Does differential phosphorus processing by plankton influence the ecological state of shallow lakes?

Area of Science:

• Limnology
• Aquatic Ecology
• Biogeochemistry

Background:

• Shallow lakes exhibit distinct turbid and clear-water states, often linked to phosphorus (P) concentrations.
• The mechanisms driving P cycling and its role in maintaining these states are not fully understood.
• Traditional methods struggle to quantify P-cycling processes in lake ecosystems.

Purpose of the Study:

• To investigate and compare phosphorus (P) cycling dynamics in turbid versus clear-water states of shallow lakes.
• To elucidate how P uptake, accumulation, and release rates differ between these contrasting lake conditions.
• To understand the role of P cycling in reinforcing either turbid or clear-water states.

Main Methods:

• Utilized 32P-PO4 as a tracer to quantify P uptake and release rates.
• Analyzed P accumulation in different plankton size fractions (picoplankton, nanoplankton, microplankton).
• Compared P-cycling kinetics in samples from turbid (unrestored) and clear-water (restored) sections of Huizhou West Lake.

Main Results:

• Turbid waters exhibited slow PO4 uptake, high particulate P, and slow P recycling, potentially supporting high phytoplankton biomass.
• Clear waters demonstrated rapid PO4 uptake, low particulate P, and high P recycling rates, possibly constraining phytoplankton growth.
• Microplankton played a significant role in P recycling in clear-water states, indicated by higher 32P-PO4 in this fraction.

Conclusions:

• P cycling dynamics differ significantly between turbid and clear shallow lake states.
• Slow P recycling in turbid states may reinforce these conditions, while rapid recycling in clear states reinforces clarity.
• P-kinetics analysis is a valuable tool for understanding state transitions and plankton community dynamics in shallow lakes.