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Dissolved Oxygen Details

Understanding Stream Health: Dissolved Oxygen (DO) and Haʻikū and Huelo Streams

In Hawaiʻi, the health of our freshwater streams is essential for both the environment and public health. The Haʻikū Community Association is committed to keeping our streams clean and healthy! One key indicator of water quality is Dissolved Oxygen (DO). This webpage provides information on dissolved oxygen levels in Haʻikū and Huelo streams and how they relate to water quality, public health, and other environmental factors.

Dissolved Oxygen: The Breath of a Stream

Dissolved oxygen, measured in milligrams per liter (mg/L), represents the amount of oxygen dissolved in water, which is vital for the survival of fish, aquatic plants, and other organisms [1]. Just like humans need air to breathe, aquatic life depends on dissolved oxygen for survival. Healthy high dissolved oxygen levels indicate a well-functioning ecosystem, while low dissolved oxygen levels can signal pollution and poor water quality [2].

Dissolved Oxygen and Stream Health, Public Health and Recreation

For the residents and visitors of Haʻikū, understanding the quality of our streams is vital for ensuring safe recreational activities. While dissolved oxygen data is not used alone to determine a stream’s safety for swimming on a particular day (public health advisories consider factors like bacteria levels), low dissolved oxygen can indicate potential problems. Decomposing organic matter and excessive algae growth can deplete dissolved oxygen levels, creating an environment unsuitable for many aquatic organisms, potentially impacting the entire food chain. Low dissolved oxygen levels can also lead to the proliferation of harmful bacteria and algae, making the water unsafe for swimming, fishing, and other water activities [3]. Regular monitoring helps us stay informed and take necessary precautions [4]. While a single “typical” dissolved oxygen level isn’t applicable across all Hawaiian streams, a generally desirable range for healthy streams falls between 6 milligrams per liter (mg/L) and 8 mg/L [13,14].

DO levels can vary depending on several factors, including:

  • Elevation: Streams at higher elevations tend to be colder and hold more DO than streams at lower elevations [13].
  • Streamflow: Faster-flowing streams generally have higher DO levels due to increased surface area for gas exchange [15].
  • Natural Features: Characteristics like waterfalls or rapids can naturally increase DO levels by incorporating air into the water [8].
  • Biological Activity: The presence of aquatic plants and decomposing organic matter can influence DO levels [16].

Some general ranges for DO in healthy Hawaiian streams:

  • Generally desirable range: 6 – 8 mg/L [5]
  • Levels below 5 mg/L: Indicate potential impairment for aquatic life [5]

What Affects Dissolved Oxygen Levels?

Several factors influence dissolved oxygen levels in streams, including:

  • Temperature: Warmer water holds less dissolved oxygen than colder water [5].
  • Flow Rate/Water Movement: Faster-flowing streams typically have higher DO levels due to increased aeration surface area for oxygen exchange with the atmosphere [6].
  • Biological Activity/Organic Matter: Decomposition of organic matter by bacteria consumes oxygen, reducing DO levels: Decomposition of organic matter by bacteria consumes dissolved oxygen [7].
  • Photosynthesis: Aquatic plants and algae produce oxygen during daylight hours, increasing DO levels [8].
  • Nutrient Levels: Excess nutrients like phosphates, nitrates and nitrites can contribute to excessive algae growth, which can deplete dissolved oxygen as it decomposes [7].
  • Salinity: More saline (salty) water holds less dissolved oxygen than water with less salinity [7].
  • Pollution: Nutrient pollution from fertilizers and sewage can lead to algal blooms that, when decomposed, reduce DO levels [9].

Understanding the Monitoring Data:

The Haʻikū Community Association website publishes stream monitoring data, including dissolved oxygen levels. However, interpreting this data requires considering other factors, and to fully understand dissolved oxygen levels, it is essential to consider various related water quality parameters:

