Hydrodynamic controls on nitrogen distribution and removal in aquatic ecosystems

Area of Science:

• Environmental Science
• Water Quality Management
• Ecosystem Dynamics

Background:

• Nitrogen (N) pollution causes water eutrophication, but the role of hydrodynamics in N cycling remains poorly understood.
• This knowledge gap limits effective water pollution control and assessment of aquatic ecosystem self-purification.
• Understanding N dynamics is vital for managing water resources and preventing eutrophication.

Purpose of the Study:

• To investigate the influence of hydrodynamic factors on nitrogen occurrence and removal in various aquatic ecosystems.
• To compare nitrogen component variations and removal rates across ditches, ponds, rivers, and reservoirs.
• To elucidate the interactions between overlying water and sediment in nitrogen removal processes.

Main Methods:

• Collected overlying water and sediment samples from diverse aquatic ecosystems (ditch, pond, river, reservoir) in the Danjiangkou Reservoir area.
• Analyzed variations in total nitrogen and its components across different water body types.
• Conducted incubation experiments to quantify nitrogen removal rates, including denitrification and anaerobic ammonium oxidation (anammox).

Main Results:

• Total nitrogen concentrations decreased significantly from ditches and ponds to rivers and reservoirs, with up to 43% reduction.
• Higher heterogeneity in nitrogen component eco-stoichiometry was observed in ditches and ponds compared to rivers and reservoirs.
• Ditches and ponds showed stronger overlying water-sediment interactions, leading to enhanced denitrification and anammox rates.

Conclusions:

• Upper reaches of agricultural catchments, specifically ditches and ponds, are critical hotspots for nitrogen removal.
• Water flow in larger systems facilitates nitrogen reduction, but initial retention is key.
• Region-specific conservation strategies are essential for mitigating nitrogen pollution and protecting water resources effectively.