Storm pulse responses of fluvial organic carbon to seasonal source supply and transport controls in a Midwestern agricultural watershed

Authors: HU, TINGYU - University Of Oklahoma; BLAIR, NEAL - Northwestern University; Papanicolaou, Athanasios - Thanos; FILLEY, TIMOTHY - University Of Oklahoma

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2023
Publication Date: 4/15/2023
Citation: Hou, T., Blair, N.E., Papanicolaou, A.N., Filley, T.R. 2023. Storm pulse responses of fluvial organic carbon to seasonal source supply and transport controls in a Midwestern agricultural watershed. Science of the Total Environment. 869. Article 161647. https://doi.org/10.1016/j.scitotenv.2023.161647.
DOI: https://doi.org/10.1016/j.scitotenv.2023.161647

Interpretive Summary: This work provides key information about the origin of organic carbon exports in streams. It answers the question from where organic material is coming from within an agricultural watershed under different storm events and land use/land cover. It also looks into the type of organic carbon that is exported from the uplands into the streams. Organic matter could transport in two phases, namely, particulate and dissolved. Storm intensity and duration as well as landuse/land cover may change the relative contribution of particulate over dissolved exports. Understanding how climate and land use interact with each other and how this interaction affects the signal of organic matter i.e., amount and phases of organic type, transported downstream, is important for evaluating the effectiveness of management practices and optimal BMP placement on carbon exports. Using a drainage network approach this work provides a scalable way of quantifying exports and phase apportioning of organic matter and identifies key controls on organic exports under different management, land cover, and storm characteristics. It provides practical tools to quantify lag times and preferential pathways on organic exports from the field to the watershed scale. This information will be valuable to scientists and natural resources managers to understand how long it will take to see the integrated effects of management practices on flux transport downstream at the watershed scale.

Technical Abstract: Storm events are the primary mechanisms of delivering fluvial OC in both dissolved (DOC) and particulate (POC) forms but amounts can vary seasonally due to the fundamental differences in transport mechanisms, which can be dependent upon land use and climate drivers. Within the low relief and poorly drained agricultural landscapes of the upper Midwest United States, land use and hydrologic management over the last 150 years, has dramatically altered both surface and subsurface flow pathways compared to the pre-settlement landscapes. High-resolution monitoring of DOC and POC concentrations within the Clear Creek Watershed (CCW) of eastern Iowa over during six storm events, spanning over two hydrological years, was employed to investigate the export mechanisms, landscape connectivity, and hydro-climatological controls of fluvial OC as it passes from the upper to lower reaches of the CCW. Our results demonstrate that event-driven dynamics favor POC over DOC where POC accounted for 54-94% of total fluvial OC export during individual events, indicating a potential DOC/POC sampling bias in the absence of high-resolution event monitoring. The relationships between event DOC and POC exports with the Normalized Difference Vegetation Index (NDVI) of landscapes at the time of storms, and antecedent dry/wet conditions, suggest a strong interaction related to surface coverage and the active production of above- and below-ground OC. Specifically, DOC and POC shared similarity in concentration profiles during events in fallow period (e.g., post-harvest in late October), when leaf canopy and soil shielding were low. In contrast, DOC and POC differed in dynamic profiles in rainfall events occurring in growing season with extensive vegetation coverage (e.g., late June), exhibiting a strong interaction between surface vegetation coverage of soil and the active OC production, as well as establishment of hydrologic connectivity between hillslope and stream. There are few examples of such high-resolution storm event sampling to explore the dynamics of fluvial OC, but efforts spanning across the drainage network are lacking to predict C sourcing and transformation in inland water systems under land use and climate change.