Water Report at Pu’ukoholā Heiau NHS
The brackish waterbody at Pu’ukoholā Heiau National Historic Site in Pōhaukole Gultch, inshore of Pelekane Bay is the only waterbody in the park. This waterbody has the appearance of a stream channel, but is frequently a stagnant pond, and experiences intermittent overland connection with the ocean.
This waterbody was sampled quarterly from the last quarter of 2007 through 2011 (and continues to be regularly sampled). During this time two notable events were observed: a likely minor algal bloom in 2009 and a flood event in 2011. Slightly elevated nutrient concentrations were observed prior to and during the bloom. Given the open canopy of the system and abundance of sunlight, nutrient concentrations will likely govern the risk of future blooms. Should a bloom occur in the future, surface scums could form depending on algal species and water temperature. In general, blue-green algae blooms and high ambient temperatures increase the risk of surface scums.
Heavy rains in this typically arid stream system in 2011 contributed a pulse of freshwater. Data from the observed flood event suggest that relatively large amounts of nutrients, especially nitrogen, were delivered to the waterbody during this event. Observations made during the freshwater flood event in progress illustrate that variability in this system in biphasic. That is, a natural range of conditions will exist during “low-flow” and these conditions are different than the conditions observed during the freshwater pulses from flood events. Future evaluations of the natural range of conditions, one of the primary goals of the I&M Program, should account for the environmental context of both low-flow and freshwater-pulse conditions.
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