Variation in Dissolved Oxygen Levels Between Agricultural and Protected Streams in Loudoun County, Virginia

Shray Vij, Ryan Seunoy Nisay 

Agricultural runoff can reduce dissolved oxygen (DO) in streams and increase the risk of hypoxia for aquatic organisms. We monitored four streams in Loudoun County, Virginia for four weeks to compare DO dynamics between two agricultural sites and two protected forested sites, and to observe the response to a 1.3 inch storm event. Sites were sampled twice daily for DO and related water quality parameters, with weekly nutrient samples. Agricultural streams had substantially lower mean DO than protected streams and a larger share of measurements below the 5.0 mg/L stress threshold. After the storm, DO in agricultural streams dropped sharply while protected sites remained within healthy ranges, suggesting reduced resilience to runoff pulses. These results indicate that agricultural land use is associated with chronic DO impairment and greater vulnerability to storm-driven hypoxia, and they support management strategies such as riparian buffer restoration and nutrient and runoff control