02135nas a2200217   4500008004100000245008800041210006900129300001000198490000700208520147500215100002301690700001901713700001801732700001801750700001601768700001601784700001501800700001501815700002301830856006401853       2019                        eng d00aIncreasing groundwater CO2 in a midcontinent tallgrass prairie: Controlling factors0 aIncreasing groundwater CO2 in a midcontinent tallgrass prairie C  a060080 v983 a<p>Alkalinity and groundwater CO2 have increased linearly from 1991&ndash;2017 at the Konza Prairie Biological Station (KPBS), a tallgrass prairie research site in northeastern Kansas. The projected increase in groundwater alkalinity (as HCO3-) and CO2 based on an earlier trend was confirmed in 2016, with predictions nearly equal to recent values (e.g., 408 ppm vs 410 ppm as HCO3-, respectively). Both the water balance and groundwater CO2 trends within the study watershed could be impacted by long-term changes in land use and climate: 1) encroachment of woody vegetation (1983&ndash;2012) as a result of the 4-year fire return interval, 2) re-introduction of bison (phased in, 1994&ndash;2006), 3) increases in air temperature, and 4) changes in precipitation patterns. If only linear processes are driving the observed water chemistry changes, then the linear increase in air temperature (1983&ndash;2017) that stimulates soil respiration may be the most likely factor enhancing groundwater HCO3- and CO2, as air temperature has risen ~1 to 1.4&deg;C over 34 years. If groundwater chemistry is driven by more threshold behaviour, woody encroachment, which was linear but in three distinct phases, may drive groundwater chemistry. The ~2 to 3&permil; decrease in the discontinuous δ13C data in the groundwater-dominated stream suggests enhanced inputs of microbially-respired labile carbon, CO2 sourced from C3 (woody vegetation), or a combination of the two.</p>1 aMacpherson, G., L.1 aSullivan, P.L.1 aStotler, R.L.1 aNorwood, B.S.1 aChudaev, O.1 aKharaka, Y.1 aHarmon, R.1 aMillot, R.1 aShouakar-Stash, O.  uhttps://www.e3s-conferences.org/10.1051/e3sconf/20199806008