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

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.

Biomarker Heatmaps: an Application of an ‘-omics’ Approach to Detect Storm-induced Source Changes in Fluvial Particulate Organic Carbon

“…%OC of samples were obtained from elemental analysis. Detailed procedures of the chemical analyses and information about quanti ed biomarkers are available in our previous publications [22,34].…”

“…In an effort to address the knowledge gaps, chemical composition changes of riverine POC have been monitored during storm events using various analytical techniques such as elemental analysis (C and N contents, C:N ratio), stable isotope measurements ( 13 C, 15 N), and biomarker analysis [22,23,21,24,25]. Often used in combination with other analytical techniques, biomarker analysis is a powerful tool that allows for the characterization of the complex composition of organic carbon by tracking biological sources through the measurement of individual organic compounds [26,27].…”

“…The sequence of in-channel algal activation followed by vascular plant inputs during storm events is commonly observed in many rivers and streams [22,12,37]. The observations of separate vascular plant inputs and the time-resolved behavior of the putative soil indicators are novel and were made possible by the combination of the high-temporal resolution sampling, the broad-spectrum biomarker analyses, and the heatmap-cluster data processing approach.…”