Fig. 1: Seasonal and overall levels of N₂O and N₂ saturation in the ponds.

a Box-whisker plots showing overall that the saturation of N₂O was lower than that for N₂ in the ponds (p < 0.001, two-sided, Supplementary Table 1). The dashed line denotes 100% atmospheric equilibrium for the gases. b, c show the saturation in N₂O had a different seasonal pattern compared to N₂ (Note the different scales on the y-axes). The solid lines in b and c represent the best fitting GAMM models (two-sided, Supplementary Table 1). d N₂O saturation increased at higher temperatures while, in contrast, e N₂ saturation declined. The lines in d and e are simple first-order linear regressions (two-sided). f Overall concentration of total inorganic nitrogen (TIN) in the ponds (n = 213 samples for 11 months in 20 ponds). g The ratio of TIN to soluble reactive phosphorous (SRP) in the ponds (n = 168 samples for 11 months for 20 ponds, SRP data omitted below the detection limit). The dashed line in g denotes the Redfield ratio of N to P of 16:1. Each box in a, f and g shows the 25th to 75th percentiles, horizontal lines the median, open circles denote outliers and whiskers extend to 1.5 times the interquartile range. n = 230 and n = 215 samples for N₂O and N₂ saturation, respectively, for 20 ponds, in 11 months from November 2019 to April 2022 (see Supplementary Table 2).