Effects of storm events on mobilisaton and in-stream processing of dissolved organic matter (DOM) in a Welsh peatland catchment.

Peatlands are important contributors of dissolved organic matter (DOM) to downstream aquatic systems. We investigated the effects of storm events on dissolved organic carbon (DOC) concentrations and DOM quality in a stream draining a Welsh peatland catchment. Intensive stream samples were collected and analysed for pH, DOC, dissolved organic nitrogen (DON), absorbance and fluorescence. Soil water samples and samples of sphagnum pore water were also collected, and a simple end-member mixing model was applied to account for changes occurring during the events. Fluorescence data were interpreted using parallel factor analysis (PARAFAC). DOC concentrations increased and pH decreased during the storm events. The soil water data and the mixing model indicated that this was due to a change of flow paths and draining of the DOC-rich acrotelm. Absorbance indices and the DOC/DON ratio suggested that the DOM released during events was less degraded. There was a striking, inversely related diurnal pattern in absorbance and fluorescence after the discharge peak. The diurnal pattern and a lack of fit with the mixing model suggested that fluorescing DOM was mainly produced in-stream. Fluorescence has been found to peak in the morning and decline during day-time due to photo-bleaching. We hypothesise that the input of additional DOM during events causes a change in the diurnal pattern, giving a peak at mid-day, when the processing of the additional DOM is highest

Source and age of dissolved and gaseous carbon in a peatland-riparian-stream continuum: a dual isotope (14C and δ13C) analysis

Radiocarbon isotopes are increasingly being used to investigate the age and source of carbon released from peatlands. Here we use combined 14C and δ13C measurements to determine the isotopic composition of soil and soil decomposition products (dissolved organic carbon (DOC), CO2 and CH4) in a peatland-riparian-stream transect, to establish the isotopic signature and potential connectivity between carbon pools. Sampling was conducted during two time periods in 2012 to investigate processes under different temperature, hydrological and flux conditions. Isotopic differences existed in the peatland and riparian zone soil organic matter as a result of the riparian depositional formation. The peatland had a mean radiocarbon age of 551 ± 133 years BP, with age increasing with depth, and δ13C values consistent with C3 plant material as the primary source. In contrast the riparian zone had a much older radiocarbon age of 1055 ± 107 years BP and showed no age/depth relationship; δ13C in the riparian zone was also consistent with C3 plant material. With the exception of DOC in September, soil decomposition products were predominately >100 %modern with 14C values consistent with derivation from organic matter fixed in the previous 5 years. Emissions of CO2 and CH4 from the soil surface were also modern. In contrast, CO2 and CH4 evaded from the stream surface was older (CH4: 310-537 years BP, CO2: 36 years BP to modern) and contained a more complex mix of sources combining soil organic matter and geogenic carbon. The results suggest considerable vertical transport of modern carbon to depth within the soil profile. The importance of modern recently fixed carbon and the differences between riparian and stream isotopic signatures suggests that the peatland (not the riparian zone) is the most important source of carbon to stream water

Release of aquatic carbon from two peatland catchments in E. Finland during the spring snowmelt period

Spring snowmelt in the arctic and boreal regions represents the most significant event in the hydrological year. We measured concentrations and fluxes of different carbon species in 2 small contrasting (control v drained) forested peatland catchments in E. Finland between April and June 2008 and compared these to long-term annual fluxes. Measurements were made using a combination of continuous sensors (CO2, temperature, pH, discharge) and routine spot sampling (DOC, POC, DIC, CO2, CH4, N2O). The highest concentrations of CO2 and CH4 in streamwater were observed under low flow conditions before the spring flood event,reflecting accumulation and downstream release of gaseous C at the end of the winter period. Over the length of the study mean CH4 concentrations were 10x higher in the drained site. The snowmelt event was associated with a dilution of DOC and CO2, with the drained catchment showing a much flashier hydrological response compared to the control site, and post-event, a slower recovery in DOC and CO2 concentrations. Fluxes of all carbon species during the snowmelt event were significant and represented 37–45% of the annual flux. This highlights the challenge of quantifying aquatic C fluxes in areas with large temporal variability and suggests that inability to ‘‘capture’’ the spring snowmelt event may lead to under-estimation of C fluxes in northern regions