Factors driving spatiotemporal variations of dissolved organic carbon dynamics from croplands

This study was to improve the understanding of the watershed characteristics (land use land cover, soil and morphology) and soil water properties driving the spatial and temporal distributions of the DOC concentrations in cornfield landscapes. Monthly field DOC concentrations were measured throughout the year in the outlets of 24 subbasins across the Chippewa River Watershed within the Corn Belt region of the Midwestern United State. These corn field measurements were benchmarked against the results sampled from predominantly forested areas within the Connecticut River Watershed. A hydrology model with a strength in agricultural watersheds was calibrated to simulate the daily soil water properties to pair with the DOC observations of each location and sample collection date. The study also explores for a scheme of reclassifying land use land cover (LULC) into the categories according to their DOC production rates. The resultant major findings were: 1) DOC concentrations in runoff from croplands are substantially higher than that from other land uses throughout the year, especially the concentrations in spring runoff/snowmelt are alarmingly high, and 2) with the identified classification scheme, gradient analysis in multivariate analysis identified that % cropland, % forested, and % mixing wetland with forest areas plus drainage extents were the most significant determinants of explaining for 82% spatial variations of DOC concentration; and 3) in addition to the LULC variables, three soil water properties: potential evapotranspiration (PET), soil water content(SW), and ground water (GW) were examined significant statistically in explaining about 81% seasonal and 54% daily variations.