Phosphorus uptake and release patterns in overwintering constructed floating wetlands.

Area of Science:

• Environmental Science
• Aquatic Ecology
• Nutrient Cycling

Background:

• Constructed floating wetlands (CFWs) are increasingly used for water quality improvement.
• Understanding nutrient dynamics, particularly phosphorus (P), in CFWs is crucial for optimizing their design and management.
• Plant senescence and regrowth significantly influence nutrient cycling within aquatic ecosystems.

Purpose of the Study:

• To evaluate phosphorus (P) uptake and release patterns in plants within CFWs during fall/winter senescence and spring regrowth.
• To compare the P cycling performance of two plant species, Pontederia cordata and Juncus effusus, in CFWs.
• To assess the potential for year-round P load reduction using CFWs.

Main Methods:

• Two mesocosm-scale CFW experiments were conducted to quantify P dynamics.
• Experiment 1 focused on P uptake during spring regrowth, while Experiment 2 focused on P release during fall senescence.
• Plant growth, plant tissue P levels, and water quality parameters (nutrients, phytoplankton) were monitored for CFW treatments and an open-water control.

Main Results:

• In spring, Juncus effusus demonstrated the highest P removal rate (0.056 g P m^-2 d^-1, 19.4% of load), followed by Pontederia cordata (0.034 g P m^-2 d^-1, 10%).
• During fall senescence, J. effusus fixed P (0.008 g P m^-2 d^-1, 2.1%), while P. cordata released P (0.014 g P m^-2 d^-1, -2.1%).
• Phosphorus was consistently released from senescing plant tissues in fall and occasionally from root sloughing in spring.

Conclusions:

• Juncus effusus exhibits significant potential for year-round phosphorus load reduction in constructed floating wetlands.
• The seasonal nutrient cycling patterns, including P release during senescence, must be considered for effective CFW management.
• Multi-season deployment of CFWs, particularly with J. effusus, can enhance overall water quality improvement efforts.