Controls on fluvial carbon efflux from eroding peatland catchments

Abstract

Global peatlands store an unparalleled proportion of total global organic carbon but it is vulnerable to erosion into fluvial systems. Fluvial networks are being recognized as areas of carbon transformation, with eroded particulate organic carbon processed to dissolved organic carbon and CO2. Existing studies indicate biodegradation and photodegradation as key processes controlling the transformation of organic carbon in fluvial systems, with initial concentrations of dissolved organic carbon (DOC) identified as a control on the rate of carbon mineralization. This study manipulates temperature and incident light intensity to investigate carbon mineralization rates in laboratory simulations of peatland sediment transport into fluvial systems. By directly measuring gaseous CO2 emissions from sampled stream water, the relationship of temperature and light intensity with carbon efflux is identified. In simulations where sediment (as particulate organic matter, POM) is absent, temperature is consistently the dominant factor influencing carbon efflux rates. This influence is independent of the initial DOC concentration of the water sample. In simulations where POM was added, representing a peatland river receiving eroded terrestrial sediment, initial DOC concentration predicts 79% of the variation in total gaseous carbon efflux whereas temperature and light intensity predict 12% and 3%, respectively. When sampled stream water's mineralization rates in the presence of added POM are analysed independently, removing DOC as a model variable, the dominant variable affecting CO2 efflux is opposite for each sample. This study presents novel data suggesting peatland erosion introduces further complexity to dynamic stream systems where rates of carbon transformation processes and the influence of specific environmental variables are interdependent. Anthropogenic climate change is identified as a leading risk factor perpetuating peatland erosion; therefore, understanding the fate of terrestrial sediment in rivers and further quantifying the benefits of protecting peatland soils will be of increasing importance to carbon budgeting and ecosystem function studies.

Towards understanding organic matter fluxes and reactivity in surface waters: Filtering impact on DOC and POC degradation

“…The POM was rinsed with DI water, to flush any DOC from the material, then weighed (0.77 g) and added to deionized water (1 L). The concentration of POM was similar to the concentration used in Brown et al (2019); 0.8 g L −1 ) which is described as a typical POM concentration from a peatland stream in the United Kingdom. However, as Brown et al (2019) also acknowledge, this is higher concentration of POM than found in non‐eroding or disturbed catchments in the United Kingdom, such as those measured in NE Scotland and Mid‐Wales by Dawson, Billett, Neal and Hill (2002); range < 0.01 to 7.22 mg C L −1 ).…”

“…The concentration of POM was similar to the concentration used in Brown et al (2019); 0.8 g L −1 ) which is described as a typical POM concentration from a peatland stream in the United Kingdom. However, as Brown et al (2019) also acknowledge, this is higher concentration of POM than found in non‐eroding or disturbed catchments in the United Kingdom, such as those measured in NE Scotland and Mid‐Wales by Dawson, Billett, Neal and Hill (2002); range < 0.01 to 7.22 mg C L −1 ). The DI water in this experiment contained no DOC; however rinsing the POM with DI water will not have removed microbes from the POM—therefore this water is not “sterile” and abiotic and biotic transformation of POC to DOC was possible.…”

“…In our study, we used the operational definition of DOC as anything smaller than 0.45 μm, whereas some studies use smaller cut-off point of It is important to accurately quantify the interactions of different pools of OC in peatland streams, as these are known to contribute directly to CO 2 losses from rivers, streams, lakes and reservoirs (Raymond et al, 2013). Understanding the interaction between DOC and POC is important to know how lab-based measurements of OC losses relate to those measured in surface waters, and therefore understand the ultimate fate of the OC as it is transported and transformed in the fluvial network (Attermeyer et al, 2018;Brown et al, 2019). The results of this study showed that in streams where the concentration of POC is high, such as in degraded peatlands like those found in the Peak District, United Kingdom, for the first few days of POC transport in the water, POC is likely to buffer the losses of DOC.…”

“…Knowing how much carbon is exported via streams and rivers is important to obtaining accurate carbon budgets of peatlands. However, to fully quantify the impact of peatlands on larger scale carbon and greenhouse gas budgets, such as the river catchments, or the global carbon cycle, it is important that the ultimate fate of this transported carbon is known (Brown, Goulsbra, & Evans, 2019). Additionally, little is known about how much of the carbon exported undergoes in‐stream processing, and how much reaches the marine environment.…”

Corrigendum

“…An error has been identified in the spelling of one of the author names in Brown, Goulsbra, and Evans (). “Claire S. Gouslbra” should be corrected to “Claire S. Goulsbra.”…”