@article {KNZ002013, title = {Effects of vegetation rooting characteristics on carbonate weathering and critical zone evolution}, journal = {Earth and Planetary Science Letters}, year = {In Press}, keywords = {LTER-KNZ}, author = {Wen, H. and Sullivan, P.L. and G. L. Macpherson and Li, L.} } @article {6284, title = {Drier streams despite a wetter climate in woody-encroached grasslands}, journal = {Journal of Hydrology}, volume = {627}, year = {2023}, pages = {130388}, keywords = {LTER-KNZ}, doi = {10.1016/j.jhydrol.2023.130388}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0022169423013306}, author = {Sadayappan, Kayalvizhi and Keen, Rachel and Jarecke, Karla M. and Moreno, Victoria and Nippert, J.B. and Kirk, M. F. and Sullivan, P.L. and Li, Li} } @article {6087, title = {Embracing the dynamic nature of soil structure: A paradigm illuminating the role of life in critical zones of the Anthropocene}, journal = {Earth-Science Reviews}, volume = {225}, year = {2022}, pages = {103873}, keywords = {LTER-KNZ}, issn = {00128252}, doi = {10.1016/j.earscirev.2021.103873}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0012825221003743}, author = {Sullivan, P.L. and Billings, S.A. and Hirmas, D. and Li, L. and Zhang, X. and Ziegler, S. and Murenbeeld, K. and Ajami, H. and Guthrie, A. and Singha, K. and Gimenez, D. and Duro, A. and Moreno, V. and Flores, A. and Cueva, A. and Koop, A. and Aronson, E.L. and Barnard, H.R. and Banwart, S.A. and Keen, R.M. and Nemes, A. and Nikolaidis, N.P. and Nippert, J.B. and Richter, D. and Robinson, D.A. and Sadayappan, K. and de Souza, L.F.T. and Unruh, M. and Wen, H.} } @article {6049, title = {Impacts of riparian and non-riparian woody encroachment on tallgrass prairie ecohydrology}, journal = {Ecosystems}, year = {2022}, keywords = {LTER-KNZ}, doi = {10.1007/s10021-022-00756-7}, url = {https://link.springer.com/10.1007/s10021-022-00756-7}, author = {Keen, Rachel M. and Jesse B. Nippert and Sullivan, P.L. and Z. Ratajczak and Ritchey, Brynn and O{\textquoteright}Keefe, K. and W. K. Dodds} } @article {5976, title = {Deepening roots can enhance carbonate weathering by amplifying CO2-rich recharge}, journal = {Biogeosciences}, volume = {18}, year = {2021}, pages = {55-75}, keywords = {LTER-KNZ}, doi = {10.5194/bg-18-55-2021}, url = {https://bg.copernicus.org/articles/18/55/2021/}, author = {Wen, H. and Sullivan, P.L. and Macpherson, G.L. and Billings, S.A. and Li, L.} } @article {KNZ002016, title = {Towards a new conceptual model for groundwater flow in merokarst systems: Insights from multiple geophysical approaches}, journal = {Hydrology and Earth System Science}, volume = {34}, year = {2020}, pages = {4697-4711}, keywords = {LTER-KNZ}, doi = {10.1002/hyp.13898}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.13898}, author = {Sullivan, P.L. and Zhang, C. and Behm, M. and Zhang, F. and G. L. Macpherson} } @article {KNZ001919, title = {Dust, impure calcite, and phytoliths: modeled alternative sources of chemical weathering solutes in shallow groundwater}, journal = {Chemical Geology}, volume = {527}, year = {2019}, pages = {118871}, abstract = {

In highly reactive, carbonate terrains that constitute more than one-fifth of critical zone landscapes, quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility, biotically-produced minerals as an integral part of leaky biogeochemical cycles, and dust-deposited minerals as important high-surface-area, first-contact solute sources. The potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock, although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems, including those in mountain and tropical settings. We present results of computer and hand-calculated (manual) inverse modeling of two years of stream-water chemistry, spanning a dry and a wet year, for a groundwater-fed headwater stream at the Konza Tallgrass Prairie Long-Term Ecological Research Site in northeastern Kansas. Weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater-fed stream, but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock. We used the mineralogy and geochemistry of local dust collected previously, estimates of a possible chemical composition of phytolith containing potassium, and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry. Average annual amounts were about: 1) 380 kg ha\−1 yr\−1 dust dissolved, 2) 80 kg ha\−1 yr\−1 bedrock carbonate dissolved, and 3) 320 kg ha\−1 yr\−1 phytoliths precipitated. Small amounts of cation exchange were also required to balance the models. There were only small differences between the computer and manual inverse models; both methods resulted in up to 4.6 times more mass of dust dissolved than bedrock. We suggest that dust weathering may be a process that occurs widely, considering the ubiquitous dust flux in continental regions.

