Lecture 6 Flashcards
Why is choosing the correct spatial and temporal scales important in ecological modelling?
It ensures accurate representation of ecosystem processes and prevents over-simplification or loss of important dynamics.
What is a 0D (zero-dimensional) model?
A model that represents the system as a single point with uniform conditions (e.g., lake-wide average).
What is a 1D (one-dimensional) model?
A model that captures gradients in one direction, such as vertical profiles in lakes or longitudinal changes in rivers.
What is a 2D (two-dimensional) model?
A model that includes horizontal gradients, useful for estuaries or coastal ecosystems.
What is a 3D (three-dimensional) model?
- A model that represents full spatial variability, incorporating vertical and horizontal changes.
- 3D Model: Ocean circulation and plankton distribution (full spatial variability).
What are Continuous Stirred Tank Reactor (CSTR) models?
Models that assume complete mixing and uniform conditions.
What are Plug Flow Reactor (PFR) models?
Models that assume no mixing in the flow direction, typically representing processes in rivers or pipes.
What is Ecospace?
A spatial extension of Ecopath and Ecosim, running multiple 0D models across a spatial grid to capture local dynamics and spatial interactions
What temporal scales are commonly used in ecological models?
Short-term (e.g., daily cycles) and long-term (e.g., decadal trends).
What are cascading models?
Models that link processes across scales to account for feedback mechanisms and interactions.
What is model validation, and why is it important?
Model validation tests the calibrated model against an independent dataset to assess its generalizability. A valid model performs well on new data, indicating robust parameters.
What is cross-validation?
- Cross-validation divides the dataset into k parts
- validates the model on one part
- while calibrating on the rest.
- The process repeats for all parts
- and the average RMSE indicates model performance.
What are potential issues with k-fold validation?
Challenges include the choice of k, increased computation time, and potential dependence between validation sets.
What are constraints in ecological models?
- Constraints limit model parameters to ensure realistic outcomes.
- ensure that ecological models produce biologically realistic and internally consistent results.
- Without them, models may predict implausible outcomes that deviate from real-world behavior.
How is spatial dimensionality used in ecological models?
0D (e.g., lakes) assumes uniformity, 1D represents gradients (e.g., depth in rivers), 2D models capture horizontal variability (e.g., lagoons), and 3D (e.g., Ecospace) represents full spatial complexity.
What is a CSTR model, and what are its assumptions?
Continuous Stirred Tank Reactor (CSTR) assumes uniform mixing and constant concentration throughout the volume, representing a 0D system with turbulent diffusion.
What is a PFR model, and how does it differ from CSTR?
Plug Flow Reactor (PFR) assumes no mixing along the flow direction and models concentration changes across distance (1D).
What are advective and diffusive transport?
Advection moves substances along with the fluid without changing concentration, while diffusion smooths concentration gradients.
What is interphase transport, and how is it modeled?
- Interphase transport describes the exchange of substances between phases (e.g., gas-liquid).
- Whitman’s two-film theory states that flux depends on the gradient between the concentration in the liquid + the partial pressure in the gas.
- Henry’s Law is a key component of interphase transport modeling (it describes the equilibrium concentration at the gas-liquid interface)
- Together with theories like Whitman’s two-film model, it provides a complete framework for understanding and predicting substance transfer between phases.
What does Fick’s law describe?
- Fick’s law describes diffusion, stating that the flux of a substance is proportional to the gradient of concentration: from high gradient to low gradient
What is Michaelis-Menten kinetics?
A model describing enzyme-substrate reactions where reaction rate increases with substrate concentration until it plateaus at Vmax.
How do adsorption processes differ in environmental models?
- Adsorption follows different isotherms like:
- Langmuir (monolayer adsorption) and
- Freundlich (heterogeneous surface adsorption).
- These models describe how substances bind to surfaces e.g. sediments.
What is Henry’s Law?
- Henry’s Law states that
- the concentration of a gas in a liquid = its partial pressure in the gas phase.
What is the bioaccumulation factor (BCF)?
- BCF is the ratio of a substance’s concentration in an organism to its concentration in water
- reflects uptake efficiency
What is the significance of partition coefficients in adsorption?
(Verteilungskoeffizient)
Partition coefficients (e.g., Koc) describe how contaminants distribute between solid and liquid phases, helping predict pollutant behavior.
