Trends in water quality of Waikolu Stream, Kalaupapa National Historical Park, Molokaʻi, Hawaii, 2007–2017

Raikow, David; Wasser, Mark; McCutcheon, Amanda; Farahi, Anne

doi:10.36967/2302153

Water quality was monitored in Waikolu Stream, Kalaupapa National Historical Park, Molokaʻi, Hawaʻi from 2007-2017. Water was collected for nutrient analyses and a sonde equipped with multiple probes was used to measure water quality parameters. The sampling regime was based on a split-panel of permanently established or “fixed” sites sampled during each sampling effort, and “temporary” sites of randomly assigned locations, for each sampling effort. Results included: • NO-3 + NO-2 regularly exceeded state water quality criteria. • TP exceeded state water quality criteria once out of three quarters evaluated. • Other nutrient concentrations were consistent with Hawaiian streams. • Waters were clear and well oxygenated. • Conditions were consistent with similar pacific island streams. • Dissolved nutrient fractions dominated base flow conditions. • Seasonality was detected for TDN, NO-3 + NO-2, chlorophyll, pH, oxygen, and temperature. • Several trends were detected; however, the magnitude of change was small and did not warrant concern. • Temporal patterns did not obviously correspond to climate conditions. • Parameters varied spatially to a limited extent, with nitrogen decreasing and temperature, specific conductance, and oxygen increasing from headwaters to the mouth. • Temporary site conditions were highly correlated with fixed sites and did not provide additional insights. Water quality in Waikolu Stream was generally good with the exception of NO-3 + NO-2 which exceeded state standards. However, concentrations of NO-3 + NO-2 were generally consistent with many streams in Hawaii and natural causes of observed concentrations may have included older soils, steep slopes, and high precipitation. Exotic species including ungulates, which are known to occur in Waikolu Valley, could have contributed to elevated N through droppings and soil erosion in the riparian zone. Waikolu Stream TDN, TDP, chlorophyll, pH, turbidity, SpC, and oxygen were consistent with streams in other well-protected NPS watersheds on pacific islands on Maui, Guam, and American Samoa. Due to the watershed’s small size, the stream’s short length, and because variation or unique conditions were not captured by using split-panel, we recommend reducing the sampling effort. For example, our observations indicate that one easily accessible site in the lower reaches of the stream (FKALA03) displays water quality that reflects the entire stream. We also recommend adding nutrient analytes to better characterize biogeochemical cycling in this stream, including TP, TN, NH+4, and PO4. A power analysis is underway to evaluate reduction of sample sites. Such a reduction will result in large cost savings for the PACN water quality monitoring program.

Trends in water quality of Waikolu Stream, Kalaupapa National Historical Park, Molokaʻi, Hawaii, 2007–2017

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