Globally prevalent land nitrogen memory amplifies water pollution following drought years

• Published in: Environmental research letters Vol. 16; no. 1; pp. 14049 - 14059
• Main Authors: Lee, M, Stock, C A, Shevliakova, E, Malyshev, S, Milly, P C D
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01-01-2021
• Subjects: climate variability; land model; nitrogen cycle; river nitrogen loads; terrestrial ecosystem model; water pollution; watershed model
• ISSN: 1748-9326; 1748-9326
• DOI: 10.1088/1748-9326/abd1a0

Enhanced riverine delivery of terrestrial nitrogen (N) has polluted many freshwater and coastal ecosystems, degrading drinking water and marine resources. An emerging view suggests a contribution of land N memory effects-impacts of antecedent dry conditions on land N accumulation that disproportionately increase subsequent river N loads. To date, however, such effects have only been explored for several relatively small rivers covering a few episodes. Here we introduce an index for quantifying land N memory effects and assess their prevalence using regional observations and global terrestrial-freshwater ecosystem model outputs. Model analyses imply that land N memory effects are globally prevalent but vary widely in strength. Strong effects reflect large soil dissolved inorganic N (DIN) surpluses by the end of dry years. During the subsequent wetter years, the surpluses are augmented by soil net mineralization pulses, which outpace plant uptake and soil denitrification, resulting in disproportionately increased soil leaching and eventual river loads. These mechanisms are most prominent in areas with high hydroclimate variability, warm climates, and ecosystem disturbances. In 48 of the 118 basins analyzed, strong memory effects produce 43% (21%-88%) higher DIN loads following drought years than following average years. Such a marked influence supports close consideration of prevalent land N memory effects in water-pollution management efforts.