KANEOHE BAY: NUTRIENT MASS BALANCE, 

 SEWAGE DIVERSION, AND 

 ECOSYSTEM RESPONSES 



Stephen V. Smith 



Hawaii Institute of Marine Biology 



University of Hawaii 



P.O. Box 1346 



Kaneohe, Hawaii 96744 



ABSTRACT 



Kaneohe Bay, Hawaii, is a coral reef/estuary ecosystem presently subjected 

 to stresses from sewage discharge and runoff. The sewage discharge is scheduled 

 to be diverted from the bay. This "relaxation" of sewage stress will be a major 

 ecosystem perturbation: the termination of a chronic stress which has been 

 imposed, with increasing intensity, on the bay over the past two decades. We 

 are treating this sewage diversion event as a controlled experiment designed to 

 ascertain ecosystem responses to such environmental perturbation. The 

 experiment is being performed by means of time-series field monitoring, 

 discrete field studies, and laboratory experiments. 



The stream runoff imposes short-term, catastrophic stress from fresh water 

 and sediment influx. The sewage accounts for about 90 percent of the 

 land-derived nutrient delivery to the bay, thus imposing an influence which 

 stimulates biological activity. 



The sediments in the bay have been a major repository for nutrients 

 discharged into the bay; nutrient release from the sediments has been, and will 

 continue to be, a significant process affecting the ecosystem. When the sewage 

 stress is relaxed, planktonic responses to that event v/ill be more rapid than 

 benthic responses, both because the plankton are immediately responsive to 

 the point-source sewage discharge, and because of characteristic high biomass, 

 efficient nutrient cycling, and Umited mobility of benthic organisms. 



INTRODUCTION 



Kaneohe Bay is a coral reef and estuary complex on the northeast 

 (windward) coast of Oahu, Hawaii (Figure 23-1). The bay was once renowned 

 as one of the most beautiful coral reef ecosystems in Hawaii. The reef 



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