Total waterborne carbon export and DOC composition from ten nested subarctic peatland catchments—importance of peatland cover, groundwater influence, and inter‐annual variability of precipitation patterns

Abstract

Waterborne carbon (C) export from terrestrial ecosystems is a potentially important flux for the net catchment C balance and links the biogeochemical C cycling of terrestrial ecosystems to their downstream aquatic ecosystems. We have monitored hydrology and stream chemistry over 3 years in ten nested catchments (0.6-15.1 km 2 ) with variable peatland cover (0%-22%) and groundwater influence in subarctic Sweden. Total waterborne C export, including dissolved and particulate organic carbon (DOC and POC) and dissolved inorganic carbon (DIC), ranged between 2.8 and 7.3 g m -2 year -1 , representing~10%-30% of catchment net ecosystem exchange of CO 2 . Several characteristics of catchment waterborne C export were affected by interacting effects of peatland cover and groundwater influence, including magnitude and timing, partitioning into DOC, POC, and DIC and chemical composition of the exported DOC. Waterborne C export was greater during the wetter years, equivalent to an average change in export of~2 g m -2 year -1 per 100 mm of precipitation. Wetter years led to a greater relative increase in DIC export than DOC export due to an inferred relative shift in dominance from shallow organic flow pathways to groundwater sources. Indices of DOC composition (SUVA 254 and a 250 /a 365 ) indicated that DOC aromaticity and average molecular weight increased with catchment peatland cover and decreased with increased groundwater influence. Our results provide examples on how waterborne C export and DOC composition might be affected by climate change. Figure 4. Correlation coefficients for linear correlations (Pearson's r) between daily runoff and DOC concentration, a 254 , SUVA 254 , and a 250 /a 365 for ten nested catchments. Significance of correlation: *p < 0.01, +p < 0.05. Correlation analysis is using data from 2007 and 2008 jointly, n = 77-217. Catchment peatland coverage indicated in % below catchment notation 2289 WATERBORNE CARBON EXPORT FROM SUBARCTIC CATCHMENTS

Aquatic DOC export from subarctic Atlantic blanket bog in Norway is controlled by seasalt deposition, temperature and precipitation

“…Aquatic export of DOC in peat-dominated catchments is usually strongly promoted by precipitation (Olefeldt et al 2013), similar to what we found in the statistical analysis of catchment DOC export, but in Table 6 the highest absolute DOC export is found in Scotland, which is not the site with the highest annual precipitation. Production of DOC per mm runoff reveals a variation between sites of 7 and 38 mg C mm -1 , where Andøya is found at the lower end.…”

“…The negative effect of current-season's discharge on DOC concentrations agrees with the generally observed diluting effect of precipitation on DOC in peatland runoff, in contrast to upland soil runoff (Köhler et al 2008). A positive relation between discharge and catchment aquatic DOC export is commonly found (Olefeldt et al 2013;Raike et al 2012). Temperature (antecedent and current) promoted DOC export in the autumn and early winter, suggesting that increased microbial activity under higher soil temperatures produces a higher store of potentially leachable DOC (Kalbitz et al 2000;Tipping et al 1999).…”

Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden

“…Our DOC fluxes are roughly in the same range as those reported from streams in permafrost-affected areas; Carey (2003) reported a flux of 1.6 g C m −2 yr −1 and Petrone et al (2006) reported values between 1.1 and 2.3 g C m −2 yr −1 for three catchments. Our export values are, however, considerably lower than many boreal forest streams (see compilation of DOC export data in Olefeldt et al, 2013).…”

“…Flux estimates of DIC from the Scandinavian boreal forest about 700 km south of Abisko in the Krycklan catchment report loads ranging from −0.7 to 1.4 g C m −2 yr −1 ; the negative value indicating a net loss between upstream and downstream measured sites. The DIC export in several sub-catchments of a wetland-influenced catchment in the Abisko area, the Stordalen mire complex, ranged from 0.6 to 3.0 g C m −2 yr −1 (Olefeldt et al, 2013) and the range in yearly DIC export from the Abiskojokken stream (Fig. 6) ranged between 1.5 and 3.2 g C m −2 yr −1 .…”

Size, age, renewal, and discharge of groundwater carbon

“…Predicting changes in atmospheric carbon dioxide (CO 2 ) and the course of climate change relies on complete and accurate estimates of the sizes and rates of exchange of all global C pools. In addition to global analyses, groundwater C is increasingly implicated in regional C cycling (Genereux et al 2013, Olefeldt et al 2013. Currently, both the size and turnover time of the global groundwater C pool (Cole et al 2007) and the influence of human domestic, industrial, and agricultural groundwater withdrawal on global C cycling are unknown.…”