Two- or three-layered box-models versus fine 3D models for coastal ecological modelling? A comparative study in the English Channel (Western Europe)

Abstract

The general trend in ecosystem modelling is to improve the spatial resolution by shifting from rough box-models to fine 3D models. Despite the continuous speeding-up of computing, 3D models involving numerous state variables may remain intractable, especially for parameter calibration, when processes with long half-life periods (i.e, from years to decades) are introduced, such as the behaviour of organic matter in sediment and population dynamics of benthic species. In these cases, a first approach can be provided by fast-running box-models, if they take into account the most crucial hydrodynamic properties of the system. In a macrotidal shelf sea such as the English Channel, the long-term horizontal transport can be summarized by the tidal residual circulation, and the vertical stratification can be sketched by a two-or three-layered integral model. This paper compares the results obtained in the English Channel area by the same biogeochemical equations of pelagic primary production, coupled to 1) a two-layered box-model 2) a three-layered box-model (i.e., with an intermediate cline layer between surface and bottom ones) and 3) a finegridded 3D model. Comparison is focused firstly on thermal stratification and summer dinoflagellate blooms in the northwestern Channel and secondly on the haline stratification and the sequence of blooms obtained in the eutrophicated Seine river plume. Comparison shows that box-models act as low-pass filters which reproduce correctly the weekly mean time-course, but greatly reduce the variance locally observed in a tide-oscillating plume region. As far as global characteristics are concerned, such as the annual primary production, or the percentage of variation in annual production after reducing the nutrient loadings, the box and 3D models gave very similar results. This conclusion reinforces the usefulness of using box-models as a first approach in long-term processes, for which a long transient phase is expected before reaching the annual periodic solution.

Progress and Challenges in Coupled Hydrodynamic-Ecological Estuarine Modeling

“…Numerous investigators have addressed the role of model complexity (Fulton et al 2003, 2004; Friedrichs et al 2006; Ménesguen et al 2007) and others have embraced the use of reduced complexity and alternative modeling approaches (Rigler and Peters 1995; NRC 2000; Pace 2001; Duarte et al 2003; Scavia et al 2006; Swaney et al 2008). Multiple modeling approaches have also been combined to inform coastal management (e.g., Stow et al 2003; Scavia et al 2004).…”

Modelling the spatial heterogeneity of ecological processes in an intertidal estuarine bay: dynamic interactions between bivalves and phytoplankton

“…Ecosystem models found in the literature explore the spatial heterogeneity of the environment at a large scale (i.e. Moll & Radach 2003, Ménesguen et al 2007). In contrast, ecosystem models on spatial variability at a small scale remain scarce.…”

“…Moll & Radach 2003 and references therein, Ménesguen et al 2007), and mainly focus on pelagic spatial patterns (i.e. phyto-and zooplankton, fish).…”

Annual cycles of chlorophyll-<i>a</i>, non-algal suspended particulate matter, and turbidity observed from space and in-situ in coastal waters

“…The validation and calibration of regional ecological models from the southern North Sea to the Bay of Biscay have been improved in recent years by the use of satellite products (Huret et al, 2007;Lacroix et al, 2007;Ménesguen and Gohin, 2006;Ménesguen et al, 2007;Shutler et al, 2011). Assimilation has also been performed with success in a biological model of the Gulf of Fos and the Rhône River plume in the Mediterranean waters (Fontana et al, 2010).…”