Investigating an Impaired Estuary: ‘Ike One o Kaʻelepulu, Knowledge from the sands of Kaʻelepulu

Abstract

Estuaries are highly productive spaces that transform nutrients into biological productsand have been heavily used and modified by people. While it is known that tropical estuariesare areas of high productivity, generally 10 to 15 times greater than coastal plain estuaries,little is known about the functionality of these systems. Changes in human population dynamicsand demographics have shifted land use and cultural values. Wetlands and flood plains havebeen developed and waterways modified without an understanding of estuarine functionality.Kaʻelepulu Estuary on Oʻahu’s eastern shore was once a highly productive area. Housingdevelopment in the area rerouted natural stream flow to prevent flooding resulting in anaccreted sand berm at the stream mouth and 0.54 km2 (134-acre) area of stagnant water.Nutrient cycling has been disrupted, dissolved oxygen crashes resulting in fish die offscontribute to pathogenic bacterial growth. The estuary now needs to be managed by periodicdredging of the sand berm to prevent street runoff flooding nearby houses and introduceoceanic water. Residents are concerned for both the health of the estuary and the pollution riskto Kailua Bay when the berm is open. This investigaton explored the impact of current estuary management and its impact to the adjacent popular beach by testing the following hypotheses: If the berm is open and the estuary has exchange with the ocean, then the water quality in the estuary will improve and there will be negligible impact to the water quality along Kailua beach. Rainfall will increase nutrient and enterococci concentrations in the stream mouth and inland sections of the estuary. Longer berm openings will correlate with greater oceanic exchange and therefore an increase in salinity at the stream mouth section post berm closure. Lastly, if community engages in the research process, then greater awareness of and attitudes towards stewardship of place will be garnered. The Watershed Investigations Education Research and Design (WIRED) outreach program has been studying the area for several years engaging local students, community members, and the environmental firm, Oceanit. This investigation engaged WIRED’s students and their school teachers to use the same well-established Department of Health protocols at thirteen sample locations distributed along the beach and estuary. Principal component analysis determined salinity, as the primary parameter to assess changes in estuarine biogeochemistry. It appears that the opening of the berm does not significantly contribute to poor water quality along the beach, especially when addressing the differences in water quality threshold limits based on freshwater input. Opening events appeared improve increase in the estuary and the duration of estuarine and coastal water exchange appears to be a factor. Runoff inferred by rain fall appears to contribute to increases enterococci and chlorophyll-a, to a lesser extent. Community participation helps to elicit more informed and engaged residents to steward this impaired system.