Modelling nutrient and chlorophyll_a dynamics in an Irish brackish waterbody

Abstract

This paper presents aspects of a research investigation into nutrient fluxes into and out of an important Irish estuary, Wexford Harbour, located in the southeast of Ireland. Details of the methodology applied, the data collection and analysis and the models used are outlined. In particular, the paper addresses modelling of chlorophyll_a production in the brackish waterbody and its dependency on light attenuation.There are three distinct stages to the research carried out: (i) collection, collation and analysis of physical, chemical and biological water quality variables; (ii) development, validation and application of a chlorophyll_a production model; (iii) development of a Geographic Information System.The nutrient and chlorophyll_a production model simulates nine interactive water quality parameters; during the first stage above these parameters were measured to provide initial conditions for the model and for calibration purposes. From measurements, relationships were derived between the water quality variables and salinity, which were used to specify initial spatially varied values of the parameters to the model at different seasons. A relationship was also developed between light intensity, turbidity and concentrations of chlorophyll_a, based on field measurements. This relationship was incorporated into the model. The paper presents chlorophyll_a predictions using this relationship and illustrates how the enhanced model can be used as an accurate modelling tool for managing coastal ecosystems. The water quality model was incorporated into the ArcView GIS system providing an easy-to-use graphical user interface to run simulations and interrogate results.

Modelling phytoplankton dynamics in a complex estuarine system

“…Brennan et al (1998) and McMahon et al (1992) also make this observation. In a modelling study of Wexford Harbour, Hartnett and Nash (2004) found that model predictions of chlorophyll-a were highly sensitive to light availability, reinforcing the previous hypothesis. Due to the importance of light limitation and its relationship with turbidity, a site-specific light attenuation function was developed for the Wexford model based on Secchi disc transparencies.…”

The effects of array configuration on the hydro-environmental impacts of tidal turbines

“…The model is capable of replicating the tidal regime, solute transport and water quality in reasonably shallow estuarine and coastal water bodies [4][5][6][7]. The governing differential equations employed by the model to ascertain the water surface elevations and depth integrated velocity fields in the horizontal plane are based on integrating the Navier-Stokes and continuity equations (three-dimensional) throughout the depth of the water column.…”

An integrated approach to trophic assessment of coastal waters incorporating measurement, modelling and water quality classification

“…The model is capable of simulating hydrodynamics, solute transport and water quality in relatively shallow estuarine and coastal waterbodies (e.g. Falconer, 1984;Lin and Falconer, 1997, Hartnett and Nash, 2004, Gao et al 2011). The model simulates ten different water quality parameters: temperature, salinity, BOD, organic, ammonia and nitrate nitrogen, dissolved oxygen, phytoplankton, organic phosphorus and orthophosphate.…”

“…This site-specific approach to light attenuation was developed by the Authors for a water quality modelling study of a second Irish estuary, Wexford Harbour (Hartnett and Nash, 2004) and was found to significantly improve the accuracy of the phytoplankton model. Similar improvements were found to occur when applied in the present research.…”