Collectively, reservoirs created by dams are thought to be an important source of greenhouse gases (GHGs) to the atmosphere. So far, efforts to quantify, model, and manage these emissions have been ...limited by data availability and inconsistencies in methodological approach. Here, we synthesize reservoir CH4, CO2, and N2O emission data with three main objectives: (1) to generate a global estimate of GHG emissions from reservoirs, (2) to identify the best predictors of these emissions, and (3) to consider the effect of methodology on emission estimates. We estimate that GHG emissions from reservoir water surfaces account for 0.8 (0.5–1.2) Pg CO2 equivalents per year, with the majority of this forcing due to CH4. We then discuss the potential for several alternative pathways such as dam degassing and downstream emissions to contribute significantly to overall emissions. Although prior studies have linked reservoir GHG emissions to reservoir age and latitude, we find that factors related to reservoir productivity are better predictors of emission.
Hundreds of dams have been proposed throughout the Amazon basin, one of the world's largest untapped hydropower frontiers. While hydropower is a potentially clean source of renewable energy, some ...projects produce high greenhouse gas (GHG) emissions per unit electricity generated (carbon intensity). Here we show how carbon intensities of proposed Amazon upland dams (median = 39 kg CO
eq MWh
, 100-year horizon) are often comparable with solar and wind energy, whereas some lowland dams (median = 133 kg CO
eq MWh
) may exceed carbon intensities of fossil-fuel power plants. Based on 158 existing and 351 proposed dams, we present a multi-objective optimization framework showing that low-carbon expansion of Amazon hydropower relies on strategic planning, which is generally linked to placing dams in higher elevations and smaller streams. Ultimately, basin-scale dam planning that considers GHG emissions along with social and ecological externalities will be decisive for sustainable energy development where new hydropower is contemplated.
The potent greenhouse gas methane (CH₄) is readily emitted from tropical reservoirs, often via ebullition (bubbles). This highly stochastic emission pathway varies in space and time, however, ...hampering efforts to accurately assess total CH₄ emissions from water bodies. We systematically studied both the spatial and temporal scales of ebullition variability in a river inflow bay of a tropical Brazilian reservoir. We conducted multiple highly resolved spatial surveys of CH₄ ebullition using a hydroacoustic approach supplemented with bubble traps over a 12-month and a 2-week timescale to evaluate which scale of variation was more important. To quantify the spatial and temporal variability of CH₄ ebullition, we used the quartile coefficients of dispersion at each point in space and time and compared their frequency distributions across the various temporal and spatial scales. We found that CH₄ ebullition varied more temporally than spatially and that the intra-annual variability was stronger than daily variability within 2 weeks. We also found that CH₄ ebullition was positively related to water temperature increase and pressure decrease, but no consistent relationship with water column depth or sediment characteristics was found, further highlighting that temporal drivers of emissions were stronger than spatial drivers. Annual estimates of CH₄ ebullition from our study area may vary by 75–174% if ebullition is not resolved in time and space, but at a minimum we recommend conducting spatially resolved measurements at least once during each major hydrologic season in tropical regions (i.e., in dry and rainy season when water levels are falling and rising, respectively).
Small water systems are important hotspots of greenhouse gas (GHG) emission, but estimates are poorly constrained as data are scarce. Small ponds are often constructed in urban areas, where they ...receive large amounts of nutrients and therefore tend to be highly productive. Here, we investigated GHG emissions, seasonal and diel variation, and net ecosystem production (NEP) from an urban pond. In monthly 24-h field campaigns during 11 months, diffusive water–atmosphere methane (CH₄) and carbon dioxide (CO₂) fluxes and CH₄ ebullition and oxidation were quantified. With oxygen (O₂) measurements, NEP was assessed. The pond was a net GHG source the entire year, with an emission of 3.4 kg CO₂ eq m−2 yr−1. The dominant GHG emission pathway was CH₄ ebullition (bubble flux, 50%), followed by diffusive emissions of CO₂ (38%) and CH₄ (12%). Sediment CH₄ release was primarily driven by temperature and especially ebullition increased exponentially above a temperature threshold of 15°C. The pond’s atmospheric CO₂ exchange was not related to NEP or temperature but likely to a high allochthonous carbon (C) input via runoff and anaerobic mineralization of C. We expect urban ponds to show a large increase in GHG emission with increasing temperature, which should be considered carefully when constructing ponds in urban areas. Emissions may partly be counteracted by pond management focusing on a reduction of nutrient and organic matter input.
Methane (CH
) strongly contributes to observed global warming. As natural CH
emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. ...This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH
ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH
ebullition data from the literature. As these temperature-ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 °C warming led to 51% higher total annual CH
ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH
emissions through a disproportional increase in ebullition (6-20% per 1 °C increase), contributing to global warming.
Methane (CH
) emissions from lakes are the largest of the emissions from freshwater ecosystems. We compile open water CH
emission estimates from individual lakes from all over the world and consider ...the three main emission pathways: diffusive; ebullitive; and storage. The relationships between emissions, environmental variables, lake characteristics and methodological approaches are investigated for the measurements from 297 lakes. We show that environmental factors, such as temperature and precipitation, act as important driving factors for CH
emissions, with higher emissions occurring where air temperature and precipitation are high. The diffusive flux of CH
was found to be positively related to dissolved organic carbon concentration. Diffusive flux is the most frequently estimated component of the total flux, while the other emission pathways are often neglected. Based on the cases where all three components of the total flux were measured (30 lakes), we estimate that measuring the diffusive emission only, and then assuming that the value obtained is a good surrogate for the total emission, would have led to a 277% underestimation of the real total flux. In addition we show that the estimation of fluxes is method-dependent with substantial differences revealed between the flux estimates obtained from different measurement techniques. Some of this uncertainty is due to technical constraints which should not be neglected, and lake CH
flux measurement techniques require thorough re-evaluation.
