@article {KNZ001971,
	title = {Increasing groundwater CO2 in a midcontinent tallgrass prairie: Controlling factors},
	journal = {E3S Web of Conferences},
	volume = {98},
	year = {2019},
	pages = {06008},
	abstract = {<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>},
	keywords = {LTER-KNZ},
	doi = {10.1051/e3sconf/20199806008},
	url = {https://www.e3s-conferences.org/10.1051/e3sconf/20199806008},
	author = {G. L. Macpherson and Sullivan, P.L. and Stotler, R.L. and Norwood, B.S.},
	editor = {Chudaev, O. and Kharaka, Y. and Harmon, R. and Millot, R. and Shouakar-Stash, O.}
}
