Haiku Water Quality: Inorganic Nutrients
Nitrates
Nitrate (NO3-) levels in freshwater streams are important indicators of water quality. Nitrate primarily enters streams through runoff from agricultural fertilizers, animal waste, and sewage. Elevated nitrate levels can lead to eutrophication, which promotes excessive algae growth and oxygen depletion, negatively impacting aquatic ecosystems.
Phosphates
The Hawaiʻi Department of Health (HDOH) does not specify a direct health threshold for phosphate levels in freshwater streams; however, the management and regulation of phosphate and other nutrients are part of broader water quality standards aimed at protecting public health and maintaining ecological balance in aquatic environments. Phosphate levels are a critical component of water quality monitoring due to their impact on eutrophication, which can lead to harmful algal blooms and oxygen depletion in water bodies, creating a potential health risk for humans and aquatic animals. This can adversely affect the safety of recreational water use.
Ammonia
High ammonia levels can pose a risk to human health, especially when the water is used for recreational activities. Ammonia can irritate the skin and eyes, and in high concentrations, it can be toxic. Elevated ammonia levels may correlate with higher instances of harmful bacteria like E. coli and enterococcus, impacting public safety (Centers for Disease Control and Prevention, 2021). The U.S. Environmental Protection Agency (EPA) recommends an acute threshold of approximately 2,200 micrograms/L for ammonia (NH₃) in freshwater, depending on temperature and pH (EPA, 2013). For chronic exposure, the EPA suggests a threshold of around 190 micrograms/L, also influenced by temperature and pH (EPA, 2013). In Hawai’i, the Department of Health aligns its water quality standards with EPA guidelines but may have additional specific regulations tailored to local conditions (Hawaiʻi Department of Health, 2018). For the most precise values and current regulations, consulting the Hawaiʻi Administrative Rules or recent publications from the Department of Health is recommended (Hawaiʻi Department of Health, 2022).
Silicon Dioxide
Silicon dioxide (SiO₂), also known as silica, is naturally present in stream water, and commonly found in sand, rock, quartz, and many minerals. While not a direct health concern itself [1], its levels can indicate potential issues like turbidity, erosion, and sedimentation, which can lead to health issues from various pollutants whose transport and water-borne proliferation may be facilitated by those stream characteristics. Silicon dioxide is generally harmless at the low concentrations typically found in streams. While there are no established health thresholds for silicon dioxide in recreational waters, high levels often accompany turbidity, which can be a concern for swimmers and snorkelers. Turbid water can limit visibility, increasing the risk of accidents and making it difficult to spot underwater hazards. Additionally, high silicon dioxide levels can indicate increased sedimentation, which can harbor harmful bacteria such as E. Coli and Enterococcus [2]. These bacteria pose risks to those swimming, fishing, or engaging in other water activities.