}, keywords = {LTER-KNZ, Chemical weathering, Critical zone, Dust, Dust deposition, Headwater stream, Inverse model, Karst, Merokarst}, doi = {10.1016/j.chemgeo.2018.08.007}, url = {https://linkinghub.elsevier.com/retrieve/pii/S000925411830398X}, author = {G. L. Macpherson and Sullivan, P.L.} } @article {KNZ001962, title = {Evolution of carbonate and karst critical zones}, journal = {Chemical Geology}, volume = {527}, year = {2019}, pages = {119223}, abstract = {

Carbonate terrains (CT) underlie one-fifth of terrestrial, ice-free land and are an important supply of potable water to the world\&$\#$39;s population, and yet processes endemic to CT critical zones (CZ) and responses of these processes to climatic and anthropogenic pressures are not well understood. Given the rapid dissolution rates and ability to generate well-developed networks of secondary porosity these landscapes can be highly sensitive to impacts from climate change (e.g., modifications of temperature, precipitation, sea level) and human disturbance (e.g., water withdrawal/diversions, changes in land use/land cover). This special issue includes 16 papers focused on CT-CZ processes and potential responses to climatic and human perturbations. Five major themes emerge from these papers, namely: (1) anthropogenic climate and land use changes alter CT-CZ weathering rate and diagenesis, (2) metal and carbon fluxes in CT-CZ will respond to increasing hydrologic variance caused by climate change, (3) endogenous and exogenous processes operating over short time periods (\<10,000 yrs) form landscape patterns in carbonate terrains, (4) rates of carbonate mineral dissolution depend on vadose zone and soil thickness, and (5) open systems may not always promote greater carbonate weathering rates in CT-CZ. These findings reflect the importance of carbonate minerals in Earth\&$\#$39;s CZ, both in terms of processes unique to carbonate minerals, as well as a predictor of future responses to anthropogenic and environmental changes.

}, keywords = {LTER-KNZ}, doi = {10.1016/j.chemgeo.2019.06.023}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0009254119303183}, author = {Sullivan, P.L. and G. L. Macpherson and Martin, J.B. and Price, R.M.} } @article {KNZ001920, title = {How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)}, journal = {Chemical Geology}, volume = {527}, year = {2019}, pages = {118989}, abstract = {

Mounting evidence suggests ecosystem changes that alter subsurface water fluxes and carbon dioxide concentrations in carbonate terrains may drive measurable changes in chemical weathering rates, stream water chemistry, and flow path evolution on human timescales. We test this idea by exploring if the encroachment of woody vegetation into grasslands in a carbonate terrain landscape at the Konza Prairie (KS, USA) has resulted in differences in landscape-stream connectivity and, thus, the behavior of stream water solutes. Woody encroachment (up to 60\% cover) at Konza has been observed on watersheds, particularly those that experience a fire return interval of four years or greater. We focus on three headwater catchments (two grassland and one woody-encroached) and a downstream confluence, and analyze stream water discharge and chemistry (major anions, cations, and dissolved nutrients) measured from 2015 to 2016.

We observe that the woody-encroached watershed exhibits a greater area-normalized solute flux and greater degree of chemodynamic behavior for most geogenic species compared to the less encroached grassland watersheds. The downstream confluence exhibits the most chemostatic behavior for these same solutes compared to the low order watersheds. We interpret the chemodynamic behavior of the woody-encroached watersheds to arise from a greater diversity of flow paths and solute sources that contribute to this stream. End member mixing analysis (EMMA) supports this hypothesis but also indicates a possible \“missing\” end member which we interpret to be solutes likely derived from clay weathering along limestone-mudstone boundaries. We invoke differences in rooting systems between grass and woody species to explain the differences in flow paths and solute generation between these headwater sites given that they sit adjacent to each other, dissect the same nearly horizontal (dip 0.1\–0.21\°NW) lithologic units, and experience the same climate. If these processes hold true at other sites, then the globally observed encroachment of woody vegetation into grasslands may deepen flow paths and enhance chemical weathering fluxes from ecosystems, and over long-time periods alter the trajectory of soil development and landscape evolution.

