The Spatiotemporal Evolution of Storm Pulse Particulate Organic Carbon in a Low Gradient, Agriculturally Dominated Watershed

Neal E Blair,Breanna Kazmierczak,Jieun Kim,A N Thanos Papanicolaou,Elmer Arthur Bettis,Jessie A Moravek,Nina Zhou,Christopher G Wilson,Timothy R Filley,Adam S Ward

doi:10.3389/frwa.2021.600649

Abstract

Streams and rivers integrate and transport particulate organic carbon (POC) from an array of aquatic and terrestrial sources. Storm events greatly accelerate the transport of POC. The sequences by which individual POC inputs are mobilized and transported are not well-documented but are predicted to be temporally transient and spatially dependent because of changes in forcing functions, such as precipitation, discharge, and watershed morphology. In this study, the 3rd−4th order agricultural stream network, Clear Creek in Iowa, U.S.A., was sampled at a nested series of stations through storm events to determine how suspended POC changes over time and with distance downstream. Carbon and nitrogen stable isotope ratios were used to identify changes in POC. A temporal sequence of inputs was identified: in-channel algal production prior to heavy precipitation, row crop surface soils mobilized during peak precipitation, and material associated with the peak hydrograph that is hypothesized to be an integrated product from upstream. Tile drains delivered relatively 13C- and 15N-depleted particulate organic carbon that is a small contribution to the total POC inventory in the return to baseflow. The storm POC signal evolved with passage downstream, the principal transformation being the diminution of the early flush surface soil peak in response to a loss of connectivity between the hillslope and channel. Bank erosion is hypothesized to become increasingly important as the signal propagates downstream. The longitudinal evolution of the POC signal has implications for C-budgets associated with soil erosion and for interpreting the organic geochemical sedimentary record.

Highlights

Substantial loss of soil organic carbon (SOC) results from land use associated with agriculture and deforestation (Lal, 2009; Amundson et al, 2015)
In this study we evaluate the conceptual model over multiple storm events to determine if it is a robust description of particulate organic carbon (POC) behavior in the same watershed
We argue that the POC is derived predominantly from the erosion of row crop soils driven by precipitation

Summary

Introduction

Substantial loss of soil organic carbon (SOC) results from land use associated with agriculture and deforestation (Lal, 2009; Amundson et al, 2015). Initial perceptions were that the loss represented a major net source of CO2 to the atmosphere (Lal, 2003). The loss may be part of a landscape-wide sink when C-budgets are broadened to include material that is transported away from the original source, and the reloading of newly exposed C-poor particle surfaces with fresh organic C (Harden et al, 1999; Berhe et al, 2007; Aufdenkampe et al, 2011; Papanicolaou et al, 2015; Doetterl et al, 2016; Wang et al, 2017). C-transport within the river corridor may be a critical control in determining whether anthropogenic land use becomes a net source or sink of atmospheric CO2

Methods

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Discussion

Conclusion