Essential Considerations for Development of Estuarine Ecological Modeling Tools

Abstract

Submerged aquatic vegetation (SAV) is frequently identified as an important resource in coastal ecosystems and used as an ecological indicator of condition. Its value as habitat can be used to assess progress in restoration and to establish management goals related to freshwater inflows. The utilization of SAV in this respect calls for numerical ecological modeling tools that facilitate the assimilation and integration of information from a variety of sources including hydrodynamic models, water quality models, field measurements and studies, site-specific experimental data, and the literature. Using a numerical model developed to predict growth and survival of the salt tolerant freshwater SAV, Vallisneria americana in the upper Caloosahatchee Estuary, Florida as an example, the importance of using purposeful data assimilation and integration with existing tools is demonstrated for ecological evaluations. The model consists of a system of three simultaneous differential equations, one for each of three state variables, solved by Euler integration with a time step of 1 day. State variables represented are total mass, number of shoots, and number of blades. The model has been applied to develop minimum freshwater inflows standards and is currently being used to test hypothesis and guide further management decisions relating to water quality and changes in freshwater flow and salinity regime in the Caloosahatchee Estuary. The importance of quantifying growth information derived experimentally and establishing relationships under different salinity, light, and water temperature conditions appropriate to the estuarine system under consideration is highlighted. The environmental conditions in Florida, with distinct wet and dry seasons and temperatures conducive to year-round growth pose several unique considerations for the development of estuarine modeling tools which are shown with model application. Analyses were conducted that illustrate the importance of considering water quality goals as they relate to water clarity for the continued survival of V. americana . The importance of a multi-year calibration and validation period that includes a range of environmental variables and the impact of multiple environmental stressors is also demonstrated.