Introduction

Microbiological Water Quality of Ko Olina Lagoons

Microbiological Water Quality of Ko Olina Lagoons

SPECIAL REPORT SR-2020-04

Microbiological Water Quality of Ko Olina Lagoons

Marek Kirs and Jaline Sergue
May 2020, viii+18 pp.

ABSTRACT

The Ko Olina Resort lagoons are extremely popular for recreational activities, however, they have not been extensively monitored for water quality. The objective of this study is to address this lack of water quality information by examining and evaluating the lagoons’ microbiological water quality over a one-year period. In 2019 (January 14 to December 11), 128 water samples were collected from the four lagoons (Kohola, Honu, Nai‘a, and Ulua). The results indicated generally good water quality as (1) enterococci were not detected in a large proportion of the samples (88%), and (2) only one sample exceeded the Hawai‘i Beach Action Value for enterococcus concentrations (130 MPN per 100 ml). In addition, no human-associated Bacteroides marker was detected in this sample, nor were Clostridium perfringens concentrations elevated, which suggested the source was not human fecal matter. The areas of brown water found in late August 2019 in the Kohola and Nai‘a lagoons were due to the extensive growth of a dinoflagellate, tentatively identified as Gymnodinium. Fecal indicator bacteria (enterococci and C. perfringens) were not associated with the blooms. The saxitoxin levels were low (0.039 µg per L) in all four lagoons and were not associated with the observed blooms, nor did it present any plausible direct risk to human health. The localized blooms were probably linked to the elevated nitrogen levels associated with the two lagoons. The blooms may possibly have resulted from the extensive use of irrigation and fertilizers during the dry summer months, and local hydrology and water exchanges may have also contributed to the observed differences. The linkage between irrigation sources, fertilizer use, and local hydrology should be further studied to more definitively determine the cause of the dinoflagellate blooms if mitigating periodic nuisance blooms in the Ko Olina lagoons is of interest.