Hydrologic connectivity with peatland soils drives very high carbon fluxes in a tropical, mountain stream

Inland waters receive large quantities of carbon from the surrounding landscape and are active sites of carbon transport, transform, and emission. Global carbon emission estimates are limited by sparse and unevenly distributed carbon flux observations, particularly in the tropics. We evaluated hydrological and metabolic controls on carbon export variability from a large peatland in a tropical ecosystem typical of the Northern Andes mountains. We recorded dissolved CO2 (pCO2), dissolved oxygen (DO), and discharge continuously at 15-minute intervals 5 m downstream of a peatland outlet (Station 1) and at 3 additional locations downstream (Stations 2, 3 and 4) from July 2019 until Jan 2020 and from June 2021 until March 2023. Continuous measurements of DO and discharge were also measured 2 km away in a stream draining an adjoining catchment (Station 5). Discrete measurements of dissolved organic carbon (DOC) and dissolved methane (pCH4) were collected June-July of 2021 and 2022. Stream discharge was a primary control on pCO2 and DOC in the stream network at both seasonal and event scales. DOC concentration increased with discharge and while pCO2 decreased during higher flows, CO2 loading increased. Pronounced seasonal changes were observed with lowest pCO2 recorded at the peatland outlet in wet months (June-August: 5,845±2,325 ppm, mean±standard deviation), and the highest in dry months (Nov-Feb, 16,677±3,685). Anoxic or hypoxic conditions persisted for over half of our study and measurements of pCH4 at the peatland outlet were very high (982±797 ppm), underscoring the importance of anaerobic activity in this system. Aerobic processes also influenced pCO2 dynamics. Aquatic metabolism at Station 5 (29 July–19 Oct 2021) was net heterotrophic, with ER exceeding GPP and net pCO2 production (mean ER: -6.5 g O2 m-2 d-1, GPP: 0.44 g O m-2 d-1). Our study highlights the role of hydrologic connectivity and diverse biogeochemical processes in shaping carbon export and cycling in páramo streams, which results in pCO2 and pCH4 levels among the highest reported in streams and rivers worldwide.内陆水域从周边景观获取大量碳，同时是碳运输、转化与排放的活跃场所。当前全球碳排放估算受限于碳通量观测站点稀疏且分布不均的问题，在热带区域尤为突出。本研究针对北安第斯山脉典型热带生态系统中的大型泥炭地，评估了水文与代谢过程对碳输出变异的调控作用。2019年7月至2020年1月，以及2021年6月至2023年3月期间，我们在泥炭地出水口下游5米处（站点1）以及下游另外3个点位（站点2、3、4），以15分钟的间隔连续监测溶解态二氧化碳（pCO2）、溶解氧（DO）与径流量；同时在邻近流域支流2公里外的站点5，同步开展溶解氧与径流量的连续监测。离散样本采集方面，我们分别于2021年和2022年的6-7月，采集了溶解态有机碳（DOC）与溶解态甲烷（pCH4）的样品。研究结果显示，在季节与事件尺度上，径流量均为该河网中pCO2与DOC的主要调控因子：DOC浓度随径流量升高而上升；尽管高流量时段pCO2有所降低，但二氧化碳负荷量却随之增加。研究观测到显著的季节变化特征：泥炭地出水口的pCO2在湿季（6-8月）处于最低水平（5845±2325 ppm，均值±标准差），而在旱季（11月至次年2月）达到最高值（16677±3685 ppm）。整个研究周期内，缺氧或低氧状态持续超过一半时长，且泥炭地出水口的pCH4监测值极高（982±797 ppm），凸显了该系统中厌氧过程的重要性。好氧过程同样对pCO2动态产生影响。站点5的水生代谢（2021年7月29日-10月19日）呈净异养状态，生态系统呼吸（ER）超过总初级生产力（GPP），伴随净pCO2生成（均值ER：-6.5 g O₂ m⁻² d⁻¹，GPP：0.44 g O m⁻² d⁻¹）。本研究凸显了水文连通性与多样生物地球化学过程在塑造帕拉莫（páramo）溪流碳输出与循环过程中的关键作用，使得该系统的pCO2与pCH4水平跻身全球已报道溪流与河流的最高之列。