Final answer:
Factors that influence the natural variation in dissolved oxygen concentration in water include dissolved organic carbon content, which affects algal blooms and sunlight penetration; temperature, which inversely affects oxygen solubility; and nutrient availability, which is essential for oxygen-producing aquatic plants and algae.
Step-by-step explanation:
The factors that influence the natural variation in dissolved oxygen (DO) concentration in water are numerous. One significant factor is the presence of dissolved organic carbon (DOC), which can block sunlight and prevent algal blooming. Algae are important in water ecosystems because they produce oxygen through photosynthesis. Therefore, in tanks with larger DOC particles, caused by two-species fish, there was less sunlight penetration, reducing the algal bloom and potentially affecting DO concentration. Conversely, tanks with single-species fish had smaller DOC particles, allowing more sunlight and thus more algal blooms, possibly increasing DO levels.
Temperature is another critical factor. Generally, the solubility of gases, including oxygen, decreases as temperature increases. This phenomenon means that warmer waters tend to have lower DO concentrations. This principle is part of the impact of thermal pollution in natural waters.
Nutrient availability also impacts DO concentration since they are essential for the growth of aquatic plants and algae, which produce oxygen. Water near shorelines often has more dissolved nutrients due to runoff, leading to potentially higher DO concentrations. Conversely, water that is deeper or farther from shore may have less available nutrients and therefore lower DO levels. Water flow and population density, such as the size and density of fish and microorganism populations, can also affect nutrient availability and DO concentration.