Chen Ming, Ayers John C
Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, Tennessee, United States of America.
PLoS One. 2024 Dec 31;19(12):e0315978. doi: 10.1371/journal.pone.0315978. eCollection 2024.
Monitoring the seasonal and diurnal variations in headwater stream metabolic regimes can provide critical information for understanding how ecosystems will respond to future environmental changes. In East Fork Creek, a headwater stream in middle Tennessee, week-long field campaigns were set up each month from May 2022 to May 2023 to collect stream metabolism estimators. In a more extensive field campaign from July 2-5 in 2022, diel signals were observed for temperature, pH, turbidity, and concentrations of Ca, Mg, K, Se, Fe, Ba, chloride, nitrate, DIC, DO, DOC, and total algae. Gross Primary Productivity (GPP) and Ecosystem Respiration (ER) were calculated based on a Bayesian model using the dissolved oxygen (DO) time series approach. DO showed diurnal swings between oversaturation in daytime and undersaturation at night, with DO amplitudes being greatest in summer. GPP measurements have a clear seasonal variation, peaking in July and staying low in winter, and strong diel signals that couple with the daily light regime variation. ER does not vary seasonally except for a slight increase in Fall which might be caused by terrestrial organic inputs. The dominant control on GPP is light intensity and on ER is temperature. East Fork Creek shows a heterotrophic metabolic regime for 54 of 57 campaign days and therefore consumes O2 and emits CO2 to the atmosphere throughout the year. If carbon inputs are not a limiting factor, the positive temperature dependence of ER may cause increased CO2 emissions from headwater streams and more frequent hypoxia events in a warming climate.
监测源头溪流代谢状况的季节性和昼夜变化，可为理解生态系统将如何应对未来环境变化提供关键信息。在田纳西州中部的一条源头溪流东叉溪，从2022年5月至2023年5月，每月开展为期一周的实地考察，以收集溪流代谢估算值。在2022年7月2日至5日进行的一次更广泛的实地考察中，观测到了温度、pH值、浊度以及钙、镁、钾、硒、铁、钡、氯化物、硝酸盐、溶解无机碳（DIC）、溶解氧（DO）、溶解性有机碳（DOC）和总藻类浓度的昼夜信号。基于贝叶斯模型，采用溶解氧时间序列方法计算了总初级生产力（GPP）和生态系统呼吸（ER）。溶解氧呈现出白天过饱和与夜间不饱和之间的昼夜波动，夏季的溶解氧振幅最大。总初级生产力测量值有明显的季节性变化，7月达到峰值，冬季保持在较低水平，并且有与每日光照变化相关的强烈昼夜信号。除秋季略有增加（可能是由陆地有机输入引起）外，生态系统呼吸没有季节性变化。对总初级生产力的主要控制因素是光照强度，对生态系统呼吸的主要控制因素是温度。在57个考察日中的54天里，东叉溪呈现出异养代谢状况，因此全年都在消耗氧气并向大气排放二氧化碳。如果碳输入不是限制因素，生态系统呼吸对温度的正依赖性可能会导致源头溪流的二氧化碳排放量增加，以及在气候变暖的情况下更频繁地出现缺氧事件。
