The dataset represents the results of floodplain soil samples collected in Navigation Pool 8 of the upper Mississippi River. The objective of the research was to assess the changes in soil chemistry and nutrient transformation at floodplain forest sites in the presence or absence of invasive reed canarygrass (RCG- Phalaris arundinacea) and determine if the RCG effect was modified by the frequency of inundation of the flood plain soils. The data are structured in a 2x4 factorial experimental design, Factor 1, the presence or absence of RCG in floodplain forest landcover and Factor 2, four levels of flood inundation frequency (0.25-0.32, 0.32-1.35, 1.35-2.35, and 2.35-4 events per year). Soil core samples were collected at 6 locations (n=6) by 2 landcovers and 4 inundation frequencies for a total of 48 sites in the June post flood period and again in August of 2019. Rates of biogeochemical transformation of nitrogen was determined for each site. Soil characteristics, Mehlich-3 metals (Al, Ca, Cu, Fe, K, Mn, Mg, Na, P, and Zn), Phosphorus (P), MgCl2 extracted P, carbon, nitrogen, nitrate-nitrite, exchangeable ammonium, and particle-size of the soil were also measured. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.