Identifying potential carbon flux responses to shifting hydroecological and climatic regimes in the Peace-Athabasca Delta

The CO2 flux response of organic carbon stored in lake sediments and littoral peat contained in sensitive, northern wetlands may contribute to accelerating atmospheric CO2 concentrations. Temperature and moisture conditions are important variables that affect the rate and quantity of CO2 released to the atmosphere from organic matter stored in lake sediments and peat. Antecedent hydroecological conditions also influence the direction and magnitude of CO2 fluxes to the atmosphere in a changing environment. To better understand and characterize the role of antecedent conditions on CO2 fluxes, this study combines paleolimnological reconstructions with laboratory incubations of littoral peat and lake sediment from two ponds in the Peace - Athabasca Delta (PAD) in Alberta to (1) investigate the role that past and present hydrological conditions plays on the amount and lability of stored organic carbon to oxidation and respiration potentials and (2) evaluate potential production of CO2 in light of anticipated future hydroecological conditions.;Lake sediment organic matter profiles of three sediment cores from PAD 31 in the southern, Athabasca-sector of the delta provide evidence for increases in the frequency of overland flood events due to the natural upstream bifurcation of the Embarras River (Embarras Breakthrough, 1982). High delta13 Corg values indicate periodic hydrological connection with Lake Athabasca water at the peak of the LIA, while lower delta13 Corg values and increasing bulk organic content indicate the development of closed-drainage conditions following water level declines into the 20th century. An inflection of organic content to lower values and higher bulk densities indicate the increasing flood frequency following the 1982 Embarras Breakthrough event.;Laboratory incubations measuring CO2 production potentials from selected lake sediment and peat depth intervals reveal site, substrate and stratigraphic differences in potential CO2 production. Mean, depth-integrated CO2 production rates are greatest during warm, moist treatments. Production of CO2 from PAD 31 peat substrates is greater than from PAD 1 peat, while PAD 1 sediments produce more CO 2 during both moist and saturated treatments. Stratigraphic-dependent CO2 production reveals that sediment and peat deposited during the LIA at PAD 1 potentially produce less CO2 than MP or 20 th century intervals. Intervals characterized by increased flooding at PAD 31 (following the 1982 Embarras Breakthrough) deposit peat and sediment that produces greater amounts of CO2 compared to earlier, less flood-dominated stratigraphic intervals. PAD 31 peat and sediment substrates are more sensitive to changes in temperature and moisture than those obtained from PAD 1. Near-surface substrates also exhibit the least temperature sensitivity of CO2 production at each site. These results suggest that more flood-prone, frequently flooded sites (PAD 31) produce and store organic matter in peat and lake sediment that may contribute greater amounts of CO2 to the atmosphere than closed-drainage sites (PAD 1). Stratigraphic differences in CO2 production also emphasize the importance of considering antecedent hydrological conditions when evaluating potential CO 2 fluxes from northern wetland environments.;Lake sediment geochemical records from a currently closed-drainage site (PAD 1) provide evidence for a three-phase hydrological history spanning the last ∼600 years, consistent with other independently identified climatic intervals in the PAD. Bulk organic carbon and nitrogen elemental and isotopic analyses of lake sediment organic matter and reconstruction of lake water delta 18O from cellulose oxygen isotope analyses reveal periods of hydrological connectivity to Lake Athabasca during the Little Ice Age (LIA) high-stand. Low delta13Corg, high C/N and variable but elevated delta 18Olw values from the beginning of the record to ∼1600 CE, align with the Medieval Period (MP), when lower water levels characterized the central interior of the PAD and this site would have been a closed-drainage basin. A shift to higher delta13Corg, lower and constant C/N and lower delta18Olw values occur during the LIA, suggesting that elevated Lake Athabasca water levels would have been capable of inundating this basin during this time. This is further supported by minimum delta18Olw values at ∼1700, when maximum discharge occurred from the Rocky Mountain glacial headwaters. A, shift to lower delta13Corg, declining C/N and variable but increasing delta18Olw values define the 20th century, reflecting a decline in water levels and the development of closed-drainage conditions at PAD 1.