Can nutrient pathways and biotic interactions control eutrophication in riverine ecosystems? Evidence from a model...

Area of Science:

• River ecology
• Aquatic primary production
• Eutrophication dynamics

Background:

• Ecological theory predicts shifts in benthic and planktonic algal dominance along river continuums.
• Mechanisms controlling algal interactions, resource competition, and ecosystem consequences are not fully understood.

Purpose of the Study:

• To mechanistically analyze factors influencing benthic and planktonic algae in rivers.
• To investigate the roles of nutrient supply pathways and grazing in regulating algal biomass and dominance.
• To compare model predictions with experimental results.

Main Methods:

• Developed a simplified numerical model of riverine algal dynamics.
• Conducted a factorial mesocosm experiment simulating river conditions.
• Analyzed the effects of nutrient pathways (hyporheic, surface, combined) and grazing across a river depth gradient.

Main Results:

• Model and experiment showed similar temporal development of algal biomass and dominance shifts.
• Algal biomass distribution is strongly influenced by nutrient supply pathways, algal detachment/sinking, and river depth.
• Nutrient enrichment increased algal biomass but did not alter interaction patterns; reduced light favored benthic algae.

Conclusions:

• Nutrient pathways, resource competition, and grazing are critical for understanding riverine eutrophication.
• Effective eutrophication management requires considering nutrient pathways (surface vs. groundwater) and biological controls, not just nutrient loads.