Ponds are small and shallow bodies of water that are abundant and widespread on Earth. They play important roles in the hydrological cycle, biodiversity, and biogeochemical cycles.
However, they also emit significant amounts of greenhouse gases, such as carbon dioxide and methane, into the atmosphere, contributing to global warming and climate change.
The magnitude and variability of pond emissions are not well understood and are often overlooked or underestimated in climate models.
A new study by researchers from Cornell University and other institutions has measured methane and carbon dioxide emissions from 30 ponds in temperate regions of Europe and North America, revealing that the smallest and shallowest ponds exhibit the greatest variability over time.
The study provides valuable insights into the drivers and patterns of pond emissions and suggested that more frequent and comprehensive sampling of ponds is needed to improve climate predictions.
Sources and Sinks of Greenhouse Gases in Ponds
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Ponds are dynamic ecosystems that exchange greenhouse gases with the atmosphere through various processes, as per Phys.org.
Carbon dioxide and methane are produced by the microbial decomposition of organic matter in the sediments and water column of ponds.
Carbon dioxide can also be produced by the respiration of aquatic organisms, such as algae, plants, and animals.
Methane can also be produced by methanogenesis, a process that converts carbon dioxide and hydrogen into methane under anaerobic conditions.
Carbon dioxide and methane can be consumed by the photosynthesis of aquatic plants and algae, which use them to produce organic matter and oxygen.
Carbon dioxide can also be consumed by methanotrophy, a process that oxidizes methane into carbon dioxide and water under aerobic conditions.
The balance between the production and consumption of greenhouse gases determines whether ponds act as sources or sinks of these gases in the atmosphere.
The balance can vary depending on several factors, such as temperature, light, oxygen, nutrient availability, organic matter input, water level, wind speed, and turbulence.
These factors can change seasonally, daily, or even hourly, creating temporal variability in pond emissions.
Moreover, these factors can also vary spatially across different ponds or within the same pond, creating spatial variability in pond emissions.
Measurements and Findings of the Study
The study was conducted by researchers from Cornell University, the University of Minnesota Duluth, the University College London, the University of Innsbruck, the University of Helsinki, and the University of Quebec at Montreal.
The researchers collected gas samples from 30 ponds (one acre or less) in temperate areas of Europe and North America during the summers of 2018 and 2019.
The ponds were selected to represent a range of sizes, depths, shapes, vegetation coverages, and land uses.
The researchers measured the concentrations of carbon dioxide and methane in the water column at three locations within each pond: the deepest point and two opposite ends (but not too close to the shore).
They also measured the fluxes of carbon dioxide and methane from the water surface to the atmosphere using floating chambers.
The results showed that pond emissions varied considerably both spatially and temporally.
The spatial variability was mainly driven by pond size and depth, with smaller and shallower ponds having higher concentrations and fluxes of carbon dioxide and methane than larger and deeper ponds.
The temporal variability was mainly driven by temperature and light, with higher concentrations and fluxes of carbon dioxide and methane during warmer and brighter periods than during cooler and darker periods.
The researchers also found that pond emissions were positively skewed, meaning that most ponds had low or moderate emissions but a few ponds had very high emissions.
The study concluded that ponds are highly variable sources of greenhouse gases in the atmosphere, especially the smallest and shallowest ones.
The study also estimated that there could be billions of ponds on Earth, though the lack of mapping systems makes it hard to know just how many exist.
Together, they could emit up to 5% of the global methane emissions, but this number could be as low as half or as high as twice that percentage due to uncertainties in measurements and extrapolations.
Implications and Recommendations for Climate Models
The study highlighted the importance of including pond emissions in climate models, as they could have significant impacts on global warming and climate change.
However, most climate models do not account for pond emissions or underestimate them due to insufficient data or coarse resolution.
The study suggested that more frequent and comprehensive sampling of ponds is needed to reduce uncertainties and improve estimates of pond emissions.
The study also recommended that future studies should investigate other factors that affect pond emissions, such as seasonality, interannual variability, regional differences, land use changes, and management practices.
The study also pointed out the potential for mitigating pond emissions by managing ponds more sustainably.
For example, reducing nutrient inputs, enhancing oxygen levels, increasing vegetation cover, restoring natural hydrology, and promoting biodiversity could help lower the production and release of greenhouse gases from ponds.
Moreover, capturing and utilizing pond emissions as a source of renewable energy could also provide economic and environmental benefits.
Pond emission measurements improve climate predictions by providing more accurate and reliable data on the sources and sinks of greenhouse gases in ponds.
By incorporating these data into climate models, we can better understand and predict the effects of ponds on global warming and climate change.
By managing ponds more sustainably, we can also reduce their emissions and enhance their ecosystem services and biodiversity. Ponds are small but important ecosystems that deserve more attention and care.
