This study was conducted on the South Fork of the Kings Creek research watershed (outlet location: 39.092281, -96.58719) within Konza Prairie Biological Station (KBPS) near Manhattan (KS, USA). At the USGS gage located on the mainstem (06879560; est. 1979), Kings Creek is a 5th order intermittent stream draining 1059-ha of tallgrass prairie that is actively managed using controlled buns at varying frequencies (1-20 year return intervals) and grazing by bison or cattle. Kings Creek ranges in elevation from 338 to 430 m above sea level and drains into the Kansas River. The region is within a midwestern continental climate, with temperatures ranging from 4 to 22°C and mean annual precipitation averaging about 780 mm/yr.

This site lies within the Flint Hills ecoregion of eastern KS and northeastern OK, has a mean annual temperature of 11.7ºC (1983-2020), and 811 mm annual precipitation (1983-2020) with high interannual variability and an estimated 75% of annual precipitation occurring during late spring and early summer (Hayden 1998, Sadayappan et al. 2023). The AIMS study catchment, the South Fork of Kings Creek, is grazed by bison year-round, and includes sub-catchments with variable prescribed burn history, but the entire study area was burned in early April 2021. The riparian vegetation is deciduous gallery forest and the highest portion of the landscape is tallgrass prairie (Dodds et al. 2004) dominated by warm-season grasses, though woody encroachment has occurred in most subwatersheds (Sadayappan et al. 2023)*. The underlying bedrock of the Flint Hills ecotone is characterized as limestone, mudstone, and shale with predominately silty clay loam soils that rest atop (Hayden 1998, Vero et al. 2018). The riparian vegetation consists of deciduous forest trees such as mature bur oak (Quercus macrocarpa), chinquapin oak (Q. muehlenbergii), hackberry (Celtis occidentalis) and in the highest portion of the landscape is tallgrass prairie with dominant grass species of big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), Indian grass (Sorghastrum nutans), and switchgrass (Panicum virgatum), though woody encroachment has occurred in most subwatersheds (Dodds et al. 2004, Sadayappan et al. 2023).
We collected samples every ~3 weeks from October 14, 2021, to October 1, 2024, at the outlet of our watershed (WHM01, approach 1) and seasonally at seven distributed sites (approach 2). We collected triplicate water samples for dissolved organic matter (DOM). We collected samples at the specified location when water was present using a syringe in a well-mixed area of the stream. We then filtered water through PES PLUS membrane syringe filters into clean, leached amber HDPE bottles following the AIMS Surface Water Chemistry SOP (Burgin 2024). Samples were refrigerated until analysis on a Horiba Aqualog spectrometer at either University of Alabama or Idaho State University. DOM excitation-emissions matrices and absorbance spectra were collected on a Horiba Aqualog from 249 to 830 nm at 5-nm increments at the University of Alabama and/or Idaho State University. Integration times varied from 2 to 4 seconds, based on sample concentration. EEMs were blank-corrected, Raleigh masked, inner filter effects were removed, and values were Raman-normalized using Aqualog software. Standard fluorescence metrics were calculated from corrected EEMs using the StaRdom package in R. These included: biological index, fluorescence index, humification index, and fluorescence at standard peaks: amino acid-like peak tyrosine (B) and amino acid-like peak tryptophan (T), humic-like peaks A and C, and humic-like peak M. Absorbance metrics were also calculated in StaRdom, including absorbance at 254 nm and absorbance at 300 nm; E2:E3, and absorbance slopes 275-295, 350-400, and 300-700, and slope ratio. Mean and standard deviation of triplicate samples are reported in data.

Dodds, W. K., K. Gido, M. R. Whiles, K. M. Fritz, and W. J. Matthews. 2004. Life on the edge: the ecology of Great Plains prairie streams. BioScience 54(3):205-216.
Hayden, B. P. 1998. Regional climate and the distribution of tallgrass prairie. Pages 19-34 in: Knapp, A. K., Briggs, J. M., Hartnett, D. C., Collins, S. L. (editors). Grassland dynamics: Long-term ecological research in tallgrass prairie. Oxford University Press, New York.
Sadayappan, K., R. Keen, K. M. Jarecke, V. Moreno, J. B. Nippert, M. F. Kirk, P. L. Sullivan, and L. Li. 2023. Drier streams despite a wetter climate in woody-encroached grasslands. Journal of Hydrology 627:130388.
Vero, S., G. Macpherson, P. Sullivan, A. Brookfield, J. Nippert, M. Kirk, S. Datta, and P. Kempton. 2018. Developing a conceptual framework of landscape and hydrology on tallgrass prairie: A Critical Zone approach. Vadose Zone Journal 17(1):1-11.