Modelling algae-duckweed interaction under chemical pressure within a laboratory microcosm

Area of Science:

• Ecotoxicology
• Ecological Modeling
• Environmental Science

Background:

• Single-species bioassays often overlook crucial species interactions when assessing contaminant effects.
• Understanding contaminant impacts on interacting species is vital for realistic ecosystem risk assessment.

Purpose of the Study:

• To investigate the effects of cadmium contamination on the dynamics of interacting duckweed (Lemna minor) and microalgae (Pseudokirchneriella subcapitata) populations.
• To develop and validate a mechanistic model for a two-species microcosm, incorporating interspecific competition and contaminant exposure.

Main Methods:

• Utilized a 2-L laboratory microcosm containing Lemna minor and Pseudokirchneriella subcapitata.
• Developed a mechanistic model using coupled ordinary differential equations to describe species dynamics, growth, settling, competition, and cadmium effects.
• Estimated model parameters via Bayesian inference using data from multiple laboratory experiments with cadmium concentrations from 0 to 50 μg·L(-1).

Main Results:

• Model parameters were estimated with biologically realistic values and reasonable uncertainties.
• Cadmium exposure reduced the growth rates of both duckweed and algae.
• Interspecific competition affected duckweed dynamics but not algal dynamics; competition intensity decreased with increasing cadmium concentration.

Conclusions:

• The combined approach of mechanistic modeling and guided experiments successfully elucidated the functioning of the algae-duckweed microcosm under cadmium stress.
• This integrated approach offers a promising framework for studying contaminant effects on ecosystem functioning by accounting for species interactions.