KANEOHE BAY SEWAGE DIVERSION EXPERIMENT: PERSPECTIVES ON ECOSYSTEM RESPONSES TO NUTRITIONAL PERTURBATION

Abstract

Kaneohe Bay, Hawaii, received increasing amounts of sewage
\nfrom the 1950s through 1977. Most sewage was diverted from the bay in 1977
\nand early 1978. This investigation, begun in January 1976 and continued
\nthrough August 1979, described the bay over that period, with particular
\nreference to the responses of the ecosystem to sewage diversion.
\nThe sewage was a nutritional subsidy. All of the inorganic nitrogen and
\nmost of the inorganic phosphorus introduced into the ecosystem were taken
\nup biologically before being advected from the bay. The major uptake was by
\nphytoplankton, and the internal water-column cycle between dissolved nutrients,
\nphytoplankton, zooplankton, microheterotrophs, and detritus supported
\na rate of productivity far exceeding the rate of nutrient loading.
\nThese water-column particles were partly washed out of the ecosystem and
\npartly sedimented and became available to the benthos. The primary benthic
\nresponse to nutrient loading was a large buildup of detritivorous heterotrophic
\nbiomass. Cycling of nutrients among heterotrophs, autotrophs, detritus, and
\ninorganic nutrients was important.
\nWith sewage diversion, the biomass of both plankton and benthos decreased
\nrapidly. Benthic biological composition has not yet returned to presewage
\nconditions, partly because some key organisms are long-lived and partly
\nbecause the bay substratum has been perturbed by both the sewage and other
\nhuman influences.