Are rivers just big streams? A pulse method to quantify nitrogen demand in a large river

Area of Science:

• Riverine ecology
• Nutrient cycling
• Water quality science

Background:

• Large rivers are increasingly recognized as major pathways for nutrient transport to coastal zones.
• The role of large rivers in nutrient processing and retention remains understudied compared to smaller streams.
• Empirical data on nutrient uptake in rivers with discharge >10000 L/s is scarce, hindering accurate assessments.

Purpose of the Study:

• To address the knowledge gap regarding nutrient uptake in large rivers.
• To present empirical data on inorganic nitrogen (N) transport and removal in the Upper Snake River.
• To compare nutrient demand in large rivers with smaller tributaries.

Main Methods:

• Utilized a pulse method to measure inorganic nitrogen (N) transport and removal.
• Focused on the Upper Snake River, Wyoming, a seventh-order river with a discharge of 12000 L/s.
• Integrated findings with a meta-analysis of existing nutrient uptake studies.

Main Results:

• The Upper Snake River exhibited high biotic demand for ammonium (NH4+) and nitrate (NO3-), comparable to smaller streams.
• Nutrient demand in large rivers may be similar to that of smaller tributaries.
• The uptake of different inorganic nitrogen forms (NH4+ vs. NO3-) scaled differently with river size.

Conclusions:

• Large rivers play a significant role in nitrogen cycling, potentially matching the biotic demand of smaller tributaries.
• Empirical data on solute dynamics in large rivers are vital for understanding network-scale nutrient export.
• Findings are essential for effective water quality management at the river network scale.