Dissolved Oxygen is one of the major indicators of water quality. Just as humans need oxygen to breathe, aquatic life needs sufficient amounts of oxygen dissolved in water to survive. Dissolved oxygen depletion can occur for several naturally occurring reasons, most of which are highly preventable or treatable (dissolved oxygen depletion can occur with pollution of the water, but this will be covered in a future post). The primary cause of oxygen depletion in a water body is from excessive algae and phytoplankton growth driven by high levels of phosphorus and nitrogen. During the nighttime hours, these photosynthetic organisms consume oxygen through respiration when engaging in active photosynthesis. Additionally, as algae and phytoplankton die, the process of decomposition also requires significant amounts of dissolved oxygen. If these blooms are dense or a die off occurs suddenly, the impacts to fish can be more severe and cause fish-kills. Temperature also plays a prominent role in dissolved oxygen levels because temperature establishes a maximum oxygen-holding capacity of water. High water temperatures (86°F or higher) reduces this holding capacity. Fish are cold blooded animals which means their body temperature and activities are regulated by the water they inhabit and warm water increases the  fish’s consumption of oxygen by accelerating their metabolic rate. Aside from temperature, weather also is a contributor to dissolved oxygen levels within a resource. On cloudy days, the production of oxygen through photosynthesis is slowed or halted. Additionally, still and windless days do not allow circulation of the water in a resource and limits surface diffusion of atmospheric oxygen. During the hot summer months, deeper ponds experience stratification as the water near the surface warms and becomes less dense than the cooler water near the bottom. As the season progresses, the cool water near the bottom becomes stagnant and depleted of oxygen. As the top layer of water cools from either a heavy rain storm or a cold front the water then mixes or “turnsover” with the deep, oxygen deficient water and a pond wide oxygen depletion can occur and harm fish populations, possibly even causing die-offs.

Considering levels of dissolved of oxygen in a pond or lake are largely caused by factors that seem out of a pond owners control, many question what can be done and get discouraged with pond management. There are several management strategies available to any pond facing dissolved oxygen issues and are best applied under the advice of a professional biologist equipped with the proper background information. In the case of stratification and increasing water temperatures, an aeration system that is custom designed to properly treat a given resource will eliminate these issues. By mixing a resource with diffused aeration bottom to top and turning it over several times a day stratification can be completely avoided. The benefits of avoiding stratification are increased dissolved oxygen levels throughout a resource and increased usable habitat for fish. Additionally, by running an aeration system at strategic times during the summer, instead of 24/7,  temperatures in the pond can be kept as low as possible. Perhaps the most important benefit to a properly built and designed aeration system is the constant optimization of dissolved oxygen levels. In a highly oxygenated environment, nutrients that cause algae blooms bind to free molecules such as Iron and precipitate out of the water column. Another strategy to combat algae growth is the application of beneficial bacteria. Beneficial bacteria out-compete  algae for available nutrients thus eliminating the aggressive blooms that can cause dissolved oxygen sags. By eliminating stratification and reducing the chances of dense algae and phytoplankton blooms, a pond owner can keep dissolved oxygen levels high and eliminate the stressors to the fish populations.

Contact Aqua Sierra today if you feel your pond experiences dissolved oxygen issues and your fish are suffering! We can solve your problems!