Spatio-temporal changes in trophic categories of infaunal polychaetes near the four wastewater ocean outfalls on Oahu, Hawaii

• This study presents 20 years of benthic monitoring data focussing on polychaetes.
• Samples were collected from every sewage outfall servicing Honolulu, Hawaii, USA.
• We examine the effect of sewage on sediment properties and polychaete assemblages.
• Aggregate polychaete species data into functional trophic categories can be useful.
• Organic enrichment was not detected beyond designated discharge zones (ZIDs).

This study examines the effect of sewage discharge on benthic polychaete assemblages in the context of their functional trophic categories. We present data spanning 20 years of monitoring benthic invertebrate assemblages and sediment properties at all 4 primary- and secondary-treatment wastewater outfalls servicing Honolulu and the island of Oahu, Hawaii, USA. Samples collected within mandated zones of initial dilution (ZIDs) near outfall discharge sites were compared to samples collected at reference stations at varying distances away. Our findings indicate that sediment properties were not affected by the outfall discharge rate or distance from each ZID. The number of polychaete species in 4 functional trophic categories (carnivore, detritivore, omnivore, and suspension feeder) did not change with the outfall solid loading rate or with distance from each ZID, thus suggesting relatively little organic enrichment. We find no evidence of heavy organic enrichment beyond the designated ZIDs at these 4 wastewater outfalls.

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