Urbanization is altering hydrologic and nitrogen (N) inputs to streams that may substantially increase nitrogen-containing trace gas emissions to the atmosphere with regional and global consequences. In the semi-arid southwestern US, human modifications of ephemerally dry stream channels interact with hydrologic and nitrogen alterations to lead to extremely high fluxes of nitrous oxide (N2O). Cumulative N2O losses ranged from 0.04 to 0.97 mg N m-2 in 6 hr for rainfall compared to 22.5-59.3 mg N m-2 for flood pulse events. Impervious channels eliminated N trace gas losses but increased delivery of water and N to downstream ecosystems and areas of focused recharge by 6 fold compared to watersheds with greater pervious channel lengths. In contrast, importation of clay into channels increased total N trace gas losses by 8-32 fold relative to more natural sand dominated channels but this result depended on the degree of wetting. Our integrated findings suggest human modification of storm water management systems to impervious channels increases delivery of water and N to downstream navigable waters and areas of focused recharge whereas importation of clay materials leads to higher N trace gas losses and reduced delivery of nitrate. Management will need to address long-term challenges of balancing tradeoffs of greenhouse N gases and N in water supplies, intermediate scale issues of enhancing recharge, and short-term issues of removing water and preventing flooding.
Lohse K.A., Gallo E.L., Brooks P.D., Meixner T., McIntosh J.C. (2013): Tradeoffs of modifications of storm water managements systems for nitrogen loss pathways in semi-arid ecosystems. Abstract B31E-0442 presented at 2013 Fall Meeting, AGU, San Francisco, CA, 9-13 Dec. .