XN000022-1994-10-26 — Page 95

WEDNESDAY, OCTOBER 26, 1994

BY

79

LOW OXYGEN LEVELS TO BLAME FOR CORAL DEATH

* * * * *

FOLLOWING IS A QUESTION BY THE HON SIMON IP AND A WRITTEN REPLY THE SECRETARY FOR PLANNING, ENVIRONMENT AND LANDS, MR TONY

IN THE LEGISLATIVE COUNCIL TODAY (WEDNESDAY);

BASON,

QUESTION : IN VIEW OF THE DEATH OF CORALS IN SAI KUNG AND MIRS BAY EARLIER THIS YEAR, WILL THE GOVERNMENT INFORM THIS COUNCIL

ANSWER

WHETHER :

(A) ANY

(B)

MR PRESIDENT,

(A)

AND

INVESTIGATION INTO THE CAUSE HAS BEEN CONDUCTED;

ANY MEASURES HAVE BEEN TAKEN TO PREVENT THIS FROM HAPPENING AGAIN IN THE FUTURE?

THE CONSULTANTS CARRYING OUT ROUTINE MARINE SURVEYS FOR THE CIVIL ENGINEERING DEPARTMENT (CED) DISCOVERED THIS SUMMER THAT MARINE LIFE OVER A SUBSTANTIAL AREA OF MIRS BAY WAS DYING. AFTER CONSULTATION WITH THE AGRICULTURE AND FISHERIES DEPARTMENT (AFD) AND THE ENVIRONMENTAL PROTECTION DEPARTMENT, CED INSTRUCTED THEIR CONSULTANTS TO UNDERTAKE A SPECIAL SURVEY ΤΟ DETERMINE THE CAUSE AND THE EXTENT OF THE EFFECT. THE SURVEY WAS UNDERTAKEN DURING THE FIRST WEEK SEPTEMBER.

-

OF

AFD

BASED ON THE SURVEY FINDINGS, THE CONSULTANTS AND CONCLUDED THAT THE SEABED KILL WAS A RESULT OF EXCEPTIONALLY LOW LEVELS OF DISSOLVED OXYGEN. THIS PHENOMENON, KNOWN AS HYPOXIA, IS NATURAL AND OCCURS EVERY YEAR, THOUGH TO A MUCH LESS SERIOUS DEGREE. HYPOXIA IS A RESULT OF STRATIFICATION OF THE WATER COLUMN WHICH HAS TWO DISTINCT LAYERS

AN UPPER, WARMER LAYER OF LOWER SALINITY AND A LOWER, COLDER LAYER OF HIGHER SALINITY. LACK OF MIXING BETWEEN THE LAYERS CAUSES A REDUCTION IN DISSOLVED OXYGEN IN THE LOWER LAYER. THIS YEAR, THE STRATIFICATION WAS ENHANCED - APPARENTLY BECAUSE OF A LACK OF HIGH WINDS FROM TYPHOONS AND THE EXCEPTIONALLY HIGH LEVELS OF RAINFALL IN HONG KONG AND GUANGDONG

WITH THE DRAMATIC RESULTS OBSERVED. THE SURVEY SHOWED THAT BY EARLY SEPTEMBER, MOST MARINE ORGANISMS, INCLUDING CORALS, WORMS, CRABS, ECHINODERMS AND ANEMONES HAD EITHER BEEN KILLED OR SEVERELY AFFECTED UP TO A LEVEL OF -2MPD OVER AN AREA OF APPROXIMATELY 100 SQUARE KILOMETRES.

-

(B)

THE PHENOMENON IS A NATURAL ONE AND NO PRACTICAL MEASURES CAN BE TAKEN TO PREVENT A RECURRENCE. HOWEVER, RAINFALL STATISTICS AND THE AGE OF THE CORALS FOUND IN MIRS BAY INDICATE THAT THIS IS PROBABLY A 1- IN-100 YEAR EVENT.

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