Experimental simulations with an ecosystem model of the Baltic Sea: A nutrient load reduction experiment

Abstract

[1] The study presents results of decadal simulations of the dynamics of the ecosystem of the Baltic Sea with a three-dimensional coupled physical chemical biological model for the 1980s. The model consists of a circulation model, which is an implementation of the Modular Ocean Model (MOM 2) for the Baltic Sea and an embedded ecosystem model based on a nine-component model (ERGOM [Neumann, 2000]). The model was driven with realistic atmospheric forcing, river loads, and atmospheric deposition of nutrients. A simulation with the realistic forcing was carried out as a control run in order to study in a further experimental simulation the response of the model ecosystem to a 50% reduction of riverine nutrient loads. It was found that the model food web reacts on the load reduction in a complex manner. The changes in dissolved nutrients and in phytoplankton display a spatial variability and different species-specific reactions. While the total biomass and nutrient inventories are reduced, there are significant regional differences. In particular, the role of cyanobacteria, which can fix atmospheric nitrogen, is important, and the biomass of cyanobacteria increases in response to the reduced loads. Although the model system needs further improvements, the present study is a step toward an understanding of the quantitative effects of a reduction of nutrient river loads to the Baltic Sea ecosystem based on a full three-dimensional coupled model.

Impact of Climate Change on Ecological Quality Indicators and Biogeochemical Fluxes in the Baltic Sea: A Multi-Model Ensemble Study

“…These are the BAltic sea Long-Term largeScale Eutrophication Model (BALTSEM) (Savchuk 2002;Gustafsson 2003), the Ecological Regional Ocean Model (ERGOM) (Neumann et al 2002), and the Swedish Coastal and Ocean Biogeochemical model coupled to the Rossby Centre Ocean circulation model (RCO-SCOBI) (Meier et al 2003;Eilola et al 2009). The models are structurally different in that ERGOM and RCO-SCOBI are threedimensional circulation models with uniformly high horizontal resolution of 5.6 and 3.7 km, respectively, while BALTSEM resolves the Baltic Sea spatially in 13 dynamically interconnected and horizontally integrated sub-basins with high vertical resolution.…”

A second-order, unconditionally positive, mass-conserving integration scheme for biochemical systems

“…Although unconditional positivity is the default in biochemistry, it is worth noting that some biochemical systems include one or more state variables that can become negative. For instance, the ERGOM model [15] includes a state variable 'oxygen concentration' that represents oxygen when positive, and hydrogen sulfide when negative. With the new schemes, this can easily be accounted for by excluding any such state variables from sets J n and K n .…”

Environmental Impacts—Marine Biogeochemistry

“…With the increasing availability of computational power, three-dimensional coupled models for the Baltic Sea that produce high-resolution results on long timescales (centuries) are now state of the art at the larger institutes (e.g. Neumann et al 2002;Eilola et al 2009). Generally, the biogeochemical functions of the coupled models are similar in that they describe transformations of N and P including inorganic nutrients and particulate organic matter comprising phytoplankton, dead organic matter and zooplankton.…”