Sedimentation in Kaneohe Bay, Oahu, Hawaii 1977 and 1978

Abstract

Sinking material was collected with sediment traps for a 13 month period in a eutrophic subtropical embayment, Kaneohe Bay, Hawaii. A ratio method was applied to distinguish sedimentation from resuspension. An annual average of 74+15% of the total material trapped had been resuspended. The resuspension rate appeared to be controlled by wind speed (p<O.OOl). The contribution of benthic diatoms to the diatom assemblage in the water column was also related to wind speed (p<O.OOl). The annual average sedimentation rates were 0.453±0.23 g.m-2.day-1 for organic carbon and 0.373+0.32 mg.m-2.day-1 for chlorophyll a. The discarded houses of the appendicularian Oikopleura longicauda Vogt (9xl0 4 houses·m-2·day-1) and fecal pellets produced by net zooplankton (2.77 cm3·m-2·day-1) contributed about 61% and 13% of the sedimentation rate of organic carbon, respectively. Detritus and phytoplankton contributed about 17% and 9% of organic carbon, respectively. The detritus contribution was calculated by difference. The sinking velocity of the discarded houses appeared to be controlled by the chemical composition of the trapped material (p<O.OOl). The contribution of suspended matter in freshwater runoff was concluded to be about 6.4% of the annual average sedimentation rate, assuming a tenfold increase in concentration of particulate organic matter in the freshwater runoff over the surface water. The annual average sedimentation rate of particulate organic carbon produced in the water column was estimated to be 0.425±0.22 gC·m-2·day-1, which was about 42% of the primary production by phytoplankton in the water column. The annual sedimentation rate including terrestrial material was 165 gC·m-2·year-1 (2 kgDW·m-2·year-1). Comparing this estimate with an independent geological estimate (132 gC·m-2·year-1) suggests significant accumulation of organic matter in the bottom sediments from non-sedimentation processes. Annual sedimentation rate excluding terrestrial material was 155 gC·m-2·year-l. About 51% of organic carbon supply was respired in the water column.