Dissolved Oxygen

Definition

Dissolved oxygen (DO) refers to the amount of oxygen that is present in water, which is essential for the survival of aquatic organisms. The concentration of dissolved oxygen in water is a crucial indicator of water quality and reflects the health of aquatic ecosystems, as it influences the metabolic processes of fish and other aquatic life forms. A sufficient level of DO is vital for sustaining biodiversity and maintaining ecological balance in freshwater and marine environments.

5 Must Know Facts For Your Next Test

1. The acceptable range of dissolved oxygen for most aquatic life is typically between 6 to 8 mg/L, but different species may have specific requirements.
2. Temperature, salinity, and pressure influence the solubility of oxygen in water; warmer water holds less dissolved oxygen compared to colder water.
3. Photosynthesis by aquatic plants and phytoplankton contributes to higher levels of dissolved oxygen during daylight hours, while respiration by organisms consumes it.
4. Pollution from agricultural runoff or wastewater can lead to decreased dissolved oxygen levels due to increased organic matter and nutrient loading.
5. Measuring dissolved oxygen is essential for assessing water quality and is often included in routine environmental monitoring programs.

Review Questions

• How does temperature affect the concentration of dissolved oxygen in aquatic environments?
  • Temperature has a significant impact on the concentration of dissolved oxygen. As water temperature increases, the solubility of oxygen decreases, meaning warmer waters hold less dissolved oxygen compared to colder waters. This can create stress for aquatic organisms that depend on sufficient DO levels, particularly during hot summer months when many species are more active.
• Discuss the relationship between eutrophication and dissolved oxygen levels in a water body.
  • Eutrophication leads to an increase in nutrient levels in water bodies, which promotes algal blooms. When these algae die and decompose, the process consumes large amounts of dissolved oxygen. This depletion can result in hypoxic conditions or dead zones where aquatic life cannot survive, highlighting how nutrient pollution directly impacts water quality and ecosystem health.
• Evaluate the implications of low dissolved oxygen levels on biodiversity and ecosystem function in aquatic systems.
  • Low dissolved oxygen levels significantly threaten biodiversity by creating conditions unfavorable for many aquatic species. Fish and invertebrates may struggle to survive, leading to declines in populations and shifts in community structure. This loss can disrupt food webs and ecosystem functions, as species interactions and nutrient cycling are altered. Maintaining adequate DO levels is therefore crucial for sustaining healthy ecosystems and their associated biodiversity.

Related terms

Eutrophication:

A process where water bodies become overly enriched with nutrients, leading to excessive growth of algae and subsequent depletion of dissolved oxygen, often resulting in dead zones.

Biochemical Oxygen Demand (BOD): A measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water; high BOD indicates low dissolved oxygen availability.

Aquatic Life: Refers to organisms that live in water, including fish, invertebrates, and plants, all of which depend on adequate levels of dissolved oxygen for survival.