}, keywords = {LTER-KNZ, Critical zone, End member mixing analysis, Karst, woody encroachment}, doi = {10.1016/j.chemgeo.2018.12.002}, url = {https://doi.org/10.1016/j.chemgeo.2018.12.002}, author = {Sullivan, P.L. and Stops, M.W. and G. L. Macpherson and Li, L. and Hirmas, D.R. and W. K. Dodds} } @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 = {

Alkalinity and groundwater CO2 have increased linearly from 1991\–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\–2012) as a result of the 4-year fire return interval, 2) re-introduction of bison (phased in, 1994\–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\–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\°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\‰ 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.

}, 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.} } @article {KNZ001921, title = {Watershed-scale chemical weathering in a merokarst terrain, northeastern Kansas, USA}, journal = {Chemical Geology}, volume = {527}, year = {2019}, pages = {118988}, abstract = {

Carbonate weathering in the merokarst landscape at the Konza Prairie (near Manhattan, KS) is governed by kinetically rapid reaction rates, similar to other carbonate settings. The geology of the site consists of repeating couplets of shale and limestone mantled by Pleistocene loess, on which most soils are built. The headwater stream that is the subject of this study is intermittent and well connected to the secondary porosity in the limestone aquifers, such that the water chemistry is groundwater-dominated. Despite increasing in situ weathering rates shown by increasing solute concentrations, long-term (~21 of 24 years) decline in stream-water discharge has reduced chemical denudation. The current chemical denudation rate is 0.02 mm yr\−1. Limestone bedrock thickness (~26.6 m) is 38\% of total bedrock thickness (~70 m); the present landscape would have taken 1\–4 million years to dissolve at current weathering rates. Despite paleogeographic reconstructions suggesting exposure for the past 260 Ma, estimates of the time to erode younger strata using current physical and chemical denudation rates are 80\–159 Ma, still much less than the age of the rocks. An alternate source of material, dust, is proposed that may slow limestone weathering, which in turn protects shales from physical erosion, thereby slowing landscape evolution.

}, keywords = {LTER-KNZ}, doi = {10.1016/j.chemgeo.2018.12.001}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0009254118305874?via\%3Dihub}, author = {G. L. Macpherson and Sullivan, P.L.} } @article {KNZ001821, title = {Developing a conceptual framework of landscape and hydrology on tallgrass prairie: A critical zone approach}, journal = {Vadose Zone Journal}, volume = {17}, year = {2018}, pages = {1 - 11}, abstract = {

Agricultural intensification and urbanization have greatly reduced the extent of tallgrass prairie across North America. To evaluate the impact of these changes, a reference ecosystem of unperturbed prairie is required. The Konza Prairie Biological Station in northeastern Kansas is a long-term research site at which a critical zone approach has been implemented. Integration of climatic, ecologic, and hydropedologic research to facilitate a comprehensive understanding of the complex environment provides the basis for predicting future aquifer and landscape evolution. We present a conceptual framework of the hydrology underpinning the area that integrates the extensive current and past research and provides a synthesis of the literature to date. The key factors in the hydrologic behavior of Konza Prairie are climate, ecology, vadose zone characteristics and management, and groundwater and bedrock. Significant interactions among these factors include bedrock dissolution driven by cool-season precipitation and hence a climatic control on the rate of karstification. Soil moisture dynamics are influenced at various timescales due to the short- and long-term effects of prescribed burning on vegetation and on soil physical characteristics. The frequency of burning regimes strongly influences the expansion of woody species in competition with native tallgrasses, with consequent effects on C and N dynamics within the vadose zone. Knowledge gaps exist pertaining to the future of Konza Prairie (a model for US tallgrass prairie)\—whether continued karstification will lead to increasingly flashy and dynamic hydrology and whether compositional changes in the vegetation will affect long-term changes in water balances.

}, keywords = {LTER-KNZ}, doi = {10.2136/vzj2017.03.0069}, url = {https://dl.sciencesocieties.org/publications/vzj/pdfs/17/1/170069}, author = {Vero, S. E. and G. L. Macpherson and Sullivan, P.L. and A.E. Brookfield and Jesse B. Nippert and Kirk, M. F. and Datta, S. and Kempton, P.} }