The chemical sodium nitrate can be used to improve what aspect in a lagoon?

Sodium nitrate is primarily used in wastewater treatment to enhance the dissolved oxygen levels in lagoons. It acts as a source of nitrogen and promotes the growth of beneficial bacteria that can assimilate nutrients and enhance the biological processes taking place in the lagoon. These bacteria require oxygen for metabolism and energy production, which can lead to improved oxygen levels in the water, supporting aquatic life and effective treatment of wastewater.

The other options, while relevant to lagoon management, do not directly relate to the primary function of sodium nitrate. Temperature control does not significantly influence or improve by adding sodium nitrate, nor does it directly affect nutrient absorption, which primarily involves the uptake of nutrients by plants or microbes. Additionally, while pH balance can be influenced by various chemical interactions, sodium nitrate is not specifically used for that purpose in lagoon systems. Its role in promoting dissolved oxygen is what makes it particularly valuable in wastewater treatment processes.