WASP Enhancements
Jassby-Platt Algal Growth Light Formulation
The Jassby-Platt formulation models how algal photosynthesis responds to light intensity using a hyperbolic tangent function, capturing both initial growth and saturation behavior.
Developed by Alan Jassby and Trevor Platt in 1976, the Jassby-Platt light-growth formulation describes the relationship between photosynthetic rate and irradiance for phytoplankton. This model effectively captures the transition from light-limited growth to light-saturated conditions without requiring additional parameters for photo inhibition. Its simplicity and empirical accuracy make it widely used in ecological modeling, especially in aquatic systems where light availability varies with depth and turbidity.
The Jassby-Platt formulation is expressed in hyperbolic tangent form, which models the saturation of algal photosynthesis with increasing light intensity.
This format is particularly useful because it captures the nonlinear response of algae to light—starting with a linear increase at low light and leveling off as light becomes saturating, without requiring additional terms for photo inhibition.
Half-Saturation Algal Growth Light Formulation
The half-saturation algal light growth function models how algal photosynthesis increases with light intensity, using a Monod-type curve that levels off as light becomes saturating.
This model assumes that light is the limiting factor for growth and that photosynthesis increases rapidly at low light levels but slows as it approaches saturation. The half-saturation constant K_s reflects the light sensitivity of the algal population: a lower K_s indicates higher efficiency at low light, while a higher K_s suggests adaptation to brighter environments.
Unlike the Jassby-Platt model, this formulation does not account for photo inhibition or nonlinear transitions but is widely used for its simplicity and ease of parameterization in ecological and bioreactor modeling.
Zappa Reaeration Function (Requires EFDC that Provides Vertical Dissapation Rate to WASP)
The Zappa reaeration function models gas exchange at the air-water interface, emphasizing the role of wave breaking in enhancing oxygen transfer to aquatic systems.
Developed by Christopher Zappa and colleagues, this formulation focuses on bubble-mediated gas transfer driven by wave dynamics, particularly in marine and estuarine environments. Unlike traditional wind-speed-based models, the Zappa function incorporates the effects of wave breaking intensity, which creates turbulence and entrains air bubbles that significantly increase the surface area for gas exchange. The function is often expressed in terms of the gas transfer velocity k, which depends on parameters like wind speed, wave slope, and breaking frequency. Zappa’s work helped refine the understanding of nonlinear interactions between wind, waves, and bubbles, showing that wave breaking can dominate reaeration under certain conditions, especially in high-energy coastal zones.
This approach is particularly valuable in modeling dissolved oxygen dynamics in surface waters, where accurate representation of reaeration is critical for predicting ecosystem health and biogeochemical cycling.