Marine water quality in Pacific Island national parks: Temporal, spatial, and chemical patterns 2008–2015

Raikow, David; Kichman, Scott; McCutcheon, Amanda; Farahi, Anne

doi:10.36967/nrr-2284328

Marine water quality was monitored along the coasts of Kaloko-Honokōhau National Historical Park on the Island of Hawaiʻi, Kalaupapa National Historical Park on Molokaʻi, War in the Pacific National Historical Park on Guam, and National Park of American Samoa on Tutuila and Ofu, from 2008 to 2015. Concentrations of nitrogen and phosphorus were measured by collecting water samples. Temperature, dissolved oxygen, salinity, turbidity, chlorophyll, and pH were measured using probes. Analyses and summaries include the ranges of water quality parameter values under ordinary conditions, trends, spatial patterns, seasonal patterns, the abundance of nutrients in dissolved and particulate forms, correlation between surface and near-bottom water measurements, and a comparison of fixed and temporary sites. Waters were low in total dissolved phosphorus (TDP), with concentrations generally at or below the 15.0 µg/L detection limit. Waters were low in total dissolved nitrogen (TDN) with concentrations centered close to the detection limit, of 0.07 mg/L with outliers up to 0.44 mg/L. Nitrate + nitrite (NO¯3 + NO¯2) concentrations ranges were centered at or below ~10 µg/L. Near-bottom waters had lower concentrations of nutrients than surface waters. Fixed and temporary sites did not differ substantially with regard to any parameter. Waters were high in dissolved oxygen, low in turbidity, and thus oligotrophic and consistent with previous studies. Results did not merit concern with regard to water quality with two exceptions: 1) Honokohau Small Boat Harbor near Kaloko-Honokōhau National Historical Park consistently released a plume of water that was cold, fresh, and high in nutrients, e.g. NO¯3 + NO¯2 up to 166 µg/L; and 2) a possible algal bloom was observed in Kaloko-Honokōhau National Historical Park in 2010 that did not appear to be caused by the harbor. Very few temporal changes were observed over the study period. A ~25% decrease in TDN was observed at Kalaupapa National Historical Park from 2013 to 2014, which continued into 2015. Decreasing salinity of 1–2 parts-per-thousand (ppt) was detected over the study period (2008–2015) in Kaloko-Honokōhau National Historical Park, Kalaupapa National Historical Park, War in the Pacific National Historical Park Asan unit, and National Park of American Samoa Ofu unit. Increasing temperatures of up to 2℃ were detected at Kaloko-Honokōhau National Historical Park and up to 1℃ at Kalaupapa National Historical Park during the latter portion of the study period; but this may have been an artifact of relatively low values at the beginning, and high values at the end of the observation period. Nutrients existed almost completely in dissolved forms. Seasonality was suggested for temperature and chlorophyll. Spatial patterns were only detected at Kaloko-Honokōhau National Historical Park with respect to the previously-known plume emanating from Honokohau Small Boat Harbor. Surface and near-bottom measurements were highly correlated.

Marine water quality in Pacific Island national parks: Temporal, spatial, and chemical patterns 2008–2015

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