Abstract. Emissions from flooded land represent a direct source of anthropogenic
greenhouse gas (GHG) emissions. Methane emissions from large, artificial water
bodies have previously been considered, with numerous studies assessing
emission rates and relatively simple procedures available to determine their
surface area and generate upscaled emissions estimates. In contrast, the role
of small artificial water bodies (ponds) is very poorly quantified, and
estimation of emissions is constrained both by a lack of data on their
spatial extent and a scarcity of direct flux measurements. In this study, we
quantified the total surface area of water bodies
< 105 m2 across Queensland, Australia, and emission rates
from a variety of water body types and size classes. We found that the
omission of small ponds from current official land use data has led to an
underestimate of total flooded land area by 24 %, of small artificial
water body surface area by 57 % and of the total number of artificial
water bodies by 1 order of magnitude. All studied ponds were significant
hotspots of methane production, dominated by ebullition (bubble) emissions.
Two scaling approaches were developed with one based on pond primary use
(stock watering, irrigation and urban lakes) and the other using size class.
Both approaches indicated that ponds in Queensland alone emit over 1.6 Mt
CO2 eq. yr−1, equivalent to 10 % of the state's entire
land use, land use change and forestry sector emissions. With limited data
from other regions suggesting similarly large numbers of ponds, high
emissions per unit area and under-reporting of spatial extent, we conclude
that small artificial water bodies may be a globally important missing
source of anthropogenic greenhouse gas emissions.
The importance of small artificial water bodies as sources of methane emissions in Queensland, Australia