Recent  

This study examined springs in north central Florida focusing on how interactions between the surface and subsurface affected the properties of groundwater microbes. We found that microbes reproduced at rates that greatly exceed those documented for any other aquifer. Although the groundwater discharged to spring runs contains low concentrations of nutrients, our results indicate that microbes have access to sources of energy and produce new cells at rates similar to surface waterbodies.

This overview of the special issue “Global change effects on terrestrial biogeochemistry at the plant–soil interface” features empirical, conceptual and modelling-based studies and outlines key findings on plant responses to elevated CO₂; soil organism responses to warming; impacts on soil organic carbon, nitrogen and mineral nutrient cycling; and water level changes affecting greenhouse gas emissions, from the Arctic to the tropics, which are crucial for deciphering feedbacks to global change.

Our study explores lipid remodeling in response to environmental stress, specifically how cell membrane chemistry changes. We focus on intact polar lipids in a phytoplankton community exposed to diverse stressors in a mesocosm experiment. The observed remodeling indicates acyl chain recycling for energy storage in intact polar lipids during stress, reallocating resources based on varying growth conditions. This understanding is essential to grasp the system's impact on cellular pools.

Despite the ocean’s importance in the carbon cycle and hence the climate, observing the ocean carbon sink remains challenging. Here, I use an ensemble of 12 models to understand drivers of decadal trends of the past, present, and future ocean carbon sink. I show that 80 % of the decadal trends in the multi-model mean ocean carbon sink can be explained by changes in decadal trends in atmospheric CO₂. The remaining 20 % are due to internal climate variability and ocean heat uptake.

Tackling climate change by adding, restoring, or enhancing forests is gaining global support. However, it is important to investigate the broader implications of this. We used a computer model of the Earth to investigate a future where tree cover expanded as much as possible. We found that some tropical areas were cooler because of trees pumping water into the atmosphere, but this also led to soil and rivers drying. This is important because it might be harder to maintain forests as a result.

We calculate the amount of anthropogenic carbon (C_ant) in the Atlantic for the years 1990, 2000, 2010 and 2020. C_ant is the carbon that is taken up by the ocean as a result of humanmade CO₂ emissions. To determine the amount of C_ant, we apply a technique that is based on the observations of other humanmade gases (e.g., chlorofluorocarbons). Regionally, changes in ocean ventilation have an impact on the storage of C_ant. Overall, the increase in C_ant is driven by the rising CO₂ in the atmosphere.

Methane (CH₄) is an important greenhouse gas and contributes to climate warming. However, the input of CH₄ from coastal areas to the atmosphere is not well defined. Dissolved and atmospheric CH₄ was determined at high spatial resolution in or above the North Sea. The atmospheric CH₄ concentration was mainly influenced by wind direction. With our detailed study on the spatial distribution of CH₄ fluxes we were able to provide a detailed and more realistic estimation of coastal CH₄ fluxes.

Seven million years ago, the marine gateway connecting the Mediterranean Sea with the Atlantic Ocean started to close, and, as a result, water circulation ceased. To find out how this phenomenon affected the fish living in the Mediterranean Sea, we examined the changes in the isotopic composition of otoliths of two common fish species. Although the species living at the surface fared pretty well, the bottom-water fish starved and eventually became extinct in the Mediterranean.

We used a soil model to replicate two litterbag decomposition experiments to examine the implications of climate, litter quality, and soil microclimate representation. We found that macroclimate was more important than litter quality for modeled mass loss. By comparing different representations of soil temperature and moisture we found that using observed data did not improve model results. We discuss causes for this and suggest possible improvements to both the model and experimental design.

During cold seasons, methane release from northern wetlands is important but often underestimated. We studied a boreal bog to understand methane emissions in spring and fall. At cold temperatures, methane release decreases due to lower production rates, but efficient methane transport through plant structures, decaying plants, and the release of methane stored in the pore water keep emissions ongoing. Understanding these seasonal processes can improve models for methane release in cold climates.