Brazil plans to meet the majority of its growing electricity demand with new hydropower plants located in the Amazon basin. However, large hydropower plants located in tropical forested regions may ...lead to significant carbon dioxide and methane emission. Currently, no predictive models exist to estimate the greenhouse gas emissions before the reservoir is built. This paper presents two different approaches to investigate the future carbon balance of eighteen new reservoirs in the Amazon. The first approach is based on a degradation model of flooded carbon stock, while the second approach is based on flux data measured in Amazonian rivers and reservoirs. The models rely on a Monte Carlo simulation framework to represent the balance of the greenhouse gases into the atmosphere that results when land and river are converted into a reservoir. Further, we investigate the role of the residence time stratification in the carbon emissions estimate. Our results imply that two factors contribute to reducing overall emissions from these reservoirs: high energy densities reservoirs, i.e., the ratio between the installed capacity and flooded area, and vegetation clearing. While the models' uncertainties are high, we show that a robust treatment of uncertainty can effectively indicate whether a reservoir in the Amazon will result in larger greenhouse gas emissions when compared to other electricity sources.
On November 2015, one of Brazil's most important watersheds was impacted by the mine waste from Fundão dam collapse in Mariana. The mine waste traveled over 600 km along the Doce River before ...reaching the sea, causing severe devastation along its way. Here we assessed trace element concentrations and cytogenotoxic effects of the released mine waste. Water samples were collected along the Doce River ten days after the disaster in two impacted sites and one non-impacted site. Sampling points were located hundreds of kilometers downstream of the collapsed dam. Water samples were used for trace element quantification and to run an experiment using Allium cepa to test cytogenotoxicity. We found extremely high concentrations of particulate Fe, Al, and Mn in the impacted sites. We observed cytogenotoxic effects such as alterations in mitotic and phase indexes, and enhanced frequency of chromosomal aberrations. Our results indicate interferences in the cell cycle in impacted sites located hundreds of kilometers downstream of the disaster. The environmental impacts of the dam collapse may not only be far-reaching but also very likely long-lasting, because the mine waste may persist in the Doce River sediment for decades.
•Higher concentrations of particulate metals were found in impacted sites.•Cytogenotoxic effects were found in the impacted sites.•Mining waste affected genetic aspects of Allium cepa.•Impacts of the tragedy are far-reaching and long-lasting.
Ant nests are ecologically important emission sources of CO2, CH4, and N2O. An updated review of the progress in studying greenhouse gas (GHG) flux from ant nests could provide a more comprehensive ...understanding of their role in this context.
We evaluate the progress in assessing GHG flux assessment through a systematic review and identify factors responsible for higher GHG emissions from ant nests.
The specific goals were to conduct a bibliographic analysis of the frequency and geographical distribution of scientific works addressing this topic, reported species, and methodologies; to relate the mean GHG flux to species‐specific characteristics of ant nests; and to identify patterns and biases responsible for reported higher GHG levels.
More data is needed on the species and habitats studied. The most frequently examined gas was CO2, and the closed chamber system was the most used method, with a wide variation in chamber size and material.
No relation was found between CO2 emissions and species‐specific characteristics, which can be explained by the fact that these data show a high variability, probably due to the abiotic factors in each study, different measurement methods, and their respective configurations.
Our study underlines the need to standardise GHG measurement methods to allow for reliable comparisons between ant species and habitats. Furthermore, it signals the need to investigate more information to build appropriate global GHG emissions models.
This progress will only be possible through collaborative studies by increasing interaction among researchers through projects on a continental or global scale.
The authors investigated the progress regarding the GHG flux assessment, identifying factors responsible for GHG emissions from ant nests.
The CO2 emissions registers present high variability, which underlines the need to standardise the measuring method to allow reliable comparisons among ant species and habitats.
Collaborative and global studies must be encouraged to close the knowledge gaps and to produce adequate worldwide GHG emissions models.
The ability of freshwater bacteria to secrete extracellular vesicles (EVs) upon interaction with viruses remains to be established. Here, we investigated for the first time if freshwater ...virus‐infected bacteria release EVs in both natural ecosystems and virus‐like particles (VLPs)‐enriched cultures. We performed a systematic study using transmission electron microscopy to visualize viruses and EVs at high resolution and single‐cell imaging analyses to quantitate nascent EVs at the surface of gram‐negative bacteria. First, by analysing freshwater samples from a tropical ecosystem (Negro River/Amazon Basin/Brazil), we captured bacteriophages‐infected bacteria releasing EVs from their outer membrane. Next, VLPs isolated from these samples and inoculated in bacterial cultures not only impacted bacteria growth and viability but also led them to a significant release of EVs (~300% increase in numbers/cell section) compared to controls. The numbers of both budding and free EVs and EVs per linear micrometre of cell envelope were significantly higher in infected bacteria. Our findings identify a yet‐not recognized capability of freshwater bacteria in generating EVs (overvesiculation) in response to viral infection. Since viruses are abundant members of aquatic ecosystems and bacteria are natural hosts for them, such interaction is an interesting event for microbial communities to be explored in freshwater ecosystems.
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