  • Conductance/Specific Conductance: Measures a stream’s ability to conduct electricity, influenced by dissolved salts and minerals. Higher dissolved oxygen levels may indicate pollution sources [10].
  • pH: Indicates the acidity or alkalinity of the water. While not directly linked to dissolved oxygen, pH levels can affect the availability of dissolved oxygen for aquatic life [7].
  • Pressure: Not typically a major factor in stream health, but changes in pressure may indicate disturbances or blockages in the stream. Changes in atmospheric pressure can influence DO levels, with higher pressure increasing DO solubility [5].
  • Phosphate: Similar to nitrates, high phosphate levels can cause nutrient pollution and subsequent DO depletion [9].
  • Nitrogen Compounds (Nitrites & Nitrates): Along with phosphates, nitrates are essential nutrients for algae. High levels of both can contribute to eutrophication and lower dissolved oxygen [7].
  • Silicon Dioxide: An essential nutrient for diatoms, a type of algae. Monitoring silicon dioxide can help assess the types of algae present, impacting dissolved oxygen consumption [10].
  • E. coli & Enterococcus: These bacteria are indicators of fecal contamination, posing a public health risk. Public health advisories consider these levels for swimming safety [11].
  • Erosion and Sedimentation: Erosion from construction sites or agricultural land, and digging and rooting of non-native feral ungulates (hooved animals such as pigs/boars) can increase organic matter entering streams, which decomposes and consumes dissolved oxygen [12]. Sedimentation, the settling of these particles, can also smother streambeds, impacting aquatic life and reducing dissolved oxygen levels.

Using the Data for Healthy Streams

By monitoring and sharing data on dissolved oxygen (DO), Conductance, pH, Salinity, Pressure, Nitrites, Nitrates, Phosphates, Silicon Dioxide, E. Coli, and Enterococcus; the HCA aims to empower residents and visitors with the knowledge to make informed decisions about stream safety. Monitoring dissolved oxygen levels and other parameters over time, can help  to identify trends and potential problems. This information can guide community efforts to:

  • Reduce nutrient runoff from fertilizers
  • Control erosion
  • Protect stream health

Looking Forward

Understanding the factors that affect dissolved oxygen levels and related water quality parameters is essential for ensuring the health and safety of our streams. The Haʻikū Community Association encourages all community members to regularly check the water quality data available on our website: https://www.haikumaui.org/water-quality-data/ to stay informed and safe. The Haʻikū Community Association also encourages responsible land management practices and minimal fertilizer use in the vicinity of stream (where rain may wash it in via stormwater flows), to minimize stream pollution. We can all play a role in keeping our streams healthy for future generations.

Sources:

  1. American Public Health Association (APHA). (2017). Standard Methods for the Examination of Water and Wastewater.
  1. U.S. Environmental Protection Agency (EPA). (2020). Water Quality Standards for Surface Waters.
  2. World Health Organization (WHO). (2011). Guidelines for Drinking-water Quality (4th ed.). WHO Press.
  3. Hawaii Department of Health (HDOH). (2019). State of Hawaii Water Quality Monitoring and Assessment Report.
  4. Boyd, C. E. (2015). Water Quality: An Introduction. Springer.
  5. Wetzel, R. G. (2001). Limnology: Lake and River Ecosystems (3rd ed.). Academic Press.
  6. Dodds, W. K. (2002). Fresh water Ecology: Concepts and Environmental Applications. Academic Press.
  7. Hem, J. D. (1985). Study and Interpretation of the Chemical Characteristics of Natural Water (3rd ed.). U.S. Geological Survey.
  8. Correll, D. L. (1998). The Role of Phosphorus in the Eutrophication of Receiving Waters: A Review. Journal of Environmental Quality, 27(2), 261-266.
  9. Allan, J. D., & Castillo, M. M. (2007). Stream Ecology: Structure and Function of Running Waters (2nd ed.) Springer.
  10. Soller, J. A., Schoen, M. E., Bartrand, T., Ravenscroft, J. E., & Ashbolt, N. J. (2010). Estimated Human Health Risks from Exposure to Recreational Waters Impacted by Human and Non-human Sources of Faecal Contamination. Water Research, 44(16), 4674-4691.
  11. Waters, T. F. (1995). Sediment in Streams: Sources, Biological Effects, and Control. American Fisheries Society.
  12. Hawaii Department of Health Clean Water Branch: https://health.hawaii.gov/cwb/clean-water-branch-home-page/water-quality-standards/
  13. US Environmental Protection Agency Aquatic Life Standards: https://www.epa.gov/wqc
  14. Wetland and Aquatic Research Center (WARC). (n.d.). Dissolved Oxygen. Retrieved from https://www.sfasu.edu/docs/degree-plans/biology-aquatic.pdf
  15. How Does Dissolved Oxygen Affect Aquatic Life? https://www.epa.gov.