Ecosystem carbonyl sulfide (COS) fluxes were employed to optimize GPP estimation across ecosystems with the Biosphere-atmosphere Exchange Process Simulator (BEPS), which was developed for simulating the canopy COS uptake under its state-of-the-art two-leaf modeling framework. Our results showcased the efficacy of COS in improving model prediction and reducing prediction uncertainty of GPP and enhanced insights into the sensitivity, identifiability, and interactions of parameters related to COS.

The addition of alkaline minerals into the ocean might reduce excessive anthropogenic CO₂ emissions. Magnesium hydroxide can be added in large amounts because of its low seawater solubility without reaching harmful pH levels. The toxicity effect results of magnesium hydroxide, by simulating the expected concentrations from a ship's dispersion scenario, demonstrated low impacts on both sensitive and local assemblages of marine microalgae when compared to calcium hydroxide.

We used the DayCent model to assess the potential impact of integrated soil fertility management (ISFM) on maize production, soil fertility, and greenhouse gas emission in Kenya. After adjustments, DayCent represented measured mean yields and soil carbon stock changes well and N₂O emissions acceptably. Our results showed that soil fertility losses could be reduced but not completely eliminated with ISFM and that, while N₂O emissions increased with ISFM, emissions per kilogram yield decreased.

Greenhouse gases are produced and consumed via a number of pathways. Quantifying these pathways helps reduce the climate and environmental footprint of anthropogenic activities. The contribution of the pathways can be estimated from the isotopic composition, which acts as a fingerprint for these pathways. We have developed the Time-resolved FRactionation And Mixing Evaluation (TimeFRAME) model to simplify interpretation and estimate the contribution of different pathways and their uncertainty.

High frequency pCO₂ measurements reveal net neutral CO₂ flux in a mesohaline reach of the Chesapeake Bay. Net off-gassing to the atmosphere begins in June when water temperatures rise above ~26ºC, continuing through November when temperatures fall below ~10ºC. Dissolved CO₂ concentrations follow day–night cycles and are especially pronounced in warm waters. From December through May, the river is largely an uninterrupted sink for CO₂ (i.e. CO₂ is drawn out of the atmosphere into the river).

Ocean alkalinity enhancement (OAE) is an emerging marine CO₂ removal method, but its environmental effects are insufficiently understood. The OAE Pelagic Impact Intercomparison Project (OAEPIIP) provides funding for a standardized and globally replicated microcosm experiment to study the effects of OAE on plankton communities. Here, we provide a detailed manual for the OAEPIIP experiment. We expect OAEPIIP to help build scientific consensus on the effects of OAE on plankton.

The European Arctic is experiencing rapid regional warming, causing glaciers that terminate in the sea to retreat onto land. Due to this process, the area of a well-studied fjord, Hornsund, has increased by around 100 km² (40%) since 1976. Combining satellite and in situ data with a mathematical model, we estimated that, despite some negative consequences of glacial meltwater release, such emerging coastal waters could mitigate climate change by increasing carbon uptake and storage by sediments.

To improve the accuracy of spatial carbon exchange estimates, we evaluated simple linear models for net ecosystem exchange (NEE) and gross primary productivity (GPP) and how they can be used to upscale the CO₂ exchange of agricultural fields. The models are solely driven by Sentinel-2-derived vegetation indices (VIs). Evaluations show that different VIs have variable power to estimate NEE and GPP of crops in different years. The overall performance is as good as results from complex crop models.

Forests face increased exposure to “compound soil and atmospheric drought” (CSAD) events due to global warming. We examined the impacts and drivers of CO₂ fluxes during CSAD events at multiple layers of a deciduous forest over 18 years. Results showed reduced net ecosystem productivity and forest-floor respiration during CSAD events, mainly driven by soil and atmospheric drought. This unpredictability in forest CO₂ fluxes jeopardises reforestation projects aimed at mitigating CO₂ emissions.