Data_Sheet_1_The Spatiotemporal Evolution of Storm Pulse Particulate Organic Carbon in a Low Gradient, Agriculturally Dominated Watershed.PDF

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.

溪流与河流会整合并输送来自各类水生与陆生源的颗粒有机碳（particulate organic carbon, POC）。暴雨事件会极大加速POC的输送过程。单个POC输入物的活化与输送序列尚未得到充分记录，但据预测，由于降水、径流量、流域地貌等驱动因子的变化，该序列具有时间瞬变性与空间依赖性。本研究以美国艾奥瓦州克利尔克里克（Clear Creek）这一3-4级农业河网为研究对象，在暴雨事件期间于嵌套布设的一系列监测站开展采样，以探明悬浮态POC随时间推移及下游距离的变化特征。研究采用碳与氮稳定同位素比值来识别POC的来源变化。研究识别出了输入物的时间序列：强降水发生前为河道内藻类生产的有机质，降水峰值时段被冲刷的垄作农田表层土壤，以及与峰值水文过程线相关的、被推测为上游集成产物的物质。地下暗管排水系统输入的POC相对贫化13C与15N，其在基流恢复阶段对总POC库的贡献较小。暴雨驱动的POC信号随河道向下游传输发生演化，其主要转化过程为：随着山坡与河道间连通性丧失，早期冲刷的表层土壤峰值信号逐渐减弱。据推测，随着信号向下游传播，河岸侵蚀的重要性将逐渐提升。POC信号的沿程演化对与土壤侵蚀相关的碳收支，以及解读有机地球化学沉积记录均具有启示意义。