In this study, we demonstrated that the composition of sediment organic matter can vary significantly within a single lake, in a close relationship with the spatial patterns of elemental inorganic geochemistry. This results from a combination of different bio-, geo- and physicochemical lake factors, and our results highlight that the potential for large spatial variability across lakes should be considered when studying carbon, nutrient and trace element cycling at lake and global scales.

Peatland catchments export significant volumes of photoreactive carbon to aquatic systems, particularly headwater streams. Delivery of photoreactive material is subject to seasonal variation, and is also influenced by the timing and magnitude of rainfall events. We suggest that photoprocessing of peatland derived carbon may contribute to carbon dioxide emissions from aquatic systems, although considerable uncertainty remains as to how much material is processed in situ within these systems.

Waters with very high pCO₂, nutrients and low oxygen concentrations were observed along the continental margin of the East Siberian Sea and well out into the deep Makarov and Canada basins during the SWERUS-C3 expedition in 2014. This water had a low saturation state with respect to calcium carbonate, down to less than 0.8 for calcite and 0.5 for aragonite, and is traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean in the western Fram Strait.

To better understand the role of oxygen for the biological carbon pump, we studied particle fluxes through hypoxic waters in the eastern tropical North Atlantic. Attenuation of organic carbon fluxes over depth was lower than expected from seawater temperatures, indicating co-effects of oxygen concentration. Differences were observed for individual organic components, suggesting that future carbon export fluxes may depend on changes in surface ocean organic matter quality under global change.

Ozone (O₃) is an air pollutant known to negatively affect vegetation. Typically, high O₃ concentrations reduce growth. This study investigated the effect of O₃ uptake on the total amount of carbon assimilated by vegetation for a Scots pine stand in Flanders over the period 1998–2013. Although the critical levels for AOT40 and POD₁, two indices currently used to estimate O₃ damage, were exceeded every year, no O₃ effects on daily and growing season GPP were found.

This study combines experimental data with results from numerical modelling. Data of an ocean acidification mesocosm experiment are used to constrain parameter values of a plankton model. Three different intensities of calcification are resolved with ensembles of optimised model results. Observed variability in data can be well explained by these ensemble model solutions. The simulated ocean acidification effect on calcification is small compared to the spread of the ensemble model solutions.

Observations from different mesocosms exposed to the same treatment level typically show variability that hinders the detection of potential treatments effects. To unearth relevant sources of variability, we developed and performed a data-based model analysis that simulates uncertainty propagation. With this method we investigate the divergence in the outcomes due to the amplification of differences in experimentally unresolved ecological factors within replicates of the same treatment level.

Based on the seasonal biochemical compositions in this study, the calorific contents of the food material were 1.0–6.1 Kcal m⁻³. We found that a major governing factor in the biochemical composition of POM was dissolved inorganic nitrogen loading from river input. The relatively larger amount of food material and the higher calorific content of the POM found in this study reflected good nutritive conditions for sustaining productive shellfish and fish populations in Gwangyang Bay, South Korea.

In coastal aquatic environments, resuspension of sediment and organic material from the seabed into the overlying water can impact biogeochemistry. Here, we used a novel modeling approach to quantify this impact for the Rhône River delta. In the model, resuspension increased oxygen consumption during individual resuspension events, and when results were averaged over 2 months. This implies that observations and models that only represent calm conditions may underestimate net oxygen consumption.

We measured methane exchange rates at the forest floor of a nutrient-rich drained peatland in southern Finland. The forest floor acted mainly as a small methane sink, but emission peaks were occasionally observed during spring and rainfall events. The strength of the sink correlated best with groundwater level and soil temperatures at 20 and 30 cm depths. Diurnal variations were also observed but they were caused by changes in ambient wind speed and not by biological processes.

Modelling seasonal cycle at the coniferous forests poses a challenge. We implemented a model for sun-induced chlorophyll fluorescence (SIF) to a land surface model JSBACH. It was used to study the seasonality of the carbon cycle in the Fenno-Scandinavian region. Comparison was made to direct CO₂ flux measurements and satellite observations of SIF. SIF proved to be a better proxy for photosynthesis than the fraction of absorbed photosynthetically active radiation.

Modern ecosystem restoration should consider a wide range of environmental characteristics, including functional ones, such as rates and patterns of ecosystem metabolism. We show that hydromorphological river restoration enhanced habitat availability and abundance of macrophytes, promoting river primary productivity and respiration. Incorporating ecosystem functioning into monitoring programs enables a more holistic assessment of river health and a better understanding of restoration effects.

We estimated the global demand for new N fixation (NNF) by terrestrial ecosystem using a DyN-LPJ model. Modelled NPP and C : N ratios of litter and soil organic matter were consistent with independent estimates. Modelled NNF was sensitive to the fraction of litter carbon respired to CO₂ during decomposition and plant-type-specific C : N ratios of litter and soil. The modelled annual NNF increased 15% due to increasing CO₂, while the future capacity of N sources to support this is unknown.