Continuous In-Stream Assimilatory Nitrate Uptake from High-Frequency Sensor Measurements.

Area of Science:

• Environmental Science
• Ecology
• Hydrology

Background:

• In situ nitrate (NO3–) sensors offer novel high-frequency stream concentration measurements.
• Understanding nitrate uptake dynamics is crucial for aquatic ecosystem health and nutrient cycling.

Purpose of the Study:

• To relate assimilatory nitrate uptake to metabolic rates using multiparameter sensor data.
• To calculate continuous nitrate uptake rates in stream reaches and a whole stream network.
• To compare nitrate uptake between forest and agricultural stream environments.

Main Methods:

• Utilized continuous 15-minute in situ sensor data over two years.
• Correlated assimilatory nitrate uptake with gross primary production (GPP).
• Calculated yearly and daily nitrate uptake rates and velocities.

Main Results:

• Strong correlations found between nitrate uptake and GPP in both forest (r2 = 0.72) and agricultural (r2 = 0.56) reaches.
• Mean yearly nitrate uptake rates were 7.4 times higher in agricultural reaches (78.3 mg N m–2 d–1) than forest reaches (10.7 mg N m–2 d–1).
• Daily uptake peaked at 47.4% of daily nitrate loading, while yearly uptake was 9.0% of total nitrogen loading.

Conclusions:

• Agricultural stream reaches exhibit significantly higher nitrate assimilation rates than forest reaches.
• Nitrate uptake is closely linked to primary production and influenced by land use.
• High-frequency sensor data provide valuable insights into dynamic nutrient cycling processes in streams.