CARIBBEAN RESEARCH INSTITUTE Sees fom iso 9 WAT R POLLUTION REPORT NO. TUS OF WATER QUALITY IN CRUZ BAY Tub STA en AND CHOCOLATE HOLE, ST. JOUN es pavid 1. Grigg and Robert P. vanEepoel 971 January, (2nd Printing - June, 1971) GOVERNMENT OF THE VIRGIN ISLANDS DEPARTMENT OF HEALTH, DIVISION OF ENVIRONMENTAT, HEALTH WATER POLLUTION REPORT Contracted By CARIBBEAN RESEARCH INSTITUTE COLLEGE OF THE VIRGIN ISLANDS REPORT ON THE STATUS OF WATER QUALITY IN CRUZ BAY AND CHOCOLATE BOM 5). AND CHOCOLATE HOLE, ST. JOHN David I. Grigg and Robert P. vanEepoel! January, 1971 (2nd Printing - June 1971) CONTENTS Page I. INTRODUCTION CRUZ BAY CHOCOLATE HOLE IV. APPENDIX I. INTRODUCTION ‘This report is a follow-up of two bays ly studied. It should be interpreted in that context and with reference to the original reports. The present is based on data coll din and of 1970, 1 ions of both bays, We wish to thank and on aerial and k Mr. Fred Nicholson, Director of the Bureau of Public Health Laboratories for once aguin the 1 Brody, R. W., D. I. Grigg, D. M. Raup and R. P. vanEepoel, Report on Estuarine Environment at Cruz Bay, St. John, Government of the Virgin Islands, Department of Health, Division of Environmental Health: "Phase I Report, A Study of the Effects of Pollutants on the Waters and Sediments of Cruz Bay", October, 1969; "Phase II Report, A S, udy of the Waters, Sedime and Biota of Chocolate Hole, St. John, with Compa: to Cruz Bay, St. John", January, 1970. ll. CRUZ BAY Water quality data were gathered in Cruz Bay on November 20, 1970 and again on December 1, 1970 and are summarized in Table 1, Between these times rough seas had stirred up the bottom of the bay considerably, ‘This was evident by increased turbidity and large amounts of benthic grasses, algae, bivalve mollusks and sponges washed up on the beach, This very high energy situation must have occured shortly before our inspection on December 1, 1970 because all of the stranded organisms were still alive at that time. Other effects of this surge action were apparent and are evident in Table 1. The temperature was lowered at all stations, reflecting the intrusion of colder water from Pillsbury Sound. Salinity was made more uniform throughout the bay; the range was compressed from 35.6 ppt - 57.5 ppt measured on November 20, 1970 to 36.0 ppt - 36.4 ppt. At all stations except #38 (deepest in the creek), pH was higher on the second occasion. There was no change at Station #38. At all but one station (#27) there was an increase in suspended solids and Secchi depth was reduced at several stations. Visibility was obviously reduced in the northeast portion of the harbor around Government House Point and the ferry dock. In fact, the reduction (compared to summer, 1969) at Station #27 off the tip of the dock was very striking: from 4.2 meters (bottom) to 2.5 meters. Color was normal around the channel light and along the reef south to Golge Point and in a narrow band east of the reef, Elsewhere color was noticeably affected by the milky cast of suspended sand fines. Snorkeling investigation showed that there was indeed suspended sand and organic particulates in the water. Much scouring has occurred in the back reef area and this area was also the source of the large number of benthic organisms found washed up on the beach, It is apparent that seasonal changes in sea and weather significantly affect the water in Cruz Bay (Table 2). For this reason, it is more likely that reliable indications of significant or permanent changes in water quality would be gained by comparing the data from winter, 1969 and winter, 1970. When this is done, the most striking difference is that dissolved oxygen in both areas was higher this December than a year ago: 6.2 mg/l as compared with 5.7 mg/l in the harbor and 5.6 mg/l] versus 4.3 mg/I in the ereek. A definite reduction in aquatic visibility is apparent, especially at Stations 414, 21, 23, 27. This is the area around Government