Search Results (4)

The main purpose of this study is to set up a biogeochemistry model for the Ria de Aveiro ecosystem and evaluate the relative importance of the main parameters and the processes occurring at the interface between the water column and the upper layer of the bottom sediment. It addresses a gap in modeling the interactions between the biogeochemical status of the water column and the upper sediment layer in the Ria de Aveiro lagoon ecosystem. Traditional modeling studies treated the bottom sediment as a rigid boundary, ignoring significant biogeochemical interactions at the interface between the water column and the upper layer of the bottom sediment. Therefore, the model integrates, besides the main biogeochemical processes within the water column, those occurring at the upper benthic layer, focusing on nitrogen (N) and phosphorus (P) cycles. This approach aims to enhance the accuracy of model predictions and understanding of the Ria de Aveiro lagoon’s biogeochemical dynamics. The study will be focused on the following coupled state variables: TN/IN and TP/IP, for total and inorganic nitrogen (N) and total and inorganic phosphorus (P), respectively, where total stands for the sum of organic and inorganic components of those elements. The model was set up and validated for some water quality stations of the Ria de Aveiro. Analysis has identified key parameters influencing TN and TP, such as nitrification, denitrification rates, and oxygen penetration. TN was found sensitive to nitrate and ammonium diffusion coefficients, while TP was influenced by iron–phosphate interactions and phosphorus mineralization. Concerning the model validation, the results demonstrated that the RMSE and MAPE values for the main variables fall within an acceptable range, given the uncertainty related to data. The model was applied to assess the impact of the following physical forcing: river flow, water temperature, and salinity on N and P status of the water column. The results clearly demonstrate that bottom layer and water column interactions play an important role in the N and P status of the water column and contribute to the N and P concentration changes of the water. The influence of river flows alone led to contrasting behaviors among the lagoon stations, with significant increases in TP levels, which may be attributed to sediment release from the sediment layer. Nevertheless, the combination of high river flows and elevated nutrient levels at the river boundaries has led to significantly increased nitrogen (N) and phosphorus (P) levels, underscoring the influence of river flow on the interaction between bottom layer sediment and the water column. High water temperatures typically lead to an increase in total phosphorus (TP) levels, indicating a possible release from the sediment layer. Meanwhile, TN levels remained stable. Salinity changes had a minor impact compared to river flow and temperature. The study emphasizes the importance of understanding interactions between the water column and sediment, particularly in shallow intertidal areas. Overall, the inclusion of biogeochemical interactions between the benthic and pelagic layers represents progress in ecosystem modeling of the Ria de Aveiro. Full article

This paper described the implementation of a forecasting system of the coupled physical and biogeochemical state of the northern Adriatic Sea and discussed the preliminary results. The forecasting system is composed of two components: the NEMO general circulation model and the BFM biogeochemical model. The BFM component includes an explicit benthic pelagic coupling providing fluxes at the sediment–water interface and the dynamic of the major benthic state variables. The system is forced by atmospheric forcing from a limited-area model and by available land-based (river runoff and nutrient load) data. The preliminary results were validated against available remote and in situ observations. The validation effort indicated a good performance of the system in defining the basin scale characteristics, while locally the forecasting model performance seemed mostly impaired by the uncertainties in the definition of the land-based forcing. Full article

Underwater disposal of mine tailings in lakes and seas has been considered favorable due to the geochemical stability obtained during long-term storage in anoxic sediments. Sulfides are stable in the ore; however, oxidation and transformation of some substances into more soluble forms may impact bioavailability processes and enhance the risk of toxic effects in the aquatic environment. The goal of this work was to construct a model for simulating the nickel (Ni) cycle in the water column and upper sediments and apply it to the mine tailing sea deposit in the Jøssingfjord, SouthWest Norway. A one-dimensional (1D) benthic–pelagic coupled biogeochemical model, BROM, supplemented with a Ni module specifically developed for the study was used. The model was optimized using field data collected from the fjord. The model predicted that the current high Ni concentrations in the sediment can be a potential source of Ni leaching to the water column until about 2040. The top 10 cm of sediments were classified as being of “poor” environmental state according to the Norwegian Quality Standards. A numerical experiment predicted that with complete cessation of the discharges there would be an improvement in the environmental state of sediment to “good” in about 20 years. On the other hand, doubling of discharge would lead to an increase in the Ni content in the sediment, approaching the boundary of the “very poor” environmental state. The model results demonstrated that Ni leaching from the sea deposits may be increased due to sediment reworking by bioturbation at the sediment–water interface. The model can be an instrument for analysis of different scenarios for mine tailing activities from point of view of reduction of environmental impact as a component of the best available technology. Full article

The invasive mussel Arcuatula senhousia has successfully colonized shallow soft sediments worldwide. This filter feeding mussel modifies sedimentary habitats while forming dense populations and efficiently contributes to nutrient cycling. In the present study, the density of A. senhousia was manipulated in intact sediment cores taken within an intertidal Zostera noltei seagrass meadow in Arcachon Bay (French Atlantic coast), where the species currently occurs at levels corresponding to an early invasion stage. It aimed at testing the effects of a future invasion on (1) bioturbation (bioirrigation and sediment mixing) as well as on (2) total benthic solute fluxes across the sediment–water interface. Results showed that increasing densities of A. senhousia clearly enhanced phosphate and ammonium effluxes, but conversely did not significantly affect community bioturbation rates, highlighting the ability of A. senhousia to control nutrient cycling through strong excretion rates with potential important consequences for nutrient cycling and benthic–pelagic coupling at a broader scale. However, it appears that the variability in the different measured solute fluxes were underpinned by different interactions between the manipulated density of A. senhousia and several faunal and/or environmental drivers, therefore underlining the complexity of anticipating the effects of an invasion process on ecosystem functioning within a realistic context. Full article