For decades the Baltic Sea has been subject to eutrophication due to heavy anthropogenic nutrient loads on the aquatic ecosystem. Quantitative projections of its effects require an understanding of its driving mechanisms, i.e., the hydrodynamics that are responsible for the physical transport and mixing and the biogeochemical nutrients pathways within the algal ecosystem and between the particulate and dissolved phases in the water and in the sediments.
A simple basin-scale hydrodynamic framework is set for the Gulf of Finland to test different descriptions of the biogeochemical transformations and determine the most robust modelling strategy.
A recently developed criterion to determine the occurrence of anoxic events, based on the amount of fresh carbon detritus in the sediments is implemented in comparison with the classical criterion based on the oxygen concentration in the bottom water.
Time-averaging of the hydrodynamics over larger than daily intervals is proved to hinder the capture of rapid mixing events jeopardizing irremediably the water quality simulation. The new carbon based criterion for anoxia shows a better dynamic response and is less sensitive to the model’s internal parameters.
An internal source in the sediments correlated to the amount of fresh detritus, to represent the release of iron-bound phosphorus is confirmed as a versatile modelling assumption.
Source: KTH
Author: Dessirier, Benoît | Soltani, Safeyeh