House Point. The average Secchi disc visibility in the harbor (2.7 meters) is apparently reduced compared to 3.2 meters (average bottom depth) last year. Visibility is very much reduced compared to summer and fall of 1969, Now the bottom is visible only in that section north and west of ; Stations #4, 5, 6, Il, 18 and in water less than 1,5 - 2 meters along the beach, Along the north shore the bottom can be seen only in less than | meter. On the other hand, most stations checked in the creek area showed an increase in water clarity. The improvement here is also evident from a boat and from aerial photos. There are now many boats anchored in the bay than a year ago, anda small floating dock has been placed off the beach to service ferry boats. Boat traffic in and out of the bay is noticeably heavier, In the creek the water color is still very bad and in the area of Stations #34 and “36, there was a great deal of oil. The septic odor of sewage was very bad here on November 20, 1970 and it was noted that where the sewer line comes out of the bulkhead near Station #30 the elbow was broken loose and sewage was being discharged upward out of the break to the water surface, Of six samples evaluated for fecal coliforms and streptococci this was the only positive sample, with 2 fecal coliform per 100 ml, In summary, Cruz Bay water quality on the whole is worse now than it was a year ago. A ing this of quality, b has been a relative improve- ment in the quality of the creek water. Presently, it seems likely that most of the change is due to seasonal wave action in Cruz Bay. This has disturbed bottom sediments in the outer bay and promoted unusual mixing between the waters of the harbor and the creek, This mixing has resulted, because of the usual inequity in these water masses, ina relative improvement of creek water quality at the expense of a simultaneous reduction in harbor water quality. It is therefore difficult to determine if Cruz Bay has sustained any permanent, long-term change in water quality. Ml, CHOCOLATE HOLE Data coll d in Ch Hole in N, ber are given in Table 3, The bay shows very few changes since our survey a year ago, Water color, visibility and bottom organisms seem to be in as good condition now as then and the bottom can still be seen throughout the bay, The only quantitative observation of note is a significantly lower salinity at Station #7, where the pond connects to the bay. This salinity depression is dly caused by ing pond water which, ing the unusual of rainfall during the past year, must now be quite brackish. Monthly averages for water quality data are given in Table 4. There are now 4-5 boats anchored in the bay and littering of the sea bottom is increasing: several cans and other items were noted. Except for these, no adverse changes were noted. oy \\ of “bs a 6. ( \ i SS YS) A CZ SOW, 6 ) We I fo =f = | ZZ J] Gj \ @ NS \ « a. \ SS N \\ \ \\\\ NY; \N Yj \ ASA Wel SS Y Sw SS y —Z SS Si \\\ \\ \ \ X\ & 0) YY ps eo PY SS \\ ee A SNe as ‘TABLE 1 CRUZ BAY, ST. JOHN WATER QUALITY DATA, NOV.-DEC., 1970 Fecal Fecal Secchi Suspended Coliform Strep ‘Temp. Sal. D. 0. Depth Solids per per Station Date °C. ho M 100 ML 100 M1 HH MG/L % Sat. MG/L. 11/20/70 28.0 37.5 8.1 6.4 102 B 27.2 0 0 = - 12/1/70 27.1 36.0 8.3 6.3 7 B 32.2 4 11/20/70 27.9 37.5 8.1 5.9 94 3.0 17.6 an < 12/1/70 27.0 36.2 8.3 6.3 97 2.8 20.6 = — 18 28. 37.5 8. 1 6.8 108 8.6 11/20/70 12/1/70 27.1 36.0 8.3 6.2 95 16.1 os pa 21 12/1/70 27.2 36.0 8.2 6.2 95 2.8 13.0 23 12/1/70 27. 36.0 8.3 6.3 97 2.3 23.7 = cone 27 11/20/70 28.0 35.6 8. 1 6.3 99 3.0 16.1 8.3 13.9 6.1 2.5 meremene resect: 27.5 36.5 o-Fr4 GaSe os 241-8 18.9 2, 30 11/20/70 28.0 87.5 8.1 5.8 2.0 0.0 12/1/70 26.8 36.0 8.2 6.1 2.3 18.0 pe 12/1/70 26.6 36.4 8.2 5. 6 i 16.2 = re 36 28.0 36.7 8.1 4 86 11/20/70 5. 0.8 14.1 12/1/70 26.6 36.2 8.2 5.4 82 = 19.1 38 11/20/70 28.2 35.7 8.0 5. 3 1.25 13.7 0 12/1/70 8.0 5. 3 80. == 21.3 6 36.4 —~AVERAGE. 27,3 36.4 8. 5 5. 6 86. 1.6 14.6