed repeatedly in these samples.

Passing down the river into the neighborhood of Pomham. a set of three samples was collected from a section of the river at no point more than a mile and a quarter from the Fields Point sewer. Three collections were made at these localities, making eighteen samples in all from this part of the river. All but three of the eighteen contained B. coli. Other sewage bacteria were also observed in some cases.

Our map shows us that the next samples were taken over the Sabins Point oyster bed, the first cultivated oyster ground we meet in passing down the river from Providence. Sixteen samples of water were collected over this bed at the two localities indicated on the map. The results of the analyses of these samples showed that seventy-five per cent. of them contained B. coli. Directly across the river on the Pawtuxet shore, the water is considerably polluted. The beaches are covered with slime and the three samples collected from the shore of Pawtuxet Neck contained B. coli and other sewage forms. Thus, at a distance of a little over two miles below the Fields Point sewer, the river water contains sewage bacteria in abundance.

A mile and one-half below the Sabins Point beds we come upon the northern limits of the large Bullock Neck oyster grounds. Eighteen samples were collected on these beds at the three localities indicated on the map. The northern one is about three and one-half miles, and the southern about four and one-half miles distant from the outlet of the Providence sewer. Four