Modelling thermal stratification and phytoplankton growth at seasonal scale in El Gergal Reservoir (Seville, Spain)

Abstract

The occurrence of algal blooms and, in general, the changes experienced by phytoplankton communities (its abundance and composition) in aquatic systems are the result of changes in the physical environment determining the light climate and the nutrient availability for algal growth. Consistent with this widely accepted view, any attempt to predict water quality changes associated to changes in phytoplankton communities, needs to be grounded on an accurate prediction of the physical environment. Our goal in this work is to develop a computational model that allows us to describe phytoplankton growth and succession in a reservoir in Southern Spain (El Gergal, Seville), at seasonal scales. Our model of El Gergal-Seville has been constructed using DYRESM-CAEDYM, a one-dimensional generic lake and reservoir ecological/hydraulic modeling tool. We will show that the model provides accurate predictions of mixing and transport processes occurring in the water column and determining the seasonal evolution of stratification in the reservoir. The sensitivity of the model to parameters describing the algal dynamics was first explored using a Regional Sensitivity Analysis. The values of the most sensitive parameters were then calibrated to reproduce the seasonal evolution of phytoplankton abundance. A five-year data set collected by EMASESA from 2001-2005 is used as the basis for model calibration/validation. Model calibration was done both using traditional trial and error procedures and more advanced automatic calibration tools (SCE). We will show results of this calibration exercise, revealing the benefits from the use of automatic calibration tools.