Fluvial Carbon Budgeting Across a Spectrum of Raised Bog Environments.

Abstract

This study set out to determine the feasibility of using in-situ fDOM measurements as a proxy for NPOC, the relationship of which was used to predict the fluvial carbon budget of the three raised bog sites, taking into account the effects of ET, flow, evading fluvial carbon and precipitation. Simple correlation between fDOM and NPOC does not provide sufficient accuracy for these Irish temperate peatlands sites, likely due to the lack of consideration of multiple complex factors within these raised bog sites such as precipitation, soil moisture, flow discharge, temperature, and pH and the hysteresis between those processes. A multivariate approach which can take these factors into account provides a statistically significant relationship between fDOM and NPOC in all three sites. However, as the relationships of all these factors are site specific this process required a high level of active sampling that should be considered if this method is to be used in a project. Once the relationship between fDOM and NPOC was determined, the hydrology of the bogs was analysed to determine the influence of this in the NPOC exports. An analysis of their flow, precipitation and evapotranspiration provided useful insights into these bogs, as two of them have natural flow regimes (Clara and All Saints) but differentiated by their vegetation cover and the other, Garryduff, has a pump system which is the main driver of its flow regime. These conditions are reflected in the hydrological assessment of this study. While Clara has higher NPOC flux, given its low discharge, it has lower NPOC export than Garryduff. Both sites show higher export in the Winter due to the high discharge rate, despite lower NPOC concentrations than in the Summer. For both sites, CO2 and CH4 evasion were less than 1% of total NPOC export, however, given some issues in evasion measurement the role of evasion in fluvial carbon export for these sites could be improved with more consistent measurements at different areas of the bogs. Overall, this study has shown the benefit of using in situ fDOM measurements as a proxy to predict NPOC using multi variate analysis in temperate raised bog systems. By taking into account the different pathways of water movement through these systems, we can better understand the drivers of fluvial carbon flux. The near natural site appears to have higher fluvial carbon flux than the degraded sites but they likely take in more carbon to begin with, highlighting the importance of considering Net Ecosystem Exchange for peatland systems, rather than focussing on individual aspects of carbon flux.