Drivers of seasonal and event scale DOC dynamics at the outlet of mountainous peatlands revealed by high frequency monitoring

Abstract

Abstract. Peatlands store about 20 % of the global soil organic carbon stock and are an important source of dissolved organic carbon (DOC) for inland waters. Recent improvements for in situ optical monitoring revealed that the DOC concentration in streams draining peatlands is highly variable, showing seasonal variation and short and intense DOC concentration peak periods. This study aimed to determine the variables driving stream DOC concentration variations at seasonal and event scales. Two mountainous peatlands (one fen and one bog) were monitored in the French Pyrenees to capture their outlet DOC concentration variability at a high frequency rate (30 min). Abiotic variables including precipitation, stream temperature and water level, water table depth and peat water temperature were also monitored at high frequency and used as potential predictors to explain DOC concentration variability. Results show that at both sites, DOC concentration time series can be decomposed into a seasonal baseline interrupted by many short and intense peaks of higher concentrations. The DOC concentration baseline is driven, at the seasonal scale, by peat water temperature. At the event scale, DOC concentration increases are mostly driven by water table increases within the peat at both sites. Univariate linear models between DOC concentration and peat water temperature or water table increases show greater efficiency at the fen site. Water recession times were derived from water level time series using master recession curve coefficients. They vary greatly between bog and fen but also within one peatland site. They partly explain the differences between DOC dynamics in the studied peatlands, including porewater DOC concentrations and the links between stream DOC concentration and water table rise. This highlights that peatland complexes are composed of a mosaic of heterogeneous peat units distinctively producing or transferring DOC to streams.

Author’s response to reviewer 1

“…Therefore, we transformed these variables using log-or square-root to approach normality (see Table 1 in the main text) considering that in linear modelling the point is not the reach strict normality of the data but to approximate normality in order to obtain satisfying distribution of the residuals i.e. Normality and Homoscedasticity of the error distribution (Venables & Ripley, 2002. Zuur et al 2009.…”

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

“…They were able to identify the most relevant hydrological processes and factors determining DOC dynamics across a range of conditions at the same site. Rosset, Gandois, Le Roux, Teisserenc, Durantez Jimenez, Camboulive, and Binet (2019) and Rosset, Gandois, Le Roux, Teisserenc, Durantez Jimenez, Camboulive, and Binet (2019); Rosset, Gandois, Le Roux, Teisserenc, Durantez Jimenez, and Camboulive (2019); Rosset et al (2020), with data from the WTD and the multiparameter station (outflow rate and DOC concentration) datasets, investigated the factors influencing DOC and particulate organic carbon (POC) export. They were able to show that in a high‐elevation peatland the majority of exported OC occurred in dissolved form during flood events.…”

Origin and fate of dissolved inorganic carbon in a karst groundwater fed peatland using δ13CDIC

“…Peatlands are thus hot spots of carbon cycling. At the watersheds scale they are the main contributors for organic carbon to surface water (Laudon et al, 2011;Rosset et al, 2019aRosset et al, , 2019b.…”

“…Within this general scheme, peatland ecosystems can be conceptualized as biogeochemical reactors constrained by a wide range of hydrometeorological, geological and ecological parameters affecting the exchange of carbon between the ecosystem (living matter), the hydrosystem (DIC and dissolved/particulate organic carbon) and the atmosphere (gaseous exchanges) (Bernard-Jannin et al, 2018;D'Angelo et al, 2021;Rosset et al, 2019aRosset et al, , 2019b.…”