Nitrates and nitrites are utilized by plants as nutrients, however abundant amounts may lead to eutrophication. Excessive amounts of nitrates in water can be caused by blasting quarry operations, over use of fertilizers nearby, animal wastes, automobile & industrial emissions, along with decomposition of plants and animals. The state criteria are 0.07 mg/L for the wet season, and 0.03 mg/L for the dry season. Cars are commonly illegally discarded alongside Kapaa Stream, leaving automobile and industrial emissions that eventually enter into the stream. Decomposition of animals and plants along with industrial wastes also are contributing factors of high levels of nitrate.

During the wet season, all but site 1 exceeded the state criteria. Heavy rainfall may have caused more runoff with fertilizers and animals waste to enter the stream, in addition to the examples listed above. The highest level though occurred in Site 6 (geo mean, 1.297 mg/L), which the closest site to the quarry. During the dry season, Site 6 was no longer monitored due to much reduced amount of water there. Site 3 then became the site of highest combined nitrate and nitrite. Among all the study sites, Site 3 is the one located next to the airfield where people fly remote-controlled airplanes.

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