From Antarctica to the tropics, ponds are the most widespread and common habitat for all plants and animals (Jeffries, 2016). Research estimates that there are 304 million natural lakes and ponds worldwide, covering a total area of approximately 4.2 million km2 (Downing et al., 2006). Ponds are biodiversity hotspots for both aquatic and terrestrial species, providing habitat for rare specialists such as fairy and tadpole shrimp. Not only are they vital for these species, but they are also vital in managing landscapes from threats such as flooding and climate change. It is known that aquatic ecosystems have a large role in managing greenhouse gases, with oceans among the most well-known of carbon sinks. However, with lakes and ponds covering such a vast expanse of area, is it possible that they are the climate’s unsung heroes?
Carbon sinks are reservoirs that absorb and store atmospheric carbon through physical and biological processes. One study concludes that the rate of carbon sequestration in ponds and small lakes may be more active in nearly all of these processes than large lakes, marine ecosystems and terrestrial ecosystems (Downing, 2010). A 500m2 pond can sequester 1000kg of carbon per year, as much as a car would produce in that time (Céréghino et al., 2014). Furthermore, smaller ponds have been shown to sequester 79-247g of organic carbon per square meter annually, a rate 20-30 times higher than woodlands, grasslands and other habitat types (Taylor et al., 2019). Although ponds only take up 0.0006% of land area in the UK, a tiny proportion compared to the 36% of grasslands (Carey et al., 2008), their high rates of carbon burial suggest that their overall contribution is significant – even when compared to much larger habitats. Thus their role in tackling climate change should not be overlooked.
Ponds are not ubiquitous, thus the effectiveness of carbon sequestration varies per site depending on factors such as substrate type and vegetation. Gilbert et al., (2014) found that permanent and naturally vegetated ponds were the most efficient at sequestering carbon, particularly those dominated by thick moss swards and aquatic grasses. These form a thick, moist blanket when the pond dries out, minimising the release of stored carbon into the atmosphere. The least efficient ponds were temporary, shallow arable ponds which lacked vegetation and were regularly disturbed. When discussing the value of ponds in carbon sequestration, it may be unhelpful to group all ponds together as their importance can vary considerably based on their composition. Furthermore, it is important to note that ponds can serve a variety of purposes. Whilst ponds capturing excess fertilisers and pesticides are useful in the fight against climate change, they may not make good wildlife ponds or facilitate biodiversity.
Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration in ponds. Photosynthesis contributes to the sequestration of carbon by turning it into oxygen and biomass. One kilogram of algae uses an average of 1.87 kilograms of carbon a day (Anguselvi et al., 2019). Algae in ponds also contribute to reducing additional greenhouse gases such as nitrous oxide (N2O). Nitrogen is a key component in chlorophyll and thus used in farm fertiliser. Excess nitrogen can become N2O, and the presence of algae in farm ponds to capture this excess can prevent it from becoming this greenhouse gas. A study has found that two thirds of farm ponds act as N2O sinks (Webb et al., 2019), making them an important contributor to combating climate change, particularly as N2O traps heat at 300x the rate of CO2.
Ponds play an important role in mitigating climate change, however, there is evidence to suggest that they can also act as carbon sources. Does this offset their sequestering benefits? Take for instance, permafrost thaw ponds. Permafrost thaw ponds in northern regions can be particularly prominent sources of carbon. As permafrosts thaw, vast amounts of carbon dioxide and methane are released, resulting in the formation of small ponds which become carbon emission hotspots (Kuhn, 2018). Although they are releasing carbon, it is not the pond itself creating these gases. Global warming is causing the permafrosts to thaw out and release the stored carbon. Although the ponds facilitate the emissions, it is perhaps misleading to label them as a carbon source in these instances.
Large habitats such as oceans and woodlands are well-known for their role in reducing greenhouse gasses and mitigating the effects of climate change, but ponds may play an equally important and largely underappreciated role. Ponds are also a fantastic tool against climate change because they give people a way in which to take action. People can easily create ponds in their own gardens and community spaces, and in this way play a part in reducing greenhouse gas emissions and contribute to the global fight against climate change.
Written by Mirran Trimble & Emily Robinson
Anguselvi, V., Masto, RE., Mukherjee, A., & Singh, PK. (2019) CO2 Capture for industries by algae, Algae, Yee Keung Wong, IntechOpen, DOI: 10.5772/intechopen.81800. Available from: https://www.intechopen.com/books/algae/co-sub-2-sub-capture-for-industries-by-algae
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Céréghino, R., Boix, D., Cauchie, HM., et al. (2014) The ecological role of ponds in a changing world. Hydrobiologia. 723, 1–6.
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Downing, JA. (2010) Emerging global role of small lakes and ponds: little things mean a lot. Limnetica. 29(1), 9-24.
Gilbert, PJ., Taylor, S., Cooke, DA., et al. (2014) Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK. Inland Waters. 4(1), 57-64.
Jeffries, MJ. (2016) Flood, drought and the inter-annual variation to the number and size of ponds and small wetlands in an English lowland landscape over three years of weather extremes. Hydrobiologia. 768, 255–272.
Kuhn, M., Lundin, EJ., Giesler, R., et al. (2018) Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands. Scientific Reports. 8, 9535.
Taylor, S., Gilbert, PJ., Cooke, DA., et al. (2019) High carbon burial rates by small ponds in the landscape. Frontiers in Ecology and the Environment. 17(1), 25-31.
Webb, JR., Hayes, NM., Simpson, GL. et al. (2019) Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink. PNAS. 116(20), 9814-9819.