Stream-aquifer and in-stream processes affecting nitrogen along a major river and contributing tributary

Area of Science:

• Environmental Science
• Hydrology
• Ecology

Background:

• Semi-arid regions with irrigated agriculture face challenges managing water and nutrient dynamics.
• Stream-riparian systems play a crucial role in nutrient cycling and water quality.
• Understanding nutrient exchange in rivers and tributaries is vital for watershed management.

Purpose of the Study:

• To assess spatio-temporal patterns of water and nutrient mass exchange in a stream-riparian system.
• To investigate nitrogen (N) and salinity trends in stream-aquifer interactions.
• To compare nutrient removal capacities between a major river and a tributary.

Main Methods:

• Field monitoring along the Arkansas River and Timpas Creek in southeastern Colorado.
• Collection of water quantity and quality data using in-stream sampling and groundwater wells.
• Application of mass balance approaches to analyze flow, N, and salinity trends.

Main Results:

• The Arkansas River showed significant nitrate-nitrogen (NO3-N) removal (average 36% decrease), with simulations indicating 44-50% mass removal.
• In-stream processes, particularly contact with organic-rich river bed sediments, were key to N removal.
• Timpas Creek exhibited negligible N concentration decreases, contrasting with the Arkansas River's capacity.

Conclusions:

• Large streams like the Arkansas River can possess significant nutrient removal capabilities, contrary to findings in other agriculturally-influenced rivers.
• Riparian and hyporheic zone processes, including denitrification, enhance nutrient removal.
• Further research into nutrient dynamics in large streams within agricultural watersheds is warranted.