Influence of density stratification and macrophytes on nutrient dynamics and resuspension in a shallow lagoon

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The proposed project aims to investigate the influence of submerged macrophytes and haline stratification on shear-induced turbulent mixing and resuspension in shallow surface waters. We will perform the study in a natural estuary which serves as an ideal reference case due to its distinct annual cycle of macrophyte growth and haline stratification. Stratification, mixing and resuspension control the accumulation and redistribution of nutrients into and out of the sediment and are therefore assumed to govern the occurrence of algal blooms in the lagoon. The research goal will be achieved in four steps. (I) First, we will examine the effects of submerged macrophytes through comparative studies of solute and particle transport dynamics between regions covered with macrophytes and regions without plant cover. (II) Secondly, we will identify the physical driving forces which govern the chemical conditions at the sediment-water interface during the period of haline stratification. We will also perform continous measurements during winter and spring in order to understand the accumulation of nutrients in the water column. (III) The solid phase and the porewaters of the sediment are analyzed with respect to phosphorous and iron species, oxygen, sulfate and pH. This will provide insight into how sorption and release dynamics will change under variable chemical conditions. (IV) Finally, the results of (I) and (II) will be used to develop and calibrate a numerical reaction transport model that can help to predict future algal blooms and support strategic estuary management.