Drivers

[sar-hartman]

Potential Drivers of DO & Temp

• temp
• recent rain
• water depth
• water velocity
• vegetation
• turbidity
• strength & duration of sunlight --> for photosynthesis

[sar-hartman]

dissolved oxygen in surface water is affected by temperature and has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved oxygen concentration is high.

[hlin-95]

https://www.fondriest.com/environmental-measurements/parameters/water-quality/dissolved-oxygen/#:~:text=The%20actual%20amount%20of%20dissolved,than%20does%20deeper%2C%20cooler%20water.

The idea of air saturation.
The idea of dissolved oxygen.

Light - As aquatic photosynthesis is light-dependent, the strength & duration of light seems to increase the dissolved oxygen produces. Besides, the dissolved oxygen produced will peak during daylight hours and decline at night.

Pressure/Altitude - Dissolved oxygen concentrations decrease as altitude increases (pressure decreases). This is true of both atmospheric and hydrostatic pressures. Water at lower altitudes can hold more dissolved oxygen than water at higher altitudes. (Gas saturation decreases by 10% per meter increase in depth due to hydrostatic pressure. )

Depth- Depth also affects the wavelengths available to plants, with red being absorbed quickly and blue light being visible past 100 m. In clear water, there is no longer enough light for photosynthesis to occur beyond 200 m, and aquatic plants no longer grow. In turbid water, this photic (light-penetrating) zone is often much shallower.

Salinity & turbidity - dissolved oxygen decreases exponentially as salt levels increase. That is why, at the same pressure and temperature, saltwater holds about 20% less dissolved oxygen than freshwater. Besides, as we mentioned above, in turbid water, this photic (light-penetrating) zone is often much shallower.

In summary, colder, deeper fresh waters have the capability to hold higher concentrations of dissolved oxygen, but due to microbial decomposition, lack of atmospheric contact for diffusion and the absence of photosynthesis, actual DO levels are often far below 100% saturation. Warm, shallow saltwater reaches 100% air saturation at a lower concentration, but can often achieve levels over 100% due to photosynthesis and aeration (The aeration will mix oxygen in water quickly, whether natural or man-made). Shallow waters also remain closer to 100% saturation due to atmospheric contact and constant diffusion.

If there is a significant occurrence of photosynthesis or a rapid temperature change, the water can achieve DO levels over 100% air saturation (super saturation). At these levels, the dissolved oxygen will dissipate into the surrounding water and air until it levels out at 100%